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Students can Download Chapter 5 Evolution Notes, Plus Two Zoology Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Zoology Notes Chapter 5 Evolution

Origin Of Life
In the solar system, earth was originated 4.5 billion years back. There was no atmosphere on early earth.

The UV rays from the sun broke up water into Hydrogen and Oxygen. Oxygen combined with ammonia and methane to form water, CO₂ and others.

Life originated four billion years. Earlier it was believed that life originated from non living things. This is the theory of spontaneous generation.

Later Louis Pasteur demonstrated that life comes only from pre-existing life. He showed that in presterilised flasks, life did not come from killed yeast while in another flask open to air, new living organisms arose from ‘killed yeast’.

Oparin and Haldane proposed that the first form of life that arose from pre-existing non-living organic molecules (e.g. RNA, protein, etc.) and it is followed by chemical evolution.

In 1953, S.L. Miller, an American scientist created similar conditions in a laboratory He created electric discharge in a closed flask containing CH4, H2, NH3 and water vapaur at 800°C. He observed the formation of amino acids.

The first non-cellular forms of life could have originated 3 billion years back i.e RNA, Protein, Polysaccharides, etc…

Later the first cellular forms (single-celled) were originated. These were occurred in water environment only.
Diagrammatic Representation of Miller’s Experiment:

Evolution Of Life Forms – A Theory
Charles Darwin was conducted a voyage ship called H.M.S. Beagle round the world and reach the conclusion that existing living forms share similarities not only among themselves but also with life forms that existed millions of years ago. There has been gradual evolution of life forms.

According to the concept of reproductive fitness, those who are better fit in an environment, produce more progeny than others and survived more. He called it as natural selection an important mechanism of evolution.

In the same time Alfred Wallace naturalist of Malay Archepelago had the same conclusion as Darvin, that all the existing life forms share similarities and share common ancestors.

What Are The Evidences For Evolution?
Evidence of evolution of life comes from fossils that found in sedimentary rocks. Different-aged rock sediments contain fossils of different life-forms. They represent extinct organisms (e.g., Dinosaurs).This type of evidence is called paleontological evidence.

Analysing the comparative anatomy and morphology, shows similarities and differences among organisms of today and those that existed years ago.

Example of homologous organs in (a) Plants and (b) Animals:

For example whales, bats, Cheetah and human share similarities in the pattern of bones of forelimbs (similar anatomical structure).

It contains the bones like humerus, radius, ulna, carpals, metacarpals and phalanges. The same structure developed along different directions due to adaptions to different needs. So they have different functions.

These structures are homologous. This type of evolution is called divergent evolution. Other examples are vertebrate hearts or brains and the thorn and tendrils of Bougainvillea.

Wings of butterfly and of birds anatomically dissimilar but they perform similar functions. These are analogous structures arise due to convergent evolution.

Other examples are the eye of the octopus and of mammals or the flippers of Penguins and Dolphins: Sweet potato (root modification) and potato (stem modification) etc.

Another evidence supporting evolution by natural selection comes from England. Before industrialisation there are more white-winged moths on trees than dark-winged.

This is due to white-coloured lichen covered the trees – in that background the white winged moth survived But after industrialisation, there were more dark-winged moths in the same area because the tree trunks became dark due to industrial smoke and soots.

Under this condition the white-winged moth did not survive due to predators, dark-winged or melanised moth survived.

Lichen are pollution indicators they cannot grow in areas that are polluted. Hence, moths that were able to camouflage themselves.

What Is Adaptive Radiation?
In this, the small black birds -Darwin’s Finches are examples. Darwin found that there were many varieties of finches in the same island.

Their original seed-eating features are changed and become insectivorous and Variety of beaks of finches that Darwin found in Galapagos Island vegetarian finches.

Here the evolution starting from a point and radiating to other areas of geography (habitats) is called adaptive radiation.

Another example is Australian marsupials. A number of different marsupials evolved from an ancestral stock within the Australian island.

Placental mammals in Australia also exhibit adaptive radiation i.e they evolved into varieties (e.g., Placental wolf and Tasmanian wolf marsupial).

Variety of beaks of finches that Darwin found in Galapagos Island:

Biological Evolution
The importance of Darwinian theory of evolution lies in natural selection.

A colony of bacteria (say A) growing on a given medium show variation in terms of feed component. A change in the medium composition results the population (say B) that can survive under the new conditions.

Here the fitness of B is better than that of A under the new conditions. Nature selects for fitness. Adaptive ability is inherited. It has a genetic basis. Fitness is the ability to adapt and get selected by nature.

Branching descent and natural selection are the two key concepts of Darwinian Theory of Evolution Before Darwin, Lamarck had conducted experiments and proposed the use and disuse of organs.

He gave the examples of Giraffes who in an attempt to forage leaves on tall trees had to adapt by elongation of their necks. As they passed on this acquired character of elongated neck to succeeding generations.

The work of Thomas Malthus on populations was influenced Darwin For example, natural resources are limited, populations are stable in size except for seasonal fluctuation.

The population size grow exponentially if reproduced maximally. Darwin was pointed that variations which are heritable, when the resource utilisation better for few, they reproduce more progeny. Hence for a period of time survivors leave more progeny and there would be a change in population characteristics.

Mechanism Of Evolution
Mendel had studied only inheritable ‘factors’ influencing phenotype, But Hugo deVries conducted experiments on evening primrose and proposed the idea of mutation. Mutations are random and directionless while Darwinian variations are small and directional.

Mutation leads to speciation called as saltation (single step large mutation).

Hardy-Weinberg Principle
Diagrammatic representation of the operation of natural selection on different traits:

(a) Stabilising
(b) Directional and
(c) Disruptive

According to Hardy-Weinberg principle allele frequencies in a population are stable and is constant from generation to generation. This is called genetic equilibrium. Sum total of all the allelic frequencies is 1.

For example, p and q represent the frequency of allele A and allele a. The frequency of AA individuals in a population is simply p2. The frequency of p appear on both the chromosomes of a diploid individual, Similarly of aa is q2, and of Aa is 2pq.

Hence, p2 + 2pq + q2 = 1. This is a binomial expansion of (p+q)2.

Disturbance in genetic equilibrium, or Hardy – Weinberg equilibrium, i.e., change of frequency of alleles in a population affected by five factors.

These are gene migration or gene flow, genetic drift, mutation, genetic recombination and natural selection.

When migration of population occurs, gene frequencies change in the original as well as in the new population. If the same change occurs by chance, it is called genetic drift.

Sometimes the change in allele frequency is different in the new sample of population that they become a different species. The original drifted population becomes founders and the effect is called founder effect.

The variation due to mutation or variation due to recombination during gametogenesis, or due to gene flow or genetic drift results in changed frequency of genes and alleles in future generation.

A Brief Account Of Evolution
About 2000 million years ago (mya) the first cellular forms of life appeared on earth. From this the cells with membranous envelop evolved and developed Some of these cells had the ability to release O₂. Slowly single-celled organisms became multi-cellular life forms.

In 1938, a fish caught in South Africa happened to be a Coelacanth which was thought to be extinct. These animals called lobefins evolved into the first amphibians that lived on both land and water.

The amphibians evolved into reptiles. They lay thick shelled eggs. Their modern descendents are the turtles, tortoises and crocodiles.

In the next 200 millions years reptiles of different shapes and sizes dominated on earth.In this period Giant ferns (pteridophytes) were present.

Land reptiles dinosaurs (biggest i.e., Tyrannosaurus rex) went back into water to evolve into fish like reptiles 200 mya (e.g. Ichthyosaurs). About 65 mya, the dinosaurs suddenly disappeared from the earth.

After the reptiles, mammals evolved on this earth. The first mammals were like shrews. Their fossils are small sized. Mammals were viviparous and protected their unborn young inside the mother’s body.

There were in South America mammals resembling horse, hippopotamus, bear, rabbit, etc. Due to continental drift, when South America joined North America, these animals were overridden by North American fauna.

Due to the same continental drift pouched mammals of Australia survived because of lack of competition. Some mammals live wholly in water are Whales, dolphins, seals and sea cows.

Origin And Evolution Of Man

Students can Download Chapter 4 Molecular Basis of Inheritance Notes, Plus Two Zoology Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Zoology Notes Chapter 4 Molecular Basis of Inheritance

The Dna
DNA is a long nucleotides polymer of deoxyribonucleotides.

1. Structure of Polynucleotide Chain:
A nucleotide has three components

1. Nitrogenous base
2. Pentose sugar (ribose in case of RNA, and deoxyribose for DNA), and
3. Phosphate group.

There are two types of nitrogenous bases.

Cytosine is common for both DNA and RNA and Thymine is present in DNA.

Uracil is present in RNA at the place of Thymine.

A nitrogenous base is linked to the pentose sugar through a N – glycosidic linkage to form a nucleoside, When a phosphate group is linked to 5′-OH of a nucleoside through phosphor ester linkage, to form nucleotide. Two nucleotides are linked through 3′-5′ phosphodiester linkage to form a dinucleotide.

Polynucleotide chain has at one end a free phosphate moiety at 5′-end of ribose sugar and other end of the polynucleotide chin the ribose has a free 3′-OH group The backbone in a polynucleotide chain is formed due to sugar and phosphates.

RNA has an additional-OH group present at 2′-position in the ribose and the uracil is found at the place of thymine.

Acidic nature of DNA was first identified by Friedrich Meischer in 1869 and it called as ‘Nuclein’.

Each strand from a DNA acts as a template for synthesis of a new strand. The two double stranded DNA thus, produced would be identical to the parental DNA molecule.

The salient features of the Double-helix DNA are

Francis Crick proposed the Central dogma in molecular biology, which states that the genetic information flows from DNA to RNA and RNA to protein. But in some viruses the flow of information is reverse direction, that is from RNA to DNA.

2. Packaging of DNA Helix:
In E. coli, they do not have a defined nucleus it is termed as ‘nucleoid’. The DNA in nucleoid is organised in large loops held by proteins.

In eukaryotes, this organisation is much more complex. Here the positively charged, basic proteins called histones are associated with DNA.

Histones are rich in the basic amino acid residues lysines and arginines. Histones are organised to form a unit of eight molecules called as histone octamer.

The beads-on-string structure in chromatin is packaged to form chromatin fibers that are further coiled and condensed at metaphase stage of cell division to form chromosomes.

The negatively charged DNA is wrapped around the positively charged histone octamer to form a structure called Nucleosome. It contains 200 bp of DNA helix.

Nucleosomes constitute the repeating unit of a structure in nucleus called chromatin, it is thread-like stained (coloured) bodies seen in nucleus. The nucleosomes in chromatin are seen as ‘beads-on- string’ structure when viewed under electron microscope (EM).

The packaging of chromatin at higher level with proteins that are called as Non-histone Chromosomal (NHC) proteins.

The Search For Genetic Material
This is the work of identification of DNA that acts as a genetic material and responsible for inheritance.

Transforming Principle:
In 1928, Frederick Griffith, in a series of experiments with Streptococcus pneumoniae (bacterium responsible for pneumonia), showed the trasformation in the bacteria.

Mice infected with the S strain (virulent) die from pneumonia infection but mice infected with the R strain do not develop pneumonia.

When Griffith was injected heat-killed S strain into mice, bacteria did not kill them. But he injected a mixture of heat-killed S and live R bacteria, the mice died and he recovered living S bacteria from the dead mice.

Biochemical Characterisation of Transforming Principle:
Oswald Avery, Colin MacLeod, and Maclyn McCarty worked on the ‘transforming principle’ of Griffith’s experiment and noticed that DNA alone from S bacteria caused R bacteria to become transformed.

They also discovered that protein-digesting enzymes (proteases) and RNA-digesting enzymes (RNases) did not affect transformation.

But the digestion with DNase inhibited transformation.

1. The Genetic Material is DNA:
Alfred Hershey and Martha Chase (1952) grew bacteriophages on a medium that contained radioactive phosphorus and some others on medium that contained radioactive sulfur.

Viruses grown in the presence of radioactive phosphorus contained radioactive DNA but not radioactive protein because DNA contains phosphorus but protein does not. Similarly, viruses grown on radioactive sulfur contained radioactive protein but not radioactive DNA because DNA does not contain sulfur.

After the infection the viral coats were removed from the bacteria by agitating them in a blender. It is concluded that proteins did not enter the bacteria from the viruses. But the DNA is the genetic material that passed from virus to bacteria.

The Hershey-Chase experiment:

2. Properties of Genetic Material (DNA versus RNA):
A molecule that act as a genetic material must possess the following features

Therefore, among the two nucleic acids, the DNA is a better genetic material.
The presence of thymine at the place of uracil also gives additional stability to DNA.
In fact, RNA being unstable, mutate at a faster rate. So the viruses having RNA genome having shorter life span mutate and evolve faster.

Rna World
RNA is genetic material as well as a catalyst. But it is reactive and hence unstable. Therefore, DNA has evolved from RNA with chemical modifications that make it more stable.

Replication
Watson and Crick (1953) proposed replication of DNA. They suggested that the two strands separate and act as a template for the synthesis of new complementary strands.

Waste-click model for semiconservative DNA replication:

1. The Experimental Proof:
DNA replicates in semi conservative manner was first shown in Escherichia coli by Matthew Meselson and Franklin Stahl performed the following experiment in 1958:

After the completion of replication, each DNA molecule have one Watson-Crick model for parental and one newly synthesised strand. This is termed as semiconservative DNA replication. semiconservative DNA replication.

Then they transferred the cells into a medium with normal 14NH4Cl and took samples at various definite time intervals as the cells multiplied, and extracted the DNA that remained as double-stranded helices.

The DNA that was extracted from the culture one generation after the transfer from 15N to 14N medium [E. coli divides in 20 minutes] had a hybrid DNA.
(Separation of DNA by Centrifugation):

DNA extracted from the culture after another generation [that is after 40 minutes, II generation] was composed of equal amounts of this hybrid DNA and of ‘light’ DNA.

In an another experiment radioactive thymidine is incorporated into DNA and was observed the semi conservative replication of DNA in Vicia faba (faba beans) by Taylor and colleagues in 1958.

2. The Machinery and the Enzymes:
In E. coli, the process of replication takes place with the help of DNA-dependent DNA polymerase, because it uses a DNA template to catalyse the polymerization of deoxynucleotides.

E. coli that has only 4.6 × 106 bp completes the process of replication within 38 minutes. Deoxyribonucleoside triphosphates have double role. Besides acting as substrates, they provide energy for polymerization reaction same as in case of ATP.

Initially the replication occur within a small opening of the DNA helix (origin of replication) called as replication fork. The DNA- dependent DNA polymerases catalyse polymerization only in one direction, that is 5¹-3’.

Here on one strand (the template with polarity 3’-5′), the replication is continuous, while on the other (the template with polarity 5′-3′), it is discontinuous. The discontinuously synthesized fragments are later joined by the enzyme DNA ligase.

In eukaryotes, the replication of DNA takes place at S-phase of the cell-cycle. A failure in cell division after DNA replication results into polyploidy(a chromosomal anomaly).

Transcription
The process of copying genetic information from one strand of the DNA into RNA is termed as transcription. In transcription only a segment of DNA is copied into RNA.

Only single stranded RNA is produced by transcription process. If the two RNA molecules are produced simultaneously it would be complementary to each other, hence would form a double stranded RNA. This would prevent the translation.

1. Transcription Unit:
DNA has three regions as transcription unit

1. A Promoter
2. The Structural gene
3. A Terminator

The two strands have opposite polarity and the DNA-dependent RNA polymerase catalyse the polymerisation in only one direction, that is, 5′-3′, the strand that has the polarity 3′-5’acts as a template, and is also referred to as template strand.

The other strand which has the polarity (5′-3′) and the sequence same as RNA (except thymine at the place of uracil), is displaced during transcription. This strand (which does not code for anything) is referred to as coding strand.
For example

The promoter is located towards 5′ – end (upstream) of the structural gene. It provides binding site for RNA polymerase.

The terminator is located towards 3′ – end (downstream) of the coding strand and it usually defines the end of the process of transcription.

2. Transcription Unit and the Gene:
A gene is the functional unit of inheritance. The DNA sequence coding for tRNA or rRNA molecule also define a gene.

Cistron is a segment of DNA coding for a polypeptide, the structural gene in a transcription unit is called as monocistronic (mostly in eukaryotes) or polycistronic (mostly in bacteria or prokaryotes).

3. Types of RNA and the process of Transcription:
In bacteria, there are three major types of RNAs:

• mRNA (messenger RNA)
• tRNA (transfer RNA), and
• rRNA (ribosomal RNA).

All three RNAs are needed to synthesise a protein in a cell. The mRNA provides the template, tRNA brings aminoacids and reads the genetic code, and RNAs play structural and catalytic role during translation.

DNA- dependent RNA polymerase that catalyses transcription of all types of RNA in bacteria. RNA polymerase binds to promoter and initiates transcription (Initiation). It uses nucleoside triphosphates as substrate and polymerises in a template and follow the rule of complementarity.

Once the polymerases reaches the terminator region, the nascent RNA and RNA polymerase falls off. This results in termination of transcription.

RNA polymerase catalyse all the three steps, which are initiation, elongation and termination.

The RNA polymerase bind with initiation factor and termination-factor to initiate and terminate the transcription, respectively.

In bacteria, the mRNA does not require any processing and transcription and translation take place in the same compartment.

In eukaryotes, there are 3 RNA polymerases in the nucleus. The RNA polymerase I transcribes rRNAs (28S, 18S, and 5.8S).

RNA polymerase III is responsible for transcription of tRNA, 5srRNA, and snRNAs (small nuclear RNAs).

The RNA polymerase II transcribes precursor of mRNA, the heterogeneous nuclear RNA (hnRNA).

Genetic Code
The process of translation requires transfer of genetic information from a polymer of nucleotides to a polymer of amino acids.
codons for various aminoacids:

For this, George Gamow, who proposed only 4 bases they have to code for 20 amino acids, the code should constitute a combination of bases.

The code should be made up of three nucleotides( triplet) and in various combination would generate 64 codons, 4³ (4 × 4 × 4) Marshall Nirenberg’s cell-free system for protein synthesis helped the code to be deciphered.

Severo Ochoa enzyme- polynucleotide phosphorylase was also helpful in polymerising RNA with defined sequences.

1. Mutations and Genetic Code:
Deletions and rearrangements in a segment of DNA result in loss or gain of a gene function.

Insertion or deletion of one or two bases, changes the reading frame from the point of insertion or deletion. Such mutations are referred to as frame-shift insertion or deletion mutations.

2. tRNA- the Adapter Molecule:
Francis Crick proposed that an adapter molecule would bind to specific amino acids. tRNA has an anticodon loop and an amino acid accepter end to which it binds to amino acids. tRNAs are specific for each amino acid.

For initiation, there is another specific tRNA that is referred to as initiator tRNA. There are no tRNAs for stop codons.

Two-dimensional structure of tRNA looks like a clover-leaf. But in three-dimensional structure of tRNA looks like inverted L.

Translation
Translation is the process of polymerisation of amino acids to form a polypeptide. The order and sequence of amino acids are defined by the sequence of bases in the mRNA. The amino acids are joined by a bond which is known as a peptide bond. Formation of a peptide bond requires energy.

The activation of amino acids with ATP and linked to tRNA- a process commonly called as charging of tRNA or aminoacylation of tRNA. If two such charged tRNAs are brought close together the peptide bond is formed.

The ribosome also acts as a catalyst (23S rRNA in bacteria is the enzyme- ribozyme) for the formation of peptide bond.

A translational unit in mRNA is start codon (AUG) and the stop codon. mRNA also has some additional sequences that are not translated they are called as untranslated regions (UTR). The UTRs are present at both 5′-end (before start codon) and at 3′-end (after stop codon). They are required for efficient translation process.

The ribosome consists two subunits; a large subunit and a small subunit. For initiation, the ribosome binds to the mRNA at the start codon (AUG) that is recognised only by the initiator tRNA.

In elongation , amino acid linked to tRNA, and bind to the codon in mRNA by forming complementary base pairs with the tRNA anticodon. The ribosome moves from codon to codon along the mRNA.

Amino acids are added one by one and translated into Polypeptide. At the end, a release factor binds to the stop codon, terminating translation and releasing the complete polypeptide from the ribosome.

Regulation Of Gene Expression
The Lac operon:
In eukaryotes, the regulation is possible in

1. transcriptional level (formation of primary transcript),
2. processing level (regulation of splicing),
3. transport of mRNA from nucleus to the cytoplasm,
4. translational level.

For example E. coli synthesised the enzyme beta-galactosidase in the medium if the disaccharide, lactose is present.

Enzyme breakdown the lactose into galactose and glucose; the bacteria use them as a source of energy. The development and differentiation of embryo into adult organisms are also a result of the coordinated regulation of expression of several sets of genes.

In a transcription unit, the activity of RNA polymerase at a promoter is regulated by proteins. These regulatory proteins act both positively (activators) and negatively (repressors). The promoter regions of prokaryotic DNA is regulated by the interaction of adjacent operators. Each operon has its specific operator and specific repressor.

For example, lac operator is present only in the lac operon and it interacts specifically with lac repressor only.

1. The Lac operon:
The function of lac operon was first shown by Jacob and Monod.

Other examples are trp operon, ara operon, his operon, val operon, etc.

The lac operon consists of one regulatory gene (i gene) and three structural genes (z, y, and a).

Hence, all the three gene products in lac operon are required for metabolism of lactose. Lactose (inducer) is the substrate for the enzyme beta-galactosidase and it regulates switching on and off of the operon.

In the presence of an inducer, such as lactose, the repressor is inactivated by the inducer. Then RNA polymerase bind to the promoter and transcription proceeds. Regulation of lac operon by repressor is referred to as negative regulation.

Human Genome Project
This is mainly aims to find out the complete DNA sequence of human genome If two individuals differ, then their DNA sequences should also be different, at least at some places.

Human Genome Project was launched in the year 1990 (HGP). Human genome consists of approximately 3 × 109 bp.

HGP was coordinated by the U.S. Department of Energy and the National Institute of Health. The project was completed in 2003.

This project also aims to solve challenges in health care, agriculture, energy production, environmental remediation.

Methodologies:
For sequencing, the total DNA from a cell is isolated and converted into random fragments of relatively smaller sizes and cloned in suitable host using vectors. The cloning resulted into amplification of each piece of DNA fragment so that it could be sequenced with ease.

The commonly used hosts are bacteria and yeast, and the vectors are called as BAC (bacterial artificial chromosomes), and YAC (yeast artificial chromosomes). The fragments are sequenced using automated DNA sequencers that was developed by Frederick Sanger.

These sequences are then arranged based on some overlapping regions present in them. Alignment of these sequences are done with computer based programs. These sequences are annotated and assigned to each chromosome. The sequence of chromosome 1 was completed only in May 2006.

Another task was the construction of genetic and physical maps on the genpme. This was made possible by knowing the polymorphism of restriction endonuclease recognition sites, and some repetitive DNA sequences.

1. Salient Features of Human Genome:

Dna Fingerprinting
The 99.9 per cent of base sequence among humans is the same. The genetic differences between two individuals is calculated by comparing the two sets of 3 × 10⁶ base pairs.

It is the identification of differences in some specific regions in DNA sequence called as repetitive DNA,
These repetitive DNA are separated from bulk genomic DNA as different pegks during density gradient centrifugation.

The bulk DNA forms a major peak and the other small peaks are referred to as satellite DNA. Depending on base composition, length of segment, and number of repetitive units, the satellite DNA is classified into many categories,

1. Micro-satellites,
2. Mini-satellites etc.

These sequences do not code for any proteins and show high degree of polymorphism. DNA from every tissue (such as blood, hair-follicle, skin, bone, saliva, sperm etc.), of an individual show the same degree of polymorphism, they become very useful identification tool in forensic applications.

The polymorphisms are inheritable from parents to children DNA fingerprinting is the basis of paternity testing, in case of disputes.

The polymorphism in DNA sequence is the basis of genetic mapping and DNA fingerprinting, Polymorphism arises due to mutations. Allelic sequence variation results inheritable mutation.

Such variation are observed in non coding DNA sequence. These mutations accumulating generation after generation, and form one of the basis of variability/polymorphism.

The different types of polymorphisms ranging from single nucleotide change to very large scale changes. For evolution and speciation, such polymorphisms play very important role.

The technique of DNA Fingerprinting was initially developed by Alec Jeffreys. He used a satellite DNA as probe. It is called as Variable Number of Tandem Repeats (VNTR).

The technique, is based on Southern blot hybridisation using radiolabeled VNTR as probe.

It involves

1. isolation of DNA,
2. digestion of DNA by restriction endonucleases,
3. separation of DNA fragments by electrophoresis,
4. transferring (blotting) of separated DNA fragments to synthetic membranes, such as nitrocellulose or nylon,
5. hybridisation using labelled VNTR probe, and
6. detection of hybridised DNA fragments by autoradiography.

The VNTR belongs mini-satellite.lt is the small DNA sequence. Its copy number varies from chromosome to chromosome in an individual. The numbers of repeat show very high degree of polymorphism.

The size of VNTR varies in size from 0.1 to 20 kb. So after hybridisation with VNTR probe, the autoradiogram gives many bands of differing sizes.

These bands give a characteristic pattern for an individual DNA. It differs from individual to individual in a population except in the case of monozygotic (identical) twins.

Students can Download Chapter 3 Principles of Inheritance and Variation Notes, Plus Two Zoology Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Zoology Notes Chapter 3 Principles of Inheritance and Variation

Mendel’s Laws Of Inheritance
Gregor Mendel, conducted hybridisation experiments on garden peas and proposed the laws of inheritance in living organisms.

Inheritance Of One Gene
Mendel crossed tall and dwarf pea plants to study the inheritance of one gene. He collected the seeds produced as a result of this cross and grew them to generate plants of the first hybrid generation. This is called the Filial progeny or the F1.

Based on these observations,
Mendel proposed that ‘factors’ (genes) transmitted from parent to offspring through the gametes, over successive generations.

Genes which code for a pair of contrasting traits are known as alleles, i.e., they are alternative forms of the same gene.

Figure: A Punnett square used to understand a typical monohybrid cross conducted by Mendel between true-breeding tall plants and true-breeding dwarf plants.

According to Mendels experiment, true breeding tall are identical or homozygous TT and true breeding dwarf pea variety are also homozygous tt.

TT and tt are called the genotype of the plant while the terms tall and dwarf are the phenotype.

The production of gametes and the formation of the zygotes in the F1 and F2 plants can be understood from a diagram called Punnett Square.

The possible gametes are written on two sides, usually the top row and left columns. All possible combinations are represented in boxes below in the squares.

In the cross of tall TT(male) and dwarf tt (female) plants, the gametes produced by them are represented by T and t respectively. The all F₁ is Tt progeny.

The F₁ plants of genotype Tf are self-pollinated. They produces gametes of the genotype T and fin equal proportion. When fertilisation takes place, the pollen grains of genotype T have a 50 percent chance to pollinate eggs of the genotype T, as well as of genotype t.

From the Punnet square it is clearthat 1/4th of the random fertilisations lead to TT, 1/2 lead to Tt and 1/4th to tt.

Diagrammatic representation of a test cross:

Based on his observations on monohybrid crosses Mendel proposed two general rules first law is Law of Dominance and the Second Law or Law of Segregation.

1. Law of Dominance:

The law of dominance explains the ratio of 3:1 in F2.

2. Law of Segregation:

A homozygous parent produces all gametes that are similar while a heterozygous one produces two kinds of gametes.

Non mendelian inheritance:
a. Incomplete Dominance:
F1 phenotype not resemble either of the two parents The inheritance of flower colour in the dog flower (snapdragon or Antirrhinum sp.) is a good example.

In a cross between true-breeding red-flowered (RR) and true breeding white-flowered plants (rr), the F1 (Rr) was pink.


Explanation of the concept of dominance:
Here the normal allele produces the normal enzyme that is needed for the transformation of a substrate S the modified allele is responsible for production of –

1. the normal/less efficient enzyme, or
2. a non-functional enzyme, or
3. no enzyme at all

In the case(i), the modified allele is equal to the unmodified allele,

Figure: Results of monohybrid cross in the plant Snapdragon, where one allele is incompletely dominant over the other allele.

But in the case (ii) and (iii) if the allele produces a non-functional enzyme or no enzyme, the phenotype may be effected.

The unmodified (functioning) allele, which represents the original phenotype is the dominant allele and the modified allele is the recessive allele. So the recessive trait arise due to non-functional enzyme or because no enzyme is produced.

b. Co-dominance
Here F1 generation resembles both parents. A good example is different types of red blood cells that determine ABO blood grouping in human beings.

ABO blood groups are controlled by the gene I. The gene (I) has three alleles I^A, I^A and i. The alleles I^A and I^B produce a slightly different form of the sugar while allele i doesn’t produce any sugar.

So I^A and I^B are completely dominant over i, and when I^A and i are present only I^A expresses and when I^B and i are present I^B expresses.

when I^A and I^B are present together they both express their own types of sugars: this is because of codominance.

For example, starch synthesis in pea seeds is controlled by one gene. It has two alleles (B and b). Starch is synthesised by BB homozygotes and bb homozygotes have lesser efficiency in starch synthesis.

After maturation of the seeds, BB seeds are round and the bb seeds are wrinkled. Heterozygotes produce
round seeds, and so B seems to be the dominant allele. But, the starch grains produced are of intermediate size in Bb seeds.

Inheritance Of Two Genes
Mendel crossed pea plant seeds with yellow colour and round shape and seeds of green colour and wrinkled shape. Yellow colour was dominant over green and round shape dominant over wrinkled.

Y for dominant yellow seed colour and y for recessive green seed colour, R for round shaped seeds and r for wrinkled seed shape. The genotypes of the parents are RRYY and rryy.

Phenotypic ratio: round yellow(9) : round green(3) : wrinkled yellow (3) : wrinkled green(1).
Figure: Result s of a dihybrid cross where the two parents differed in two pairs of contrasting traits: seed colour and seed shape.

1. Law of Independent Assortment:
Based on dihybrid crosses (crosses between plants differing in two traits) Mendel proposed Law of Independent Assortment.

The law states that when two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters’.

In the dihybrid cross the phenotypes round-yellow; Wrinkled- yellow; round- green and wrinkled- green appeared in the ratio 9:3:3:1.

The segregation of 50 percent R and 50 per cent ris independent from the segregation of 50 percent Y and 50 percent y. Therefore, 50 percent of the r bearing gamete has Y and the other 50 percent has y.

Similarly, 50 percent of the R bearing gamete has Yand the other 50 percent hasy. Thus there are four genotypes of gametes (four types of pollen and four types of eggs). The four types are RY, Ry, rY and ry.

2. Chromosomal Theory of Inheritance:
According to Mendel law, factors (genes) are discrete units, but its existence was not proved In 1900, three Scientists (de Vries, Correns and von Tschermak) independently rediscovered Mendel’s results on the inheritance of characters.

Walter Sutton and Theodore Boveri noted that the behaviour of chromosomes was parallel to the behaviour of genes and used chromosome movement to explain Mendel’s laws.

Sutton united the chromosomal segregation with Mendelian principles and called as chromosomal theory of inheritance.

Experimental proof for the chromosomal theory of inheritance was given by Thomas Hunt Morgan and his colleagues. This led to discovery that variation occurs during sexual reproduction His studies were conducted on tiny fruit files, Drosophila melanogaster.

3. Linkage and Recombination:
Morgans dihybrid crosses in Drosophila reveals genes that are sex-linked.

They found that some genes were very tightly linked (showed very low recombination), while others were loosely linked (showed higher recombination).

His student Alfred Sturtevant found that frequency of recombination between gene pairs on the same chromosome is equivalent to the distance between genes and ‘mapped’ their position on the chromosome.

Sex Determination
Henking (1891) studied the spermatogenesis in an insects and X body. The ‘X body’ of Henking was given the name X-chromosome (sex chromosome).

Grasshopper is an example of XO type of sex determination in which the males have only one X-choromosome besides the autosomes, whereas females have a pair of X-chromosomes.

Insects and mammals including man:
XY type of sex determination is seen where both male (XY- heterogametic) and female (XX- homogametic) have same number of chromosomes. Both males and females bear same number of autosomes. i.e males have autosomes plus XY, while female have autosomes plus XX.

Male heterogamety:
In XO type and XY type, males produce two different types of gametes, Such types of sex determination mechanism is seen in drosophila and human male respectively.

Female heterogamety:
In birds the total number of chromosome is same in both males and females. But females produce two types of gametes.

Female birds have one Z and one W chromosome, where as males have a pair of Z-chromosomes besides the autosomes.

1. Sex Determination in Humans:
Out of 23 pairs of chromosomes, 22 pairs are same in both males and females; these are the autosomes. A pair of X-chromosomes are present in the female, whereas X and Y chromosome are present in males.

During spermatogenesis two types of gametes are produced of which 50 per cent carry the X- chromosome and the rest 50 per cent has Y-chromosome besides the autosomes.

Females produce only one type of ovum with an X-chromosome. In case the ovum fertilises with a sperm carrying X-chromosome the zygote develops into a female (XX) and with Y-chromosome results into a male offspring.

Mutation
It is the sudden change in the genetic make up of an organism. The loss (deletions) or gain (insertion/ duplication) of a segment of DNA, result in alteration in chromosomes. Alteration in chromosomes results in abnormalities or aberrations.

There are many chemical and physical factors that induce mutations. They are called as mutagens. Eg- physical mutagen – UV radiations.

Genetic Disorders
1. Pedigree Analysis:
It is the study of the family history of inheritance of a particular trait. Such an analysis of traits in a several of generations of a family is called the pedigree analysis. For this the standard symbols are used.

In human beings it helps to trace the inheritance of a specific trait, abnormality or disease. A number of disorders in human beings have been found to be associated with the inheritance of altered genes or chromosomes.

2. Mendelian Disorders:
Genetic disorders are classified into two categories. Mendelian disorders and Chromosomal disorders.

Haemophilia:
Haemophilia is the X-linked recessive trait that is transmitted from carrier female to male progeny in the zig-zag manner (Sex linked recessive disease) This is the bleeders disease mainly observed in family of Queen Victoria.

In an affected individual a simple cut will result in non-stop bleeding. The heterozygous female (carrier) for haemophilia transmit the disease to sons.

Sickle-cell anaemia:
This is an autosome linked recessive trait transmitted from parents to the offspring when both the partners are carrier for the gene. The disease is controlled by a single pair of allele, HbA and HbS.

The homozygous individuals for HbS (Hb^SHb^S) show the diseased phenotype. Heterozygous (Hb^AHb^S) individuals are carrier of the disease.

The defect is caused by the substitution of Glutamic acid by Valine at the sixth position of the beta globin chain of the haemoglobin molecule.

It is due to the single base substitution at the sixth codon of the beta globin gene from GAG to GUG.

The mutant haemoglobin molecule under low oxygen tension causing the change in the shape of the RBC from biconcave disc to elongated sickle like structure.

Phenylketonuria:
This is an autosomal recessive trait. This is due to the deficiency of enzyme that converts the amino acid
phenylalanine into tyrosine. As a result of this phenylalanine is accumulated and converted into phenylpyruvic acid.

Accumulation of these in brain results in mental retardation. These are also excreted through urine.

3. Chromosomal disorders:
Failure of segregation or non-disjunction of chromosomes during cell division results in the gain or loss of a chromosome(s), called aneuploidy. For example

Failure of cytokinesis results in an increase in a whole set of chromosomes in an organism. This phenomenon is known as polyploidy. This is mainly seen in plants.

If an additional copy of a chromosome is added. This is called trisomy Eg- Down’s Syndrome and Klinefelter’s syndrome or lack of copy of a chromo^ome( monosomy) Eg- Turner’s syndrome.

Down’s Syndrome: (Trisomy of 21):
The affected individual is short statured with small round head, furrowed tongue and partially open mouth. Palm is broad with characteristic palm crease. Physical, psychomotor and mental development is retarded.

Klinefelter’s Syndrome:
This is due to the trisomy of sex chromosome 44 autosomes+XXY. Individuals show feminine development i.e development of breast, i.e., Gynaecomastia Such individuals are sterile.

Turner’s Syndrome:
This is due to absence of one of the X chromosomes, i.e. 44 autosomes+ XO, Such females are sterile. The ovaries are rudimentary and lack other secondary sexual characters.

Students can Download Chapter 2 Reproductive Health Notes, Plus Two Zoology Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Zoology Notes Chapter 2 Reproductive Health

Reproductive health – problems and strategies
The Govt of India has started family planning (1951)and ‘Reproductive and Child Health Care (RCH)
programmes’ that helps
1. To create awareness among people about various reproduction related aspects.

2. Introduction of sex education in schools to avoid myths and misconceptions about sex-related aspects.

3. The information about reproductive organs, adolescence and related changes, safe and hygienic sexual practices, sexually transmitted diseases (STD), AIDS, etc., would help adolescent age group to lead a reproductively healthy life.

4. The information of available birth control options, care of pregnant mothers, post-natal care of the mother and child, importance of breastfeeding, equal opportunities for the male and the female child, etc., are the important components build up a socially responsible and healthy society.

5. The ban on amniocentesis for sex-determination helps to legally check increasing female foeticides, massive child immunisation, etc., are some programmes.

Population Explosion And Birth Control
According to the census report of 2001

Population increased due to decreased

1. Maternal mortality rate (MMR)
2. Infant mortality rate (IMR)

According to the 2001 census report, the population growth rate was 1.7 per cent.
Marriageable age raised to 18 years for females and 21 years for males. Government was taken measures to check this population growth rate by the contraceptive methods.

An ideal contraceptive should be user-friendly, easily available, effective and reversible with no or least side-effects.. Natural/Traditional, Barrier, lUDs, Oral contraceptives, Injectables, Implants and Surgical methods.

Natural Methods:
Periodic abstinence – Here the couples avoid or abstain from coitus from day 10 to 17 of the menstrual cycle.

Withdrawal or coitus interruptus is another method in which the male partner withdraws his penis from the vagina just before ejaculation so as to avoid insemination.

Lactational amenorrhea This method is based on the fact that ovulation and therefore the cycle do not occur during the period of intense lactation following parturition. So chances of conception are almost nil.

Barrier Method:
Condoms (Nirodh’) are barriers made of thin rubber/ latex sheath that are used to cover the penis in the male or Wagina and cervix in the female, just before coitus. This can prevent conception.

Use of condoms have additional benefit of protecting the user from STDs and AIDS. Both the male and the female condoms are disposable.

Diaphragms, cervical caps and vaults are also barriers made of rubber that are inserted into the female reproductive tract to cover the cervix during coitus. So it helps to prevent conception by blocking the entry of sperms through the cervix.

Intra Uterine Devices (lUDs):
IUDs are ideal contraceptives for the females. These devices are inserted by doctors or expert nurses in the uterus through vagina.

Two types are copper releasing lUDs (CuT, Cu7, Multiload 375) and the hormone releasing lUDs (Progestasert, LNG-20)

IUDs increase phagocytosis of sperms within the uterus and the Cu ions released suppress sperm motility and the fertilising capacity of sperms.

The hormone releasing lUDs make the uterus unsuitable for implantation It is one of most widely accepted methods of contraception in India.

Oral contraceptives(pills) contain either progestogens or progestogen-estrogen combinations.

Pills have to be taken daily for a period of 21 days starting within the first five days of menstrual cycle. After a gap of 7 days (during which menstruation occurs) it has to be repeated in the same pattern to prevent conception.

It helps to inhibit ovulation and implantation as well as to prevent entry of sperms, eg-Saheli.

Saheli-a new oral contraceptive for the females-was developed by scientists at Central Drug Research Institute (CDRI) in Lucknow.

Administration of progestogens or progestogen-estrogen combinations or lUDs within 72 hours of coitus have been found to be very effective as emergency contraceptives to avoid possible pregnancy due to rape or casual unprotected intercourse.

Surgical Methods (Sterilisation):

In male it is called ‘vasectomy’ a small part of the vas deferens is removed or tied up through a small incision on the scrotum.

In female, ‘tubectomy’ a small part of the fallopian tube is removed or tied up through a small incision in the abdomen or through vagina.

Medical Termination Of Pregnancy (MTP)
Government of India legalised MTP in 1971 to avoid its misuse. So it helps to check indiscriminate and illegal female foeticides which are reported to be high in India.

It is important to avoid unwanted pregnancies either due to casual unprotected intercourse or failure of the contraceptive used during coitus or rapes.

MTPs are also essential in the cases where continuation of the pregnancy could be harmful or even fatal either to the mother or to the foetus or both.

MTPs are considered relatively safe during the first trimester, i.e., upto 12 weeks of pregnancy.

Sexually Transmitted Diseases (STD_s)
Diseases or infections which are transmitted through sexual inter course are called sexually transmitted diseases (STD) or venereal diseases (VD) or reproductive tract infections (RTI).
Common STDs.

Early symptoms of most of these are minor and include itching, fluid discharge, slight pain, swellings, etc., in the genital region.

Hepatitis-B and HIV are transmitted by sharing of injection needles, surgicaljnstruments, etc. with infected persons and transfusion of blood, from an infected mother to the foetus.

All diseases are completely curable except hepatitis-B, genital herpes, and HIV infections.
The important steps to control STDs are given below.

Infertility
In the case of infertility, corrections are not possible, the couples could be assisted to have children through certain special techniques commonly known as assisted reproductive technologies (ART).

Students can Download Chapter 1 Human Reproduction Notes, Plus Two Zoology Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Zoology Notes Chapter 1 Human Reproduction

The Male Reproductive System
It consists of

Diagrammatic view of male reproductive system:

The testes are seen in a pouch called scrotum. It helps in maintaining the low temperature of the testes (2 – 2.5° C).

Each testis has about 250 compartments called testicular lobules. Each lobule contains one to three highly coiled seminiferous tubules in which sperms are produced.

Seminiferous tubule:
It consists of

The male germ cells produce sperm Sertoli cells provide nutrition to the germ cells. Leydig cells secrete testicular hormones called androgens:

Male sex accessory ducts:
It consists of
The seminiferous tubules of the testis open into rete testis

The vasa efferentia open into epididymis. The epididymis leads to vas deferens. It receives a duct from seminal vesicle and opens into urethra as the ejaculatory duct.

The urethra extends through the penis to its external opening called urethral meatus. The penis is the male external genitalia made up of special tissue that helps in erection of the penis to facilitate insemination.

The enlarged end of penis called the glans penis is covered by a loose fold of skin called foreskin.

Male accessory glands:
It consists of

Secretions of these glands constitute the seminal plasma (fructose, calcium and certain enzymes). The secretions of bulbourethral glands helps in the lubrication of the penis.

The Female Reproductive System
It consists of

Digrammatic sectional view of female reproductive system:

Ovaries (primary female sex organ) produce the female gamete (ovum) and several steroid hormones (ovarian hormones).

Each ovary is about 2 to 4 cm in length and is connected to the pelvic wall and uterus by ligaments.

Female accessory ducts:
It consists of
The oviducts (fallopian tubes – 10 – 12 cm long)
uterus
vagina
Its parts

The uterus opens into vagina through a narrow cervix. The cavity of the cervix is called cervical canal. The wall of the uterus has three layers of tissue.

1. External perimetrium
2. Middle myometrium and
3. Inner endometrium

The endometrium undergoes cyclical changes during menstrual cycle while the myometrium exhibits strong contraction during delivery of the baby.

Female external genitalia:
It consists of

1. Mons pubis (cushion of fatty tissue covered by skin and pubic hair)
2. Labia majora (fleshy folds of tissue extend down from the mons pubis and surround the vaginal opening)
3. Labia minora (paired folds of tissue under the labia majora)
4. Hymen (opening of the vagina is often covered partially by a membrane)
5. Clitoris (tiny finger-like structure which lies above the urethral opening)

The hymen is torn during the first coitus (intercourse). Mammary glands (paired structures (breasts)). 15-20 mammary lobes containing clusters of cells called alveoli. The cells of alveoli secrete milk, which is stored in the cavities of alveoli.

Gametogenesis
Spermatogenesis:

Some of the spermatogonia( diploid) called primary spermatocytes undergo meiosis. First meiotic division (reduction division) leading to formation of two equal haploid cells called secondary spermatocytes, second meiotic division produce four equal haploid spermatids.

The spermatids are transformed into spermatozoa (sperms) by the process called spermiogenesis.

After spermiogenesis, sperm heads become embedded in the Sertoli cells, and are finally released from the seminiferous tubules by the process called spermiation.
The GnRH stimulates secretion of two gonadotropins

1. Luteinising hormone (LH)
2. Follicle stimulating hormone (FSH).

LH acts at the Leydig cells and secrete androgens that stimulate the process of spermatogenesis. FSH acts on the Sertoli cells and stimulates secretion of some factors which help in the process of spermiogenesis.

Sperm:
Structure of sperm
It consists of

The sperm head is covered by a cap-like structure, acrosome (contains the enzymes that help fertilisation of the ovum).

The middle piece possesses numerous mitochondria, which produce energy for the sperm motility.

The human male ejaculates about 200 to 300 million sperms during a coitus of which 60 per cent sperms have normal shape and 40 per cent of show vigorous motility.

The Secretions of epididymis, vas deferens, seminal vesicle and prostate are essential for maturation and motility of sperms.

The seminal plasma with the sperms constitute the semen.

Oogenesis:
Oogonia are formed in embryonic stage udergores meiotic division to form primary oocytes. Primary oocyte then surrounded by a layer of granulosa cells and forms primary follicle.

During puberty 60,000-80,000 primary follicles are found in each ovary. The primary follicle is surrounded by more layers of granulosa and become secondary follicles.

Spermatogenesis

The secondary follicle become a tertiary follicle with fluid filled cavity called antrum. The primary oocyte within the tertiary follicle completes its first meiotic division( unequal division) and forms large haploid secondary oocyte and a tiny first polar body.

The tertiary follicle changes into the mature follicle or Graafian follicle.
Diagrammatic section view of ovary:

The secondary oocyte then forms a new membrane called zona pellucida surrounding it.

Menstrual Cycle
Diagrammatic representation of various events during a menstrual cycle:

1. The menstrual phase:
First menstruation begins at puberty and is called menarche. In human females it is repeated at interval of about 28/29 days.

The menstrual flow is due to the breakdown of endometrial lining of the uterus and its blood vessels which forms liquid that comes out through vagina.

Menstruation only occurs if the released ovum is not fertilised. Lack of menstruation may be indicative of pregnancy.

2. The follicular phase:
During this phase, the primary follicles grows into mature Graafian follicle and endometrium of uterus regenerates through proliferation.

3. The ovulatory phase:
Both LH and FSH attain a peak level in the middle of cycle (about 14th day).

4. The luteal phase:
Remaining parts of the Graafian follicle transform into corpus luteum. The corpus luteum secretes large amounts of progesterone which helps in the maintenance of the endometrium (implantation of the fertilized ovum).

In the absence of fertilisation, the corpus luteum degenerates. This causes disintegration of the endometrium leading to menstruation.In human beings, menstrual cycles ceases around 50 years of age termed as menopause.

Fertilisation And Implantation
During copulation (coitus) semen is released by the penis into the vagina (insemination).

Ovum surrounded by few sperms:

During fertilisation, a sperm comes in contact with the zona pellucida layer of the ovum and induces changes in the membrane that block the entry of additional sperms.

The secretions of the acrosome help the sperm enter into the cytoplasm of the ovum through the zona pellucida and the plasma membrane. This induces the completion of the meiotic division of the secondary oocyte and forms a second polar body and a haploid ovum (ootid).

All the haploid gametes produced by the female (ova) have the sex chromosome X whereas in the male gametes (sperms) the sex chromosome could be either X or Y, hence, 50 per cent of sperms carry the X chromosome while the other 50 per cent carry the Y.

The zygote carrying XX would develop into a female baby and XY would form a male. During fertilisation, a sperm comes in contact with the zona pellucida layer of the ovum and induces changes in the membrane that block the entry of additional sperms.

Transport of ovum, fertilisation and passage of growing embryo through fallopian tube:

The secretions of the acrosome help the sperm enter into the cytoplasm of the ovum through the zona pellucida and the plasma membrane. This induces the completion of the meiotic division of the secondary oocyte and forms a second polar body and a haploid ovum (ootid).

All the haploid gametes produced by the female (ova) have the sex chromosome X whereas in the male gametes (sperms) the sex chromosome could be either X orY, hence, 50 percent of sperms carry the X chromosome while the other 50 percent carry the Y.

The zygote carrying XX would develop into a female baby and XY would form a male. The mitotic division of zygote is called cleavage and forms 2, 4, 8, 16 daughter cells called blastomeres. The embryo with 8 to 16 blastomeres is called a morula. The morula continues to divide and transforms into blastocyst then it moves into the uterus.

The outer layer of blastocyst is called trophoblast and an inner group of cells called inner cell mass. The trophoblast layer gets attached to the endometrium and the inner cell mass gets differentiated as the embryo.

Later the blastocyst becomes embedded in the endometrium of the uterus. This is called implantation and it leads to pregnancy.

The milk produced during the initial few days of lactation is called colostrum which contains several antibodies provide resistance for the new-born babies.

Students can Download Chapter 8 Environmental Issues Notes, Plus Two Botany Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Botany Notes Chapter 8 Environmental Issues

Air pollution
Pollutants are harmful substances that affect growth and yield of crops and cause premature death of plants. In animals they affect the respiratory system and causes diseases.

Smoke stacks of thermal power plants, smelters and other industries release particulate and gaseous air pollutants together with harmless gases, such as nitrogen, oxygen, etc.

Electrostatic precipitator:

These are separated using electrostatic precipitator which can remove over 99 per cent particulate matter present in the exhaust from a thermal power plant.

At high voltage the electrons produced in an instrument are attached to dust particles giving them a net negative charge. These charged dust particles are attracted by collecting plates. Then reducing the velocity of air between the plates which help the dust to fall.

Automobiles are the largest source of air pollution in big cities .It is avoided by using lead-free petrol or diesel and catalytic converters, (platinum-palladium and rhodium as the catalysts) for reducing emission of poisonous gases.

If once fitted the catalytic converter, there must be used unleaded petrol because lead in the petrol inactivates the catalyst.

1. Controlling Vehicular Air Pollution:
A Case Study of Delhi:
Analysis showed that in 1990s, Delhi ranked fourth among the 41 most polluted cities of the world. The serious air pollution problems in Delhi was reduced after filing public interest litigation (PIL) in the Supreme Court of India. After that Delhi govt, orderd of using compressed natural gas (CNG) in public transport, i.e., buses.

The supply of CNG for major distribution centres through pipelines is difficult. In the meantime Delhi govt, is also taken parallel steps for reducing vehicular pollution that is to

Control pollution in big cities:

1. Avoid the use of old vehicles
2. Use of unleaded petrol
3. Use of low-sulphur petrol and diesel
4. Use of catalytic converters in vehicles,
5. Application of strict pollution level norms for vehicles, etc.

The new auto fuel policy introduced by the Government of India is to reduce the sulphur and aromatic content in petrol and diesel fuels.

The goal, according to the roadmap, is to reduce sulphur to 50 ppm in petrol and diesel and bring down the level to 35 percent. For these purpose, vehicle engines should be upgraded.

The Bharat Stage II (equivalent to Euro-ll norms) is applicable to all automobiles throughout the country from April 1, 2005.

Analysis shows that, great reduction in CO₂ and SO₂ level in Delhi between 1997 and 2005. In India, the Air (Prevention and Control of Pollution) Act came into force in 1981, but was amended in 1987 to include noise as an air pollutant. It causes psychological and physiological disorders in humans.

It is necessary to reduce noise by using sound absorbing materials in industries. Govt, laws are there to reduce noise pollution around hospitals and schools by avoiding the use of air – horns, restriction in the use of loudspeakers etc.

Water Pollution And Its Control
To safeguard water resources, Government of India has passed the Water (Prevention and Control of Pollution) Act, 1974. It helps to maintain the water bodies clean.

1. Domestic Sewage and Industrial Effluents:
About 0.1 per cent impurities present in domestic sewage unfit for human use. Domestic sewage mainly contains biodegradable organic matter, which is decomposed by bacteria and other micro-organisms. The amount of organic matter present in sewage can be measured by Biochemical Oxygen Demand (BOD).

For the biodegradation of organic matter by micro-organisms require plenty of oxygen, it results in sharp decline in dissolved oxygen. This causes mortality of fish and other aquatic creatures.

Presence of large amounts of nutrients in waters also causes excessive growth of planktonic(free-floating) algae, called an algal bloom which gives colour to the water bodies. Algal blooms cause lose of the water quality and fish mortality. Some are toxic to human beings and animals.
Effect of sewage discharge on some important characteristics of water:

Presence of excessive nutrients cause water hyacinth (Eichhornia crassipes), to grow in plenty, it causes blocks in our waterways. These are plants of the world’s most problematic aquatic weed called Terror of Bengal’. They grow abundantly in eutrophic water bodies, and lead to an imbalance in the ecosystem of the water body.
View of algal bloom:

Sewage from homes and hospitals contain undesirable pathogenic microorganisms it causes outbreak of serious diseases, such as dysentery, typhoid, jaundice, cholera, etc.

Domestic sewage from industries like petroleum, paper manufacturing, metal extraction and processing, chemical manufacturing, etc. contains as mercury, cadmium, copper, lead, etc.

The concentration of DDT is increased at successive trophic levels, it starts at 0.003 ppm in water, it can ultimately can reach 25 ppm in fish-eating birds, through biomagnification.

High concentrations of DDT disturb calcium metabolism in birds, which causes the thinning of eggshell and their premature breaking, causing decrease in bird populations.

Eutrophication is the natural aging of a lake by nutrient enrichment of soil. It occurs when nitrates and phosphates reaches water bodies by run off water.
Biomagnification of DDT in aquatic food chain:

Pollutants from man’s activities like effluents from the industries and homes can accelerate the aging process. This phenomenon is called Cultural or Accelerated Eutrophication. It causes depleting oxygen content of water and results the death of fish and other aquatic organisms.

Heated (thermal) wastewaters from thermal power plants destroy the growth of aquatic organisms. But it promote the growth of aquatic organisms in cold waters.

2. A Case Study of Integrated Waste Water Treatment:
An example of such an initiative was put into practice at the town of Areata, situated along the northern coast of California. Biologists from the Humboldt State University, and the townspeople created an integrated water treatment process within a natural system.
The cleaning occurs in two stages-

Ecological sanitation:
It is a sustainable system for handling human excreta, using dry composting toilets. This is a practical, hygienic, efficient and cost-effective solution to human waste disposal.

Here human excreta is recycled and reduces the need for chemical fertilisers. This is the basis of ‘EcoSan’ toilets in many areas of Kerala and Sri Lanka.

Solid Wastes
Solid wastes especially municipal solid wastes are wastes from homes, offices, stores, schools, hospitals, etc. contain, comprise paper, food wastes, plastics, glass, metals,rubber, leather, textile, etc. These are subjected to Sanitary landfills in which wastes are dumped in a depression after packed and covered with dirt everyday because burning is not practicable.

In metros Landfills are not really a good solution since the amount of garbage generation increased largely that these sites are getting filled too. Also there is danger of seepage of chemicals, etc., from these landfills polluting the underground water resources.

Kabadiwallahs and rag-pickers doing the of separation of materials for recycling. The biodegradable materials are put into deep pits in the ground for natural breakdown.

State Governments had decided to reduce the use of plastics and use of eco-friendly packaging. It is done by use of natural fibre carry-bags and avoid polythene bags.

1. Case Study of Remedy for Plastic Waste:
A plastic sack manufacturer Ahmed Khan in Bangalore has found a solution for problem of accumulating plastic waste. About 8 years ago, in collaboration with R. V. College of Engineering and the Bangalore City Corporation, he realised that the

Bitumen is a water repellant substance helps to increase road life. The raw material for creating Polyblend is any plastic film waste that brought about by rag pickers.

Electronic wastes (e-wastes) mainly contains irreparable computers and other electronic goods. It is generated in the developed world and are exported to developing countries, mainly to China, India and Pakistan where metals like copper, iron, silicon, nickel and gold are recovered during recycling process. In developing countries, during the recycling process workers are exposed to toxic substances.

Agro-chemicals And Their Effects
In the period of green revolution use of inorganic fertilizers, pesticides, herbicides, fungicides, etc. has increased crop production manifold. These chemical substances are toxic to other micro organisms in the soil and affect the terrestrial ecosystems. It also adversely affects the aquatic ecosystem and result the eutrophication of water bodies.

1. Case Study of Organic Farming:
Ramesh Chandra Dagar, a farmer in Sonipat, Haryana, in his agriculture land, he included

• Bee-keeping
• Dairy management
• Water harvesting, and
• Composting as a chain of processes, which support each other.

It is an example of sustainable agricultural method. There is no need to use chemical fertilisers for crops, as cattle excreta (dung) are used as manure. Crop waste is used to create compost, which can be used as a natural fertiliser or can be used to generate natural gas for satisfying the energy needs of the farm.

Radio Active Wastes
Nuclear energy is useful in many ways especially to generate electricity. But the disasters that occurred as accidental leakage in the Three Mile Island and Chernobyl incident and safe disposal of radioactive wastes are the main problems.

It was also realised that nuclear energy radiation is damaging to biological organisms, because it causes mutations. At high doses, nuclear radiation is lethal but at lower doses, it creates various disorders and cancer. Storage of nuclear waste must done in shielded containers buried within the rocks, about 500 m deep below the earth’s surface.

Greenhouse Effect And Global Warming
The term ‘Greenhouse effect’ has been derived from a phenomenon that occurs in a greenhouse. It looks like a small glass house and is used for growing plants especially during winter. It does not allow heat to escape.

The greenhouse effect is a naturally occurring phenomenon that is responsible for heating of Earth’s surface and atmosphere. If greenhouse effect is not there, the average temperature at surface of Earth would have been -18°C rather than the present average of 15°C.

The incoming raditions of sunlight reaches the earth’s surface re-emits heat in the form of infrared radiation but part of this does not escape into space as atmospheric gases (e.g., carbon dioxide, methane, CFC and nitrogen oxides) absorb a major fraction of it.

The molecules of these gases radiate heat energy, and a major part of which again comes to Earth’s surface, thus heating it up once again This cycle is repeated many a times. This leading to global warming.

To reduce the emission of green house gases it is necessary to

1. Cutting down use of fossil fuel
2. Improving efficiency of energy usage
3. Reducing deforestation
4. Planting trees and slowing down the growth of human population.

Ozone Depletion In The Stratosphere
There are two type of ozone that is ‘bad’ ozone, formed in the lower atmosphere (troposphere) that harms plants and animals. ‘Good’ ozone- this ozone is found in the upper part of the atmosphere (stratosphere), and it acts as a shield and absorbing ultraviolet radiation from the sun.

UV rays are harmful to living organisms since DNA and proteins of living organisms absorb it, and breaks the high energy chemical bonds within these molecules.

The thickness of the ozone in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units (DU).
Ozone hole in antartica area It is measured by Dobson unit:

Ozone gas is continuously formed by the action of UV rays on molecular oxygen, and also degraded into molecular oxygen in the stratosphere.

The balance between production and degradation of ozone in the stratosphere is disrupted due to
chlorofluorocarbons (CFCs).

It was first noticed in Antarctic region.

To reduce the emission of CFCs and other ozone depleting chemicals, an international treaty was formed known as the Montreal Protocol, signed at Montreal (Canada) in 1987.

Degradation By Improper Resource Utilisation And Maintenance
The important improper resource utilisation practices are
(1) Soil erosion and desertification:
The fertility of top-soil is lost due to over-cultivation, unrestricted grazing, deforestation and poor irrigation practices, resulting in arid patches of land. It result in the creation of desert.

(2) Waterlogging and soil salinity:
Irrigation without proper drainage of water leads to waterlogging in the soil. It also causes the deposition of salts on the land surface or starts collecting at the roots of the plants. This increased salt content and reduce the growth of crops and damaging to agriculture.

Deforestation

Deforestation occurs due to growing human population for timber, firewood, and several other purposes. Slash and burn agriculture, commonly called as Jhum cultivation in the north-eastern states of India, has also contributed to deforestation.

The ash is used as a fertiliser and the land is then used for farming or cattle grazing. The farmers then move on to other areas and repeat this process.
The consequences of deforestation are

1. Increased carbon dioxide concentration in the atmosphere
2. Loss of biodiversity due to habitat destruction
3. Disturbs hydrologic cycle
4. Causes soil erosion, and lead to desertification

Reforestation is the process of restoring a forest that once existed but was removed.

1. Case Study of People’s Participation in Conservation of Forests:
In 1731, the king of Jodhpur in Rajasthan asked one of his ministers to arrange wood for constructing a new palace. The minister and workers went to a forest near a village, inhabited by Bishnois, to cut down trees. Bishnois are opposed the act of ministers. Of which Amrita Devi-.her three daughters and hundreds of other Bishnois followed her, and thus lost their lives saving trees.

Another movement started at Garhwal Himalaya in 1974 was – Chipko Movement, here local women showed enormous bravery in protecting trees from the axe of contractors.

In 1980s Government of India has introduced the concept of Joint Forest Management (JFM) this is helpful to local communities for getting benefit of various forest products (e.g., fruits, gum, rubber, medicine, etc.) and thus the forest can be conserved in a sustainable manner.

Students can Download Chapter 7 Ecosystem Notes, Plus Two Botany Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Botany Notes Chapter 7 Ecosystem

Ecosystem – structure And Function
Interaction of biotic and abiotic components form the physical structure that is characteristic for each type of ecosystem. Different types of plant and animal species of an ecosystem gives its species composition. Life of species occupying different strata is called stratification For example, trees occupy top vertical strata of a forest, shrubs and herbs and grasses occupy the bottom layers.

Productivity
The primary energy source for functioning of an ecosystem is solar energy.

It is highest in a coral reef of aquatic ecosystems and in tropical rain forest of terrestrial ecosystems
Productivity is of two types

(a) Primary productivity:
It refers to the productivity at producer level. It is divided into two

1. Gross primary productivity – It refers to total photosynthesis i.e total amount of food formed by the producers
2. Net primary productivity – It refers to gross production minus losses by respiration and decomposition.

(b) Secondary productivity:
It is defined as the rate of formation of new organic matter by consumers. The annual net primary productivity of the whole biosphere is approximately 170 billion tons (dry weight) of organic matter.

Decomposition

Decomposition is a complex process of enzymatic reaction and involves the step-wise degradation of detritus (dead organic matter and excreta of animals and plants). It involves following processes.

Fragmentation of detritus:
Leaching:
It is process by which simple and water soluble compounds like simple sugars and inorganic nutrients move downward along with percolating gravitational water.

Catabolism:
It is the enzymatic break down of organic compound.

Humification:
It is process by which simplified detritus is changed into dark coloured amorphous substance called humus.

Mineralisation:
It involves the release of inorganic subtances (Water, C02, etc) and other nutrients (NH4+, Ca++, Mg++, K+, etc.) in the soil.
Decomposition cycle in terrestrial ecosystem:

Decomposition is largely an oxygen-requiring process. The rate of decomposition is controlled by chemical composition of detritus and climatic factors.

Energy flow
Of the incident solar radiation less than 50 percent of it is photosynthetically active radiation (PAR). Plants capture only 2-10 percent of the PAR. solar energy captured by plants flows through different organisms of an ecosystem.

Energy flow is the key function of an ecosystem. It is determined by two basic laws of thermodynamics.

First law of thermodynamics states that energy is neither created nor destroyed, but can betransffered from one component to another, or transformed from one state to another.

Second law of thermodynamics states that every energy transformation involves degradation or dissipation of energy from a concentrated to a dispersed form due to metabolic functions. Dissipation of energy occures as heat. The remaining energy used in the synthesis of plant biomass.

Producers in a terrestrial ecosystem, include herbaceous and woody plants and an aquatic ecosystem are species like phytoplankton, algae, and higher plants. The energy trapped by the producer is passed on to a consumer.

They are hence called consumers. If animals feed on the producers, they are called primary consumers (herbivores.), and if the animals eat other animals which in turn eat the plants they are called secondary consumers.

The consumers that feed on these herbivores are carnivores, i.e primary carnivores Those animals that depend on the primary carnivores for food are called as secondary carnivores.
A simple grazing food chain (GFC) is depicted below:

The detritus food chain (DFC) begins with dead organic matter. It is made up of decomposers which are heterotrophic organisms, mainly fungi, and bacteria. They get energy from dead organic matter or detritus. These are also known as saprotrophs.

Detritus food chain is connected with the grazing food chain at some levels: some animals in an ecosystem are Omnivores, eg-cockroaches, crows, etc. These natural interconnections of food chains make it a food web.
Trophic levels in an ecosystem:

The different steps of food chain is known as trophic level. Producers belong to the first trophic level, herbivores (primary consumer) to the second and carnivores (secondary consumer) to the third. The amount of energy decreases at successive trophic levels. Detritus or dead biomass that serves as an energy source for decomposers.

Energy flow through different trophic levels:

Ecological pyramids
An ecological pyramid is a graphical representation of an ecological parameter, like number or biomass or accumulated energy at different trophic levels in a food chain in as ecosystem.
The three ecological pyramids are

The idea of ecological pyramids was developed by Charles Elton. An ecological pyramid may be upright (taping towards the tip) or inverted (widens towards the tip).

The base of each pyramid represents the producers or the first trophic level while the apex represents tertiary or top level consumer.

In most ecosystems, all the pyramids, of number, of energy, and biomass are upright, i.e., producers are more in number and biomass than the herbivores, and herbivores are more in number and biomass than the carnivores. Also energy at a lower trophic level is always more than at a higher level.

Ecological Succession
The successive replacement of biotic communities in an area over a period of time is known as ecological or biotic succession.

Basic types of succession:
Primary succession:
Primary succession which starts from the primitive substratum, where there was no previously any sort of living matter e.g. land formed by volcanic lava, development of forest climax on a barren land may take about 1,000 years.

Secondary Succession:
Secondary succession which starts from previously built up substrata with already existing living matter. Such areas include burned or cut forests, flooded lands, etc. such successions are comparatively more rapid. Time taken is about 50 – 100 years in case of a grassland and about 100 – 200 years for a forest.

1. Succession of Plants:
Depending mainly upon the nature of the environment succession is of two types hydrarch-starting in regions where water is in plenty, xerarch- where moisture is present in minimal amounts such as dry deserts, rocks, etc.

If succession occurs in medium water conditions, they are called mesarch.

Hydrarch:
It involves the ecological succession in the newly formed pond or lake.

Nutrient Cycling

It varies in different kinds of ecosystems. Nutrients are continuously exchanged between organisms and their physical environment. These exchanges are called nutrient cycling / biogeochemical cycles.
Nutrient cycles are of two types:

1. gaseous and
2. sedimentary

Cycles of gaseous matter are called gaseous cycles. The reservoir of gaseous matter is atmosphere, (e.g.,
nitrogen, carbon cycle).

Cycles of mineral matter are called Sedimentary cycles. The reservoir of mineral matter is lithosphere, (e.g., sulphur and phosphorus cycle.)

1. Ecosystem – Carbon Cycle:
Carbon cycling occurs through atmosphere, ocean and through living and dead organisms. The amount of carbon fixed in the biosphere through photosynthesis annually is 4 × 1013 kg. Decomposition of dead organic matter and fossil fuel, through respiratory activities, burning of wood, forest fire, deforestation and volcanic activity releasing CO₂ in the atmosphere.
Carbon cycle in biosphere:

2. Ecosystem – Phosphorus Cycle:
Phosphorus is a major component of biological membranes, nucleic acids, and cellular energy transfer systems. The natural reservoir of phosphorus is rock, which contains phosphorus in the form of phosphates.

When rocks are weathered, minute amounts of these phosphates dissolve in soil solution and are absorbed by the roots of the plants. The waste products and the dead organisms are decomposed by phosphate-solubilising bacteria releasing phosphorus.

Ecosystem Services
The products of ecosystem processes are named as ecosystem services, for example,

Robert Constanza and his colleagues have very recently tried to put price tags on nature’s life-support services. Researchers have put an average price tag of US $ 33 trillion a year on these fundamental ecosystems services. It is nearly twice the value of the global gross national product GNP which is US $ 18 trillion. Out of the total cost of various ecosystem services.

Students can Download Chapter 6 Organisms and Populations Notes, Plus Two Botany Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Botany Notes Chapter 6 Organisms and Populations

Organism And Its Environment

Regional and local variations within each biome lead to the formation of a wide variety of habitats.

The existence of life not only in favourable habitat but it occurs in scorching Rajasthan desert, rain-soaked Meghalaya forests, deep ocean trenches, torrential streams, permafrost polar regions, high mountain tops, boiling thermal springs, and stinking compost pits.

1. Major Abiotic Factors:
Temperature:
The average temperature on land varies seasonally, it decreases from the equator towards the poles and from plains to the mountain tops. It ranges from minus degree Celsius in polar areas and high altitudes to more than 50°C in tropical deserts in summer.

It is clear that mango trees cannot grow in temperate countries like Canada and Germany, and the snow leopards are not found in Kerala forests.

Actually temperature affects the kinetics of enzymes which influence the basal metabolism, activity and other physiological functions of the organism.

Water:
The productivity and distribution of plants is dependent on water. For aquatic organisms the quality (chemical composition, pH) of water is important.

The salt concentration (salinity in parts per thousand), is less than 5 per cent in inland waters, 30 – 35 per cent the sea and > 100 per cent in some hypersaline lagoons.

Freshwater animals cannot live for long in sea water and vice versa because of the osmotic problems.

Light:
It is an important factor for photosynthesis.

Small plants (herbs and shrubs) growing in forests are adapted to photosynthesise under very low light conditions because of tall canopied trees. Many plants require sunlight for the initiation of photoperiodic flowering.

Animals require the diurnal and seasonal variations in light intensity and duration (photoperiod) fortiming their foraging, reproductive, and migratory activities. The spectral quality of solar radiation is important for life.

The UV component of the spectrum is harmful to many organisms while other colour components of the visible spectrum are important for marine plants living at different depths of the ocean.

Soil:
The nature and properties of soil dependent on the climate and the weathering process. The characteristics of the soil determine the water holding capacity.

These characteristics, pH, mineral composition, and topography determine the vegetation in any area. In the aquatic environment, the sediment-characteristics determine the type of benthic animals in ocean.

2. Responses to Abiotic Factors:
During the course of millions of years many species would have evolved constant internal (within the body) environment that permits maximum efficiency of biochemical reactions and physiological functions that results overall ‘fitness’ of the species.

A person is able to do his/her work in temperature is 25°C when it is extremely hot or cold outside. It could be achieved at home, in the car while travelling, and at workplace by using an air conditioner in summer and heater in winter. Here the person’s homeostasis is maintained by artificial means.

How do other living organisms cope with the situation?
(i) Regulate:
Some organisms maintain their homeostasis by keeping up constant body temperature, constant osmotic concentration, etc.

Birds, mammals, and some lower vertebrate and invertebrate species are capable of such regulation i.e thermoregulation and osmoregulation. This is the characteristics of mammals to live in Antarctica or in the Sahara desert.

In summer season body of man sweat, it provide cooling effect. In Winter season, vyhen the temperature is much lower than 37°C, man start to shiver, a kind of exercise which produces heat and raises the body temperature. Plants do not have such mechanisms to maintain internal temperatures.

(ii) Conform:
Majority of animals and all plants cannot maintain a constant internal environment.

If the stressful external conditions are remain only for a short duration, the organism has two other alternatives.

(iii) Migrate:
The organism move temporarily from the stressful habitat to a more favourable area and return when stressful period is over. Some persons moving from Delhi to Shimla in summer season. During winter some birds from Siberia and other extremely cold northern regions migrate to Keolado National Park (Bhartpur) in Rajasthan.

(iv) Suspend:
In bacteria, fungi and lower plants produce thick walled spores during unfavourable Conditions. They germinate in suitable environment.

In higher plants the seeds and vegetative reproductive structures are dormant during adverse condition and germinate after getting favourable moisture and temperature.

In animals, especially bears go into hibernation during winter. Some snails and fish go into aestivation to avoid summer. Under unfavourable conditions many zooplankton species in lakes and ponds are subject to diapause, a stage of suspended development.

3. Adaptations:
Some organisms are subjected to physiological and behavioural adjustments. These responses are called adaptations Kangaroo rat in North American deserts is capable of meeting all its water requirements through its internal fat oxidation. It has the ability to concentrate its urine.

Opuntia, their leaves are reduced to spines and the flattened stems do photosynthesis. Mammals of colder climates have shorter ears and limbs to minimise heat loss. This is an Allen’s Rule In the polar seas aquatic mammals like seals have a thick layer of fat (blubber) below their skin that acts as an insulator and reduces loss of body heat.

In high altitude, some organism feels altitude sicknes due to low atmospheric pressure and low 02. Its symptoms include nausea, fatigue, and heart diseases. But, gradually get adapted and stop experiencing altitude sickness by increasing red blood cell production, decreasing the binding capacity of hemoglobin and by increasing breathing rate.eg- Many tribes live in the high altitude of Himalayas.

Archaebacteria seen in hot springs and deep sea hydrothermal vents where temperature is more than 1000°C.

Many fish thrive in Antarctic waters where the temperature is below 0°c. A large variety of marine invertebrates and fish live at great depths in the ocean where the pressure could be > 100 times the normal atmospheric pressure.

Desert lizards keep their body temperature constant by behavioural means. They bask in the sun and absorb heat when their body temperature drops, but move into shade when the surrounding temperature starts increasing.

Some species are capable of burrowing into the soil to escape from the above-ground heat.

Populations
1. Population Attributes:
Population has birth rates and death rates. The rates are expressed as the change in numbers with respect to the members of the population. If in a pond there are 20 lotus plants last year and through reproduction 8 new plants are added, so the current population is 28, birth rate is 8/20 = 0.4 offspring per lotus per year.

If 4 individuals in a laboratory population of 40 fruit flies died in a week, the death rate in the population during that period is 4/40 = 0.1 individuals per fruit fly per week.

Another attribute of a population is sex ratio. A population at any given time is composed of individuals of different ages. If the age distribution is plotted for the population, the resulting structure is called an age pyramid.

The shape of the pyramid indicates the growth status of the population i.e

1. growing,
2. stable and
3. declining.

Another important attribute of population is population Representation of age pyramids for human population density (designated as N) Total number is the measure of population density, it is difficult to determine if the counting is impossible.

In an area, if there are 200 Parthenium plants but only a single huge banyan tree with a large canopy, the population density of banyan is low when compared to that of Parthenium. In such cases, the per cent cover or biomass is the measure of the population size.

Number of fish caught pertrap is good measure of its total population density in the lake. The tiger census in our national parks and tiger reserves is based on pug marks and fecai pellets.

2. Population Growth:
Changes in population density that determined by four basic processes, natality, immigration mortality, and emigration.

1. Natality refers to the number of births during a given period
2. Mortality is the number of deaths in the population during a given period.
3. Immigration is the movement of individuals into the population
4. Emigration is the movement of individuals out of the population.

N is the population density at time t, then its density at time t + 1 is
Nt + 1 =Nt + [(B + I) – (D + E)]
Population density increase if the number of births plus the number of immigrants (B + I) is more than the number of deaths plus the number of emigrants (D + E).

If a new habitat is just being colonised, immigration contribute to population growth than birth rates.

Growth Models:
(i) Exponential growth:
When the resources in the habitat are unlimited, each species has the ability to grow in number. Here the population grows in an exponential or geometric fashion.

Population growth curve a when responses are not limiting the growth, plot Is exponential, b when responses are limiting the growth, plot is logistic, K ts carrying capacity

If in a population of size N, the birth rates are represented as b and death rates as d, then the increase or decrease in N during a unit time period t (dN/dt) will be

r is called the ‘intrinsic rate of natural increase’it is important for assessing impacts of any biotic or abiotic factor on population growth.

The above equation shows the exponential or geometric growth and results J-shaped curve The integral form of the exponential growth equation as

N_t = Population density after time t, N₀ = Population density at time zero, r = intrinsic rate of natural increase, e = the base of natural logarithms (2.71828).

(ii) Logistic growth:
Limited resources leads to competition between individuals and the ‘fittest’ individual will survive and reproduce. Governments of many countries introduced restraints to limit human population growth.

In nature, a given habitat has resources to support a maximum possible number, beyond which no further growth is possible. This is called as nature’s carrying capacity (K) for that species in that habitat.

So the population growth in limited resources show initially a lag phase, followed by phases of acceleration and deceleration and finally an stationary phase, and the population density reaches the carrying capacity.

A plot of N in relation to time (t) results in a sigmoid curve. This type of population growth is called Verhulst-Pearl Logistic Growth equation. It is represented by
dN/dt = rN\(\frac{(K-N)}{K}\)
Where N = Population density at time t
r = Intrinsic rate of natural increase
K= Carrying capacity

3. Life History Variation:
Populations evolve to maximise their reproductive fitness, called as Darwinian fitness. Some organisms breed only once in their lifetime (Pacific salmon fish, bamboo) while others breed many times during their lifetime (most birds and mammals). Some produce a large number of small-sized offspring (Oysters, pelagic fishes) while others produce a small number of large-sized offspring (birds, mammals).

4. Population Interactions:
It occurs between species. Interspecific interactions arise from the interaction of populations of two different species. It is beneficial, detrimental or neutral (neither harm nor benefit) to one of the species or both. Assigning a ‘+’sign for beneficial interaction, sign for detrimental and 0 for neutral interaction,
Population Interactions

Both the species benefit in mutualism and both lose in competition. In both parasitism and Predation one species is benifitted and the other is harmed (host and prey).

In commensalism one species is benefitted and the other is neither benefitted nor harmed. In amensalism one species is harmed whereas the other is unaffected.

(i) Predation:
In predation, the energy stored at consumer level from plants are transferred to the next. So the consumer level energy transfer mainly takes place from prey to predator. For example prey is deer and predator is tiger.

The introduction of prickly pear cactus into Australia causes the spreading of these plants into millions of hectares. Later the cactus was controlled by cactus-feeding predator (a moth) from its natural habitat. This is an example of Biological control methods.

Predators also help in maintaining species diversity in a community, by reducing the intensity of competition among competing prey species. In an American Pacific Coast, the starfish Pisaster is an important predator.

In a field experiment, when all the starfish were removed from intertidal area, more than 10 species of invertebrates became extinct within a year, because of interspecific competition.

If a predator overexploits its prey, it become extinct. Later predator become extinct for the lack of food. This is the reason why predators in nature are ‘prudent’.

Prey species also have defense mechanism to reduce the impact of predation. Some species of insects and frogs are cryptically-coloured (camouflaged) so the prey cannot be detected easily by the predator. If the prey is poisonous, it cannot be attacked by the predators. Eg- Monarch butterfly is distasteful to its predator (bird).

Plants have evolved some morphological and chemical defences against herbivores. Thorns (Acacia, Cactus) are morphological defence. Many plants produce and store chemicals that affect the herbivores digestion, reproduction and finally kill it.

The weed Calotropis produces poisonous cardiac glycosides and that affect cattle or goats browsing on this plant. Chemical substances that extract from plants (nicotine, caffeine, quinine, strychnine, opium, etc.,) are defences against grazers and browsers.

(ii) Competition:
The competition mainly for resources that takesplace among same species and different species. For example flamingoes coming into shallow South American lakes compete with resident fishes for their common food, the zooplankton in the lake.

In interference competition, the feeding efficiency of one species is reduced due to other species, even if resources (food and space) are abundant. So, in competition the fitness of one species is lower in the presence of another species.

According to Gause, when resources are limiting the competitively superior species eliminate the other species, This is an example of competitive exclusion.

When the goats introduced in the Galapagos island, Abingdon tortoise become extinct due to the greater browsing efficiency of the goats.

Another evidence of competition in nature is called ‘competitive release’. Some species restricted to small geographical area because of the presence of a competitively superior species.

Connell’s elegant field experiments showed that on the rocky sea coasts of Scotland, the larger and competitively superior barnacle Balanus dominates the intertidal area, and eliminates the smaller barnacle Chathamalus.

Actually the herbivores and plants are more adversely affected by competition than carnivores.
Gause’s Competitive Exclusion Principle’ states that two closely related species competing for the same resources cannot co-exist, as a result competitively inferior one is eliminated.

Some species shows ‘resource partitioning’.that is, if two species compete for the same resource, they avoid competition by choosing different times for feeding or different foraging patterns.

MacArthur showed that five closely related species of warblers living on the same tree were able to avoid competition and co-exist due to behavioural differences in their foraging activities.

(iii) Parasitism:
Many parasites are host-specific. Some parasites evolved special adaptations such as the

The life cycles of parasites consist of one ortwo intermediate hosts or vectors to facilitate parasitisation. The human liver fluke depends on two intermediate hosts to complete its life cycle. The malarial parasite needs a vector (mosquito) to cause disease in other hosts.

Majority of the parasites reduce the survival, growth and reproduction of the host and reduce its population density.

In Brood parasitism parasitic bird lays its eggs in the nest of its host and the host incubate them. The eggs of the parasitic bird resemble the host’s egg in size Examples of brood parasitism are cuckoo (koel) and the crow.

(iv) Commensalism:
This is the interaction in which one species benefits and the other is neither harmed nor benefited. An epiphytic orchid on a mango branch, and barnacles growing on the back of a whale get benefit. But the mango tree and the whale is neither harmed nor benefited.

The cattle egret and grazing cattle is an example of commensalism. Another example of commensalism is the interaction between sea anemone with stinging tentacles and the clown fish.

(v) Mutualism:
In this interaction both partner species are benefitted. Examples are Lichens (between a fungus and algae), mycorrhizae (between fungi and the roots of higher plants). The fungi help the plant in the absorption of essential nutrients from the soil while the plant in turn provides the energy-yielding carbohydrates.

Some examples of mutualism are found in plant-animal relationships. Plants need animals for pollinating their flowers and dispersing their seeds. Plants offer rewards in the form of pollen and nectar for pollinators and juicy and nutritious fruits for seed dispersers.

The Mediterranean orchid- Ophrys. petal of its flower shows the similarity with female bee in size, colour and markings. The male bee is attracted and ‘pseudocopulates’ with the flower, When this same bee pseudocopulates’ with another flower, it transfers pollen to it and thus, pollinates the flower.

Students can Download Chapter 5 Biotechnology and its Applications Notes, Plus Two Botany Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Botany Notes Chapter 5 Biotechnology and its Applications

Biotechnological Applications In Agriculture
The important methods that useful for increasing food production are

The Green Revolution helped to increase food production in many fold but it is not enough to meet the demand of growing human population. Here Genetically modified crops are the possible solution for this crisis.

GM (Genetically Modified) plants are useful in many ways

1. Made crops more tolerant to abiotic stresses (cold, drought, salt, heat).
2. Reduced reliance on chemical pesticides (pest-resistant crops).
3. Helped to reduce post harvest losses.
4. Increased efficiency of mineral usage by plants
5. Enhanced nutritional value of food, e.g., Vitamin ‘A’ enriched Golden rice.

Eg-Bt cotton, Bt corn, rice, tomato, potato, and soyabean, etc have a gene for resistance to insects.

Bt Cotton
Bt toxin producing cry genes are isolated from Bacillus thuringiensis and inserted into the several crop plants such as cotton. The isolation of genes depends upon the crop and the targeted pest because most Bt toxins are insect-group specific,
For example

Insecticidal protein of some species of Bacillus thuringiensis that kill certain insects such as lepidopterans (tobacco budworm, armyworm), coleopterans (beetles) and dipterans (flies, mosquitoes).

Bt toxin protein exist as inactive protoxins but it is converted into an active form in the presence of the alkaline pH of insect gut. The activated toxin binds to the surface of midgut epithelial cells and create pores that cause cell swelling and lysis and results in the death of insect.

Pest Resistant Plants:
Nematode Meloidegyne incognitia infects the roots of tobacco plants and causes a great reduction in yield. It is nessary to control the attack of insect pest.

The best method used to prevent the attack of nematode is RNA interference (RNAi). It involves silencing of a specific mRNA of nematode.

Here the complementary dsRNA molecule that binds to and prevents translation of the mRNA (silencing).

After the insertion of nematode-specific genes by Agrobacterium vectors into the host plant, it produce both sense and antisense RNA in the host cells. These two RNA’s being complementary to each other formed a double-stranded (dsRNA) that initiated RNAi and silenced the specific mRNA of the nematode.

Biotechnological Applications In Medicine
The recombinant DNA technological processes that helpful in the mass production of safe and more effective therapeutic drugs.

1. Genetically Engineered Insulin:
Insulin for diabetes was extracted from pancreas of slaughtered cattle and pigs, it caused allergic disease in some patients. In humans, insulin is synthesised as a prohormone which contains an extra stretch called the C peptide. It is removed and converted into a fully mature and functional insulin.

It consists of two short polypeptide chains: chain A and chain B, that are linked together by disulphide bridges.

2. Gene Therapy:
It is the replacement of defective gene by functional gene. This is done by transferring the functional gene into the individual cells, tissues or embryo to treat a disease.

The first reported case of gene therapy was adenosine deaminase (ADA) deficiency that seriously affected the functioning of the immune system. It is due to the deficiency of gene for adenosine deaminase.

Before genetic engineering, ADA deficiency cured by bone marrow transplantation or enzyme replacement therapy.

In the first step of gene therapy, lymphocytes from the blood of the patient are cultured and functional ADA cDNA is introduced in it. Then, these cells are return back to the patient. So that the patient requires frequently such genetically engineered lymphocytes.

The permanent cure for such disease is to introduce functional ADA cDNA into cells at early embryonic stages.

3. Molecular Diagnosis:
Early diagnosis of disease is possible by

Low concentration of a bacteria or virus can be detected by amplification of their nucleic acid by PCR. It is used to detect HIV in suspected AIDS patients and detect mutations in suspected cancer patients It is also used to identify genetic disorders.

The presence of mutated gene can be detected by a probe. A single stranded DNA or RNA, tagged with a radioactive molecule. It is then hybridise to its complementary DNA in a clone of cells. By using autoradiography it is observed that the probe not have any complimentarity with the mutated gene.

Transgenic Animals
Out of many transgenic animals such as rats, rabbits, pigs, sheep, cows fish, etc. 95 percent of transgenic animals are mice.
Importance of such animals are
(i) Normal physiology and development:
Transgenic animals can be used to study of how genes are regulated, and how they affect the normal functions of the body and its development, e.g., study of insulin-like growth factor.

(ii) Study of disease:
Transgenic animals can be used to know, how genes contribute to the development of disease. Today transgenic models exist for many human diseases such as cancer, cystic fibrosis, rheumatoid arthritis and Alzheimer’s disease.

(iii) Biological products:
Transgenic animals that produce useful biological products. For example the introduction of genes which codes for a particular product such as human protein (-antitrypsin) used to treat emphysema. Another examples of disease treated are phenylketonuria (PKU) and cystic fibrosis.

In 1997, the first transgenic cow, Rosie, produced human protein-enriched milk (2.4 grams per litre). The milk contained the human alpha-lactalbumin. It is nutritionally a more balanced product for human babies than natural cow-milk.

(iv) Chemical and vaccine safety testing:
Transgenic animals carry genes that sensitive to toxic substances than non-transgenic animals. So they are exposed to the toxic substances and the effects studied.

Ethical Issues
Some ethical standards are maintained to evaluate the morality of all human activities that are either useful or harmful because the genetically modified organisms have unpredictable results.

Today the patents are given for products and technologies that make use of the genetic materials, plants, and other biological resources, that have long been identified, developed, and used by farmers and indigenous people of a specific region/country. This is an important problem.

For example, it is estimated that 200,000 varieties of rice grown in India. Of which Basmati rice is distinct for its aroma and flavour. It is significant because this variety was referred in ancient texts, folklore, and poetry.

In 1997, an American company got patent rights on Basmati rice. It was helped the company to sell a ‘new’ variety of Basmati in the US and abroad. It is derived from Indian farmer’s varieties. But the patenting procedure restricts the selling and exporting of Basmati rice by other countries.

Similar attempts have also been made to patent uses, products, and processes based on Indian traditional herbal medicines, e.g., turmeric neem.

Therefore it is necessary to resist these patent applications of other countries/individuals because they permanently take overfull control of our resources.

Biopiracy

Industrialised nations are financially rich but poor in biodiversity and traditional knowledge But the developing nations is rich in biodiversity and traditional knowledge related to bio-resources.

Here the sharing between developed and developing countries for traditional knowledge related to bio-resources has not been take place on the basis of compensatory payment. Therefore, some nations are developing laws to prevent such unauthorised exploitation of their bio-resources and traditional knowledge.

Recently Indian Parliament cleared the second amendment of the Indian Patents Bill, that takes such issues related to patents.

Students can Download Chapter 3 Strategies for Enhancement in Food Production Notes, Plus Two Botany Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Botany Notes Chapter 3 Strategies for Enhancement in Food Production

Animal Husbandry
It is the agricultural practice of breeding and raising livestock which deals with the care and breeding of livestock like buffaloes, cows, pigs, horses, cattle, sheep, camels, goats, etc., that are useful to humans.

It includes poultry farming and fisheries also. Fisheries include rearing, catching and selling offish, mollusks and crustaceans (prawns, crabs, etc.).

1. Management of Farms and Farm Animals:
The modem practices of farm management improves and enhances food production.

a. Dairy Farm Management:
It is the management of animals for milk and its products for human consumption. Diairyfarm management includes processes and systems that increase yield and improve quality of milk.
It includes

b. Poultry Farm Management:
It is the management of chicken, ducks, turkey and geese for food or their eggs.

Recently, the spread of ‘bird flu virus’ affected the egg industy and chicken consumption. The causative virus is H5N1.

2. Animal Breeding:
It aims for increasing the yield of animals and improving the desirable qualities of the produce.
The term ‘breed’ refers to a group of animals related by descent and similar in general appearance, features, size, configuration, etc.

When breeding is between animals of the same breed it is called inbreeding, while crosses between different breeds are called outbreeding.

Inbreeding

The progenies are evaluated and superior among them are identified for further mating.

The strategy used for developing purelines in cattle is the same as Mendel was practiced. Thus inbreeding is necessary for evolving a pureline in any animal. Inbreeding increases homozygosity.

It exposes harmful recessive genes that are eliminated by selection. It also helps in the accumulation of superior genes and elimination of less desirable genes. But the continued inbreeding reduces fertility and productivity. This is called inbreeding depression.

It is overcome by mating with unrelated superior animals of the same breed. This is usually helps to
restore fertility and yield.

Out-breeding
It is the breeding of the unrelated animals of the same breed (but having no common ancestors), or between different breeds (cross-breeding) or different species (inter-specific hybridisation).

(A) Out-crossing:
It is mating of animals within the same breed, but having no common ancestors on either side of their pedigree up to 4-6 generations. The offspring produced called as out-cross. It is the method used for increasing milk production, growth rate in beef cattle, etc.

(B) Cross-breeding:
It is the method of mating superior males of one breed with superior females of another breed. The progeny hybrid animals are used for commercial production.
Eg-Hisardale is a new breed of sheep developed in Punjab by crossing Bikaneri ewes and Marino rams.

Interspecific hybridisation
It is the method of mating of male and female animals of different species, the progeny shows combined desirable features of both the parents with economic value, e.g., mule.
Mule:

Controlled breeding experiments are carried out using artificial insemination. The semen is collected from the male parent and injected into the reproductive tract of the selected female.

Semen can be stored in freezing state and used later. Artificial insemination helps to overcome several problems of normal matings.
To improve chances of successful production of hybrids, other technique is used.

Multiple Ovulation Embryo Transfer Technology (MOET)
In this method, a cow is given hormones, with FSH-like activity, to induce follicular maturation and super ovulation, it produce 6 – 8 eggs/cycle. This animal isthen mated with an elite bull or artificially inseminated. The fertilised eggs at 8 – 32 cells stages, are removed and transferred to surrogate mother.

The genetic mother is available for another round of super ovulation. This technology is useful for cattle, sheep, rabbits, buffaloes, mares, etc.

3. Bee-keeping
Bee-keeping or apiculture is an age-old cottage industry for the maintenance of hives of honeybees for the production of honey. Honey is a food of high nutritive value and used in medicine. Beeswax, obtained from them are used in the preparation of cosmetics and polishes. It is an income-generating industry.

Bee-keeping can be practiced in the area having wild shrubs, fruit orchards and cultivated crops grows.
The most common species used is Apis indica.
For successful bee-keeping it requires

Bees are the pollinators of many crop species such as sunflower, Brassica, apple and pear. Keeping beehives in crop fields during flowering period increases pollination efficiency and improves the crop yield and honey yield.

4. Fisheries
It is an industry for the catching, processing or selling offish, shellfish or other aquatic animals. Some of the freshwater fishes Catla, Rohu and common carp and the marine fishes Hilsa, Sardines, Mackerel and Pomfrets are commercially important.

Fisheries provides income and employment to millions of fishermen and farmers Aquaculture and pisciculture is used to increase the production of aquatic plants and animals Increasd production offish and their products are coming under blue Revolution’.

Plant Breeding
This technology aims to increase yields .Here Green Revolution plays an important role to meet the national requirements in food production .This is achieved through development of high-yielding and disease resistant varieties in wheat, rice, maize, etc.

1. What is Plant Breeding?
It is the purposeful manipulation of plant species to create desired plant types that are good for cultivation, better yields and disease resistant. Major food crops of today are developed from domesticated varieties that obtained from conventional plant breeding practices.

Today the crop improvement programme mainly based on genetics, molecular biology and tissue culture, Plant breeders give importance to crop yield and quality, increased tolerance to environmental stresses (salinity, extreme temperatures, drought), resistance to pathogens (viruses, fungi, and bacteria) and increased tolerance to insect pests.

Main steps of plant breeding for developing a new genetic variety of a crop are

(i) Collection of variability:
Genetic variability is mainly created from wild relatives of the crop. For this all wild varieties, species and relatives of the cultivated species are collected and preserved. The entire collection (of plants/seeds) having all the diverse alleles for all genes in a given crop is called germplasm collection.

(ii) Evaluation and selection of parents:
The selected plants with desirable combination of characters are multiplied and used in the process of hybridisation.

(iii) Cross hybridisation among the selected parents:
The desired characters from two different plants (parents) are combined and produce hybrids. One parent with high protein quality is combined with disease resistance of other parent. This is a very time-consuming and tedious process because the pollen grains from the male parent are collected and placed on the stigma of female parent.

(iv) Selection and testing of superior recombinants:
It is the testing of progeny that have the desired character combination. This step yields plants that are superiorto both of the parents.

(v) Testing, release and commercialisation of new cuttivars:
The newly selected progenies are evaluated for their yield, quality, disease resistance, etc. It is done by growing these plants in the research fields and recording their performance under ideal fertiliser application, irrigation, and other crop management practices.

The evaluation is followed by testing the materials in farmers fields, for at least three growing seasons at several locations in the country. These progenies are then evaluated in comparison to the best available local crop cultivar.

The agriculture contribution to India’s GDP is 33 percent and employs nearly 62 percent of the population. After India’s independence, the main challenge was to produce food for the increasing population. The development of several high yielding varieties of wheat and rice led to the dramatic increase in food production in our country. This is called as the Green Revolution.

Wheat and Rice

This was due to the development of semi-dwarf varieties of wheat and rice. Nobel laureate Norman E. Borlaug, at International Centre for Wheat and Maize had developed semi-dwarf wheat.

In 1963, high yielding and disease resistant wheat Sonalika and Kalyan Sona, were developed in India. Semi-dwarf rice varieties were developed from IR – 8 and Taichung Native-1. Later better-yielding semi dwarf varieties Jaya and Ratna were developed in India.

Sugarcane:
Saccharum barberi of north India had poor sugar content and yield. But Saccharum officinarumm of south India had thicker stems and higher sugar content but did not grow well in north India.

These two species are crossed to get sugar cane varieties combining the desirable qualities of high yield, thick stems, high sugar and ability to grow in the sugar cane areas of north India.

Millets:
The successfully developed millets in India are Hybrid maize, jowar and bajra. They are high yielding and resistant to water stress.

2. Plant Breeding for Disease Resistance:
Breeding of cultivars resistant to disease increases food production. It helps to reduce the dependence on the use of fungicides and bacteriocides. Before breeding, it is important to know about the causative organism and the mode of transmission.

Methods of breeding for disease resistance
It is done by the conventional breeding techniques (hybridisation and selection) or by mutation breeding. Conventional breeding is facing some difficulties because the limited number of disease resistant genes present in crop varieties orwild relatives.

These are either multiplied ordirectly used in breeding. Other breeding methods used are selection amongst somaclonal variants and genetic engineering.

Crop varieties resistant to bacteria, fungi and viruses

Mutation
It is the method of changing the base sequence within genes resulting in the creation of a new character not found in the parental type. It is done by inducing mutations artificially or by using chemicals or radiations (like gamma radiations), and selecting and using the plants that have the desirable character. This process is called mutation breeding.

Eg-In mung bean, resistance to yellow mosaic virus and powdery mildew were induced by mutations. Wild relatives of cultivated species have resistant characters but very low yield. So it is a need to introduce the resistant genes into the high-yielding cultivated varieties.

3. Plant Breeding for Developing Resistance to Insect Pests:
Insect resistance in host crop plants can be developed in many ways particularly morphological, biochemical or physiological manner.

The above insect resistance is made by hybridization techniques.
Crop varieties resistant to pest

4. Plant Breeding for Improved Food Quality:
In the world about three billion people suffer from micronutrient ( particularly iron, vitamin A, iodine and zinc), protein and vitamin deficiencies or ‘hidden hunger’. Diets lacking essential micronutrients increase the risk for disease, reduce lifespan and reduce mental abilities.

Biofortification
It is the breeding of crops with higher levels of vitamins minerals, proteins and healthier fats.

1. Maize hybrids possess twice the amount of the amino acids (lysine and tryptophan).
2. Wheat variety, Atlas 66, with a high protein content,
3. Iron-fortified rice variety have five times iron content.

The Indian Agricultural Research Institute, New Delhi has also released several vegetable crops that are rich in vitamins and minerals.

1. Vitamin A-enriched carrots, spinach, pumpkin etc.
2. Vitamin C enriched bitter gourd,bathua, mustard, and tomato;
3. Iron and calcium enriched spinach and bathua;
4. Protein enriched beans – broad, lablab, French and garden peas.

Single Cell Protein (SCP):
More than 25 per cent of human population is suffering from hunger and malnutrition So the new alternate sources of proteins for animal and human nutrition is Single Cell Protein (SCP). Eg- Spirulina (source of good Protein).

Spirulina can grown on waste water from potato processing plants straw, molasses, animal mannure and even sewage to produce large quantities and food rich in protein, minerals, fats, carbohydrate and vitamins. This method of growing spirulina in waste waters reduces environmental pollution.

About 250 Kg cow produces 200 g of protein per day. But 250g of micro-organism like Methylophilus methylotrophus, expected to produce 25 tonnes of protein. Microbes like mushrooms are cultivated in large scale and it is an acceptable as food.

Tissue Culture
It is method in which plants are regenerated from explants. The capacity to generate a whole plant from any cell/explant is called totipotency.
Tissue culture medium

1. carbon source -sucrose
2. inorganic salts
3. vitamins
4. amino acids
5. growth regulators like auxins, cytokinins etc.

Micropropagation
It is the tissue culture method useful for the propagation of a large number of plants in very short durations.

All plants developed are genetically identical to the original plant, i.e., they are somaclones.
Many important food plants like tomato, banana, apple, etc. produced on commercial scale using this method.

Meristem culture
It is tissue culture method in which Healthy plants are developed from diseased plants or infected with a virus.

Here the meristem is taken from apical and axillary part and grow it in vitro to obtain virus-free plants Eg- banana, sugarcane, potato, etc.

Somatic hybridization
Here protoplast is isolated from plants by using enzymes. Isolated protoplasts from two different varieties of plants having desirable character are fused to get hybrid protoplasts, which can be further grown to form a new plant.

These hybrids are called somatic hybrids.
Eg- Protoplast of tomato is fused with that of potato and grown to form new hybrid plants containing the characters of tomato and potato. But here the desired combination of characters are not fully expressed for its commercial utilisation.

Students can Download Chapter 2 Sexual Reproduction in Flowering Plants Notes, Plus Two Botany Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Botany Notes Chapter 2 Sexual Reproduction in Flowering Plants

Flower – A Fascinating Organ Of Angiosperms
Flower shows aesthetic, ornamental, social, religious and cultural importance. They are used as symbols for conveying human feelings such as love, affection, happiness, grief etc.

Pre-Fertilisation: Structures And Events
The Hormonal and Structural changes leads to the differentiation and development of the floral primordium.

1. Stamen, Microsporangium and Pollen Grain:
A typical stamen consist of the long and slender stalk called the filament, and the bilobed structure called the anther. The number and length of stamens are variable in flowers of different species.

A typical angiosperm anther is bilobed i.e. dithecous.
It is a four-sided (tetragonal) structure consisting of four microsporangia located at the corners, two in each lobe. The microsporangia develop further and become pollen sacs.

Structure of microsporangium:
In young condition anther consist of cells called the sporogenous tissue. It is surrounded by four wall layers.

1. Epidermis
2. Endothecium
3. Middle layers
4. Tapetum.

The outer three wall layers shows protective function and help in breaking of anther to release the pollen. The innermost wall layer is the tapetum possessing more than one nucleus. It nourishes the developing pollen grains.

Microsporoqenesis:
During the development of anther, cells of the sporogenous tissue undergo meiotic divisions to form microspore tetrads. This is called microsporogenesis.

At maturity the microspores dissociate from each other and develop into pollen grains.

Pollen grain:
Pollen grain has hard outer layer called the exine, it is made up of sporopollenin (resistant organic material- not degraded by enzyme).

Exine surface shows Germ pores through which pollen tube come out. Exine shows different patterns and designs.

The inner wall of the pollen grain is called the intine. It is thin and continuous layer made up of cellulose and pectin. The cytoplasm of pollen grain is surrounded by a plasma membrane.

When the pollen grain mature, it contains two cells, the bigger vegetative cell and the smaller generative cell.

Pollen grains of many species cause severe allergies and bronchial infections leading to chronic respiratory disorders- asthma, bronchitis, etc. For example Parthenium or carrot grass causes pollen allergy.

Pollen grains are nutritious
The pollen tablets are used as food supplements. In western countries pollen products are used as tablets and syrups. Pollen consumption is important to increase the performance of athletes and race horses.

Pollen products

The viability of pollen grains is important in the success of fertilisation. The period of viability of pollen grains is variable and depends on the temperature and humidity.

In some cereals such as rice and wheat, pollen grains lose its viability within 30 minutes of their release, and in some members of Rosaceae, Leguminosae and Solanaceae, they maintain viability for months.

2. The Pistil, Meqasporangium (ovule) and Embryo sac:
The gynoecium is the female reproductive part. It consist of a single pistil (monocarpellary) or more than one pistil (multicarpellary). If more than one pistils are fused togetherthey are called syncarpous or free they are called apocarpous.

Each pistil has three parts the stigma, style and ovary. The stigma is the place where pollen grains falls. The style is the elongated slender part beneath the stigma.

The broad basal part of the pistil is the ovary. Inside the ovary is the ovarian cavity (locule). The placenta is located inside the ovarian cavity. The number of ovules in an ovary are different. It is one (wheat,paddy, mango) to many (papaya, water melon, orchids).

The Megasporangium (Ovule):
The ovule is a small structure attached to the p|acenta by means of a stalk called funicle. The body of the ovule fuses with funicle in the region called hilum (junction between ovule and funicle).

Each ovule has one or two protective envelopes called integuments. It covers entire ovule except at the tip where a small opening called the micropyle.

Opposite the micropylar end, is the chalaza, representing the basal part of the ovule. Enclosed within the integuments is a mass of cells called the nucellus.

Cells of the nucellus have abundant reserve food materials. Embryo sac or female gametophyte is located at there.

Ovule structure

Megasporoqenesis:
It is the process of formation of megaspores from the megaspore mother cell. A single megaspore mother cell (MMC) is differentiates in the micropylar region of the nucellus.

It is a large cell containing dense cytoplasm and a prominent nucleus. The MMC undergoes meiotic division to form female gametophyte.

In most flowering plants, only one megaspore is functional while other three degenerates. Functional megaspore develops into the female gametophyte (embryosac). This is termed as monosporic development.

The nucleus of the functional megaspore undergoes three repeated mitotic division to form 8 nucleate embryosac. After the 8-nucleate stage, cell walls are formed leading to the organisation of the typical female gametophyte or embryo sac.

Six of the eight nuclei are surrounded by cell walls and organised into cells; the remaining two nuclei, called polar nuclei are situated below the egg apparatus in the large central cell.

Three cells are arranged at the micropylar end and constitute the egg apparatus. It consists of two synergids and one egg cell. The synergids have special cellular thickenings at the micropylartip called filiform apparatus, it helps to guide the pollen tubes into the synergid.

Three cells at the chalazal end are called the antipodals. The large central cell has two polar nuclei.

3. Pollination:
It is the transfer of pollen grains to the stigma of a pistil.

Kinds of Pollination:
Depending on the source of pollen, pollination is divided into three types,
(i) Autogamy:
It is the transfer of pollen grains from the anther to the stigma of the same flower. In such flowers pollen release and stigma receptivity are at the same time and the anthers and the stigma should lie close to each other.

Some plants such as Viola, Oxalis, and Commelina produce two types of flowers – chasmogamous flowers (exposed anthers and stigma) and cleistogamous flowers (do not open flower). Cleistogamous flowers possible to the seed-set even in the absence of Pollinators.

Cleistogamous flowers

(ii) Geitonogamy:
Transfer of pollen grains from the anther to the stigma of another flower of the same plant. Functionally geitonogamy is a type of crosspollination but it is genetically similar to autogamy since the pollen grains come from the same plant.

(iii) Xenogamy:
Transfer of pollen grains from anther to the stigma of a different plant. This type of pollination occurs between genetically different species.

Agents of Pollination:
Pollination takesplace with abiotic (wind and water) and biotic (animals) agents. Majority of plants use biotic agents for pollination.

Wind pollination:
Pollen grains are light and non-sticky. They possess well-exposed stamens and feathery stigma. Such flowers have a single ovule in each ovary and numerous flowers packed into an inflorescence.
Example -corn cob – Here stigma and style which wave in the wind to trap pollen grains. Wind-pollination is more common in grasses.

Wind pollinated plant with well expesed stamens

Water Pollination:
Water Pollinated plants are mostly monocotyledons. In the lower plants such as algae, bryophytes and pteridophytes required water for the transport of male gametes and fertilisation.

Some examples of water pollinated plants are Vallisneria and Hydrilla (fresh water) and Zostera (marine sea- grasses).

In Vallisneria, the female flower reach the surface of water by the long stalk and the male flowers or pollen grains are released on to the surface of water. The anthers eventually reach the female flowers and the stigma.

In seagrasses, female flowers are submerged in water and the pollen grains are released inside the water. Pollen grains are long and ribbon like, some of them reach the stigma and results pollination.

In a majority of aquatic plants such as water hyacinth and water lily, the flowers emerge above the level of water and are pollinated by insects or wind.

Animal pollination:
Animals pollinating agents are Bees, butterflies, flies, beetles, wasps, ants, moths, birds (sunbirds and humming birds) and bats.

Bees are the dominant biotic pollinating agent.
Larger animals such as some primates (lemurs), arboreal (tree-dwelling) rodents, or even reptiles (gecko lizard and garden lizard) have also been reported as pollinators in some species.

The flowers pollinated by flies and beetles secrete foul odours to attract these animals. Flowers in turn provide rewards to the animals in the form of Nectar and pollen grains.

In some species flower provide safe places to lay eggs. Eg-tallest flower of Amorphophallus (Flower- 6 feet in height).

The plant Yucca and moth cannot complete their life cycles without each other. The moth deposits its eggs in the locule of the ovary and the flower in turn gets pollinated by the moth. The larvae of the moth come out of the eggs as the seeds start developing.

Outbreeding Devices
In plants the continued self-pollination result in inbreeding depression. Flowering plants have some devices to prevent self pollination and to promote cross pollination.

1. In some species, pollen release and stigma receptivity are not at the same time.
2. In some other species, the anther and stigma are placed at different positions so that the pollen cannot come in contact with the stigma of the same flower. Both these devices prevent autogamy.
3. In some other species self-incompatibility is the genetic mechanism Here pollen cannot germinate on the stigma of the same flower or other flowers of the same plant by inhibiting pollen germination or pollen tube growth in the pistil.
4. Another device to prevent self-pollination is the production of unisexual flowers. If both male and female flowers are present on the same plant such as castor and maize (monoecious), it prevents autogamy but not geitonogamy.

In papaya, male and female flowers are present on different plants. This condition prevents both autogamy and geitonogamy.

Pollen-pistil Interaction:
After pollination, the pistil recognize pollen of the wrong type( incompatible )or the right type(compatible). If it is of the right type, the pistil accepts the pollen and promotes post-pollination events that leads to fertilisation. If the pollen is of the wrong type, the pistil rejects the pollen by preventing pollen germination on the stigma or the pollen tube growth in the style.

Pollen-pistil interaction is a kind of dialogue mediated by chemical components of the pollen interacting with those of the pistil.

Pollen tube grows through the tissues of the stigma and style and reaches the ovary. The generative cell divides and forms the two male gametes during the growth of pollen tube in the stylar region.

Then it enters into the ovule through the micropyle and reaches the synergids. It is reported that filiform apparatus present at the micropylar part of the synergids guides the entry of pollen tube.

Artificial hybridization:
It is the method for the crop improvement programme. It aims for the creation of’superior’ varieties.lt is done by emasculation and bagging techniques.

Emasculation is not necessary for unisexual flowers. Here female flower buds are bagged before the flowers open. When the stigma becomes receptive, pollination is carried out using the desired pollen and the flower rebagged.

Double Fertilisation
By the help of filifiorm apparatus the pollen tube releases the two male gametes into the cytoplasm of the synergid. Then it fuses with the egg cell to form diploid zygote. This process is called syngamy.

The other male gamete moves towards the two polar nuclei located in the central cell and fuses with them to produce a triploid primary endosperm nucleus (PEN). This type of fusion contains three haploid nuclei, it is called triple fusion.

Post-Fertilisation: Structures And Events
Double fertilization leads to the development of endosperm and embryo, maturation of ovule into seed and ovary into fruit. These are called as post-fertilisation events.

1. Endosperm:
It serve as nutrition for the developing embryo. In most plants, the PEN undergoes successive nuclear divisions to give rise to free nuclei. This stage of endosperm development is called free-nuclear endosperm. Later cell wall formation occurs and the endosperm becomes cellular.

The tender coconut contains free-nuclear endosperm and the surrounding white kernel is the cellular endosperm. Some times the endosperm completely consumed by the developing embryo (e.g., pea, groundnut, beans) before seed maturation or it is persist in the mature seed (e.g. castor and coconut) and be used up during seed germination.

2. Embryo:
The micropylarend of the embrysac sac contains zygotes which divide only after the endosperm is formed. The early stages of embryo development (embryogeny) are similar in both monocotyledons and dicotyledons.

Dicotyledonous embryo consists of an embryonal axis and two cotyledons. The portion of embryonal axis above cotyledons is the epicotyl, which terminates with the plumule. The cylindrical portion below the cotyledons is hypocotyl that terminates at its lower end in the radical or root tip. The root tip is covered with a root cap.

Embryos of monocotyledons possess only one cotyledon. In the grass family the cotyledon is called scutellum that rs situated towards one side of the embryonal axis. At its lower end, the embryonal axis consists of radical and root cap enclosed by sheath called coleorhiza.

The portion of the embryonal axis above the level of attachment of scutellum is the epicotyl. Epicotyl has a shoot apex and a few leaf primordia enclosed by a sheath called the coleoptile.

3. Seed:
In angiosperms, the seed is the fertilised ovule. Seeds are formed inside fruits. It consists of seed coat, cotyledon and an embryo axis. The cotyledons stores food reserves.

The micropylar region facilitates entry of oxygen and water into the seed during germination. As the seed matures, its water content is reduced and metabolic activity of the embryo slows down. This inactive state of embryo is called dormancy.

If seed get suitable conditions, they germinates. During the embryo development ovules mature into seeds, the ovary develops into a fruit, integuments of ovules develops into seed coats and ovary wall becomes wall of fruit called pericarp.

Many fruits have evolved mechanisms for dispersal of seeds.

Dehydration and dormancy of mature seeds are important for storage So this is advantageous and to be used as food through out the year and also to raise crop in the next season.

In some species, the seeds lose viability within a few months but some seeds can remain alive for hundreds of years.

• The oldest seed is lupine, Lupinus arcticus excavated from Arctic Tundra.
• The seed germinated and flowered after of 10,000 years of dormancy.
• The 2000 years old viable seed – Date palm, Phoenixdactylifera discovered during the archeological excavation at King Herod’s palace near the Dead Sea.

Apomixis And Polyembryony
In some flowering plant species of Asteraceae and grasses produce seeds without fertilisation, it is called apomixis.

Hybrids are widely used in cultivation as food and vegetable crops because of increased productivity, but their production is expensive for the farmers.

If these hybrids are made into apomicts, there is no segregation of characters in the hybrid progeny. So the farmers can use these apomictic seeds to raise new crop year after year without losing the desirable characters.

Students can Download Chapter 1 Reproduction in Organisms Notes, Plus Two Botany Notes helps you to revise the complete Kerala State Syllabus and score more marks in your examinations.

Kerala Plus Two Botany Notes Chapter 1 Reproduction in Organisms

Asexual Reproduction

Binary fission in Amoeba

Budinq in yeast

Formation of zoospore

In plants the asexual reproduction mainly by the units of vegetative propagative structures. They are

1. Runner
2. Rhizome
3. Sucker
4. Tuber
5. offset
6. bulb.

They are capable of giving rise to new offspring. These structures are called vegetative

In water bodies, aquatic plant ‘water hyacinth’ is an invasive weed, called as the ‘Terror of Bengal’. Because it can propagate and spread all over the water body in a short period of time. It depletes the amount of oxygen, which leads to death of fishes.

Another examples of vegetative propagation are the origin of new plants from the buds (called eyes) of the potato tuber, from the rhizomes of banana and ginger.

In some plants adventitious buds arise from the notches present at margins of leaves eg- Bryophyllum. So it is used for the commercial propagation of plants.

Sexual Reproduction
It involves formation of the male and female gametes of the same individual or different individuals of the opposite sex. These gametes fuse to form the zygote which develops to form the new organism.

So the offsprings are not identical to the parents or amongst themselves. They are different in external morphology, internal structure, and physiology.

The growth period of organisms before reproduction is called the juvenile phase (vegetative phase).This phase shows variable durations in different organisms.

It is found that some plants flower throughout the year and some others that show seasonal flowering. But few plants exhibit unusual flowering phenomenon;

In animals, the juvenile phase is followed by morphological and physiological changes. But the duration of reproductive phase is varying in different organisms.

Some animals lay their eggs throughout the year but others seasonally. The females of placental mammals exhibit cyclical changes in the ovaries as well as hormones during the reproductive phase.

Many mammals exhibit such cycles only during favourable seasons in their reproductive phase, they are called as seasonal breeders. The other mammals are reproductively active throughout their reproductive phase they are called continuous breeders.

The end of reproductive phase is called as senescence or old age. Later it leads to death. In both plants and animals, hormones and environmental factors regulate the reproductive processes and behavioural expressions of organisms.
Events in sexual reproduction: It involves

1. pre-fertilisation
2. fertilisation
3. post-fertilisation

1. Pre-fertilisation Events:
These include gametogenesis and gamete transfer.

a. Gametogenesis:
It is the process of formation of two types of haploid gametes – male and female.

Sexuality in organisms:
Both the male and female reproductive structures are present in the same plant, they are bisexual or on different plants, they are unisexual.

Homothallic and monoecious are used to denote the bisexual condition Eg-some fungi and plants. Heterothallic and dioecious are used to denote unisexual condition.

In flowering plants, the unisexual male flower is staminate, i.e., bearing stamens, while the unisexual female flower is pistillate i.e bearing pistils.

In some flowering plants, both male and female flowers are present on the same individual (monoecious) eg- cucurbits and coconuts or on separate individuals (dioecious) eg- papaya and date palm.

Cell division during gamete formation:
Diploid parent that produces haploid gametes by reduction division meiotic division. But the haploid parent produces gametes by mitoticdivision.

Members of monera, fungi, algae, and bryophytes have haploid plant body, but pteridophytes, gymnosperms, angiosperms, and human beings have diploid parent body.

b. Gamete Transfer:
In most organisms, male gamete is motile and the female gamete is stationary. But few fungi and algae both types of gametes are motile.

They need water as a medium through which the male gametes moves. In algae, bryophytes and pteridophytes. water is the medium through which the gamete transfer takes place.

In seed plants, pollen grains are the carriers of male gametes, and ovule have the egg. In dioecious animals the gametes are formed in different individuals and the organism have special mechanism for gamete transfer.

In bisexual, self-fertilising plants, e.g. peas, transfer of pollen grains to the stigma takes place when it come in contact with the stigma. But in cross pollinating plants pollination agency helps the transfer. Pollen grains germinate on the stigma and the pollen tubes carrying the male gametes reach the ovule and discharge male gametes near the egg.

2. Fertilisation:
It is the fusion of gametes. This process is called syngamy leads to the formation of a diploid zygote.

In most aquatic organisms, such as algae, fishes and amphibians syngamy occurs outside the body of an organism (water) This type of gametic fusion is called external fertilisation.

For this, male partner release a large number of gametes into the surrounding medium (water). This is the case of bony fishes and frogs where a large number of offspring are produced.

One disadvantage is that the offspring are here prey, subjected to the attack of the predators. In terrestrial fungi, reptiles birds, mammals, and plants (bryophytes, pteridophytes, gymnosperms, and angiosperms), syngamy occurs inside the body of the organism, it is called internal fertilisation.

Here the male gamete is motile and has to reach the egg for fertilisation. In seed plants, the non-motile male gametes are carried to female gamete by pollen tubes.

3. Post-fertilisation Events:
It involves events afterthe formation of zygote.

a. The Zygote:
In fungi and algae, zygote develops a thick wall that is resistant to descication and damage. It undergoes a period of rest before germination.

In organisms with haplontic life cycle, zygote divides by meiosis to form haploid spores that grow into haploid individuals.

b. Embrvoaenesis:
It is the process of development of embryo from the zygote. During embryogenesis, zygote undergoes cell division and cell differentiation (modifications to form specialised tissues and organs).

In oviparous animals like reptiles and birds, the fertilised eggs are covered by hard calcareous shell, it undergoes period of incubation and young ones hatch out.

On the other hand, in viviparous animals, the zygote develops into a young one inside the body of the female organism. Afterthe period of growth, they are delivered out.

In flowering plants, the zygote is formed inside the ovule. The sepals, petals and stamens of the flower wither and fall off.

Kinds of fruits showing seeds and pericarp