Kerala Syllabus 10th Standard Biology Guide Chapter 8 The Paths Traversed by Life
Question 1.
What are the theories related to the origin of life on earth and are discussed even today?
Answer:
The Panspermia Theory and the Theory of Chemical Evolution are the theories related to the origin of life on earth and are discussed even today.
Question 2.
Explain the Panspermia Theory and the Theory of Chemical Evolution.
Answer:
The Panspermia argues that life originated in some other planet in the universe and accidentally reached the earth. The organic substances obtained from the meteors that fell on earth support this.
The hypothesis that evolved into the theory of chemical evolution is that life originated as a result of the changes that occurred in the chemical substances in seawater, under specific conditions in primitive earth. This theory is generally accepted by the scientific world due to its experimental evidences. The Russian scientist A.I. Oparin (1924) and the British scientist
J.B.S.Haldane (1929) are the proponents of this theory.
Question 3.
Explain the Theory of Chemical Evolution.
Answer:
The Russian scientist A.I. Oparin and the British scientist J.B.S. Haldane are the proponents of the theory of chemical evolution. Atmosphere of primitive earth contained gases like hydrogen, nitrogen, carbondioxide, hydrogen sulphide, Methane, ammonia and water vapour. No free oxygen was not present on primitive earth. Sources of energy of primitve earth was thunder and lightning, ultraviolet radiations and volcanic eruptions.
The earth cooled and the water vapour condensed. Incessant rains led to the formation of oceans and other water bodies. Molecules like monosaccharides, amino acids and fatty acids, nitrogen bases were formed in the oceans as a result of chemical reactions. Complex molecules like polysaccharides, proteins, fats, nucleotides, etc., were formed from simple molecules. Followed by Nucleicacids are formed covered by a lipid layer. This leads to the formation of primitive cell.
Question 4.
Prepare a table containing the comparison between chemical evolution and Urey – Miller experiment.
Answer:
| Situations | Primitive earth | Urey – Miller experiment |
| 1.Atmosphere | Contained gases like hydrogen, nitrogen, carbon dioxide, hydrogen sulphide, methane, ammonia, water vapour. | Contain methane, ammonia and water vapour |
| 2. Source of energy | Lightning, Ultra Violet rays, Volcanic eruptions. | High voltage electricity |
| 3. Products | Monosaccharides, amino acids, fatty acids, nitrogenbases, polysaccharides, proteins fats, nucleotides. | Amino acids |
Question 5.
Prepare a brief description about Urey- Miller experiment.
Answer:
Urey and Miller conducted their experiment by artificially recreating the atmosphere of primitive earth that contained methane, ammonia, hydrogen and water vapour. In the place of natural energy sources like thunder and lightning in the atmosphere of primitive earth, high voltage electicity is passed through the gaseous mixture in the glass flask. Then, this gaseous mixture*was cooled with the help of a condensor.
The sediment substances were seperated and when observed, organic molecules such amino acids, were found. Later many scientists designed similar experiments and more organic compounds were synthesized. This finally gave more acceptance to the OParin – Haldane hypothesis.
Question 6.
How primitive cell were formed?
Answer:
From the organic molecules formed as a result of chemical evolution, primitive cell were formed 3800 millions of years ago.
Question 7.
Explain the origin of prokaryotes.
Answer:
From the organic molecules formed as a result of chemical evolution, primitive cell were formed 3800 millions of years ago. From the primitive cell prokaryotes were formed 3500 millions of years ago.
Question 8.
Explain the origin of eukaryotes.
Answer:
From the organic molecules formed as a result of chemical evolution, primitive cell were formed 3 800 millions of years ago. From the primitive cell prokaryotes were formed 3500 millions of years ago. Eukaryotes were formed 1500 millions of years ago. The origin of eukaryotic cells having membrane bound cell organelles originated from prokaryotic cells.
Question 9.
Explain about the origin of multicellular organisms.
Answer:
The origin of eukaryotic cells having membrane-bound cell organelles from prokaryotic cells is a milestone in the history of evolution. Multicellular organisms were formed 1000 millions of years ago. Gradually colonies of eukaryotic cells were formed. This led to the emergence of multicellular organisms.
Question 10.
Prepare a geological time scale related to the major eras of origin of life on earth. .
Answer:
Origin of life on earth 3800 million years ago. Origin of prokaryotes 3500 million years ago. Origin of eukaryotes 1500 million years ago. Origin of multicellular organisms 1000 million years ago.
Question 11.
Prepare a flowchart related to origin of multicellular organisms.
Answer:
Question 12.
What are acquired characters?
Answer:
The Characters developed during the lifetime of organisms are called acquired characters.
Question 13.
Explain Lamarckism?
Answer:
Many scientists have attempted to explain the history of evolution from primitive cells to the biodiversity that exists today. The first attempt among them was by Jean Baptist Lamarck, a French biologist.
According to Lamarck giraffes had short necks in the beginning. When they faced food scarcity, they stretched their necks to reach out tall trees. The characters developed during the lifetime of organisms are called acquired characters. Lamarck explained that these characters accumulate through generations and lead to the formation of new species. Thus giraffes with long necks emerged through generations. But this argument was not accepted by the scientific world as these acquired characters are not inheritable.
Question 14.
Which peculiarity of the finches attracted Darwin?
Answer:
Finches were one among the organisms observed and closely studied by Darwin in the Galapagos island. Though the finches look similar to one another, the differences in their beaks attracted Darwin.
Question 15.
How do the differences in their beaks help finches in their survival?
Answer:
Insectivore finches have small beaks and those that feed on cactus plants have long and sharp beaks. There were also woodpecker finches that feed on worms from the holes in tree trunks using small twigs taken with its sharp beak. The ground finches that feed on seeds with large beaks were also present. The differences in their beaks help finches in their survival. It is clear that the finches Darwin observed had beaks adapted to their feeding habits.
The Theory of Natural Selection
Question 16.
Explain the Theory of Natural Selection.
Answer:
The ‘Theory of Natural Selection’ was put forward by Daiwin. Every species produce more number of offsprings than that can survive on earth. They compete among one another for food, space and mates. The competition becomes hard when the number of organisms is greater and the availability of resources is less. Many variations are visible in organisms. You are also aware of how these variations occur.
These variations may be favourable or unfavourable. Those with favourable variations survive in the struggle for existence. Others are eliminated. Variations that are inherited through generations and repeated differently help to form species different from their ancestors. This type of selection, done by nature, leads to the diversity of species that we see around us. This is the explanation of Darwin’s Theory which is known as the theory of natural selection.
Question 17.
What are the limitations of Darwinism?
Answer:
During Darwin’s period, there was no idea regarding genes, chromosomes, etc. Though Darwin identified that continuous variations occurred in organisms, he could not explain the reasons for these variations.
Question 18.
What is Neo Darwinism?
Answer:
Though Darwin identified that continuous variations occurred in organisms, he could not explain the reasons for these variations. Later it was explained that mutations that caused variations led to the evolution of organisms. Darwinism was revised in the light of new information from the branches of genetics, cytology, geology and paleontology. This modified version of Darwinism is known as Neo Darwinism.
Mutation Theory
Question 19.
Explain Mutation Theory.
Answer:
This theory was formulated by a Dutch scientist, Hugo de Vries. Changes in genes is one of the reasons for variations in organisms. Sudden changes that occur in genes are called mutations. Mutation theory explains that new species are formed by the inheritance of such changes. Later it was explained that mutations that cause variations lead to the evolution of species.
Evidences of Evolution
Question 20.
What are the evidences to support evolution?
Answer:
There are many evidences to support the evolution of new species. Paleontology, comparative morphology, physiology and modem molecular biology provide evidences to validate evolution.
Question 21.
What are fossils? What is the importance of fossil study?
Answer:
Fossils are the remnants of primitive organisms. Fossils may either be the body, its parts or imprints of organisms. The age of fossils can be calculated scientifically. They are categorised on the basis of geological time scale and their peculiarities are studied. The inferences arrived at from such studies are
- Primitive fossils have simple structure.
- Recently formed fossils have complex structure.
- Certain fossils are connecting links between different species.
Question 22.
How morphological studies become an evidence for evolution?
Answer:
The forelimbs of organisms differ in their external appearance. Differences in their external appearances are their adaptations to live in their own habitats. But these forelimbs are made up of blood vessels, nerves, muscles and bones. Organs that are similar in structure and perform different functions are called homologous organs. Anatomical resemblances justify the inferences that all organisms evolved from a common ancestor.
Question 23.
What are the inferences that we get from the study of biochemistry and physiology?
Answer:
Microbes, plants and animals are different in their appearance. But there are close resemblances in their cell structure and physiology.
- Enzymes control chemical reactions
- Energy is stored in ATP molecules.
- Genes determine hereditary traits.
- Carbohydrates, proteins and fats are the basic substances.
From these facts, it is clear that different species that exist today have a common ancestor.
Question 24.
How many amino acids differ in the chain of haemoglobin in man and chimpanzee?
Answer:
No amino acids differ in the chain of haemoglobin in man and chimpanzee.
Man and chimpanzee have no difference in the amino acids of chain of haemoglobin.
Question 25.
What is the difference in the number of amino acids in the chain of haemoglobin in man and gorilla?
Answer:
Man and gorilla have no difference in the number of amino acids of chain of haemoglobin: But there is a change in one amino acid.
Question 26.
Which organism is close to man from the evolutionary point of view? What is the reason for this?
Answer:
Chimpanzee: Man and chimpanzee have no difference in the amino acids of chain of haemoglobin.
Question 27.
What is the importance of Molecular biology?
Answer:
Through a comparative study of protein molecules in different species, the evolutionary relationship among organisms can be identified. This is an effective method to draw the evolution showing the branching of organisms from a common ancestor. Molecular studies help to find out the evolutionary relationship of different species of organisms.
Question 28.
Which organism is the closest to humans in specific characters?
Answer:
Chimpanzee
Question 29.
How Anthropoidea, Cercopithecoidea and Hominoidea are related to each other?
Answer:
Humans, chimpanzee, gorilla, orangutan, gibbon and monkeys are included in the category Anthropoidea. This is further classified into Cercopithecoidea and Hominoidea.
Question 30.
Has a species directly evolved from another species? Why?
Answer:
No. Organisms which have evolved from a common ancestor show many resemblances.
Question 31.
What are the characteristics of the organisms which belong to the group hominoidea?
Answer:
Gibbon, Orangutan, Gorilla, Chimpanzee and Man belongs to hominoidea. They have developed brain and freely movable hands.
Question 32.
“Man evolved from monkeys ”. How would you respond to this statement?
Answer:
The given statement is an incorrect one. Man belongs to Hominoidea and Monkeys belong to Cercopithecoidea.
Question 33.
Prepare a table which contains the features of organisms that can be included in the evolutionary history of modern man.
Answer:
| Organism | Fossil found from | Features |
| Ardipithecus ramidus | Africa | Most primitive member of the human race |
| Australopithecus afarensis | Africa | Slender body |
| Homo habilis | Africa | Made weapons from stones and bone pieces |
| Homo erectus | Africa and Asia | Thick chin and large teeth, have the ability to stand erect |
| Homo neanderthalensis | Europe and Asia | Contemporary to modern man |
| Homo sapiens | France | Modern man |
Question 34.
Does the interference of human beings have a negative impact on the existence of organisms and nature itself?
Answer:
Biodiversity at global level has increased much recently than ever before. But this biodiversity is on a dangerous decline due to the interference of human beings. Statistics indicate that if these conditions persist, 1/4 th species of organisms will vanish from the earth within the next 50 years. If it happens* it will be the largest and the sixth mass extinction of species on earth.
Question 35.
Will the unwise interference of intelligent human beings destroy the continuity of life on earth?
Answer:
Today we are aware of the challenges raised by climatic changes brought in by human interventions and the extinction of organisms. Individuals and organizations are actively participating in programmes for the conservation of nature. This solidifies the reality that human life is possible on earth only with the existence of many other diverse ecosystems. Human beings are capable of foreseeing far-reaching consequences and taking necessary precautions in this regard. This leaves us with hopes of a future life on earth.
Let Us Assess
Question 1.
Which concept is put forward by The Theory of Natural Selection?
a. Origin of life
b. Origin of species
c. Origin of eukaryotes
d. Chemical evolution of life
Answer:
b. Origin of species
Question 2.
List the main concepts that indicate how the biodiversity seen today has been developed from prokaryotes.
Answer:
The origin of eukaryotic cells having membrane bound cell organelles originated from prokaryotic cells. Gradually colonies of eukaryotic cells were formed. This led to the emergence of multicellular organisms.
Question 3.
How does the interference of human beings in nature influence the process of evolution? How do these affect the existence of other organisms?
Answer:
Due to the interference of human beings in nature, many organisms lose their natural habitat. This leads to extinction. This also affects the other organisms which depend on them.
Question 4.
What are the evidences that substantiate the theories of evolution? Identify and explain them.
Answer:
Evidences from fossil study.
- Primitive fossils have simple structure.
- Recently formed fossils have complex structure.
- Certain fossils are connecting links between different species.
- Can be infered as organisms with complex structure are formed from organisms with simple structure.
Evidences from morphological studies’.
The forelimbs of organisms differ in their external appearance. Differences in their external appearances are their adaptations to live in their own habitats. But these forelimbs are made up of blood vessels, nerves, muscles and bones. Organs that are similar in structure and perform different functions are called homologous organs. Anatomical resemblances justify the inferences that all organisms evolved from a common ancestor.
Evidences from the study of biochemistry and physiology.
Microbes, plants and animals are different in their appearance. But there are close resemblances in their cell structure and physiology.
- Enzymes control chemical reactions.
- Energy is stored in ATP molecules.
- Genes determine hereditary traits.
- Carbohydrates, proteins and fats are the basic substances.
From these facts, it is clear that different species that exist today have a common ancestor.
Evidences from the study of Molecular biology.
Through a comparative study of protein molecules in different species, the evolutionary relationship among organisms can be identified. This is an effective method to draw the evolution showing the branching of organisms from a common ancestor. Molecular studies help to find out the evolutionary relationship of different species of organisms.
Kerala Syllabus 10th Standard Biology Guide