Important Questions for CBSE Class 12 Biology Chapter 6 - Evolution 2024-25

Very Short Answer Questions.            (1 Mark)

1. Name one fish-like reptile that evolved from a land reptile about 200 million years ago?

Ans: Ichthyosaurs are fish-like reptiles that evolved from land reptiles about 200 million years ago.

2. For a long time, it was believed that life originated from decaying matter. What is this theory known as? Name the scientist who experimentally disproved this theory.

Ans: According to the theory of spontaneous generation life originated from decaying matter however, Louis Pasteur disproved the theory.

3. If the abiotic origin of life is in progress on a planet other than earth, what should be the conditions there?

Ans: If the abiotic origin of life is in progress on a planet other than earth then, extremely high temperatures, volcanic storms, reducing atmosphere containing CH4, NH3, H2, and water vapors should be the key conditions there.

4. Name the person who proposed that population tends to increase geometrically while food production increases arithmetically.

Ans: Thomas Malthus proposed that population tends to increase geometrically while food production increases arithmetically

5. Name the scientist who had also come to a similar conclusion as that of Darwin about natural selection as a mechanism of evolution. Which place did he visit to come to conclusions?

Ans: Alfred Wallace was a naturalist and worked in the Malay Archipelago. He also came up to a similar conclusion as that of Darwin about natural selection as a mechanism of evolution.

6. Name any two vestigial organs found in the human body?

Ans: Vermiform appendix, wisdom teeth are the two vestigial organs found in the human body.

7. What is the cause of speciation according to Hugo De Vries?

Ans: Mutations are the cause of speciation according to Hugo De Vries.

8. Name the phenomenon by which rapid speciation takes place?

Ans: Genetic drift is the phenomenon by which rapid speciation takes place.

9. Name the two scientists who set up a special experiment to prove Oparin’s theory of the origin of life?

Ans: Urey and Miller were the two scientists who set up a special experiment to prove Oparin’s theory of the origin of life.

10. Name the common ancestor of apes and man?

Ans: Dryopithecus is the common ancestor of apes and man.

11. Which period is known as the “Age of amphibians”?

Ans: The Carboniferous period is known as the “Age of amphibians”.

12. What provided energy for abiotic synthesis on primitive earth?

Ans: Very high temperatures due to lightning or UV – rays provided energy for abiotic synthesis.

13. Who showed that life comes from pre-existing life?

Ans: Louis Pasteur showed that life comes from pre-existing life.

14. What is meant by Gene pool?

Ans: Gene pool refers to the total of different kinds of genes pooled by all the members of a population.

15. Which period is called the “Age of Reptiles”.

Ans: The Jurassic period is called the “Age of Reptiles”.

16. Name the species of human beings which is most closely related to modern man.

Ans: Cro-magnon is the species of human beings that are most closely related to modern man.

17. What is the “Founder’s effect”?

Ans: Sometimes a change in frequency of an allele is so different in the new sample of a population that they become a whole new species altogether hence, the original drifted population becomes founder and this effect is known as the Founder’s effect.

Short Answer Questions                              (2 Marks)

1. Explain the Oparin-Haldane theory of the chemical evolution of life.

Ans: The first life form could have come from pre-existing, non-living organic molecules (such as the RNA, Proteins) and the formation of life was preceded by chemical evolution. This theory suggests that life arose gradually from inorganic molecules, with amino acids working as the building blocks. These then combine to make complex polymers that might get assembled into structures that were capable of sustaining and replicating themselves. Oparin considered these as colonies of proteins that clustered together to carry out metabolism, whereas, Haldane thought of them as macromolecules that were enclosed in membranes to build up cell-like structures.

2. Distinguish between convergent and divergent evolution giving one example of each.

Ans: The differences between divergent and convergent evolution are:  

3. What is adaptive radiation? Explain with an example.

Ans: Adaptive radiation is defined as an evolutionary process producing new species from a single, rapidly diversifying lineage. This process occurs due to natural selection. Example: Darwin finches, found in Galapagos Island. A variety of finches present in Galapagos Island arose from a single species, which reached this land accidentally. As a result, innumerable new species evolved, diverged, and adapted thus occupying new habitats. These finches developed diverse eating habits, and various kinds of beaks suiting their feeding habits. 

4. How did Louis Pasteur disprove spontaneous generation theory?

Ans: Louis Pasteur showed that in pre-sterilized flasks, life did not originate from killed yeast whereas, in the other flask which was open to the air, new organisms originated from the dead yeast.

5. Define homologous organs? Give one example of an organ homologous to the hand of man?

Ans: Homologous organs are the ones that are similar in their basic structure and embryonic development but function differently. Example: Bones of forelimbs of whales, bats, birds, and humans.

6. What is the role of variation in evolution?

Ans: Variations are important for the survival of species in any environment. If a population of reproducing organisms are suited to a particular niche and if it gets altered, the population could wipe out; however, with certain variations, they can survive in the changing environment as well. 

7. Describe one evidence that decisively proves that birds have evolved from reptiles?

Ans: The missing link between birds and reptiles is the evidence that proves that birds have evolved from reptiles.  Archaeopteryx showed that “Birds evolved from reptiles”. These are organisms that show characteristics of both birds (such as the presence of wings, feathers in the body) as well as of reptiles (jaws with identical teeth, etc).

8. What is the study of fossils called? Mention any three points how the fossils throw light on past life?

Ans: The study of fossils is known as paleontology. It has been concluded that fossils throw light on past life as:

• A cross-section of Earth’s crust shows the arrangement of sediments one over another. 

• Each sediment contains different life forms which most probably got extinct during the formation of particular sediment.

• Connecting or missing links contain characters of different groups.

9. Why has natural selection not eliminated sickle–cell anemia?

Ans: Sickle cell anemia is not eliminated during natural selection as in some cases, SCA is beneficial since it provides a natural defense system against malarial parasites.

10. Life originated from the earth’s inorganic atmosphere in the post, but this no longer happens today. Give two reasons?

Ans: Life cannot be originated in the present-day atmosphere because of the following reasons: 

(i) Temperature of the present-day atmosphere is much less than that of the primitive atmosphere.

(ii) The present-day atmosphere is oxidizing and not reducing in nature due to the presence of oxygen.

11. If you discovered a fossil bird with scales on the body and teeth in the beak. What would you conclude about its position in the animal kingdom?

Ans: Since the fossil bird shows both avian and reptilian characters, such as scales on the body and teeth in the beak hence, it is more likely to be considered as a connecting link between the reptiles and the birds.

12. What is speciation? List any two events that lead to speciation?

Ans: Speciation refers to the origin of new species or phenomena of development of new species from pre-existing ones.

The two events which lead to speciation are – Genetic drift, mutation, and natural selection.

13. Would you consider the wings of a butterfly and a bat as homologous or Analogous and why?

Ans: Wings of butterflies and bats are said to be analogous because they originated from different parts – for example, butterfly wings originated from skin, feathers and in bats, wings originated from forelimbs; however, both of them perform the same function which is flying.

14. Define natural selection? Who else along with Charles Darwin proposed it as the mechanism of evolution?

Ans: Natural selection is a process of selection in nature in which individuals with those characteristics which enable them to survive better in natural conditions would outnumber others who are less adapted under the same natural conditions Alfred

Wallace also proposed the same mechanism of evolution and called it “survival of fittest”.

15. A chimpanzee can hold objects by its hand and an elephant by the trunk. Are these organs Analogous or homologous?

Ans: These organs are analogous as they are performing the same function which is holding objects but have originated from different parts, for example, forelimbs in chimpanzees and nose in elephants.

16. Differentiate between convergent and divergent evolution?

Ans: 

The difference between convergent and divergent evolution is as follows:

17. Bring out differences between De Vries mutations and Darwinian Variations?

Ans: The difference between De Vries mutations and Darwinian variations are:

Short Answer Question (3 Marks)

1. (i) State the Hardy-Weinberg principle.

Ans: According to the Hardy-Weinberg principle, the allele frequency in a population is stable and constant from generation to generation.

(ii) When there is a disturbance in the Hardy-Weinberg equilibrium, what would it result in?

Ans: When there is a disturbance in the Hardy-Weinberg equilibrium, it would result in evolution.

(iii) According to this principle, what is the total of all allelic frequencies?

Ans: According to this principle, what is the total of all allelic frequencies is one. 

2. Classify the following as examples of homology and analogy

(i) Hearts of fish and crocodile

Ans: The hearts of fish and crocodiles are an example of homology.

(ii) Wings of butterflies and birds

Ans: Wings of butterflies and birds are an example of an analogy.

(iii) Eyes of Octopus and Mammals

Ans:  The eyes of Octopus and Mammals are an example of analogy.

(iv) Tubers of potato and Sweet potato

Ans: Tubers of potato and Sweet potato is an example of analogy.

(v) Thorns of Bougainvillea and spines of Opuntia

Ans:  Thorns of Bougainvillea and spines of Opuntia is an example of analogy.

(vi) Thorn of Bougainvillea and tendrils of cucurbits.

Ans: Thorn of Bougainvillea and tendrils of cucurbits is an example of homology.

3. Stanley Miller and Harold Urey experimented by recreating in the laboratory the probable conditions of the atmosphere of the primitive earth.

(i) What was the aim of the experiment?

Ans:  Stanley Miller and Harold Urey experimented by recreating in the laboratory the probable conditions of the atmosphere of the primitive earth. The experiment aimed to prove Oparin's theory of the origin of life.

(ii) In what forms was the energy supplied for chemical reactions to occur?

Ans: Electric discharge using electrodes.

(III) For how long was the experiment run continuously? Name two products formed.

Ans: One week; amino acids and sugar.

4. Study the figures given below and answer the following question.

i) Under the influence of which type of natural selection would graph (a) become like the graph (b).

ii ) What could be the likely reason for new variations arising in a population.

iii) Who suggested natural selection as the mechanism of evolution?

Ans: 

(i) Graph (a) would become like the graph (b) under the influence of the disruptive and elective type of natural selection.

(ii) Because individuals at the extremes contribute more offspring compared to those in the center and produce two peaks in the distribution of a trait which leads to new variations arising in a population.

(iii) Charles Darwin suggested natural selection as a mechanism of evolution.

5. Fill up the blanks left in the table showing Era, period, and organism.

Ans: (A) Quaternary (B) Cenozoic (C) Cretaceous (D) Mesozoic (E) Carboniferous (F) Paleozoic

6. (i) In which part of the world, the Neanderthal man lived?

Ans: The Neanderthal man lived near Eastern and Central Asia

(ii) What was his brain’s capacity?

Ans: Their brain capacity was 1400 c.c.

(iii) Mention the advancement which Neanderthal man showed over Homoerectus.

Ans:  The advancements were:

• More brain capacity

• Use of hides to cover body 

• Burial of the dead.

7. Figures given below are of Darwin’s finches?

Variety of beaks of Darwin's finches.

(a) Mention the specific geographical area where these were found.

(b) Name and explain the phenomenon that has resulted in the evolution of such diverse species in the region.

(c) How did Darwin visit the particular geographical area?

Ans: (a) Galapagos Island.

(b) Adaptive radiation - The process of evolution of different species in a given geographical area starting from a point and radiating to other areas of geography (habitats) is called adaptive radiation.

(c) Through sea voyage in a sailing ship called H.M.S. Beagle.

8. Give examples to show evolution by anthropogenic action.

Ans: Excess use of herbicides pesticides etc. has resulted in the selection of resistant varieties on a much lesser time scale. The same is true for antibiotic or drug-resistant microbes.

Examples of pesticides are- Aldrin, Methomyl, and examples of herbicides are Acetochlor, Dinosep.

9. By taking industrial melanism as an example, explain the concept of natural selection by evolution?

Ans: Natural selection is a mechanism through which populations of living creatures adapt to changes to survive. It claims that because of the survival of the fittest, species evolve rapidly. Minimal differences are preserved and transmitted, giving rise to new forms over time.

A collection of moths was discovered in the year 1850. White-winged moths outnumbered dark-winged moths in this collection. The population of dark-wringed moths rose with industrialization. The explanation for this is because, throughout the post-industrial period, tree trunks became darkened by industrial smoke, preventing the white-winged moth from surviving. However, it is also known that before industrialization, trees were coated with thick growths of off-white-colored lichens, allowing white-winged moths to thrive while dark-colored moths were easily identified by predators. As a result, it may be argued that nature chooses the best species for the job.

10. Who were the two scientists that experimented to synthesize organic molecules abiotically? How did they provide the probable condition of the primitive earth in this experiment?

Ans: Urey and Miller tried to create in the laboratory similar conditions which might have existed in the early primitive atmosphere. A mixture of water vapors methane, ammonia, and hydrogen is exposed to electric discharge in a closed chamber, this fluid thus formed is allowed to stand for several weeks as a result, amino acids e.g. glycerine and alanine are formed from the fluid. They suggested that electric discharge produced during lightning in the primitive atmosphere of the earth might have resulted in the formation of organic compounds.

11. What is Biogenetic law? How comparative embryology does provide evidence for evolution?

Ans: It has become evident from embryological studies that there was one developmental pattern. In all organisms, life begins with a unicellular structure. The embryos of fish, frog, turtle, bird, and man resemble one another so closely that it becomes difficult to distinguish them.

Mammalian embryo passes through fish–like, amphibian-like, reptiles like and bird-like stages during the development of an organism (ontogeny), some of the evolutionary steps (phylogeny) are repeated in different groups of organisms. This leads Ernst Haeckel to formulate a famous theory – “Recapitulation Theory / Biogenetic Law which states that “Ontogeny recapitulates phylogeny” The sequence of embryonic development shows striking similarity e.g. appearance of gill cleft and notochord in embryonic development of all vertebrates from fish to man.

12. Chemical insecticides remain useful only for a limited time. Explain concerning evolution with a suitable example.

Ans: Chemical pesticides are used in agricultural fields to get rid of various pests and insects that cause crop loss. These chemical insecticides affect some of the pest's metabolic characteristics, resulting in the pest's death.

However, these pests develop immunity over time as a result of various generations. Pests that are resistant to these insecticides are born as a result of mutations. These insecticides will thereafter be useless. As a result, you should avoid using these insecticides.

13. What are the facts that support Darwin’s theory of Natural selection?

Ans: The following facts that support Darwin’s theory of Natural selection

1. Overproduction: - All organisms tend to multiply at a high rate but all organisms can’t survive.

2. Struggle for Existence: - Because of limitation of space and food all the offspring resulting in overproduction will not survive and they will compete with one another to grow. This develops a struggle for existence not only among individuals of different species but also among the same species.

3. Variations:  No two individuals of the same species are exactly alike even coming out from the same parental stock.

4. Survival of fittest:  The individuals with useful variation will survive during the struggle of existence while those with less fortunate variation would perish.

14. Trace the important events or stages of human development?

Ans: The common ancestor of apes and man is the primate Dryopithecus that lived about 15 million years ago the human evolution is as follows : 

1. Australopithecus:  They are 4ft, with a brain capacity – 500 to 650 cc. They have bipedal locomotion, are omnivorous, and have an erect posture. They used stone weapons for hunting and lived in caves.

2. Homo Erectus:  They showed an increase in brain size They are good hunters, ate meat domesticate animals, and discover fire.

3. Netherlands man:  They were short with heavy brows retreating forehead large jaws and stooped postures They wore clothes, good hunters, and tool makers.

4. Cromagnonman:  They were completely erect and 6 ft tall. He used bones as tools and was a cave dweller. They are excellent tool makers and fine artists.

5. Homo sapiens:  They have a brain capacity of 1450cc. and skull much thicker. His intelligence has enabled him to adapt and control the environment. He started agriculture.

15. What are the three different ways in which selection may occur.

Ans: The three different ways in which selection may occur are as below: 

(i) Stabilising selection: Individuals with an intermediate value of heritable phenotypic characteristics are favored over other individuals.

(ii) Directional selection: Individuals with one extreme of heritable phenotypic characteristics have an advantage over individuals in a population.

(iii) Disruptive selection: Individuals with either extreme or heritable phenotypic characteristics have an advantage over individuals with intermediate phenotypes.

16. State in what ways Stanley miller simulated the condition of : 

i) Primitive atmosphere on earth.

ii) Energy source at the time of origin of life.

iii) Formation of organic molecules of life.

Ans: i) A fluid containing a mixture of methane, ammonia, hydrogen, and water vapor in a closed flask.

ii) Energy source during the origin of life was Sun. This energy is provided by electric discharge using electrodes in this experiment.

iii) The organic molecules which are formed during the experiment are amino acids.

17. What is Biogeography? How Darwin’s finches provide biogeographical evidence in favor of evolution.

Ans: The branch of geography which deals with the study of the pattern of distribution of plants and animals is called Biogeography.

Example: Galapagos islands- Charles Darwin during his voyage found that animals of these islands resemble those of South American islands. For example birds of Galapagos Island also known as Darwin’s finches do not resemble birds of South America therefore, he stated that finches were derived from ancestral stock that had emigrated from the mainland to the island and underwent profound changes under different environmental conditions.

18. How did Louis Pasteur successfully demolish the popular theory of spontaneous generation?

Ans: Louis Pasteur used a special swan-necked flask for the experiment. He took a mixture of sugar and yeast powder, filled it in the flask, then boiled it as a steady current of steam rushed out from the S-shaped tube –causing the death of all microorganisms. After this, the flask remained unchanged, however, when the neck of the flask was cut-off, a thick growth of microorganisms was observed which presumed that there are microorganisms that could not reach the flask in the initial stage, however, in the second phase, they came in direct contact with the solution.

Long Answer Questions (5 Marks)

1. What does Hardy Weinberg’s principle state? What are the factors which affect Hardy Weinberg’s equilibrium?

Ans: A. to Hardy Weinberg’s principle, allele frequency in a population is stable and is constant from generation to generation i.e. total gene pool remains constant. This is called genetic equilibrium e.g. In a diploid organism, suppose ‘p’ represents the frequency of allele ‘A’ and ‘q’ represents the frequency of allele ‘q’. 

$\mathrm{p}^{2}+2 \mathrm{pq}+\mathrm{q}^{2}=1$

Factors affecting Hardy – Weinberg Equilibrium : 

(i) Gene flow: When the migration of a section of a population to another place starts, gene frequency changes in both the original as well as in the new population.

(ii) Genetic drift: If by chance a particular allele frequency decrease or increases in a population.

(iii) Mutations: They are sudden changes in the genotype which are carried over a generation. 

(iv) Genetic recombination: Sometimes changes in the frequency of an allele are different in a new sample of the population as they become new species.

(v) Natural selection: Process by which individuals with particular heritable characteristics survive and reproduce at a higher rate than other individuals favored by natural selection tend to be more common in the next generation than in the parent generation.

2. How do Darwin and Hugo de Vries think about the Mechanism of Evolution?

Ans: 

Darwin: Darwinian variations are gradual, small, and directional Hugo deVries: put forth the idea of mutations, mutations are sudden random and directional

3. With the help of a suitable diagram, represent the operation of natural selection on different traits.

Ans: Natural selection is a basic mechanism of evolution, along with mutation, migration, and genetic drift.

Darwin's idea of evolution by natural selection is simple but misunderstood. To know the same, consider a population of beetles:

1. There is variation in traits: Example, some beetles are green while others are brown. 

2. There is differential reproduction: Since the environment can't support unlimited population growth, not all individuals get to reproduce to their full potential. For example, green beetles are eaten by birds and survive to reproduce less than brown beetles.

3. There is Heredity: The brown beetles which survive have brown baby beetles since this trait has a genetic basis.

4. Result: The more advantageous trait, brown coloration allows beetles to have more offspring, thus it becomes more common in the population. If this continues, ultimately all the individuals in the population would come out to be brown.

4. What does Oparin – Haldane hypothesis about the origin of life suggests.

Ans: According to Oparin and Haldane’s Biochemical hypothesis, the origin of life occurs in three stages.

The first life form could have come from pre-existing, non-living organic molecules (such as the RNA, Proteins) and the formation of life was preceded by chemical evolution. This theory suggests that life arose gradually from inorganic molecules, with amino acids working as the building blocks. These then combine to make complex polymers that might get assembled into structures that were capable of sustaining and replicating themselves. Oparin considered these as colonies of proteins that clustered together to carry out metabolism, whereas, Haldane thought of them as macromolecules that were enclosed in membranes to build up cell-like structures.

5. What is chemogeny?

Ans: Chemogeny or chemical evolution suggests that most of the primitive forms of life would have been generated spontaneously from some inorganic matter as a result of the action of special external forces e.g. electric charge, UV-light, etc.

1. Saturated and unsaturated hydrocarbons were feasted when temp cooled to 900 Celsius or even below this.

2. From hydrocarbons, small chain compounds of carbon, hydrogen, and oxygen are formed which condense to form sugar.

3. Ketones and aldehydes condense, polymerizes to form fatty acids.

4. Ammonia, hydrocarbon, and water reacted to form amino acids.

5. Hot sea water rich in primary organic compounds reacted to form nucleotides.

6. What is biogeny?

Ans. Biogeny or biological evolution is a stage that consists of

i) Formation of nucleic acids by polymerization of nucleotides.

ii) Giant molecules of nucleoproteins tend to be aggregated in various combinations to form large colloidal particles called coacervates.

iii) The development of the plasma membrane resulted in the accumulation of different substances inside coacervates and the occurrence of certain internal reactions leading to the development of the cell.

7. What is Cognogeny?

Ans. Cognogeny involves the differentiation and diversification of living beings from the simplest first living cell. The first organism that evolved was chemoautotrophic bacteria which later converted to tree autotrophic bacteria example- green algae.

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