NCERT Solutions Class 12 Biology Chapter 7 Evolution

Question. Explain antibiotic resistance observed in bacteria in light of Darwinian selection theory.
Answer. Darwinian theory of natural selection states that environment selects organisms with favourable variation and these organisms thus survive and reproduce. It is observed when bacterial populations are exposed to certain antibiotic, the sensitive bacteria could not tolerate and hence died due to the adverse environment. Whereas some bacteria that developed mutation became resistant to the particular antibiotic and survived. As a result such resistant bacteria survive and multiply quickly as compared to other sensitive bacteria. So, the whole population is regained by multiplication of resistant variety and antibiotic resistant gene becomes widespread in the bacterial population.

Question. Find out from newspapers and popular science articles any new fossil discoveries or controversies about evolution.
Answer. A recent study of fossil revealed a small terrestrial dinosaur with feathers covering the limb and body. This finding established that feathers evolved earlier than wing and may be functioning as thermoregulator to face adverse conditions. These newly developed feathers earlier helped in gliding and then flying.

Question. Attempt giving a clear definition of the term species.
Answer. Species can be defined as a group of reproductively isolated population which can interbreed among each other.

Question. Try to trace the various components of human evolution (hint: brain size and function, skeletal structure, dietary preference, etc.)
Answer.

Human Ancestors	Time of Origin	General Features
1. (a) Dryopithecus (b) Ramapithecus	15 mya	Ape-like, hairy, arms and legs of same length, large brain, ate soft fruits and leaves, walked like gorillas and chimpanzees. More man-like, walked more erect, teeth like modern man.
2.Australopithecus	2 mya	Fossils found in Tanzania and Ethiopia, man-like primates, 4 feet tall, walked upright, ate fruit, hunted with stone weapons, brain capacity was 400–600 cc.
3. Homo habilis	2 mya	Fossils found in East Africa, first human-like being, brain capacity 650–800 cc, did not eat meat.
4. Homo erectus (Java man)	1.5 mya	Fossils found in Java, brain capacity 900 cc, ate meat.
5. Homo sapiens neanderthalensis (Neanderthal man)	100,000–40,000 year ago	Fossils found in east and central Asia, brain size 1400 cc, used hides to protect body, buried their dead.
6. Homo sapiens (Modern man)	75,000–10,000 years ago	Developed cave art, agriculture, started human civilisation.
	18,000 years ago	Prehistoric cave art developed.
	10,000 years back	Agriculture started.

 

Question. Find out through internet and popular science articles whether animals other than man has self-consciousness.
Answer. Many animals other than humans have self consciousness. For example, dolphins and chimpanzees are considered highly intelligent. They have a sense of self and they also recognise others among themselves and others. They communicate with each other by whistles, tail-slapping, and more body movements.

Question. List 10 modern-day animals and using the internet resources link it to a corresponding ancient fossil. Name both.
Answer. List of modern day animals and their ancient fossils
S. No. Modern day animals         Corresponding ancient fossil
(i)               Man                          Homo sapiens neanderthalensis
(ii)        Chimpanzee                     Dryopithecus
(iii)       Gorilla                              Dryopithecus
(iv)       Orangutan                       Dryopithecus
(v)        Gibbon                            Propliopithecus
(vi)       Nautilus                          Gypceros
(vii)      Octopus                          Belemnite
(viii)     Elephant                         Stegolophodon
(ix)      Camel                             Procamelus
(x)        Horse                             Pliohippus 

Question. Practice drawing various animals and plants.
Answer. Draw labelled diagrams of various animal and plants from your text book.

Question. Describe one example of adaptive radiation.
Answer. Darwin’s finches in the Galapagos Island once had a common ancestor but with evolution they modified into different types according to their food habitat.

Question. Using various resources such as your school library or the internet and discussions with your teacher, trace the evolutionary stages of any one animal, say horse.
Answer. The evolution of horse is represented as
(i) Eohippus: This stage is characterised by a short head and neck. It had four functional toes and a splint of 1 and 5 on each hind limb and a splint of 1 and 3 in each forelimb. The molars were short crowned that were adapted for grinding the plant diet.
(ii) Mesohippus: It was slightly taller than Eohippus. It had three toes in each foot.
(iii) Merychippus: It had the size of approximately 100 cm. Although it still had three toes in each foot, but it could run on one toe. The side toe did not touch the ground. The molars were adapted for chewing the grass.
(iv) Pliohippus: It resembled the modern horse and was around 108 cm tall. It had a single functional toe with splint of second and fourth in each limb.
(v) Equus: Pliohippus gave rise to Equus or the modern horse with one toe in each foot. They have incisors for cutting grass and molars for grinding food.

Question. Can we call human evolution as adaptive radiation?
Answer. No, human evolution cannot be called as adaptive radiation because parent species of Homo sapiens have evolved by progressive evolution from Homo habilis to Homo erectus lineage.

 

NCERT Solutions for Class 12 Biology Chapter 7 Evolution MCQs

Choose and write the correct option in the following questions.

Question. Stabilising selection favours
(a) only one extreme form of a trait
(b) both the extreme forms of a trait
(c) intermediate form of a trait
(d) none of these
Answer. C

Question. The most accepted line of descent in human evolution is
(a) Australopithecus → Ramapithecus → Homo sapiens → Homo habilis
(b) Homo erectus → Homo habilis → Homo sapiens
(c) Ramapithecus → Homo habilis → Homo erectus → Homo sapiens
(d) Australopithecus → Ramapithecus → Homo erectus → Homo habilis → Homo sapiens.
Answer. C

Question. Disruptive selection favours
(a) only one extreme form of a trait
(b) both the extreme forms of a trait
(c) intermediate form of a trait
(d) none of these
Answer. B

Question. Thorn of Bougainvillea and tendril of Cucurbita are examples of
(a) vestigial organs
(b) retrogressive evolution
(c) analogous organs
(d) homologous orgAnswer.
Answer. D

Question. The theory of spontaneous generation stated that 
(a) life arose from living forms only
(b) life can arise from both living and non-living
(c) life can arise from non-living things only.
(d) life arises spontaneously, neither from living nor from the non-living.
Answer. C

Question. Darwin’s Finches are an excellent example of
(a) brood parasitism
(b) connecting links
(c) adaptive radiation
(d) seasonal migration.
Answer. C

Question. Palaentological evidences for evolution refer to the 
(a) development of embryo
(b) homologous organs
(c) fossils
(d) analogous orgAnswer.
Answer. C

Question. Which one of the following scientist’s name is correctly matched with the theory put forth by him?
(a) de Vries – Natural selection
(b) Mendel – Theory of Pangenesis
(c) Weismann – Theory of continuity of germplasm.
(d) Pasteur – Inheritance of acquired characters.
Answer. C

Question. Which of the following organs are homologous?
(a) Forelimbs of man and wings of bat
(b) Wings of Bat and bird
(c) Wings of Bat and Petrodactyl
(d) None of these
Answer. A

Question. Homologous organs show
(a) natural selection
(b) divergent evolution
(c) parallel evolution
(d) convergent evolution
Answer. B

Question. Analogous organs arise due to
(a) divergent evolution
(b) artificial selection
(c) genetic drift
(d) convergent evolution
Answer. D

Question. Evolution of life shows that life forms had a trend of moving from
(a) land to water
(b) dryland to wet land
(c) fresh water to sea water
(d) water to land
Answer. D

Question. The bones of forelimbs of whale, bat, cheetah and man are similar in structure, because
(a) one organism has given rise to another
(b) they share a common ancestor
(c) they perform the same function
(d) they have biochemical similarities
Answer. B

NCERT Solutions for Class 12 Biology Chapter 7 Evolution Assertion-Reason Questions

In the following questions a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

Question. Assertion : Disruptive selection changes the population into two or more groups.
Reason : This type of selection favours average sized individuals.
Answer. C

Question. Assertion : Genetic drift refers to changes in allele frequency.
Reason : Heritable variations enable survival of the fittest.
Answer. B

Question. Assertion : Founder effect may lead to formation of new species.
Reason : Founders carry all the parental gene pool to a new location.
Answer. C

Question. Assertion : Louis Pasteur’s experiments showed that new organisms appeared in an open flask with heat-killed yeast.
Reason : Life arises from pre-existing life
Answer. B

Question. Assertion : Among the primates, chimpanzee is the closest relative of the present day humans.
Reason : DNA matching shows that human similarity is 100% with chimpanzee.
Answer. A

Question. Assertion : The earliest cells used RNA as their hereditary molecule.
Reason : DNA evolved from RNA.
Answer. B

Question. Assertion : Hardy Weinberg principle explains the occurrence of variations in population and species.
Reason : It concludes that disturbances in genetic equilibrium results in evolution.
Answer. D

Question. Assertion : Excessive use of herbicides and pesticides has no effect on resistant varieties of microbes.
Reason : Pathogenic bacteria are appearing in very short period of time because of chemical resistance.
Answer. D

Question. Assertion : Wings of butterfly and birds show analogy.
Reason : Analogous organs are anatomically different but functionally similar.
Answer. A

Question. Assertion : Darwin’s finches have different types of modified beaks according to their feeding habits.
Reason : Adaptive radiation leads to development of structures with different function arising from a common ancestor.
Answer. A

NCERT Solutions for Class 12 Biology Chapter 7 Evolution Case-based/Source-based Question

1. A student was simulating Urey and Miller’s experiment to prove the origin of life. The set-up used by the student is given.

Question. Find out the reasons why he could not get desired results.
Answer. He could not get desired results because:
(a) O₂ was used instead of H₂.
(b) Temperature maintained was 80°C instead of 800°C.

Question. What conclusion was drawn by Urey and Miller through this experiment?
Answer. It was concluded that life could have come from pre-existing non-living organic molecules and their formation was preceded by chemical evolution.

Question. Compare the conclusion drawn with the theory of spontaneous generation.
Answer. Urey and Miller proved that life originated abiogenetically whereas theory of spontaneous generation emphasised that units of life called spores were transferred to different planets including Earth. 

2. Darwin found the varieties of finches that in travelled to Galapagos Islands and observed variations in them.

Question. What role does an individual organism play as per Darwin’s theory of natural selection?
Answer. An individual organism passes on the variations, mutations and adaptations from one generation to another.

Question. How did Darwin explain the existence of different varieties of finches on Galapagos Islands?
Answer. Darwin explained it as the process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats), called adaptive radiation.

Question. What is “fitness of an individual” according to Darwin?
Answer. According to Darwin, “fitness of an individual” is the ability of an organism to survive and pass on its genes to future generations.

3. Study the diagram given below and answer the following questions:

Question. Mention the specific geographical region where these organisms are found.
Answer. Australia

Question. Name and explain the phenomenon that has resulted in the evolution of such diverse species in the region.
Answer. Adaptive radiation (Divergent evolution) has resulted in this evolution. 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. It is the development of different functional structures from a common ancestral form.

Question. Explain giving reasons the existence of placental wolf and Tasmanian wolf sharing the same habitat.
Answer. Placental wolf and Tasmanian wolf share similar habitat due to convergent evolution and evolved into unrelated group of organisms.

4. Refer to the figure given below and answer the questions that follow:

Question. Recognise and explain the process by which Tasmanian wolf evolved.
Answer. Tasmanian wolf evolved by the process of adaptive radiation. It is the process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats).

Question. Give one example of an animal that has evolved along with Tasmanian wolf. Name the process that result in evolution of wolf and Tasmanian wolf.
Answer. Examples of animals: Tiger cat/banded ant eater/Marsupial rat. Convergent evolution has resulted in evolution of wolf and Tasmanian wolf.

Question. Compare and contrast the two animals shown.
Answer. Wolf is a placental mammal, whereas Tasmanian wolf is a marsupial mammal.

NCERT Solutions for Class 12 Biology Chapter 7 Evolution Very Short Answer Questions

Question. Life originated from earth’s inorganic atmosphere in past but not today. Suggest two reason.
Answer. (i) Presence of free oxygen in present day atmosphere.
(ii) Very high temperatures.

Question. How can you suggest that biochemistry gives evidence for organic evolution? 
Answer. In the same species or group of organisms, similar type of proteins are found, thus supporting organic evolution.

Question. State the significance of the study of fossils in evolution. 
Answer. Fossils represent extinct organisms. They show life forms restricted to certain geological time spans existing in the past. Show ancestry of present day organisms are connecting links between two groups of organisms. 

Question. What is fossil?
Answer.Fossils are the remains or impressions of ancient organisms preserved in sedimentary rocks or other media.

Question. How do we compute the age of a fossil? 
Answer. By radiocarbon dating.

Question. Identity the examples of convergent evolution from the following: 
(i) Flippers of penguins and dolphins
(ii) Eyes of octopus and mammals
(iii) Vertebrate brains
Answer. (i) Flippers of penguins and dolphins
(ii) Eyes of octopus and mammals

NCERT Solutions for Class 12 Biology Chapter 7 Evolution Short Answer Questions

Question. If abiotic origin of life is in progress on a planet other than earth, what should be the condition there? Explain.
Answer. The atmosphere will be reducing, i.e., no free oxygen will be present. There must be continuous supply of energy like that from lightning, thunder, volcanic eruption and stellar radiation. The presence of autocatalyst or self-replicating molecules is essential.

Question. What must have provided energy for the warmth for life to originate on primitive earth? Name the first organism to release oxygen into the atmosphere. 
Answer. Energy for life to originate must have been provided by heat, cosmic rays and lightning.
Cyanobacteria was the first organism to release oxygen into the atmosphere.

Question. Write the Oparin and Haldane’s hypothesis about the origin of life on Earth. How does meteorite analysis favour this hypothesis? 
Answer. The hypothesis stated that life originated from pre-existing non-living organic molecules (e.g.,RNA, protein, etc.). When the meteorites were analysed, it was observed that presence of similar compounds was confirmed which conclude that similar process is going on elsewhere in the space.

Question. Mention the contribution of S.L. Miller’s experiments on Origin of Life. 
Answer. S.L. Miller created an environment in laboratory similar to the one that existed before life originated.In a closed flask containing CH₄, H₂, NH₃ and water vapour at 800°C, electric discharge was created.The conditions were similar to those in primitive atmosphere. After a week, they observed presence of amino acids and complex molecules like sugars, nitrogen bases, pigments and fats in the flask.This provided experimental evidence for the theory of chemical origin.

Question. Convergent evolution and divergent evolution are the two concepts explaining organic evolution. Explain each one with the help of an example. 
OR
Differentiate between divergent and convergent evolution. Give one examples of each.
Answer. Convergent evolution: When more than one adaptive radiation appeared to have occurred in an isolated geographical area and two or more groups of unrelated animals resemble each other for similar mode of life or habitat, it is called convergent evolution, e.g., Australian marsupials,placental mammals.
Divergent evolution: In some animals, the same structures developed along different directions due to adaptations to different needs. This is known as divergent evolution. For example,forelimbs of whales, bats, cheetah and human perform different functions but have similar anatomical structure with similar bones arranged in similar segments.

Question. Explain convergent evolution with the help of two examples. 
Answer. Different structures evolved similarly due to same functions. This is called convergent evolution.
Examples:
(i) Wings of butterfly and birds.
(ii) Sweet potato (root modification) and potato (stem modification).

NCERT Solutions for Class 12 Biology Chapter 7 Evolution Long Answer Questions

Question. Fitness is the end result of the ability to adapt and get selected by nature. Explain with suitable example. 
Answer. Fitness is based on certain characteristics which are inherited and the ability to adapt to the changing environment. It is the end result of adaptation because a fit individual survives and unfit individuals are eliminated from the population. Individuals continuously compete with each other in a population for food, space and light. The one which is better adapted and naturally selected by nature survives and reproduces.
For example, industrial evidence: It is a case of natural selection.
In England, it was observed before industrialisation that white-winged moths were more than dark-winged moths. But the situation became reversed after industrialisation. During preindustrialisation,the tree trunks were covered by white lichens and on white-background dark-coloured moths can be picked up. During post industrialisation, the tree trunks were covered by dust, coal particles and thus became dark. On such trunks, white moths could be easily picked up. Thus, it was found that industrial melanism supports evolution by natural selection.

Question. (a) How does Hardy−Weinberg equation explain genetic equilibrium?
(b) Describe how does this equilibrium get disturbed which may lead to founder effect.
Answer. (a) Hardy-Weinberg equation is p² + 2pq + q² = 1. This means that the sum total of all the allelic frequencies is 1. In a diploid, p² means that the probability an allele AA with a frequency of p appear on both the chromosomes of a diploid individual will be p². Similarly of allele aa is q², and of Aa is 2pq.
(b) The equilibrium gets disturbed due to genetic drift which refers to the changes in allele frequencies of a population occurring by chance. The change in allele frequency may be so different that the population becomes a different species, the original population becomes founders and such an effect is called founder effect.

Question. Evolution is a change in gene frequencies in a population in response to changes in the environment in a time scale of years and not centuries. Justify this statement with reference to DDT. How does the theory of Hugo de Vries support this? 
Answer. When DDT was used for the first time, maximum mosquitoes died but few survived due to variation in a population. These mosquitoes showed resistance to DDT and survived to reproduce successfully in the presence of DDT and gradually such mosquito population became DDT resistant within a time span of few years.
According to Hugo de Vries, evolution is caused by sudden large differences in the population and not minor variations.

Question. Describe the three different ways by which Natural Selection can affect the frequency of a heritable trait in a population. 
Answer.
- Gene migration or gene flow: When individuals migrate to another place or population, new genes or alleles are added to new population and are lost from old population, in turn changing the frequencies. When gene migration occurs many times, it is called gene flow.
- Genetic drift: Changes occurring in frequencies by chance is called genetic drift. Sometimes, due to changes in allele frequency in new population, some form a different species. This effect is called founder effect and the original drifted population is called founder.
- Mutation: Advantageous mutations lead to new phenotypes and over few generations, result in speciation.
- Genetic recombination: During gametogenesis, variations due to recombination result in new phenotypes.
- Natural selection: Heritable variations that enable survival of the fittest will leave greater number of progeny. Natural selection can have following three effects:

(a) Stabilisation: Larger number of individuals acquire mean character value so peak gets higher and narrower.
(b) Directional change: Large number of individuals acquire value other than mean character value so peak shifts in one direction.
(c) Disruption: Large number of individuals acquire peripheral character values at both ends of the distribution curve and hence 2 peaks are formed.

Question. (a) Name the primates that lived about 15 million years ago. List their characteristic features.
(b) (i) Where was the first man-like animal found?
(ii) Write the order in which Neanderthals, Homo habilis and Homo erectus appeared on earth. State the brain capacity of each one of them.
(iii) When did modern Homo sapiens appear on this planet? 
Answer. (a) Primates called Dryopithecus and Ramapithecus lived 15 million years ago.
Their characteristic features are:
(i) They were hairy and walked like gorillas and chimpanzees.
(ii) Ramapithecus was more man-like.
(iii) Dryopithecus was more ape-like.
(b) (i) First man-like animal was found in Ethiopia and Tanzania.
(ii) The order of appearance from the earliest to the latest is:
Homo habilis, Homo erectus, Neanderthals.
The brain capacity of Homo habilis is 650–800 cc, of Homo erectus is 900 cc and of Neanderthals is 1400 cc.
(iii) Modern Homo sapiens appeared between 75,000–10,000 years ago.