NCERT Exemplar Class 12 Biology Solutions Chapter 7 Structural Organisation in Animals

NCERT Exemplar Class 12 Biology Solutions Chapter 7 Evolution Multiple Choice Questions:

Question:1

Which of the following is used as an atmospheric pollution indicator?
a. Lepidoptera
b. Lichens
c. Lycopersicon
d. Lycopodium

Answer:

The answer is the option (b) Lichens
Explanation: Air is the primary source of most elements for Lichens as they do not have roots. They will not grow in the polluted areas and thus are used as a reliable indicator of atmospheric pollution.

Question:2

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:

The answer is the option (c) life can arise from non-living things only.
Explanation: The theory assumes that life could have formed from non-animated matters.

Question:3

Animal husbandry and plant breeding programmes are examples of:
a. reverse evolution
b. artificial selection
c. mutation
d. natural selection

Answer:

The answer is the option (b) artificial selection
Explanation: Animal husbandry and plant breeding programmes rely on human intervention. Desirable characteristics are introduced in plants and animals through manipulation.

Question:4

Palaeontological evidences for evolution refer to the:
a. development of embryo
b. homologous organs
c. fossils
d. analogous organs

Answer:

The answer is the option (c) fossils
Explanation: In fact, the study of fossils is called palaeontology. The term‚ paleo' is related to old and historical items.

Question:5

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. the have biochemical similarities

Answer:

The answer is the option (b) they share a common ancestor
Explanation: Similar structure is an indication of common ancestry.

Question:6

Analogous organs arise due to:
a. divergent evolution
b. artificial selection
c. genetic drift
d. convergent evolution

Answer:

The answer is the option (d) convergent evolution
Explanation: Analogous organs have evolved from different ancestors, but all of them show a similar function. Hence, they show convergent evolution.

Question:7

represents an equation used in:
a. population genetics
b. mendelian genetics
c. biometrics
d. molecular genetics

Answer:

The answer is the option (a) population genetics
Explanation: population genetics

Question:8

The appearance of antibiotic-resistant bacteria is an example of:
a. adaptive radiation
b. transduction
c. pre-existing variation in the population
d. divergent evolution

Answer:

The answer is the option (c) pre-existing variation in the population
Explanation: Adaptive radiation is related to the evolution of different designs for a single organ according to the varied needs of different groups. Transduction is related to the transfer of viral or bacterial genetic material. Divergent evolution is related to homologous organs.

Question:9

Evolution of life shows that life forms had a trend of moving from:
a. land to water
b. dryland to wetland
c. freshwater to seawater
d. water to land

Answer:

The answer is the option (d) water to land
Explanation: Most primitive organisms live in water, while most complex organisms live on land. This signifies that the evolution of life moved from water to land

Question:10

Viviparity is considered to be more evolved because:
a. the young ones are left on their
b. the young ones are protected by a thick shell
c. the young ones are protected inside the mother's body and are looked after they are born leading to more chances of survival
d. the embryo takes a long time to develop

Answer:

The answer is the option (c) the young ones are protected inside the mother's body and are looked after they are born leading to more chances of survival
Explanation: the young ones are protected inside the mother's body and are looked after they are born leading to more chances of survival

Question:11

Fossils are generally found in:
a. Sedimentary rocks
b. Igneous rocks
c. Metamorphic rocks
d. Any type of rock

Answer:

The answer is the option (a) Sedimentary rocks
Explanation: Fossil can't be found in Igneous rocks as they are formed from lava. Metamorphic rocks are made from igneous or sedimentary rocks.

Question:12

For the MN-blood group system, the frequencies of M and N alleles are 0.7 and 0.3, respectively. The expected frequency of MN-blood group bearing organisms is likely to be
a. 42%
b. 49%
c. 9%
d. 58%

Answer:

The answer is the option (a) 42%
Explanation: This can be solved by using the binomial expression:

Here, M=a and N=b


In this equation ; value of 2MN=0.42=42%

Question:13

Which type of selection explains industrial melanism observed in the moth, Boston Bulgaria:
a. Stabilising
b. Directional
c. Disruptive
d. Artificial

Answer:

The answer is the option (b) Directional
Explanation: Industrial melanism is acquired by most of the individuals of the population. Hence, it is an example of a directional change.

Question:14

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:

The answer is the option
(c) Ramapithecus→Homo habilis→Homo erectus→Homo sapiens
Explanations: Ramapithecus→Homo habilis→Homo erectus→Homo sapiens

Question:15

Which of the following is an example for link species?
a. Lobe fish
b. Dodo bird
c. Seaweed
d. Chimpanzee

Answer:

The answer is the option (a) Lobe fish
Explanation: Lobe fish shows characters from cartilaginous fishes and amphibia. They belong to bony fishes. As they show characters from two different groups of animals, they are considered as link species.

Question:16

Match the scientists listed under column 'I' with ideas listed column 'II'.

a. i-M; ii-P; iii-N; iv-O
b. i-P; ii-M; iii-N; iv-O
c. i-N; ii-P; iii-O; iv-M
d. i-p; ii-O; iii-N; iv-M

Answer:

The answer is the option (b) (i) P; (ii) M; (iii) N; (iv) O
Explanation: (i) P; (ii) M; (iii) N; (iv) O

Question:17

In 1953 S. L. Miller created primitive earth conditions in the laboratory and gave experimental evidence for the origin of the first form of life from preexisting non-living organic molecules. The primitive earth conditions created include:
a. low temperature, volcanic storms, atmosphere rich in oxygen
b. low temperature, volcanic storms, reducing atmosphere
c. high temperature, volcanic storms, non-reducing atmosphere
d. high temperature, volcanic storms, reducing atmosphere containing , , etc.

Answer:

The answer is the option (d) high temperature, volcanic storms, reducing atmosphere containing , etc.

Question:18

Variations during mutations of meiotic recombination are:
a. random and directionless
b. random and directional
c. small and directional
d. random, small and directional

Answer:

The answer is the option (a) random and directionless
Explanation: random and directionless

Very Short Answer Type Questions:

Question:1

What were the characteristics of life forms that had been fossilised?

Answer:

Fossilised life forms are characterised by some hard parts that are preserved between layers of rocks.

Question:2

Did aquatic life forms get fossilised? If yes, where do we come across such fossils?

Answer:

Yes, aquatic life forms also get fossilised, and they are found in oil wells and sedimentary rocks.

Question:3

What are we referring to when we say 'simple organisms' or 'complex organisms'?

Answer:

we define simple and complex organisms based on the division of labour and relative level of organisation in the organisms.

Question:4

How do we compute the age of a living tree?

Answer:

Age of a living tree can be determined by measuring the girth of the trunk and comparing the diameter to the average growth factor of that species. Information regarding the average growth factor of a species is historically available.

Question:5

Give an example of convergent evolution and identify the features towards which they are converging.

Answer:

Convergent evolution is the occurrence of a similar evolution in species of different lineage. It happens in isolated geographical areas. Flippers of dolphin and penguin serve a similar purpose but have different origins.

Question:6

How do we compute the age of a fossil?

Answer:

Carbon dating is used to find the age of a fossil. The relative presence of radioactive carbon , which decays over time, is calculated to compute the age of a fossil.

Question:7

What is the most important pre-condition for adaptive radiation?

Answer:

The most important pre-condition for adaptive radiation is Common ancestry.

Question:8

How do we compute the age of a rock?

Answer:

Carbon dating is used to find the age of a rock. The relative presence of radioactive carbon , which decays over time, is calculated to compute the age of a rock.

Question:9

When we talk of functional macromolecules (e.g. proteins as enzymes, hormones, receptors, antibodies etc.), towards what are they evolving?

Answer:

Functional macromolecules can evolve into living forms.

Question:10

In a certain population, the frequency of three genotypes is as follows:

What is the likely frequency of B and b alleles ?

Answer:

Frequency of B alleles =
Frequency of b alleles = 1-Frequency of B alleles=47%

Question:11

Among the five factors that are known to affect Hardy-Weinberg equilibrium, three factors are gene flow, genetic drift, and genetic recombination. What are the other two factors?

Answer:

Mutation and Natural Selection

Question:12

What is the founder effect?

Answer:

The founder's effect is the loss of genetic variation that results when a new population is created by an exceedingly small number of individuals from a larger population.

Question:13

Who among the Dryopithecus and Ramapithecus was more man-like?

Answer:

Ramapithecus

Question:14

By what Latin name was the first hominid known?

Answer:

Homo habilis

Question:15

Among Ramapithecus, Australopithecines and Homo habilis -who probably did not eat meat?

Answer:

Homo habilis

Short Answer Type Questions:

Question:1

Louis Pasteur's experiments, if you recall, proved that life can arise from only pre-existing life. Can we correct this as life evolves from pre-existent life or otherwise, we will never answer the question as to how the first forms of life arose? Comment.

Answer:

In this experiment, Louis Pasteur used two flasks - a sterilised flask and another flask which was open to the air. Killed yeast did not produce a new organism in a sterilised flask, while new organisms were found in the second flask. This experiment helped in rejecting the theory of spontaneous generation.
Later Miller showed through an experiment, that organic molecules could develop from inorganic molecules, which can eventually lead to the origin of life. So, Miller's experiment could provide a correction to Pasteur's observation.

Question:2

The scientists believe that evolution is gradual. But extinction, part of evolutionary story, is 'sudden' and 'abrupt' and also group-specific. Comment whether a natural disaster can be the cause for the extinction of species.

Answer:

Most scientists agree on the theory of dinosaur's extinction, claiming that a meteor strike led to the dinosaur's large scale destruction and eventual extinction. This theory suggests that a natural disaster can, in fact, be the cause for the extinction of species.

Question:3

Why is nascent oxygen supported to be toxic to aerobic life forms?

Answer:

Due to the highly reactive nature of nascent oxygen, there is a possibility that they react with many molecules such as DNA. Nascent oxygen is threatening to life forms as this can potentially result in unwanted mutations.

Question:4

While creation and presence of variation are directionless, natural selection is directional as it is in the context of adaptation. Comment.

Answer:

Though variation occurs in each subsequent generation, only a few variations are retained, which are pass the test of natural selection. Hence, creation and presence of variation are directionless, but natural selection and adaptation are directional.

Question:5

The evolutionary story of moths in England during industrialisation reveals, that 'evolution is reversible'. Clarify this statement.

Answer:

White-winged moths thrive in tree trunks with a white background, but when the tree trunks become dark, the white-winged moths perished. Post industrialisation, tree trunks turned dark due to pollution leading to a drop in the population of white-winged moths. In this scenario, dark-winged moths reappeared and survived. Thus, the evolution of white wings was reversed because of pollution. This shows that evolution is apparently reversible.

Question:6

Comment on the statement that "evolution and natural selections are result or consequence of some other processes but themselves are not processed".

Answer:

Evolution, in the context of, life's success is treated as a process, but it appears to be a result of some other processes in the context of how life evolved from simple forms. Among the scientific community, this issue is still a point of debate.

Question:7

State and explain any three factors affecting allele frequency in populations.

Answer:

Factors which affect allele frequency in populations:

1. Genetic Drift: Due to random sampling, there are changes in the frequency of a gene variant. Genetic drift may cause a gene variant to disappear completely and result in reduced genetic variation.
2. Genetic Recombination: When offspring with traits different from parents are produced, it is called genetic recombination.
3. Natural Selection: The nature selects only the traits which help an organism to survive in the changed conditions. Natural selection leads to survival of the fittest. Traits that are unfit to survive, perish in the long run, which paves the way for the evolution of a new species.

Question:8

Gene flow occurs through generations. Gene flow can occur across language barriers in humans. If we have a technique of measuring specific allele frequencies in a different population of the world, can we not predict human migratory patterns in pre-history and history? Do you agree or disagree? Explain your answer.

Answer:

Yes, it is possible to understand gene flow in different populations of the world with the human genome project, which is now turning into a reality. This can help us in assessing and predicting human migratory patterns in pre-history and history.

Question:9

How do you express the meaning of words like race, breed, cultivars or variety?

Answer:

Race: A race is kept below the species and is an informal taxon. Members from different races of the same species can interbreed.
Breed: A breed is a specific group of domestic animals which are homogenous in appearance, which has been achieved through selective breeding.
Cultivar: A cultivar is a selected group of plants which can be raised through vegetative propagation.
Variety: Variety is similar to a race but used for the plants.

Question:10

When we say, "survival of the fittest", does it mean that
a. those who are fit only survive, or
b. those that survive are called fit? Comment.

Answer:

Survival of fittest means that those that survive are called fit. Organisms with useful adaptions survive in the long run and are considered to be fit.

Question:11

Enumerate three most characteristic criteria for designating a Mendelian population.

Answer:

The three most important criteria for designating a Mendelian population are as follows:

• The population must be sufficiently large.
• Free flow of genetic materials is ensured through sexual reproduction.
• There should be negligible or nil migration in the population.

Question:12

"Migration may enhance or blur the effects of selection". Comment.

Answer:

As natural selection involves the selection of a beneficial gene and rejection of a harmful gene; migration can disturb natural selection by interfering with the gene pool of the population. Hence, migration may enhance or blur the effects of natural selection.

Long Answer Type Questions:

Question:1

Name the law that states that the sum of allelic frequencies in a population remains constant. What are the five factors that influence these values?

Answer:

Hardy Weinberg Principle states that the sum of allelic frequencies in a population remains the same through generations. The total of allelic frequencies in a population is 1.
Frequency of allele A=p
Frequency of allele a=q

In a diploid individual,
Frequency of allele
Frequency of allele
Frequency of allele
This can be shown by the following equation which is derived from the algebraic identity

The extent of evolutionary change can be evaluated by measuring the difference between the measured values of these values from the expected value.
Following five factors influence these values:

1. Gene migration or gene flow
2. Genetic drift
3. Genetic recombination
4. Mutation
5. Natural selection

Question:2

Explain divergent evolution in detail. What is the driving force behind it? Answer:

Divergent evolution is the accumulation of differences that leads to the formation of new species. When two groups of the same species get isolated from each other, they adapt to different circumstances. Natural selection and adaptation result in variations that accumulate over various generations, which results in the origin of new species.
Homologous organs are similar in basic design but serve different purposes in different organisms. These homologous organs are results of divergent evolution. Forelimbs of mammals and birds are good examples of divergent evolution. While mammals use their forelimbs for walking, running and other chores, birds use forelimbs (modified into wings) for flight adaptations. In both cases, forelimbs are supported by humerus, radio -ulna, carpals, and metacarpals. This may indicate common ancestry.

Question:3

You have studied the story of Pepper moths in England. Had the industries been removed, what impact could it have on the moth population? Discuss.

Answer:

Before industrialisation in England, the population of black-winged moths was less than the population of white-winged moth. Due to the industrial revolution, tree trunks became darker because of the accumulation of industrial smoke or soot and reduction in the population of lichens.
This provided camouflaging advantage to black-winged moths, and thus, the population of black-winged moth gradually started to increase. However, white-winged moths' survival was threatened as predators would now find them easily. If industries are removed, the population of white-winged moths should again increase.
This showed that evolution is apparently reversible.

Question:4

What are the key concepts in the evolution theory of Darwin?

Answer:

The two prominent concepts in the evolutionary theory of Darwin are natural selection and branching descent.
Natural Selection: All living beings adapt to changing environmental conditions by developing useful adaptations. Organisms, which can survive the changes, will produce more progenies and thereby maintain their lineage. Nature selects only those who are fit to survive, leaving behind the rest to perish. Therefore, we can conclude that natural selection plays an important role in evolution.
Branching Descent: Branching descent follows the popular premise that all life forms are branched from a common origin. This is often referred to as the "Tree of Life" illustrated in the following diagram.

Fishes and Amphibians have a common ancestor. Amphibians have been considered as ancestors to other land animals such as reptiles, mammals and even birds.
Darwin used various proofs to show that living beings have evolved from a common ancestor through branching.

Question:5

Two organisms occupying a particular geographical area (say desert) show similar adaptive strategies. Taking examples describe the phenomenon.

Answer:

Organisms found in the same geographical area often have similar adaptations, and this is called convergent evolution. It is commonly observed in desert plants, although not all of them are closely related.
Cereus Peruvianus a cactus species primarily found in the South America and Euphorbia Virosa show similar adaptations such as fleshy succulent stem, deeper roots, and absence of leaves to conserve water. Modified fleshy succulent greenish stem participate in photosynthesis, as leaves are modified into spines to reduce water loss through transpiration. These are examples of analogous organs which manifest convergent evolution.

Question:6

We are told that evolution is a continuing phenomenon for all living things. Are humans also evolving? Justify your answer.

Answer:

Some scientists have studied human evolution and have shared following observations that suggest modern humans are also evolving:
Since the discovery of farming about 10,000 years ago human evolution has worked at lightning speed as scientists have observed multiple genetic difference between hunter gatherers and current humans.
Human reproductive period is longer than it was 10,000 years ago. Life expectancy has also more than doubled from earlier.
Lactase persistence into adulthood is another sign of human evolution. As young ones stop consuming milk after a certain age, they become lactose intolerance. But, human beings consume milk throughout their life as they get it from domesticated animals.
Humans have also developed resistance to many infectious diseases. This is another sign of evolution.
However, evolution in humans can only happen through genetic drift as a modern means of transport has blurred geographical boundaries, making geographical isolation impossible.

Question:7

Had Darwin been aware of Mendel's work, would he be able to explain the origin of variations? Discuss.

Answer:

Mendel observed reproduction in pea plants to come up with his theories on variations. Through these experiments, Mendel could attribute the origin of variations to some factors.
Darwin was from the same era as Mendel and would have had access to the same technology and information as Mendel had. Darwin was out on an exploration, and it would not have been possible to conduct an experiment similar to the one conducted by Mendel. The goals and focus of their experiments were quite different from each other. Because of these factors, it seems highly unlikely that Darwin would have been able to explain the origin of variations.