CBSE Class 12 Biology Evolution Worksheet Set D

Very Short Answer Questions

Question: Among Ramapithecus, Australopithecous and Homo habilis, who probably did not eat meat?
Answer. Homo habilis

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: 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: Coelacanth was caught in South Africa. State the significance of discovery of Coelacanth in the evolutionary history of vertebrates. 
Answer.Coelacanth evolved as first amphibian (lived on both land and water). It is an ancestor of modern day frogs and salamanders.

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: 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.

Question: State the significance of Coelacanth in evolution.
Answer. It is an ancestor of amphibians.

Question: List 10 modern-day animals and using the internet resources link it to a corresponding ancient fossil. Name both. 
Answer. 

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.

Short Answer Questions

Question: Branching descent and natural selection are the two key concepts of Darwinian theory of evolution. Explain each concept with the help of a suitable example. 
Answer. Branching descent: Different species descending from the common ancestor get adapted in different habitats, e.g., Darwin’s finches—varieties of finches arose from grain eaters; Australian marsupials evolved from common marsupial.
Natural selection: It is a process in which heritable variations enable better survival of the species to reproduce in large number, e.g., white moth surviving before the industrial revolution and black moth surviving after industrial revolution; long-necked giraffe survived the evolution process; DDT-resistant mosquitoes survive. (Any suitable example)

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: Explain divergent evolution with two examples. 
Answer. Some structures developed along different directions due to adaptations to different needs performing different functions. This is called divergent evolution. Examples:
(i) Forelimbs of whales, bat, cheetah and humans have similar pattern of bones.
(ii) Thorns of Bougainvillea and tendrils of Cucurbita are modifications of stem.

Question: While creation and presence of variation is directionless, natural selection is directional as it is in the context of adaptation. Comment. 
Answer. Creation and variation occur in a sexually reproducing population as a result of crossing-over during meiosis and random fusion of gametes and independent assortment of genes. It is however the organisms that are selected over a period of time which are determined by the environmental conditions. In other words, the environment provides the direction with respect to adaptations so that the organisms are more and more fit in terms of survival.

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: In a certain population, the frequency of three genotypes is as follows.
Genotypes: BB Bb bb
Frequency: 22% 62% 16%
What is the likely frequency of B and b alleles? 
Answer. Frequency of B allele = all of BB + ½ of Bb = 22 + 31 = 53%
Frequency of b allele = all of bb + ½ of Bb = 16 + 31 = 47%.

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: Protein synthesis machinery revolves around RNA but in the course of evolution it was replaced by DNA. Justify.
Answer. Since RNA was unstable and prone to mutations, DNA evolved from RNA with chemical modifications that makes it more stable.
DNA has double stranded nature and has complementary strands. These further resist changes by evolving a process of repair.

Long Answer Questions

Question: How do fossils help us in understanding the evolutionary history?
Answer. (i) Paleontological evidences
- The study of fossil is called paleontology.
- Fossils are the remains or impressions of past organisms preserved in sedimentary rocks or other media.
- Different-aged rock sediments in earth’s crust indicate the presence of fossils of different life forms which died during the sediment formation.
- A variety of fossils ranging from the modern organisms to extinct organisms can be observed.
- By studying the different sedimentary layers, the geological time period in which the organism existed can be predicted, e.g., Dinosaurs.

Question: State the contribution of Louis Pasteur in understanding the origin of life on earth. Explain the procedure that he followed to arrive at his conclusion. 
Answer. Louis Pasteur dismissed the theory of spontaneous generation and demonstrated that life came from pre-existing life. He took two long-necked flasks. He left one flask with a straight neck and the other was bent to from an ‘S’ shape. He put sterile broths in both the flasks. He placed killed yeast in pre-sterilised bent flask and the other flask was left open to air.
After several weeks he observed that the straight neck flask was discoloured and cloudy, while the curved flask had not changed. Thus he concluded that the germs in air were able to fall unobstructed down the straight necked flask while they got trapped in the curved flask.

Question: Evolution is a change in gene frequencies in a population in response to changes in theenvironment 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: State the theory of Biogenesis. How does Miller’s experiment support this theory?
Answer. The theory of biogenesis states that a living organism arises from another living organism.
For Miller’s experiment: - Life appeared 500 million years after formation of earth.
- Different theories were given to explain the origin of life.
(i) Theory of special creation: According to this theory, God created life by his divine act of creation.
(ii) Theory of panspermia/cosmozoic theory: According to early Greek thinkers, units of life called spores or panspermia came from outer space and developed into living forms. This theory was rejected as spores cannot survive extreme cold, dryness or UV rays from Sun, which are required to be crossed to reach earth.

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.

Question: What are analogous structures? How are they different from homologous structures? Provide one example for each. 
OR
Differentiate between homology and analogy. Give one example of each.

Answer.

Question: (a) Differentiate between analogous and homologous structures.
(b) Select and write analogous structures from the list given below:
(i) Wings of butterfly and birds
(ii) Vertebrate hearts
(iii) Tendrils of Bougainvillea and Cucurbita
(iv) Tubers of sweet potato and potato 
Answer. (a)  Differences between analogous and homologous structures

(b) Wings of butterfly and birds.
Tubers of sweet potato and potato.