Tamil Nadu 10th Standard Science Book Solution | Lesson 19 – Origin And Evolution Of Life

Lesson 19. Origin And Evolution Of Life

Origin And Evolution Of Life - Book Back Answer

Lesson 19. > Origin And Evolution Of Life

I. Choose the best answer

1. Biogenetic law states that ______________

  1. Ontogeny and phylogeny go together
  2. Ontogeny recapitulates phylogeny
  3. Phylogeny recapitulates ontogeny
  4. There is no relationship between phylogeny and ontogeny

Ans ; Ontogeny recapitulates phylogeny

2. The ‘use and disuse theory’ was proposed by ______________.

  1. Charles Darwin
  2. Ernst Haeckel
  3. Jean Baptiste Lamarck
  4. Gregor Mendel

Ans ; Jean Baptiste Lamarck

3. Palaeontologist deal with

  1. Embryological evidences
  2. Fossil evidences
  3. Vestigial organ evidences
    All the above

Ans ; Fossil evidences

4. The best way of direct dating fossils of recent origin is by

  1. Radio–carbon method
  2. Uranium lead method
  3. Potassium–argon method
  4. Both (a) and (c)

Ans ; Radio–carbon method

5. The term Ethnobotany was coined by

  1. Khorana
  2. J.W. Harsbberger
  3. Ronald Ross
  4. Hugo de Vries

Ans ; J.W. Harsbberger

II. Fill in the blanks

1. The characters developed by the animals during their life time, in response to the environmental changes are called __________.

Ans ; Adaptation

2. The degenerated and non-functional organs found in an organism are called __________.

Ans ; Vestigial

3. The forelimb of bat and human are examples of __________ organs.

Ans ; Homologous

4. The theory of natural selection for evolution was proposed by __________.

Ans ; Charles Darwin

IV Match the following

Column A Column B
1. Atavismcaudal vertebrae and vermiform appendix
2. Vestigial organsa forelimb of a cat and a bat’s wing
3. Analogous organsrudimentary tail and thick hair on the body
4. Homologous organsa wing of a bat and a wing of an insect
5. Wood parkradiocarbon dating
6. W.F. LibbyThiruvakkarai
Ans ; 1 – C, 2 – A, 3 – D, 4 – B, 5 – F, 6 – E

V. Answer in a word or sentence

1, A human hand, a front leg of a cat, a front flipper of a whale and a bat’s wing look dissimilar and are adapted for different functions. What is the name given to these organs?

Homologous organs

2. Which organism is considered to be the fossil bird?


3. What is the study of fossils called?


VI. Short answers questions

1. The degenerated wing of a kiwi is an acquired character. Why is it an acquired character?

  • Kiwi isa flightless bird. The degenerated wing in Kiwi is an example for organ of disuse.
  • When there is a change in the environment, the animals respond to the change.
  • They develop adaptive structures (acquired characters).

2. Why is Archaeopteryx considered to be a connecting link?

  • Archaeopteryx is considered to be aconnecting link because it links between reptiles and birds.
  • It had wings with feathers like a bird. It has long tail, clawed digits and conical teeth like a reptile.

3. Define Ethnobotany and write its importance.

Ethnobotany is the study of a region’s plants and their practical uses through the traditional knowledge of local culture of people.


  • It provides traditional uses of plant.
  • It gives information about certain unknown and known useful plants.
  • The ethnomedicinal data will serve as a useful source of information for the chemists, pharmacologists.
  • Tribal communities utilise ethnomedicinal plant and prepare medicine to cure manydiseases.

4. How can you determine the age of the fossils?

  • The age of fossils is determined by radioactive elements present in it.
  • They may be carbon, Uranium, lead or pottasium.
  • It is used in paleobotany and anthropology for determining the age of human fossils and manuscripts.

VII. Long answer questions

1. Natural selection is a driving force for evolution-How?

Natural selection is a driving force for evolution.


  • Living beings have the ability to reproduce more individuals and form their own progeny.
  • This will increase reproductive potential leading to over production

Struggle for existence:

  • Due to over production, a geometric ratio of increase of population occurs.
  • This creates an intense competition among the organisms for food and space leading to
  • The struggle for existence are of three types:

a. Intraspecific struggle:

Competition among the individuals of same species.

b. Interspecific struggle:

Competition between the organisms of different species living together.

c. Environmental struggle:

Natural conditions like extream heat or cold, drought and floods can affect the existence of organisms.


  • The occurrence of variation is a characteristic feature of all plants and animals.
  • Small variations are important for evolution.
  • According to Darwin, favourable variations are useful to the organism.
  • Unfavourable variations are harmful or useless to the organism.

Survival of the fittest or Natural selection

  • During the struggle for existence, the organisms which can overcome the challenging situation, survive and adapt to the surrounding environment.
  •  Organisms which are unable to face the challenges, are unfit to survive and disappear.
  • The process of selection of organisms with favourable variation is called as natural 5 selection. )

Origin of species:

According to Darwin, new species originates by the gradual accumulation of favourable variations for a number of generations.

2. How do you differentiate homologous organs from analogous organs?

Homologous organsAnalogous organs
1. The homologous organsare those which have been inherited from common ancestors with similar developmental pattern in embryos.The analogous organs look similar and perform similar function but they have  different origin and developmental pattern.
2. The fore limbs of mammals are homologous structures.‘The wings of a bird, wings of an insect are similar.
3. The mode of development and basic structure of bone is similar.The development is similar, but their bone structures are different.

3. How does fossilization occur in plants?

  • 2 million years ago tree trunks that got buried along the river, incourse of time the organic matter was replaced by silica and was fossilized.
  • They retained their colour, shape and texture and was converted into solid rocks.
  • The annular rings, the texture, colours of the layers, nodes and every properties of plants are still visible.

VIIL. Higher Order Thinking Skills (HOTS)

1. Arun was playing in the garden. Suddenly he saw a dragon fly sitting on a plant. He observed the wings of it. He thought it looked similar to a wing of a crow. Is he correct? Give reason for your answer.

Yes, he is correct.

Reason: The function of the wings of a crow (the wings of a bird) and wings of an insect are similar, but the basic structure is different.

2. Imprints of fossils tell us about evolution How?

  • Fossils are remains or impressions of organisms that lived in the remote past.
  • Fossil provide the evidence that the present animal have originated from previously existing ones through the process of continuous evolution.

3. Octopus, cockroach and frog all have eyes. Can we group these animals together to establish a common evolutionary origin. Justify your answer

  • Octopus, cockroach and frog all have eyes.
  • Octopus-belongs to mollusc which have simple eye without lens.
  • Cockroach are invertebrate have compound eyes.
  • Frog which is vertebrate, have highly specialised lens.
  • However, all of them perform the same function that is vision.
  • Thus a common evolutionary origin can be established on the basis of eye.


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