NCERT Class 12 Biology Exemplar Chapter –7 Evolution Part 3

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Very Short Answer Type Questions

Question 1:

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


The characteristic of life forms that had been fossilised are as follows:

i. The early fossils were simple life forms which evolved into complex life forms later.

ii. Fossilised organisms hard body surface which allowed them to get preserved and fossilised.

Question 2:

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


Many aquatic life forms did get fossilised.

The remains of aquatic life forms get fossilised in the sediments of the water bodies. Later, sediments form the part of sedimentary rocks in which fossils, are deposited. Such fossils of sea creatures are found in mountains as opposed to deep-sea beds.

This is because the rocks in which the fossils are found used to be all the bottom of the water bodies. Due to the changes in the crustal plates over time, the ocean sediments were pushed up to form mountains.

Question 3:

What are we referring to? When we say ‘simple organisms’ or ‘complex organisms’.


The terms ‘Simple organisms’ and ‘complex organisms’ are used to classify the organisms based on the period of their evolution.

‘Simple Organisms’ are primitive organisms whereas ‘complex organisms’ are advanced organisms.

‘Simple Organisms’ have simple structural and functional organisation whereas ‘complex organisms’ have complex structural and functional organisations.

‘Complex organisms’ evolved from ‘Simple Organisms’.

These terms are used to refer to the complexity of the division of labour.

These terms are also used to refer to the relative level of organisation in the organisms.

Question 4:

How do we compute the age of a living tree?


The age of a living tree is calculated by either counting the number of rings present in the trunk of the tree or by comparing the diameter of the trunk of the tree with average growth factor of that tree (which is found from records).

The method of calculating the age of the tree by counting the number of annual growth rings of the tree is known as Dendro-Chronology.

The diameter of the tree is found by dividing the circumference of the tree trunk by 3.14. Then the diameter is multiplied with the tree’s average growth factor to find the approximate age of the tree in years.

The growth factor of the tree is the annual gain in width of the trunk. This growth factor is available from records. Or this can also be found by measuring the rings of a dead tree from the same species.

Question 5:

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


Convergent evolution refers to the appearance of similar features in species of different lineages.

Convergent evolution forms analogous structures.

Analogous organs refer to those organs that are not anatomically similar but perform similar functions i.e., they evolved from different ancestors.

Example of convergent evolution is –

Wings of birds and butterflies, they perform similar function of flying but have different anatomically, i.e., different bone structures, different wing coverings, different shape and size.

Question 6:

How do we compute the age of a fossil?


The age of a fossil can be calculated by radioactive dating.

In this technique a comparison is done between the naturally occurring radioactive isotopes with that of the decay product, using known decay rates.

Some of the techniques used are radio-carbon dating, potassium-argon dating, uranium lead dating, etc.

Question 7:

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


Adaptive radiation is a process in which organisms diversify rapidly from an ancestral species into various new forms when a change in the environment makes new resources available or new environmental niches open.

The most important pre-condition for adaptive radiation is geographic barrier or an isolated habitat.

Question 8:

How do we compute the age of a rock?


The age of a rock can be computed by natural radio-active decay of certain elements.

The radio-active half-life (the amount of time required for one half of the parent atoms to be converted to daughter atoms) is used to calculate the age of the rock.