Subject

Biology

Class

CBSE Class 12

Pre Boards

Practice to excel and get familiar with the paper pattern and the type of questions. Check you answers with answer keys provided.

Sample Papers

Download the PDF Sample Papers Free for off line practice and view the Solutions online.
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 Multiple Choice QuestionsShort Answer Type

21.

Why do lepidopterans die when they feed on Bt cotton plant? Explain how does it happen.

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22.

In situ conservation can help endangered / threatened species. Justify the statement.

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 Multiple Choice QuestionsLong Answer Type

23.

Public all over India is very much concerned about the deteriorating air quality in large parts of North India. Alarmed by this situation the Resident’s Welfare Association of your locality organised an awareness programme entitled ‘Bury not burn’. They invited you, being a biology student to participate.
(a) How would you justify your arguments that promote burying and discourage burning?
(Give two reasons)
(b) With the help of flow charts, one for each practice, depict the chain of events that follow.

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24.

(a) Arrange the following hormones in the sequence of their secretion in a pregnant woman.
(b) Mention their source and the function they perform.

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25.

State and explain the ‘law of independent assortment’ in a typical Mendelian dihybrid cross.

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26.

Discuss the role of healthy ecosystem services as a prerequisite for a wide range of economic, environmental and aesthetic goods and services.


Ecosystem services are the products of ecosystem processes. Forests are the major source of ecosystem services and are
prerequisite for environmental, aesthetic goods and indirect economic values in the following ways:
1. Environmental Values
(i) Carbon-fixation Huge amount of CO2 in the atmosphere is removed naturally and fixed by plants into organic
molecules and energy through photosynthesis. All the other trophic levels, i.e. consumers depend upon this
energy produced by them.
(ii) Release of oxygen by the producers as a byproduct in the process of photosynthesis, improves the air quality
and supports life on earth.
(iii) Soil Soil formation and soil protection are the major ecosystem services accounting for nearly 50% of their total
worth. Plant cover protects the soil from drastic changes in temperature. There is little wind or water erosion as
soil particles are not exposed to them. The soil remains spongy and fertile. There are not landslides and no floods.
(iv) Nutrient cycling There is no depletion of nutrients, but the same are repeatedly circulated.
2. Economic Value
(i) Ecosystem services provide certain economical important products also. These include timber, paper, rubber,
wax, medicines, cosmetics, resins, etc.
(ii) Ecosystem also provides other benefits such as aid in pollination. Bees and other insects of natural ecosystem visit
nearby farmlands to pollinate crops.
3. Other aesthetic values Natural ecosystems are a source of spiritual, cultural and aesthetic values.

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