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

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 Multiple Choice QuestionsShort Answer Type

21.

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.

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22.

Scientists have succeeded in recovering healthy sugarcane plants from a diseased one.

1. Name the part of the plant used as explant by the scientists.

2. Describe the procedure the scientists followed to recover the healthy plants.

3. Name this technology used for crop improvement.

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23.

A. Name the enzyme that catalyses the transcription of hnRNA.

B. Why does the hnRNA need to undergo changes ? List the changes hnRNA undergoes and where in the cell such changes take place.


A. hnRNA is designated as heterogeneous nuclear RNA. Transcription of hnRNA is catalyses by – RNA polymerase II.

B. During primary transcription formation the mRNA contains both coding and non-coding regions called as exons and introns. The sequence is then subjected to splicing (process of removal of introns form primary transcript).

hnRNA then undergo capping and tailing.
Capping is a process where addition of methyl guanosine triphosphate takes place at 5' end of hnRNA, while tailing is done by the addition 200- 300 adenylate residues at 3' end. The final mRNA is then transported outside of nucleus by nuclear pore to the cytoplasm for translation.

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24.

(i) Write the scientific names of the two species of filarial worms causing filariasis.

(ii) How do they affect the body of infected person(s)?

(iii) How does the disease spread?

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25.

Name the genus to which baculoviruses belong. Describe, their role in the integrated pest management programmes.

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26.

Unambiguous, universal and degenerate are some of the terms used for the genetic code. Explain the salient features of each one of them.

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27.

Water is very essential for life. Write any three features both for plants and animals which enable them to survive in water scarce environment. 

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28.

How do organisms cope with stressful external environmental conditions which are localised or of short duration?

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29.

A. State the consequence if the electrostatic precipitator of a thermal plant fails to function.

B. Mention any four methods by which the vehicular air pollution can be controlled.

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30.

A. Draw a labelled diagram of L.S. of an embryo of grass (any six labels).

B, Give reason for each of the following:

(i) Anthers of angiosperm flowers are described as dithecous.
(ii) Hybrid seeds have to be produced year after year.

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