Subject

biology

Class

CBSE Class 12

Pre Boards

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Sample Papers

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 Multiple Choice QuestionsShort Answer Type

1.

Identify 'a' and 'b' in the figure given below representing proportionate number of major vertebrate taxa.



In the given figure, 

a represents amphibians, and 

 b represents mammals

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2.

Name any two types of cells that act as 'cellular barriers' to provide innate immunity in humans.


Natural killer in the blood and macrophages in the tissues are two types of cells that act as 'cellular barriers' to provide innate immunity in humans.

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3.

How is 'stratification' represented in a forest ecosystem?


Stratification is the vertical distribution of different species occupying different levels. Stratification in the forest is represented by

i) Trees occupying the top layer

ii) Shrubs occupy the second layer. 

iii) Herbs and grasses the bottom most layers.

 

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4.

State the cause of accelerated eutrophication.


Causes of accelerated eutrophication:

i) Industrial wastes which are a great source of nitrogen and phosphorous that over-stimulate the algal growth.

ii) Sewage and agricultural wastes also lead to increase in temperature and BOD of the water body thereby leading to algal blooms.

 

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5.

Why do algae and fungi shift to sexual mode of reproduction just before the onset of adverse conditions?


Organisms such as fungi and algae switch to sexual mode of reproduction during adverse conditions because sexual reproduction brings variation into the individuals, some of which might help the individuals to adapt to the changed conditions and survive. This ensures the continuity of species.

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6.

Mention the type of host cells suitable for the gene guns to introduce an alien DNA.


Plant cells are considered suitable for the gene guns to introduce an alien DNA.

 

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7.

How does the gene 'I' control ABO blood groups in humans? Write the effect the gene has on the structure of red blood cells.


In humans, the ABO blood groups are controlled by a gene called gene I. It has three alleles, namely IA, IB and i. Two of the three alleles IA and I B dominate over i. But IA and I B express themselves in each other’s presence and hence are co-dominant.

Showing the Genetic Basis of Blood Groups in Human Population is given as follows:

 

Allele from Parent 1

Allele from Parent 2

Genotype of offspring

Blood type of offspring

I A

I A

I A I A

A

I A

I B

I A I B

AB

I A

i

I A i

A

I B

I A

I A I B

AB

I B

I B

I B I B

B

I B

i

I B i

B

i

i

i i

O


These alleles help to determine the structure of the red blood cells. The plasma membrane of red blood cells has sugar polymers that protrude out from its surface and the kind of sugar is regulated by the gene 'I' of ABO blood group. The alleles IA and IB produce A and B types of sugar, while allele i does not produce any sugar. Thus when allele ‘IA and IA’ and ‘I A and i‘ are present together then the red blood cells have sugar A on the surface. When IB and I B or IA and i are present then sugar B is found on the surface. When IA and I B are present both A and B sugar are found on the cell surface. While blood group O does not bear any sugar.

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8.

Give an example of an organism that enters 'diapause' and why.


Zooplankton under unfavorable enters ‘diapause’ which is a state of suspended development.

 

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9.

What are 'true breeding lines' that are used to study inheritance pattern of traits in plants?


True breeding line is one that, having undergone continuous self-pollination, shows the stable trait inheritance and expression for several generations.

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10.

Write the name of the organism that is referred to as the 'Terror of Bengal'.


Water hyacinth (Eichhornia crassipes) is referred to as the 'Terror of Bengal'.

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