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CBSE Class 12 Biology Solved Question Paper 2015

Short Answer Type

How many chromosomes do drones of honeybee possess? Name the type of cell division involved in the production of sperms by them.

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What is a cistron?

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3. Retroviruses have no DNA. However, the DNA of the infected host cell does possess viral DNA. How is it possible?

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4. Why do children cured by enzyme-replacement therapy for adenosine deaminase deficiency need periodic treatment?

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5. List two advantages of the use of unleaded petrol in automobiles as fuel.

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Why do moss plants produce very large number of male gametes? Provide one reason. What are these gametes called?

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(a) Select the homologous structures from the combinations given below :
(i) Forelimbs of whales and bats
(ii) Tuber of potato and sweet potato
(iii) Eyes of octopus and mammals
(iv) Thorns of Bougainvillea and tendrils of Cucurbita

(b) State the kind of evolution they represent.

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(a) Why are the plants raised through micro-propagation termed as somaclones?
(b) Mention two advantages of this technique.

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Explain the different steps involved during primary treatment phase of sewage.

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10. What is mutualism? Mention any two examples where the organisms involved are commercially exploited in agriculture.

Mutualism is the interaction between the organisms of two species in which both organisms are benefited.
Examples of the organisms involved that are commercially exploited in agriculture are as follows:
(i) Rhizobium which is a mutual relationship between bacteria and leguminous plants is used as a biofertiliser. These enrich the nutrient quality of the soil by fixing atmospheric nitrogen into organic forms..
(ii) Mycorrhiza which is an association of the soil fungus and the roots of higher plants. Farmers use Mycorrhiza commercially in agriculture as it improves the soil quality and plant growth and development, reduces soil erosion, help the plants absorb phosphorous from the soil. Plants having such associations show resistance to root-borne pathogens, tolerance to salinity and drought.

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