Trace the life-cycle of malarial parasite in the human body when

Subject

Biology

Class

CBSE Class 12

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Sample Papers

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 Multiple Choice QuestionsShort Answer Type

21. How does industrial melanism support Darwin’s theory of Natural Selection? Explain.
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22. List the salient features of double helix structure of DNA. 
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23. How are the structural genes activated in the lac operon in E.coli
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24. Trace the life-cycle of malarial parasite in the human body when bitten by an infected female Anopheles. 


Plasmodium (malarial parasite) requires two hosts – human and mosquitoes to complete its life cycle. Plasmodium enters the human body as sporozoites (infectious form) through the bite of infected female Anopheles mosquito. The parasites initially multiply within the liver cells and then attack the red blood cells (RBCs) resulting in their rupture. The rupture of RBCs leads to release of a toxic substance, haemozoin, which is responsible for the chill and high fever recurring every three to four days. When a female Anopheles mosquito bites an infected person, these parasites enter the mosquito’s body and undergo further development. The parasites multiply within the mosquito’s body to form sporozoites that are stored in their salivary glands. When these mosquitoes bite a human, the sporozoites are introduced into his/her body, thereby initiating the another cycle.


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25.

(a) Tobacco plants are damaged severely when infested with Meloidegyne incognitia. Name and explain the strategy that is adopted to stop this infestation.

(b) Name the vector used for introducing the nematode specific gene in tobacco plant.
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26.

(a) Explain the phenomena of multiple allelism and co-dominanace taking ABO blood group as an example.

(b) What is the phenotype of the following:

(i) IAi

(ii) i i

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27.

(a) List any three ways of measuring population density of a habitat.

(b) Mention the essential information that can be obtained by studying the population of an organism. 
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28. How is the amplification of a gene sample of interest carried out using Polymerase Chain Reaction (PCR)? 
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29.

(a) What is the programme called that is involved in improving success rate of production of desired hybrid and herd size of cattle?

(b) Explain the method used for carrying this programme for cows. 
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 Multiple Choice QuestionsLong Answer Type

30.

(a) Explain the significance of ecological pyramids with the help of an example.

(b) Why are the pyramids referred to as upright or inverted?
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