CBSE Class 12

Pre Boards

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Sample Papers

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 Multiple Choice QuestionsShort Answer Type


Suggest a method to ensure an anamnestic response in humans.

Anamnestic response is the quick and intense response which occurs when an individual encounters a particular antigen for the second time. It is aided by the memory of primary response stored by B-cells. By the administration of a dead or attenuated pathogen in the body of person, a secondary immune response can be ensured due to the presence of memory cells in the body.



A mature embryo sac in a flowering plant may possess 7-cells, but 8-nuclei. Explain with the help of a diagram only.

A typical angiospermic embryo sac is 8-nucleated and 7-celled.



How does the application of the fungal genus, Glomus, to the agricultural farm increase the farm output?

The application of Glomus to agricultural field increases the farm output by increasing the nutrient availability to the crops. Glomus develops symbiotic association with the roots of plants, called mycorrhiza. It absorbs phosphorus from the soil and passes it to the plants it associates with. In return, it derives sugars from the host plant cells for its survival.
Thus, it acts as a biofertiliser. This association has other advantages also, like
(i) Resistance to root borne pathogens
(ii) Tolerance to salinity and drought
(iii) Increase in plant growth and development



State the fate of a pair of autosomes during gamete formation.

During gamete formation, the homologous pair of autosomes gets separated from each other and moves to different gametes, so that each gamete receives haploid set of chromosomes.



Mention the evolutionary significance of the following organisms:

The evolutionary significance of given organisms are as
(a) Shrews The first mammals. These were long tailed, insectivorous, squirrel-like organisms. They gave rise to primitive primates. For example, leones, tarsiers at the beginning of the Palaeocene era.
(b) Lobefins The first amphibians. Modern day frogs and salamanders have evolved from them.
(c) Homo habilis The first human-like primates, lived in Africa about 2 million years ago. They had brain capacity of 700 cc. Also called handy man as they were first and most skillful tool makers.
(d) Homo erectus They appeared after Homo habilis, 1.7million years ago. They had large brain capacities, i.e. 800-1100 cc and were omnivores.



In an agricultural field, there is a prevalence of the following organisms and crop diseases which are affecting the crop yield badly:
(a) White rust (b) Leaf and stripe rust
(c) Black rot (d) Jussids
Recommend the varieties of crops the farmers should grow to get rid of the existing problem and thus, improve the crop yield.

Normal varieties of crops are prone to infection by various pathogens which lead to poor growth of crops. To get rid of existing problems, the farmers should grow improved hybrid varieties as these are mostly resistant to most pathogens and give higher yield.
Crop disease - Hybrid variety
(a) White rust - Pusa Swarnim
(b) Leaf and stripe rust  - Himgiri
(c) Black rot Pusa - Shubhra
(d) Jussids Pusa - Sem 3



Plenty of algal bloom is observed in a pond in your locality.
(a) Write what has caused this bloom and how does it affect the quality of water.
(b) Suggest a preventive measure.

(a) The presence of large amounts of nutrients in water leads to algal bloom. These nutrients (nitrogen and phosphorus) are added to water bodies from fertilisers that get issolved in soil and are washed off by water bodies. Algal bloom affects the quality of water in the
following ways:
(i) It causes deterioration of water quality making it unfit to use.
(ii) Eutrophication (natural ageing of water bodies) is accelerated, resulting in hypoxic conditions (i.e. low oxygen), killing off the aquatic diversity.

(b) To prevent the algal bloom, the farmers instead of using chemical nutrients must start using natural products like manures produced using vermicomposting. Biodegradable materials should be used, that are readily decomposed and are phosphate free. Awareness should be created among people about the effects of dumping waste in water bodies.



What role does an individual organism play as per Darwin’s theory of natural selection?

According to the Darwin’s theory of natural selection, the role of an individual organism is to pass on the necessary variations, changes or mutations that has been selected by the native, from present generation to the next.



What is biopiracy?

Biopiracy refers to the use of bioresources by multinational companies and other organisations without proper authorisation from people and countries concerned.



Our government has intentionally imposed strict conditions for M.T.P. in our country. Justify giving a reason.

MTP or induced abortion is termination of pregnancy due to certain medical reasons. Government of India legalised MTP in 1971 with strict conditions to avoid its misuse.