CBSE Class 12

Pre Boards

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Sample Papers

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 Multiple Choice QuestionsShort Answer Type


Name the source plants of heroin drug. How is it obtained from the plants?

Papaver somniferum is the source plant of heroin drug. This is obtained by Acetylation of morphine, which is extracted from the latex of poppy plant (Papaver somniferum).


How do cytokine barriers provide innate immunity in humans?

Cytokine inhibits viral replication. They form an innate immune system by forming physical barriers. 

Cytokine barriers: Virus-infected cells secretes proteins call interferons which protect non-infected cells from further viral infection.


Mention the chemical change that proinsulin undergoes, to be able to act as mature insulin.

The proinsulin is cleaved to remove extra stretch called the C-peptide to form mature insulin having only A-chain and B-chain joined by a disulphide bond.


Write the effects of heroin on the human body.

Heroin is depressant and slow down body functions.


Write the names of the following :
(a) A 15 mya primate that was ape-like
(b) A 2 mya primate that lives in East African grasslands

(a) 15 mya, primates called Dryopithecus was more ape-like.

(b) 2 mya, Australopithecines lived in East African grasslands.


Write the dual purpose served by Deoxyribonucleoside triphosphates in the polymerisation.

Deoxyribonucleoside triphosphates (DTPs) purpose:

(i) DTPs serves as substrates i.e. nucleotides during replication.

(ii) DTPs supply energy for polymerisation reaction by breaking of high energy terminal phosphates bond.


How did a citizen group called Friends of Arcata Marsh, Arcata, California, USA, help to improve water quality of the marshland using Integrated Waste Water Treatment ? Explain in four steps.

Wastewater including sewage can be treated in an integrated manner, by utilising a mix of natural and artificial processes.

  1. The conventional sedimentation, filtering and chlorine treatments are given. After this stage, lots of dangerous pollutants like dissolved heavy metals still remain.
  2. To combat this, an innovative approach was taken and the biologists developed a series of six connected marshes over 60 hectares of marshland.
  3. Appropriate plants, algae, fungi and bacteria were seeded into this area, which neutralises, absorb and assimilate the pollutants. Hence, as the water flows through the marshes, it gets purified naturally.
  4. The marshes also constitute a sanctury, with a high level of biodiversity in the form of fishes, animals and birds.


Name two diseases whose spread can be controlled by the eradication of Aedes mosquitoes.

Dengue and Chikungunya are the two disease whose spread can be controlled by the eradication of Aedes mosquitoes.


Your advice is sought to improve the nitrogen content of the soil to use for cultivation of a non-leguminous terrestrial crop.

(a) Recommend two microbes that can enrich the soil with nitrogen.

(b) Why do leguminous crops not require such enrichment of the soil?

(a) Azospirillum, Azotobacter, Anabaena, Oscillatoria, etc.

(b) Leguminous crops have a symbiotic association with Rhizobium bacteria which traps N2 directly from the atmosphere and provides it to the plant and in turn gets food and shelter.


You have obtained a high yielding variety of tomato. Name and explain the procedure that ensures retention of the desired characteristics repeatedly in large populations of future generations of the tomato crop.

  1. Micropropagation (a type of vegetative propagation) ensures retention of the desired characteristics repeatedly in large populations of future generations of the tomato crop.
  2. A small part of the plant is excised and grown under a sterile condition in special nutrient medium to obtain many such plants which would be genetically identical to the original plants.