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CBSE Class 12 Biology Solved Question Paper 2018

Short Answer Type

21.

Give an example of a bacterium, a fungus and an insect that are used as biocontrol agents.

22.

How has the development of bioreactor helped in biotechnology?

23.

Name the most commonly used bioreactor and describe its working.

24.
Explain the roles of the following with the help of an example each in recombinant DNA technology:
(a) Restriction Enzymes
(b) Plasmids

(a) Restriction enzymes :

Restriction enzymes belong to the class of enzymes nucleases which breaks nucleic acids by cleaving their phosphodiester bonds.
Since Restriction endonucleases cut DNA at specific recognition site, they are used to cut the donor DNA to isolate the desired gene.
The desired gene has sticky ends which can be easily ligated to cloning vector cut by same restriction enzymes having complementary sticky ends to form recombinant DNA
An example is EcoR1 which is obtained from E.coli bacteria “R” strain which cuts DNA at specific palindromic Recognition site.
5‘ GAATTC 3‘
3‘ CTTAAG 5‘

(b) Plasmids :

Plasmids are autonomous, extrachromosomal circular double-stranded DNA of bacteria
Since they are small and self replicating,they are used as cloning vectors in genetic engineering.
Some plasmids have antibiotic resistance genes which can be used as marker genes to identify recombinant plasmids from non-recombinant ones.
The plasmids are cut and ligated with desired genes and transformed into a host cell for amplification to obtain the desired products.
An example of artificially modified plasmids is pBR322 ( constructed by Bolivar and Rodriguez) or pUC (constructed at university at California).

25.

Differentiate between Parthenocarpy and Parthenogenesis. Give one example of each.

26.

Medically it is advised to all young mothers that breastfeedings is the best for their newborn babies. Do you agree? Give reasons in support of your answer.

27.

Draw a diagram of a mature human sperm. Label any three parts and write their functions.

28.

Expand VNTR and describe its role in DNA fingerprinting.

29.

List any two applications of DNA fingerprinting technique.

30.

Looking at the deteriorating air quality because of air pollution in many cities of the country, the citizens are very much worried and concerned about their health. The doctors have declared a health emergency in the cities where the air quality is very severely poor.

(a) Mention any two major causes of air pollution.

(b) Write the two harmful effects of air pollution on plants and humans.

(c) As a captain of your school Eco-club, suggest any two programmes you would plan to organise in the school so as to bring awareness among the students on how to check air pollution in and around the school