Past Year Paper - Solutions, Biology(Set - 2), 2015, Class 12, Biology | Additional Study Material for NEET PDF Download

 Page 1


  
 
CBSE XII  |  Biology 
Board Paper – 2015 – All India - Set 2 (Solution) 
 
  www.topperlearning.com  1 
CBSE 
Class XII Biology 
Board Paper – 2015 – All India (Set 2)  
SOLUTION 
 
SECTION A 
 
1. Advantages of unleaded petrol in automobiles as fuel: 
i. Automobiles equipped with a catalytic converter should use unleaded petrol 
because lead in the petrol inactivates the catalysts of the converter. 
ii. Use of unleaded petrol prevents the release of poisonous gases such as nitrous oxide 
in the environment. 
 
2. Retroviruses have RNA as genetic material. After the entry of the virus into the body of 
the host, the virus enters macrophages where the RNA genome of the virus replicates to 
form viral DNA with the help of the reverse transcriptase enzyme.      
 
3. Adenosine deaminase enzyme deficiency is caused by the deletion of the gene for 
adenosine deaminase which is essential for the functioning of the immune system. 
 
4. A cistron is a segment of DNA which codes for a polypeptide.  
 
5. Drones of honey bee possess 16 chromosomes. The sperms in honey bee are produced 
by mitosis.  
 
SECTION B 
 
6. Mutualism is the relationship between two organisms where both are benefited for 
food, shelter and substratum for attachment. 
Two examples:  
i. Mycorrhizae are the mutualistic relationship between fungi and the roots of higher 
plants. The fungus helps in mineral nutrition of the plant with which it is associated 
and obtains, in turn, carbohydrates from the plant. 
ii. Nitrogen-fixing bacteria Rhizobium live in the root nodules of legumes. The bacteria 
derive nutrition from the host plant but fix atmospheric nitrogen and make it 
available to the plants.  
OR 
 
  
Page 2


  
 
CBSE XII  |  Biology 
Board Paper – 2015 – All India - Set 2 (Solution) 
 
  www.topperlearning.com  1 
CBSE 
Class XII Biology 
Board Paper – 2015 – All India (Set 2)  
SOLUTION 
 
SECTION A 
 
1. Advantages of unleaded petrol in automobiles as fuel: 
i. Automobiles equipped with a catalytic converter should use unleaded petrol 
because lead in the petrol inactivates the catalysts of the converter. 
ii. Use of unleaded petrol prevents the release of poisonous gases such as nitrous oxide 
in the environment. 
 
2. Retroviruses have RNA as genetic material. After the entry of the virus into the body of 
the host, the virus enters macrophages where the RNA genome of the virus replicates to 
form viral DNA with the help of the reverse transcriptase enzyme.      
 
3. Adenosine deaminase enzyme deficiency is caused by the deletion of the gene for 
adenosine deaminase which is essential for the functioning of the immune system. 
 
4. A cistron is a segment of DNA which codes for a polypeptide.  
 
5. Drones of honey bee possess 16 chromosomes. The sperms in honey bee are produced 
by mitosis.  
 
SECTION B 
 
6. Mutualism is the relationship between two organisms where both are benefited for 
food, shelter and substratum for attachment. 
Two examples:  
i. Mycorrhizae are the mutualistic relationship between fungi and the roots of higher 
plants. The fungus helps in mineral nutrition of the plant with which it is associated 
and obtains, in turn, carbohydrates from the plant. 
ii. Nitrogen-fixing bacteria Rhizobium live in the root nodules of legumes. The bacteria 
derive nutrition from the host plant but fix atmospheric nitrogen and make it 
available to the plants.  
OR 
 
  
  
 
CBSE XII  |  Biology 
Board Paper – 2015 – All India - Set 2 (Solution) 
 
  www.topperlearning.com  2 
Ex situ conservation is the conservation of selected rare plants or animals in places 
outside their natural homes. Ex situ conservation of biodiversity has been employed in 
i. Gene banks: These are institutes which maintain stocks of viable seeds, live 
growing plants, tissue culture and frozen germplasm with the whole range of 
genetic variability. 
ii. Cryopreservation: Cryopreservation can maintain tissue culture, embryos, gametes, 
animal cells or tissues. Endangered organisms are cryopreserved so that they can 
be revived to help in conservation. 
iii. Orchards: Plants with recalcitrant seeds are grown in orchards where all possible 
strains and varieties are maintained. 
iv. Tissue culture: It is carried out through callus formation, embryoids, pollen grain 
culture and shoot tip culture for plants which are either seedless, have recalcitrant 
seeds, variable seed progeny or where a clone is to be maintained. 
 
7.  
(a) Plants raised through micropropagation are termed somaclones because they are 
genetically identical to the original plant from which they are grown. 
(b) Advantages of micropropagation: 
i. A large number of plants can be raised from a single individual plant within a 
relatively short period and in limited space. 
ii. Virus-free healthy plants can be produced from the shoot apical meristem. 
 
8. The effluent from the primary treatment is passed to aeration tanks where air is 
pumped into it. The useful aerobic microbes grow into flocs (masses of bacteria 
associated with fungal filaments) and consume the major part of the organic matter in 
the effluent which reduces BOD of the effluent. The effluent is then passed into a 
settling tank where bacterial flocs are allowed to sediment. This sediment is called 
activated sludge. 
 
9.   
(a) The combinations with analogous structures are 
i. Eyes of octopus and mammals. 
ii. Tubers of sweet potato and potato. 
(b) These analogous structures represent convergent evolution. 
 
10. A moss plant is unable to complete its life cycle in a dry environment because 
i. In mosses, fertilisation of male and female gametes takes place in water. 
ii. The male gametes antherozoids swim in water to reach the eggs for sexual 
reproduction to take place. 
 
 
 
Page 3


  
 
CBSE XII  |  Biology 
Board Paper – 2015 – All India - Set 2 (Solution) 
 
  www.topperlearning.com  1 
CBSE 
Class XII Biology 
Board Paper – 2015 – All India (Set 2)  
SOLUTION 
 
SECTION A 
 
1. Advantages of unleaded petrol in automobiles as fuel: 
i. Automobiles equipped with a catalytic converter should use unleaded petrol 
because lead in the petrol inactivates the catalysts of the converter. 
ii. Use of unleaded petrol prevents the release of poisonous gases such as nitrous oxide 
in the environment. 
 
2. Retroviruses have RNA as genetic material. After the entry of the virus into the body of 
the host, the virus enters macrophages where the RNA genome of the virus replicates to 
form viral DNA with the help of the reverse transcriptase enzyme.      
 
3. Adenosine deaminase enzyme deficiency is caused by the deletion of the gene for 
adenosine deaminase which is essential for the functioning of the immune system. 
 
4. A cistron is a segment of DNA which codes for a polypeptide.  
 
5. Drones of honey bee possess 16 chromosomes. The sperms in honey bee are produced 
by mitosis.  
 
SECTION B 
 
6. Mutualism is the relationship between two organisms where both are benefited for 
food, shelter and substratum for attachment. 
Two examples:  
i. Mycorrhizae are the mutualistic relationship between fungi and the roots of higher 
plants. The fungus helps in mineral nutrition of the plant with which it is associated 
and obtains, in turn, carbohydrates from the plant. 
ii. Nitrogen-fixing bacteria Rhizobium live in the root nodules of legumes. The bacteria 
derive nutrition from the host plant but fix atmospheric nitrogen and make it 
available to the plants.  
OR 
 
  
  
 
CBSE XII  |  Biology 
Board Paper – 2015 – All India - Set 2 (Solution) 
 
  www.topperlearning.com  2 
Ex situ conservation is the conservation of selected rare plants or animals in places 
outside their natural homes. Ex situ conservation of biodiversity has been employed in 
i. Gene banks: These are institutes which maintain stocks of viable seeds, live 
growing plants, tissue culture and frozen germplasm with the whole range of 
genetic variability. 
ii. Cryopreservation: Cryopreservation can maintain tissue culture, embryos, gametes, 
animal cells or tissues. Endangered organisms are cryopreserved so that they can 
be revived to help in conservation. 
iii. Orchards: Plants with recalcitrant seeds are grown in orchards where all possible 
strains and varieties are maintained. 
iv. Tissue culture: It is carried out through callus formation, embryoids, pollen grain 
culture and shoot tip culture for plants which are either seedless, have recalcitrant 
seeds, variable seed progeny or where a clone is to be maintained. 
 
7.  
(a) Plants raised through micropropagation are termed somaclones because they are 
genetically identical to the original plant from which they are grown. 
(b) Advantages of micropropagation: 
i. A large number of plants can be raised from a single individual plant within a 
relatively short period and in limited space. 
ii. Virus-free healthy plants can be produced from the shoot apical meristem. 
 
8. The effluent from the primary treatment is passed to aeration tanks where air is 
pumped into it. The useful aerobic microbes grow into flocs (masses of bacteria 
associated with fungal filaments) and consume the major part of the organic matter in 
the effluent which reduces BOD of the effluent. The effluent is then passed into a 
settling tank where bacterial flocs are allowed to sediment. This sediment is called 
activated sludge. 
 
9.   
(a) The combinations with analogous structures are 
i. Eyes of octopus and mammals. 
ii. Tubers of sweet potato and potato. 
(b) These analogous structures represent convergent evolution. 
 
10. A moss plant is unable to complete its life cycle in a dry environment because 
i. In mosses, fertilisation of male and female gametes takes place in water. 
ii. The male gametes antherozoids swim in water to reach the eggs for sexual 
reproduction to take place. 
 
 
 
  
 
CBSE XII  |  Biology 
Board Paper – 2015 – All India - Set 2 (Solution) 
 
  www.topperlearning.com  3 
SECTION C 
11.  
(a) The doctor injects the preformed antitoxin into the patient’s body. 
(b) The vaccine stimulates the production of antibodies against the antigen for inducing 
active acquired immunity. 
(c) The injection was given to prevent tetanus. It provides acquired immunity. 
 
12. Satellite DNA are small, non-coding, but inheritable, sequences of bases which can be 
separated as satellites from the bulk DNA during density gradient centrifugation. 
Satellite DNA shows polymorphism which forms the basis of DNA fingerprinting. The 
short nucleotide repeats in DNA are specific in each individual and vary in number from 
person to person but are not inherited. These are called ‘variable number tandem 
repeats’, also called minisatellites. Individuals inherit these repeats from their parents 
which are used as genetic markers in a personal identity test. 
 
13. The given equation represents the gene frequency of the total population according to 
Hardy–Weinberg law. In this equation, suppose a gene has two alleles A and a and p is 
the frequency of occurrence of the dominant allele A and q is the frequency of 
occurrence of the recessive allele a in the parental generation. 
Then according to the equation   
p
2
 + 2pq + q
2
 = 1, 
where p
2
  = frequency of occurrence of individuals with homozygous dominant alleles 
(AA) 
2pq = frequency of occurrence of heterozygous individuals (Aa) 
q
2
 = frequency of occurrence of individuals with homozygous recessive alleles (aa) 
  
Page 4


  
 
CBSE XII  |  Biology 
Board Paper – 2015 – All India - Set 2 (Solution) 
 
  www.topperlearning.com  1 
CBSE 
Class XII Biology 
Board Paper – 2015 – All India (Set 2)  
SOLUTION 
 
SECTION A 
 
1. Advantages of unleaded petrol in automobiles as fuel: 
i. Automobiles equipped with a catalytic converter should use unleaded petrol 
because lead in the petrol inactivates the catalysts of the converter. 
ii. Use of unleaded petrol prevents the release of poisonous gases such as nitrous oxide 
in the environment. 
 
2. Retroviruses have RNA as genetic material. After the entry of the virus into the body of 
the host, the virus enters macrophages where the RNA genome of the virus replicates to 
form viral DNA with the help of the reverse transcriptase enzyme.      
 
3. Adenosine deaminase enzyme deficiency is caused by the deletion of the gene for 
adenosine deaminase which is essential for the functioning of the immune system. 
 
4. A cistron is a segment of DNA which codes for a polypeptide.  
 
5. Drones of honey bee possess 16 chromosomes. The sperms in honey bee are produced 
by mitosis.  
 
SECTION B 
 
6. Mutualism is the relationship between two organisms where both are benefited for 
food, shelter and substratum for attachment. 
Two examples:  
i. Mycorrhizae are the mutualistic relationship between fungi and the roots of higher 
plants. The fungus helps in mineral nutrition of the plant with which it is associated 
and obtains, in turn, carbohydrates from the plant. 
ii. Nitrogen-fixing bacteria Rhizobium live in the root nodules of legumes. The bacteria 
derive nutrition from the host plant but fix atmospheric nitrogen and make it 
available to the plants.  
OR 
 
  
  
 
CBSE XII  |  Biology 
Board Paper – 2015 – All India - Set 2 (Solution) 
 
  www.topperlearning.com  2 
Ex situ conservation is the conservation of selected rare plants or animals in places 
outside their natural homes. Ex situ conservation of biodiversity has been employed in 
i. Gene banks: These are institutes which maintain stocks of viable seeds, live 
growing plants, tissue culture and frozen germplasm with the whole range of 
genetic variability. 
ii. Cryopreservation: Cryopreservation can maintain tissue culture, embryos, gametes, 
animal cells or tissues. Endangered organisms are cryopreserved so that they can 
be revived to help in conservation. 
iii. Orchards: Plants with recalcitrant seeds are grown in orchards where all possible 
strains and varieties are maintained. 
iv. Tissue culture: It is carried out through callus formation, embryoids, pollen grain 
culture and shoot tip culture for plants which are either seedless, have recalcitrant 
seeds, variable seed progeny or where a clone is to be maintained. 
 
7.  
(a) Plants raised through micropropagation are termed somaclones because they are 
genetically identical to the original plant from which they are grown. 
(b) Advantages of micropropagation: 
i. A large number of plants can be raised from a single individual plant within a 
relatively short period and in limited space. 
ii. Virus-free healthy plants can be produced from the shoot apical meristem. 
 
8. The effluent from the primary treatment is passed to aeration tanks where air is 
pumped into it. The useful aerobic microbes grow into flocs (masses of bacteria 
associated with fungal filaments) and consume the major part of the organic matter in 
the effluent which reduces BOD of the effluent. The effluent is then passed into a 
settling tank where bacterial flocs are allowed to sediment. This sediment is called 
activated sludge. 
 
9.   
(a) The combinations with analogous structures are 
i. Eyes of octopus and mammals. 
ii. Tubers of sweet potato and potato. 
(b) These analogous structures represent convergent evolution. 
 
10. A moss plant is unable to complete its life cycle in a dry environment because 
i. In mosses, fertilisation of male and female gametes takes place in water. 
ii. The male gametes antherozoids swim in water to reach the eggs for sexual 
reproduction to take place. 
 
 
 
  
 
CBSE XII  |  Biology 
Board Paper – 2015 – All India - Set 2 (Solution) 
 
  www.topperlearning.com  3 
SECTION C 
11.  
(a) The doctor injects the preformed antitoxin into the patient’s body. 
(b) The vaccine stimulates the production of antibodies against the antigen for inducing 
active acquired immunity. 
(c) The injection was given to prevent tetanus. It provides acquired immunity. 
 
12. Satellite DNA are small, non-coding, but inheritable, sequences of bases which can be 
separated as satellites from the bulk DNA during density gradient centrifugation. 
Satellite DNA shows polymorphism which forms the basis of DNA fingerprinting. The 
short nucleotide repeats in DNA are specific in each individual and vary in number from 
person to person but are not inherited. These are called ‘variable number tandem 
repeats’, also called minisatellites. Individuals inherit these repeats from their parents 
which are used as genetic markers in a personal identity test. 
 
13. The given equation represents the gene frequency of the total population according to 
Hardy–Weinberg law. In this equation, suppose a gene has two alleles A and a and p is 
the frequency of occurrence of the dominant allele A and q is the frequency of 
occurrence of the recessive allele a in the parental generation. 
Then according to the equation   
p
2
 + 2pq + q
2
 = 1, 
where p
2
  = frequency of occurrence of individuals with homozygous dominant alleles 
(AA) 
2pq = frequency of occurrence of heterozygous individuals (Aa) 
q
2
 = frequency of occurrence of individuals with homozygous recessive alleles (aa) 
  
  
 
CBSE XII  |  Biology 
Board Paper – 2015 – All India - Set 2 (Solution) 
 
  www.topperlearning.com  4 
 
14. A monohybrid cross is a cross where two forms of a single trait are hybridised. Mendel 
crossed pure tall pea plant with a pure dwarf pea plant and obtained all tall plants in 
the first filial generation. The character which appeared in the F 1 generation is called 
dominant character, whereas the character which is not expressed in the F 1 generation 
is called recessive. After inter-crossing the hybrids of the F 1 generation, he obtained tall 
and dwarf progeny in the ratio 3:1 (phenotypic ratio), but the genetic ratio was 1:2:1 
which is TT, Tt and tt. 
 
 
 
Such a cross depicts the law of dominance in which all traits are controlled by a pair of 
factors called genes. In a dissimilar pair of factors, one member of the pair is dominant, 
while the other is recessive. 
 
15. Apomixis is the mode of reproduction which does not involve formation of zygote 
through gametic fusion.  
Significance of apomixis: 
i. Adventives embryos are better clones than cuttings. 
ii. Embryos formed through apomixes are generally free from infections. 
Hybrid varieties provide higher and better yield. If hybrid seeds are produced every 
year, they do not maintain hybrid characters due to segregation of traits. Moreover, 
production of hybrid seeds every year is very costly. This can be avoided by introducing 
apomixes in hybrid seeds. 
 
  
Page 5


  
 
CBSE XII  |  Biology 
Board Paper – 2015 – All India - Set 2 (Solution) 
 
  www.topperlearning.com  1 
CBSE 
Class XII Biology 
Board Paper – 2015 – All India (Set 2)  
SOLUTION 
 
SECTION A 
 
1. Advantages of unleaded petrol in automobiles as fuel: 
i. Automobiles equipped with a catalytic converter should use unleaded petrol 
because lead in the petrol inactivates the catalysts of the converter. 
ii. Use of unleaded petrol prevents the release of poisonous gases such as nitrous oxide 
in the environment. 
 
2. Retroviruses have RNA as genetic material. After the entry of the virus into the body of 
the host, the virus enters macrophages where the RNA genome of the virus replicates to 
form viral DNA with the help of the reverse transcriptase enzyme.      
 
3. Adenosine deaminase enzyme deficiency is caused by the deletion of the gene for 
adenosine deaminase which is essential for the functioning of the immune system. 
 
4. A cistron is a segment of DNA which codes for a polypeptide.  
 
5. Drones of honey bee possess 16 chromosomes. The sperms in honey bee are produced 
by mitosis.  
 
SECTION B 
 
6. Mutualism is the relationship between two organisms where both are benefited for 
food, shelter and substratum for attachment. 
Two examples:  
i. Mycorrhizae are the mutualistic relationship between fungi and the roots of higher 
plants. The fungus helps in mineral nutrition of the plant with which it is associated 
and obtains, in turn, carbohydrates from the plant. 
ii. Nitrogen-fixing bacteria Rhizobium live in the root nodules of legumes. The bacteria 
derive nutrition from the host plant but fix atmospheric nitrogen and make it 
available to the plants.  
OR 
 
  
  
 
CBSE XII  |  Biology 
Board Paper – 2015 – All India - Set 2 (Solution) 
 
  www.topperlearning.com  2 
Ex situ conservation is the conservation of selected rare plants or animals in places 
outside their natural homes. Ex situ conservation of biodiversity has been employed in 
i. Gene banks: These are institutes which maintain stocks of viable seeds, live 
growing plants, tissue culture and frozen germplasm with the whole range of 
genetic variability. 
ii. Cryopreservation: Cryopreservation can maintain tissue culture, embryos, gametes, 
animal cells or tissues. Endangered organisms are cryopreserved so that they can 
be revived to help in conservation. 
iii. Orchards: Plants with recalcitrant seeds are grown in orchards where all possible 
strains and varieties are maintained. 
iv. Tissue culture: It is carried out through callus formation, embryoids, pollen grain 
culture and shoot tip culture for plants which are either seedless, have recalcitrant 
seeds, variable seed progeny or where a clone is to be maintained. 
 
7.  
(a) Plants raised through micropropagation are termed somaclones because they are 
genetically identical to the original plant from which they are grown. 
(b) Advantages of micropropagation: 
i. A large number of plants can be raised from a single individual plant within a 
relatively short period and in limited space. 
ii. Virus-free healthy plants can be produced from the shoot apical meristem. 
 
8. The effluent from the primary treatment is passed to aeration tanks where air is 
pumped into it. The useful aerobic microbes grow into flocs (masses of bacteria 
associated with fungal filaments) and consume the major part of the organic matter in 
the effluent which reduces BOD of the effluent. The effluent is then passed into a 
settling tank where bacterial flocs are allowed to sediment. This sediment is called 
activated sludge. 
 
9.   
(a) The combinations with analogous structures are 
i. Eyes of octopus and mammals. 
ii. Tubers of sweet potato and potato. 
(b) These analogous structures represent convergent evolution. 
 
10. A moss plant is unable to complete its life cycle in a dry environment because 
i. In mosses, fertilisation of male and female gametes takes place in water. 
ii. The male gametes antherozoids swim in water to reach the eggs for sexual 
reproduction to take place. 
 
 
 
  
 
CBSE XII  |  Biology 
Board Paper – 2015 – All India - Set 2 (Solution) 
 
  www.topperlearning.com  3 
SECTION C 
11.  
(a) The doctor injects the preformed antitoxin into the patient’s body. 
(b) The vaccine stimulates the production of antibodies against the antigen for inducing 
active acquired immunity. 
(c) The injection was given to prevent tetanus. It provides acquired immunity. 
 
12. Satellite DNA are small, non-coding, but inheritable, sequences of bases which can be 
separated as satellites from the bulk DNA during density gradient centrifugation. 
Satellite DNA shows polymorphism which forms the basis of DNA fingerprinting. The 
short nucleotide repeats in DNA are specific in each individual and vary in number from 
person to person but are not inherited. These are called ‘variable number tandem 
repeats’, also called minisatellites. Individuals inherit these repeats from their parents 
which are used as genetic markers in a personal identity test. 
 
13. The given equation represents the gene frequency of the total population according to 
Hardy–Weinberg law. In this equation, suppose a gene has two alleles A and a and p is 
the frequency of occurrence of the dominant allele A and q is the frequency of 
occurrence of the recessive allele a in the parental generation. 
Then according to the equation   
p
2
 + 2pq + q
2
 = 1, 
where p
2
  = frequency of occurrence of individuals with homozygous dominant alleles 
(AA) 
2pq = frequency of occurrence of heterozygous individuals (Aa) 
q
2
 = frequency of occurrence of individuals with homozygous recessive alleles (aa) 
  
  
 
CBSE XII  |  Biology 
Board Paper – 2015 – All India - Set 2 (Solution) 
 
  www.topperlearning.com  4 
 
14. A monohybrid cross is a cross where two forms of a single trait are hybridised. Mendel 
crossed pure tall pea plant with a pure dwarf pea plant and obtained all tall plants in 
the first filial generation. The character which appeared in the F 1 generation is called 
dominant character, whereas the character which is not expressed in the F 1 generation 
is called recessive. After inter-crossing the hybrids of the F 1 generation, he obtained tall 
and dwarf progeny in the ratio 3:1 (phenotypic ratio), but the genetic ratio was 1:2:1 
which is TT, Tt and tt. 
 
 
 
Such a cross depicts the law of dominance in which all traits are controlled by a pair of 
factors called genes. In a dissimilar pair of factors, one member of the pair is dominant, 
while the other is recessive. 
 
15. Apomixis is the mode of reproduction which does not involve formation of zygote 
through gametic fusion.  
Significance of apomixis: 
i. Adventives embryos are better clones than cuttings. 
ii. Embryos formed through apomixes are generally free from infections. 
Hybrid varieties provide higher and better yield. If hybrid seeds are produced every 
year, they do not maintain hybrid characters due to segregation of traits. Moreover, 
production of hybrid seeds every year is very costly. This can be avoided by introducing 
apomixes in hybrid seeds. 
 
  
  
 
CBSE XII  |  Biology 
Board Paper – 2015 – All India - Set 2 (Solution) 
 
  www.topperlearning.com  5 
16.   
 
Organism Medicinal value Bioactive molecule 
i. Streptococcus  
 
Clot buster for removing clots from 
blood vessels of heart attack patients 
Enzyme  
 
ii. Monascus Blood cholesterol lowering agents Statins 
iii. Trichoderma Immunosuppressant drug Cyclosporine A 
 
OR 
Methanogens are methane-producing bacteria used during the production of biogas. 
The methanogenic bacteria digest the organic mass to produce marsh gas during the 
secondary treatment of sewage. Marsh gas is a mixture of gases containing methane, 
hydrogen sulphide and carbon dioxide which forms biogas. 
 
17. Potential applications of genetically modified plants: 
i. GMO crops are more tolerant to abiotic stresses. 
ii. They have reduced the dependency on chemical pesticides. 
iii. They have enhanced the nutritional value of food such as vitamin A-enriched rice. 
 
18. The structure of insulin consists of two short polypeptide chains—chain A and chain 
B—linked together by disulphide bridges. In mammals, including human beings, insulin 
is synthesised as a pro-hormone which contains an extra stretch called the C peptide 
which is removed during maturation into insulin. The rDNA technique was for 
assembling of insulin into the mature form.  
In 1983, Eli Lily, an American company, prepared two DNA sequences corresponding to 
A and B chains of human insulin and introduced them in the plasmids of E. coli to 
produce insulin chains. Chains A and B were produced separately, extracted and 
combined by creating disulphide bonds to form human insulin.