CBSE Biology All India Past year paper (solutions) - 2018, Class 12 | Additional Study Material for NEET PDF Download

 Page 1


  
 
CBSE XII  |  Biology 
Board Paper – 2018 Solution 
 
  
CBSE 
Class XII Biology 
Board Paper 2018 (Set 3) Solution 
 
SECTION A 
 
1. Cytokines, such as interferons, are directly involved in protecting the non-
infected cells from viral infection or by activating mechanisms for cells such 
as macrophages. 
  
2. Deoxyribonucleoside triphosphates are used as substrates in DNA 
polymerisation.They also provide energy to drive the DNA polymerisation 
reaction. 
 
3.  
(a) Dryopithecus existed about15 million years ago and were more ape-like. 
(b) Australopithecus roamed the Eastern African Grasslands about 2 million 
years ago. 
 
4. Proinsulin contains polypeptide chains A and B, which are linked together by 
disulphide bridges, and another polypeptide called C peptide. The C peptide 
is removed during maturation, which converts the inactive proinsulin into 
mature insulin. 
 
5. Dengue fever and chikungunya are diseases whose spread can be controlled 
by the eradication of Aedes mosquitoes. 
 
  
Page 2


  
 
CBSE XII  |  Biology 
Board Paper – 2018 Solution 
 
  
CBSE 
Class XII Biology 
Board Paper 2018 (Set 3) Solution 
 
SECTION A 
 
1. Cytokines, such as interferons, are directly involved in protecting the non-
infected cells from viral infection or by activating mechanisms for cells such 
as macrophages. 
  
2. Deoxyribonucleoside triphosphates are used as substrates in DNA 
polymerisation.They also provide energy to drive the DNA polymerisation 
reaction. 
 
3.  
(a) Dryopithecus existed about15 million years ago and were more ape-like. 
(b) Australopithecus roamed the Eastern African Grasslands about 2 million 
years ago. 
 
4. Proinsulin contains polypeptide chains A and B, which are linked together by 
disulphide bridges, and another polypeptide called C peptide. The C peptide 
is removed during maturation, which converts the inactive proinsulin into 
mature insulin. 
 
5. Dengue fever and chikungunya are diseases whose spread can be controlled 
by the eradication of Aedes mosquitoes. 
 
  
  
 
CBSE XII  |  Biology 
Board Paper – 2018 Solution 
 
  
SECTION B 
 
6. Wastewater, including sewage, can be treated in an integrated manner by 
utilising a mix of the artificial and natural processes. 
It has been done in the town of Arcata, in the northern coast of California. 
The treatment is done in four stages: 
i. In the first stage, physical impurities are removed by the conventional 
sedimentation, filtering and chlorine treatment. 
ii. In the second stage, biologists developed a series of six connected marshes 
over 60 hectares of marshland. 
iii. Appropriate plants, algae, fungi and bacteria were seeded into this area 
which help in neutralising, absorbing and assimilating pollutants. 
iv. Finally, as the water flows through the marshes, it gets purified naturally. 
 
7.  
(a) Two microbes which can enrich the soil with nitrogen are Nostoc and 
Azospirillium. 
(b) Leguminous plants contain rhizobium bacteria in their root nodules. 
These bacteria convert atmospheric nitrogen to a form which can be used 
by plants. This decreases nitrogen deficiency in the soil and makes it 
fertile. 
 
8. Plant breeding is the purposeful manipulation of plant species in order to 
create desired plant types which are better suited for cultivation, give better 
yields and are disease resistant.  
Main steps in breeding a new genetic variety of a crop: 
(a) Collection of variability 
(b) Evaluation and selection of parents 
(c) Cross hybridisation among selected parents 
(d) Selection and testing of superior recombinants 
(e) Testing, release and commercialisation of new cultivars 
9.  
(a) Heroin is obtained from Papaversomniferum which is commonly known 
as the poppy plant. Chemically, heroin is a diacetylmorphine which is 
obtained by acetylation of morphine. 
 
(b) Heroin acts as a depressant which means it slows body functions. It can 
lead to slower rates of breathing, slower heart beats, vomiting, nausea 
etc.  
 
 
 
 
 
Page 3


  
 
CBSE XII  |  Biology 
Board Paper – 2018 Solution 
 
  
CBSE 
Class XII Biology 
Board Paper 2018 (Set 3) Solution 
 
SECTION A 
 
1. Cytokines, such as interferons, are directly involved in protecting the non-
infected cells from viral infection or by activating mechanisms for cells such 
as macrophages. 
  
2. Deoxyribonucleoside triphosphates are used as substrates in DNA 
polymerisation.They also provide energy to drive the DNA polymerisation 
reaction. 
 
3.  
(a) Dryopithecus existed about15 million years ago and were more ape-like. 
(b) Australopithecus roamed the Eastern African Grasslands about 2 million 
years ago. 
 
4. Proinsulin contains polypeptide chains A and B, which are linked together by 
disulphide bridges, and another polypeptide called C peptide. The C peptide 
is removed during maturation, which converts the inactive proinsulin into 
mature insulin. 
 
5. Dengue fever and chikungunya are diseases whose spread can be controlled 
by the eradication of Aedes mosquitoes. 
 
  
  
 
CBSE XII  |  Biology 
Board Paper – 2018 Solution 
 
  
SECTION B 
 
6. Wastewater, including sewage, can be treated in an integrated manner by 
utilising a mix of the artificial and natural processes. 
It has been done in the town of Arcata, in the northern coast of California. 
The treatment is done in four stages: 
i. In the first stage, physical impurities are removed by the conventional 
sedimentation, filtering and chlorine treatment. 
ii. In the second stage, biologists developed a series of six connected marshes 
over 60 hectares of marshland. 
iii. Appropriate plants, algae, fungi and bacteria were seeded into this area 
which help in neutralising, absorbing and assimilating pollutants. 
iv. Finally, as the water flows through the marshes, it gets purified naturally. 
 
7.  
(a) Two microbes which can enrich the soil with nitrogen are Nostoc and 
Azospirillium. 
(b) Leguminous plants contain rhizobium bacteria in their root nodules. 
These bacteria convert atmospheric nitrogen to a form which can be used 
by plants. This decreases nitrogen deficiency in the soil and makes it 
fertile. 
 
8. Plant breeding is the purposeful manipulation of plant species in order to 
create desired plant types which are better suited for cultivation, give better 
yields and are disease resistant.  
Main steps in breeding a new genetic variety of a crop: 
(a) Collection of variability 
(b) Evaluation and selection of parents 
(c) Cross hybridisation among selected parents 
(d) Selection and testing of superior recombinants 
(e) Testing, release and commercialisation of new cultivars 
9.  
(a) Heroin is obtained from Papaversomniferum which is commonly known 
as the poppy plant. Chemically, heroin is a diacetylmorphine which is 
obtained by acetylation of morphine. 
 
(b) Heroin acts as a depressant which means it slows body functions. It can 
lead to slower rates of breathing, slower heart beats, vomiting, nausea 
etc.  
 
 
 
 
 
  
 
CBSE XII  |  Biology 
Board Paper – 2018 Solution 
 
  
10. The Hardy–Weinberg principle states that the frequency of occurrence of 
alleles of a gene in a population remains constant through generations unless 
disturbances such as mutations and non-random mating are introduced.  
 
Let us assume that a gene has two alleles in a population, A and a. If p is the 
frequency of occurrence of dominant allele A, and q is the frequency of 
occurrence of dominant allele a, the genotype frequency in the offspring is 
represented as 
(p + q)
2
 = p
2
 + 2pq + q
2
 = 1, 
wherethe frequency of genotypes, AA is p
2
, that of aa is q
2
 and that of Aa is 
2pq.  
Hence, the total of all allelic frequencies remains constant, i.e. 1. 
OR 
In prokaryotes, such asE. coli, although they do not have a defined nucleus, 
DNA is not scattered throughout the cell. DNA (being negatively charged) is 
held with some proteins (whichhave positive charges) in a region termed 
‘nucleoid’. DNA in the nucleoid is organised in large loops held by proteins. 
 
 
SECTION C 
 
11.  
(a) Differences between analogous and homologous structures: 
Analogous Structure Homologous Structure 
These structures have similarity in 
function, but different internal 
structures. 
These structures have similarity in 
internal structures, but different 
functions. 
They are based on convergent 
evolution. 
They are based on divergent 
evolution. 
Example: Flippers of penguin and 
dolphin 
Example: Forelimbs of human and 
bat 
 
(b) Among the given alternatives, examples of analogous structures are 
Wings of butterfly and birds: Both are used for flying, but both have 
different internal structures.  
 
Tubers of sweet potato and potato: Both are used for food storage. 
However, the tuber of sweet potato is a modification of an underground 
root, while the tuber of potato is a modified stem. 
 
 
 
 
 
Page 4


  
 
CBSE XII  |  Biology 
Board Paper – 2018 Solution 
 
  
CBSE 
Class XII Biology 
Board Paper 2018 (Set 3) Solution 
 
SECTION A 
 
1. Cytokines, such as interferons, are directly involved in protecting the non-
infected cells from viral infection or by activating mechanisms for cells such 
as macrophages. 
  
2. Deoxyribonucleoside triphosphates are used as substrates in DNA 
polymerisation.They also provide energy to drive the DNA polymerisation 
reaction. 
 
3.  
(a) Dryopithecus existed about15 million years ago and were more ape-like. 
(b) Australopithecus roamed the Eastern African Grasslands about 2 million 
years ago. 
 
4. Proinsulin contains polypeptide chains A and B, which are linked together by 
disulphide bridges, and another polypeptide called C peptide. The C peptide 
is removed during maturation, which converts the inactive proinsulin into 
mature insulin. 
 
5. Dengue fever and chikungunya are diseases whose spread can be controlled 
by the eradication of Aedes mosquitoes. 
 
  
  
 
CBSE XII  |  Biology 
Board Paper – 2018 Solution 
 
  
SECTION B 
 
6. Wastewater, including sewage, can be treated in an integrated manner by 
utilising a mix of the artificial and natural processes. 
It has been done in the town of Arcata, in the northern coast of California. 
The treatment is done in four stages: 
i. In the first stage, physical impurities are removed by the conventional 
sedimentation, filtering and chlorine treatment. 
ii. In the second stage, biologists developed a series of six connected marshes 
over 60 hectares of marshland. 
iii. Appropriate plants, algae, fungi and bacteria were seeded into this area 
which help in neutralising, absorbing and assimilating pollutants. 
iv. Finally, as the water flows through the marshes, it gets purified naturally. 
 
7.  
(a) Two microbes which can enrich the soil with nitrogen are Nostoc and 
Azospirillium. 
(b) Leguminous plants contain rhizobium bacteria in their root nodules. 
These bacteria convert atmospheric nitrogen to a form which can be used 
by plants. This decreases nitrogen deficiency in the soil and makes it 
fertile. 
 
8. Plant breeding is the purposeful manipulation of plant species in order to 
create desired plant types which are better suited for cultivation, give better 
yields and are disease resistant.  
Main steps in breeding a new genetic variety of a crop: 
(a) Collection of variability 
(b) Evaluation and selection of parents 
(c) Cross hybridisation among selected parents 
(d) Selection and testing of superior recombinants 
(e) Testing, release and commercialisation of new cultivars 
9.  
(a) Heroin is obtained from Papaversomniferum which is commonly known 
as the poppy plant. Chemically, heroin is a diacetylmorphine which is 
obtained by acetylation of morphine. 
 
(b) Heroin acts as a depressant which means it slows body functions. It can 
lead to slower rates of breathing, slower heart beats, vomiting, nausea 
etc.  
 
 
 
 
 
  
 
CBSE XII  |  Biology 
Board Paper – 2018 Solution 
 
  
10. The Hardy–Weinberg principle states that the frequency of occurrence of 
alleles of a gene in a population remains constant through generations unless 
disturbances such as mutations and non-random mating are introduced.  
 
Let us assume that a gene has two alleles in a population, A and a. If p is the 
frequency of occurrence of dominant allele A, and q is the frequency of 
occurrence of dominant allele a, the genotype frequency in the offspring is 
represented as 
(p + q)
2
 = p
2
 + 2pq + q
2
 = 1, 
wherethe frequency of genotypes, AA is p
2
, that of aa is q
2
 and that of Aa is 
2pq.  
Hence, the total of all allelic frequencies remains constant, i.e. 1. 
OR 
In prokaryotes, such asE. coli, although they do not have a defined nucleus, 
DNA is not scattered throughout the cell. DNA (being negatively charged) is 
held with some proteins (whichhave positive charges) in a region termed 
‘nucleoid’. DNA in the nucleoid is organised in large loops held by proteins. 
 
 
SECTION C 
 
11.  
(a) Differences between analogous and homologous structures: 
Analogous Structure Homologous Structure 
These structures have similarity in 
function, but different internal 
structures. 
These structures have similarity in 
internal structures, but different 
functions. 
They are based on convergent 
evolution. 
They are based on divergent 
evolution. 
Example: Flippers of penguin and 
dolphin 
Example: Forelimbs of human and 
bat 
 
(b) Among the given alternatives, examples of analogous structures are 
Wings of butterfly and birds: Both are used for flying, but both have 
different internal structures.  
 
Tubers of sweet potato and potato: Both are used for food storage. 
However, the tuber of sweet potato is a modification of an underground 
root, while the tuber of potato is a modified stem. 
 
 
 
 
 
  
 
CBSE XII  |  Biology 
Board Paper – 2018 Solution 
 
  
12. The following steps were taken utilising Agrobacterium as a transforming 
vector for tobacco plants to make them immune against the infestation of the 
nematode Meloideogyneincognitia: 
1. Suitable plasmid vectors are chosen and the specific nematode gene is 
inserted into it. 
2. The recombinant plasmids are introduced into the competent 
Agrobacterium cells. 
3. The transformed Agrobacterium cells are screened and selected to infect 
the tobacco plants. 
4. Agrobacterium infection on the tobacco plant cultures leads to insertion 
and integration of nematode-desired DNA fragment within the tobacco 
plant. 
5. Correct insertion of nematode gene into the host tobacco plants leads to 
silencing of an essential housekeeping gene of the Meloideogyneincognitia 
pest by RNAi. 
 
13.  
(a) It is correct to state that India has greater ecosystem diversity than 
Norway. The primary reason for the same is that India lies primarily in 
the tropical and sub-tropical zones, whereas Norway lies near the Arctic 
region. This exposes India to greater amounts of sunshine and hence 
greater level of productivity at all trophic levels as compared to Norway. 
Also, India has greater geographical, topological and climatic diversity 
compared to Norway, leading to greater biodiversity. 
 
(b)  
Genetic Biodiversity Species Biodiversity 
Genetic biodiversity refers to the 
number of genes and their alleles 
found in organisms. 
Speciesbiodiversity refers to the 
number of species per unit area. 
It is the trait of the species. It is the trait of the community. 
It always increases as we move up 
the biological organisation. 
It may or may not increase to a 
greater extent as we move up the 
ladder of biological organisation. 
 
OR 
(i) Due to the discharge of urban sewage into the river body, growth of micro-
organisms involved in the degradation of organic sewage by utilising 
oxygen rapidly increases, leading to a huge increase in the BOD (Biological 
Oxygen Demand) of the river body. This will also generate an oxygenic 
condition within the river body leading to the widespread death of aquatic 
lifeforms, resulting in destruction of the aquatic ecosystem and degrading 
water quality of the river. 
(ii) Micro-organisms involved in biodegradation of organic matter in the 
receiving water body consume a lot of oxygen, and as a result there is a 
Page 5


  
 
CBSE XII  |  Biology 
Board Paper – 2018 Solution 
 
  
CBSE 
Class XII Biology 
Board Paper 2018 (Set 3) Solution 
 
SECTION A 
 
1. Cytokines, such as interferons, are directly involved in protecting the non-
infected cells from viral infection or by activating mechanisms for cells such 
as macrophages. 
  
2. Deoxyribonucleoside triphosphates are used as substrates in DNA 
polymerisation.They also provide energy to drive the DNA polymerisation 
reaction. 
 
3.  
(a) Dryopithecus existed about15 million years ago and were more ape-like. 
(b) Australopithecus roamed the Eastern African Grasslands about 2 million 
years ago. 
 
4. Proinsulin contains polypeptide chains A and B, which are linked together by 
disulphide bridges, and another polypeptide called C peptide. The C peptide 
is removed during maturation, which converts the inactive proinsulin into 
mature insulin. 
 
5. Dengue fever and chikungunya are diseases whose spread can be controlled 
by the eradication of Aedes mosquitoes. 
 
  
  
 
CBSE XII  |  Biology 
Board Paper – 2018 Solution 
 
  
SECTION B 
 
6. Wastewater, including sewage, can be treated in an integrated manner by 
utilising a mix of the artificial and natural processes. 
It has been done in the town of Arcata, in the northern coast of California. 
The treatment is done in four stages: 
i. In the first stage, physical impurities are removed by the conventional 
sedimentation, filtering and chlorine treatment. 
ii. In the second stage, biologists developed a series of six connected marshes 
over 60 hectares of marshland. 
iii. Appropriate plants, algae, fungi and bacteria were seeded into this area 
which help in neutralising, absorbing and assimilating pollutants. 
iv. Finally, as the water flows through the marshes, it gets purified naturally. 
 
7.  
(a) Two microbes which can enrich the soil with nitrogen are Nostoc and 
Azospirillium. 
(b) Leguminous plants contain rhizobium bacteria in their root nodules. 
These bacteria convert atmospheric nitrogen to a form which can be used 
by plants. This decreases nitrogen deficiency in the soil and makes it 
fertile. 
 
8. Plant breeding is the purposeful manipulation of plant species in order to 
create desired plant types which are better suited for cultivation, give better 
yields and are disease resistant.  
Main steps in breeding a new genetic variety of a crop: 
(a) Collection of variability 
(b) Evaluation and selection of parents 
(c) Cross hybridisation among selected parents 
(d) Selection and testing of superior recombinants 
(e) Testing, release and commercialisation of new cultivars 
9.  
(a) Heroin is obtained from Papaversomniferum which is commonly known 
as the poppy plant. Chemically, heroin is a diacetylmorphine which is 
obtained by acetylation of morphine. 
 
(b) Heroin acts as a depressant which means it slows body functions. It can 
lead to slower rates of breathing, slower heart beats, vomiting, nausea 
etc.  
 
 
 
 
 
  
 
CBSE XII  |  Biology 
Board Paper – 2018 Solution 
 
  
10. The Hardy–Weinberg principle states that the frequency of occurrence of 
alleles of a gene in a population remains constant through generations unless 
disturbances such as mutations and non-random mating are introduced.  
 
Let us assume that a gene has two alleles in a population, A and a. If p is the 
frequency of occurrence of dominant allele A, and q is the frequency of 
occurrence of dominant allele a, the genotype frequency in the offspring is 
represented as 
(p + q)
2
 = p
2
 + 2pq + q
2
 = 1, 
wherethe frequency of genotypes, AA is p
2
, that of aa is q
2
 and that of Aa is 
2pq.  
Hence, the total of all allelic frequencies remains constant, i.e. 1. 
OR 
In prokaryotes, such asE. coli, although they do not have a defined nucleus, 
DNA is not scattered throughout the cell. DNA (being negatively charged) is 
held with some proteins (whichhave positive charges) in a region termed 
‘nucleoid’. DNA in the nucleoid is organised in large loops held by proteins. 
 
 
SECTION C 
 
11.  
(a) Differences between analogous and homologous structures: 
Analogous Structure Homologous Structure 
These structures have similarity in 
function, but different internal 
structures. 
These structures have similarity in 
internal structures, but different 
functions. 
They are based on convergent 
evolution. 
They are based on divergent 
evolution. 
Example: Flippers of penguin and 
dolphin 
Example: Forelimbs of human and 
bat 
 
(b) Among the given alternatives, examples of analogous structures are 
Wings of butterfly and birds: Both are used for flying, but both have 
different internal structures.  
 
Tubers of sweet potato and potato: Both are used for food storage. 
However, the tuber of sweet potato is a modification of an underground 
root, while the tuber of potato is a modified stem. 
 
 
 
 
 
  
 
CBSE XII  |  Biology 
Board Paper – 2018 Solution 
 
  
12. The following steps were taken utilising Agrobacterium as a transforming 
vector for tobacco plants to make them immune against the infestation of the 
nematode Meloideogyneincognitia: 
1. Suitable plasmid vectors are chosen and the specific nematode gene is 
inserted into it. 
2. The recombinant plasmids are introduced into the competent 
Agrobacterium cells. 
3. The transformed Agrobacterium cells are screened and selected to infect 
the tobacco plants. 
4. Agrobacterium infection on the tobacco plant cultures leads to insertion 
and integration of nematode-desired DNA fragment within the tobacco 
plant. 
5. Correct insertion of nematode gene into the host tobacco plants leads to 
silencing of an essential housekeeping gene of the Meloideogyneincognitia 
pest by RNAi. 
 
13.  
(a) It is correct to state that India has greater ecosystem diversity than 
Norway. The primary reason for the same is that India lies primarily in 
the tropical and sub-tropical zones, whereas Norway lies near the Arctic 
region. This exposes India to greater amounts of sunshine and hence 
greater level of productivity at all trophic levels as compared to Norway. 
Also, India has greater geographical, topological and climatic diversity 
compared to Norway, leading to greater biodiversity. 
 
(b)  
Genetic Biodiversity Species Biodiversity 
Genetic biodiversity refers to the 
number of genes and their alleles 
found in organisms. 
Speciesbiodiversity refers to the 
number of species per unit area. 
It is the trait of the species. It is the trait of the community. 
It always increases as we move up 
the biological organisation. 
It may or may not increase to a 
greater extent as we move up the 
ladder of biological organisation. 
 
OR 
(i) Due to the discharge of urban sewage into the river body, growth of micro-
organisms involved in the degradation of organic sewage by utilising 
oxygen rapidly increases, leading to a huge increase in the BOD (Biological 
Oxygen Demand) of the river body. This will also generate an oxygenic 
condition within the river body leading to the widespread death of aquatic 
lifeforms, resulting in destruction of the aquatic ecosystem and degrading 
water quality of the river. 
(ii) Micro-organisms involved in biodegradation of organic matter in the 
receiving water body consume a lot of oxygen, and as a result there is a 
  
 
CBSE XII  |  Biology 
Board Paper – 2018 Solution 
 
  
sharp decline in dissolved oxygen downstream from the point of sewage 
discharge. This causes mortality of fish and other aquatic creatures. 
(iii) Presence of large amounts of nutrients in waters also causes excessive 
growth of algae, called an algal bloom, which imparts a distinct colour to 
water bodies. Algal blooms cause deterioration of the water quality and 
fish mortality. Some bloom-forming algae are extremely toxic to human 
beings and animals. 
 
14. The sex chromosomes in birds are determined as Z and W. The male is 
homomorphic (ZZ) and the female is heteromorphic (ZW). W chromosome 
carries female sex-determining genes and duplication of Z chromosome 
indicates the male sex. So, in case of chicks, the sex is determined by the 
egg and not by the sperm. 
 
The difference between sex mechanisms of humans and birds is that the 
male is homomorphic (ZZ) and the female is heteromorphic (ZW) in birds, 
whereas the male is heteromorphic (XY) and the female is homomorphic (XX) 
in humans. 
 
15. Out-breeding: Out-breeding is the breeding of unrelated animals of the same 
breed or of different breeds or different species.  
Out-crossing: Mating of animals within the same breed but having no 
common ancestor on either side of their pedigree up to 4–6 generations is 
known as out-crossing. Offspring of such mating is called an outcross. A 
single out-cross often helps to overcome inbreeding depression.  
Cross-breeding: In cross-breeding, the superior male of one breed is mated 
with a superior female of another breed. It allows the desirable qualities of 
two different breeds to be combined.