CBSE Biology Past year paper Delhi (Set - 2) Solutions - 2012, Class 12 | Additional Study Material for NEET PDF Download

 Page 1


  
 
CBSE XII |  Biology 
Board Paper 2012 – Delhi – Set 2 (Solution) 
 
     
CBSE 
Class XII Biology (Theory) 
Board Paper 2012 – Delhi (Set 2) 
Solution 
Time: 3 hours  Total Marks: 70 
 
SECTION A 
 
1. Ans. Cucurbits are monoecious as they bear both staminate and pistillate 
flowers on the same plant, while papaya plants are dioecious as the staminate 
and pistillate flowers are borne on two different plants. 
 
2. Ans. Inflated yellow seeds are dominant over constricted green seeds. 
 
3. Ans. Phytophagous insects feed on plant sap and other parts of the plant. 
 
4. Ans. The interaction between Cuscuta and shoe flower bush is called parasitism. 
Cuscuta coils around the host plant and sends its haustoria into the host tissue 
for the absorption of food. 
 
5. Ans. Oogenesis starts during the period of foetal development and completes 
only after the onset of puberty. Spermatogenesis begins at puberty. 
 
6. Ans. Smoking of tobacco releases carbon monoxide in the body, thereby 
depleting the oxygen content which is bound to the haemoglobin. 
 
7. Ans. The study of fossils is significant in evolution as 
(i) Fossil records provide missing links between two groups of organisms. 
(ii) The fossils occur in various strata of rock. The lowest strata carry the fossils 
of primitive groups, whereas the upper strata contain the complex group of 
organisms. 
8. Ans.   
(a) Sonalika is the semi-dwarf variety of wheat which is high-yielding and 
disease resistant. 
(b) Zonkey is an interspecific hybrid mammal which is a cross between zebra 
and donkey. 
 
 
 
 
 
 
Page 2


  
 
CBSE XII |  Biology 
Board Paper 2012 – Delhi – Set 2 (Solution) 
 
     
CBSE 
Class XII Biology (Theory) 
Board Paper 2012 – Delhi (Set 2) 
Solution 
Time: 3 hours  Total Marks: 70 
 
SECTION A 
 
1. Ans. Cucurbits are monoecious as they bear both staminate and pistillate 
flowers on the same plant, while papaya plants are dioecious as the staminate 
and pistillate flowers are borne on two different plants. 
 
2. Ans. Inflated yellow seeds are dominant over constricted green seeds. 
 
3. Ans. Phytophagous insects feed on plant sap and other parts of the plant. 
 
4. Ans. The interaction between Cuscuta and shoe flower bush is called parasitism. 
Cuscuta coils around the host plant and sends its haustoria into the host tissue 
for the absorption of food. 
 
5. Ans. Oogenesis starts during the period of foetal development and completes 
only after the onset of puberty. Spermatogenesis begins at puberty. 
 
6. Ans. Smoking of tobacco releases carbon monoxide in the body, thereby 
depleting the oxygen content which is bound to the haemoglobin. 
 
7. Ans. The study of fossils is significant in evolution as 
(i) Fossil records provide missing links between two groups of organisms. 
(ii) The fossils occur in various strata of rock. The lowest strata carry the fossils 
of primitive groups, whereas the upper strata contain the complex group of 
organisms. 
8. Ans.   
(a) Sonalika is the semi-dwarf variety of wheat which is high-yielding and 
disease resistant. 
(b) Zonkey is an interspecific hybrid mammal which is a cross between zebra 
and donkey. 
 
 
 
 
 
 
  
 
CBSE XII |  Biology 
Board Paper 2012 – Delhi – Set 2 (Solution) 
 
     
 
SECTION B 
9. Ans.        
(a) In the thymus, immature lymphocytes differentiate into antigen-sensitive 
lymphocytes. After maturation in the thymus, they migrate to secondary 
lymphoid organs.   
(b) The cells released from the thymus are called T-lymphocytes. These 
lymphocytes are responsible for cell-mediated immunity which defends the 
body against virus, fungi and some bacteria which have entered the host 
cells. Helper T-cells stimulate B-cells to produce antibodies and killer T-cells 
migrate to the site of infection. 
                                      
10. Ans.  The clown fish protects itself from predators by attaching itself to the body 
of sea anemone which possesses stinging tentacles. The sea anemone does not 
get any benefit from the clown fish. This interaction is called commensalism as 
one species is benefited, whereas the other species is neither harmed nor 
benefited. 
 
11. Ans. 
(a) Cysts formed in bacteria and fungi help them to survive in unfavourable 
conditions and germinate in favourable conditions. 
(b) Higher plants, seeds and vegetative structures germinate to form new plants 
under favourable temperature and moisture conditions, thereby reducing 
metabolic activity. 
(c) Animals stay at favourable conditions by going into hibernation during 
winter and aestivation during summer. For example, bears go into 
hibernation and snails go into aestivation. 
(d) Many zooplankton are known to enter diapause, a stage of suspended 
development under unfavourable conditions. 
 
12. Ans. 
(a) DNA ligase enzyme helps in joining the two ends of fragments, having the 
same kind of sticky ends. 
(b) Meloidogyne incognita is a nematode which infects the roots of tobacco plant. 
If Meloidogyne incognita consumes cells with the RNAi gene, the DNA forms 
sense and antisense RNA in the host cells. These two RNAs, being 
complementary to each other, form double-stranded RNA which binds to and 
prevents translation of the mRNA of the nematode. The parasite could not 
survive in a transgenic host expressing specific interfering RNA and dies. The 
transgenic plant therefore gets protected from the parasite. 
 
 
 
Page 3


  
 
CBSE XII |  Biology 
Board Paper 2012 – Delhi – Set 2 (Solution) 
 
     
CBSE 
Class XII Biology (Theory) 
Board Paper 2012 – Delhi (Set 2) 
Solution 
Time: 3 hours  Total Marks: 70 
 
SECTION A 
 
1. Ans. Cucurbits are monoecious as they bear both staminate and pistillate 
flowers on the same plant, while papaya plants are dioecious as the staminate 
and pistillate flowers are borne on two different plants. 
 
2. Ans. Inflated yellow seeds are dominant over constricted green seeds. 
 
3. Ans. Phytophagous insects feed on plant sap and other parts of the plant. 
 
4. Ans. The interaction between Cuscuta and shoe flower bush is called parasitism. 
Cuscuta coils around the host plant and sends its haustoria into the host tissue 
for the absorption of food. 
 
5. Ans. Oogenesis starts during the period of foetal development and completes 
only after the onset of puberty. Spermatogenesis begins at puberty. 
 
6. Ans. Smoking of tobacco releases carbon monoxide in the body, thereby 
depleting the oxygen content which is bound to the haemoglobin. 
 
7. Ans. The study of fossils is significant in evolution as 
(i) Fossil records provide missing links between two groups of organisms. 
(ii) The fossils occur in various strata of rock. The lowest strata carry the fossils 
of primitive groups, whereas the upper strata contain the complex group of 
organisms. 
8. Ans.   
(a) Sonalika is the semi-dwarf variety of wheat which is high-yielding and 
disease resistant. 
(b) Zonkey is an interspecific hybrid mammal which is a cross between zebra 
and donkey. 
 
 
 
 
 
 
  
 
CBSE XII |  Biology 
Board Paper 2012 – Delhi – Set 2 (Solution) 
 
     
 
SECTION B 
9. Ans.        
(a) In the thymus, immature lymphocytes differentiate into antigen-sensitive 
lymphocytes. After maturation in the thymus, they migrate to secondary 
lymphoid organs.   
(b) The cells released from the thymus are called T-lymphocytes. These 
lymphocytes are responsible for cell-mediated immunity which defends the 
body against virus, fungi and some bacteria which have entered the host 
cells. Helper T-cells stimulate B-cells to produce antibodies and killer T-cells 
migrate to the site of infection. 
                                      
10. Ans.  The clown fish protects itself from predators by attaching itself to the body 
of sea anemone which possesses stinging tentacles. The sea anemone does not 
get any benefit from the clown fish. This interaction is called commensalism as 
one species is benefited, whereas the other species is neither harmed nor 
benefited. 
 
11. Ans. 
(a) Cysts formed in bacteria and fungi help them to survive in unfavourable 
conditions and germinate in favourable conditions. 
(b) Higher plants, seeds and vegetative structures germinate to form new plants 
under favourable temperature and moisture conditions, thereby reducing 
metabolic activity. 
(c) Animals stay at favourable conditions by going into hibernation during 
winter and aestivation during summer. For example, bears go into 
hibernation and snails go into aestivation. 
(d) Many zooplankton are known to enter diapause, a stage of suspended 
development under unfavourable conditions. 
 
12. Ans. 
(a) DNA ligase enzyme helps in joining the two ends of fragments, having the 
same kind of sticky ends. 
(b) Meloidogyne incognita is a nematode which infects the roots of tobacco plant. 
If Meloidogyne incognita consumes cells with the RNAi gene, the DNA forms 
sense and antisense RNA in the host cells. These two RNAs, being 
complementary to each other, form double-stranded RNA which binds to and 
prevents translation of the mRNA of the nematode. The parasite could not 
survive in a transgenic host expressing specific interfering RNA and dies. The 
transgenic plant therefore gets protected from the parasite. 
 
 
 
  
 
CBSE XII |  Biology 
Board Paper 2012 – Delhi – Set 2 (Solution) 
 
     
 
13.  Ans.   
 
 
14.  Filariasis is caused by Wuchereria bancrofti and Wuchereria malayi. 
Symptoms:  
(i) Fever 
(ii) Legs may become swollen resembling those of an elephant. 
It is transmitted to a healthy person through the bite of female mosquito vectors. 
 
15. Ans. Streptococcus is used in the production of streptokinase which is used as a 
clot buster for removing clots from blood vessels of heart attack patients. 
 
OR 
 
Mycorrhiza is the symbiotic association between fungal hypha and roots of seed-
bearing plants. The fungal symbiont in these associations absorbs phosphorus 
from soil and passes it to the plant. Thus, mycorrhizae act as a biofertiliser. 
The genus of fungi Glomus forms a mycorrhizal association with plants. 
 
Page 4


  
 
CBSE XII |  Biology 
Board Paper 2012 – Delhi – Set 2 (Solution) 
 
     
CBSE 
Class XII Biology (Theory) 
Board Paper 2012 – Delhi (Set 2) 
Solution 
Time: 3 hours  Total Marks: 70 
 
SECTION A 
 
1. Ans. Cucurbits are monoecious as they bear both staminate and pistillate 
flowers on the same plant, while papaya plants are dioecious as the staminate 
and pistillate flowers are borne on two different plants. 
 
2. Ans. Inflated yellow seeds are dominant over constricted green seeds. 
 
3. Ans. Phytophagous insects feed on plant sap and other parts of the plant. 
 
4. Ans. The interaction between Cuscuta and shoe flower bush is called parasitism. 
Cuscuta coils around the host plant and sends its haustoria into the host tissue 
for the absorption of food. 
 
5. Ans. Oogenesis starts during the period of foetal development and completes 
only after the onset of puberty. Spermatogenesis begins at puberty. 
 
6. Ans. Smoking of tobacco releases carbon monoxide in the body, thereby 
depleting the oxygen content which is bound to the haemoglobin. 
 
7. Ans. The study of fossils is significant in evolution as 
(i) Fossil records provide missing links between two groups of organisms. 
(ii) The fossils occur in various strata of rock. The lowest strata carry the fossils 
of primitive groups, whereas the upper strata contain the complex group of 
organisms. 
8. Ans.   
(a) Sonalika is the semi-dwarf variety of wheat which is high-yielding and 
disease resistant. 
(b) Zonkey is an interspecific hybrid mammal which is a cross between zebra 
and donkey. 
 
 
 
 
 
 
  
 
CBSE XII |  Biology 
Board Paper 2012 – Delhi – Set 2 (Solution) 
 
     
 
SECTION B 
9. Ans.        
(a) In the thymus, immature lymphocytes differentiate into antigen-sensitive 
lymphocytes. After maturation in the thymus, they migrate to secondary 
lymphoid organs.   
(b) The cells released from the thymus are called T-lymphocytes. These 
lymphocytes are responsible for cell-mediated immunity which defends the 
body against virus, fungi and some bacteria which have entered the host 
cells. Helper T-cells stimulate B-cells to produce antibodies and killer T-cells 
migrate to the site of infection. 
                                      
10. Ans.  The clown fish protects itself from predators by attaching itself to the body 
of sea anemone which possesses stinging tentacles. The sea anemone does not 
get any benefit from the clown fish. This interaction is called commensalism as 
one species is benefited, whereas the other species is neither harmed nor 
benefited. 
 
11. Ans. 
(a) Cysts formed in bacteria and fungi help them to survive in unfavourable 
conditions and germinate in favourable conditions. 
(b) Higher plants, seeds and vegetative structures germinate to form new plants 
under favourable temperature and moisture conditions, thereby reducing 
metabolic activity. 
(c) Animals stay at favourable conditions by going into hibernation during 
winter and aestivation during summer. For example, bears go into 
hibernation and snails go into aestivation. 
(d) Many zooplankton are known to enter diapause, a stage of suspended 
development under unfavourable conditions. 
 
12. Ans. 
(a) DNA ligase enzyme helps in joining the two ends of fragments, having the 
same kind of sticky ends. 
(b) Meloidogyne incognita is a nematode which infects the roots of tobacco plant. 
If Meloidogyne incognita consumes cells with the RNAi gene, the DNA forms 
sense and antisense RNA in the host cells. These two RNAs, being 
complementary to each other, form double-stranded RNA which binds to and 
prevents translation of the mRNA of the nematode. The parasite could not 
survive in a transgenic host expressing specific interfering RNA and dies. The 
transgenic plant therefore gets protected from the parasite. 
 
 
 
  
 
CBSE XII |  Biology 
Board Paper 2012 – Delhi – Set 2 (Solution) 
 
     
 
13.  Ans.   
 
 
14.  Filariasis is caused by Wuchereria bancrofti and Wuchereria malayi. 
Symptoms:  
(i) Fever 
(ii) Legs may become swollen resembling those of an elephant. 
It is transmitted to a healthy person through the bite of female mosquito vectors. 
 
15. Ans. Streptococcus is used in the production of streptokinase which is used as a 
clot buster for removing clots from blood vessels of heart attack patients. 
 
OR 
 
Mycorrhiza is the symbiotic association between fungal hypha and roots of seed-
bearing plants. The fungal symbiont in these associations absorbs phosphorus 
from soil and passes it to the plant. Thus, mycorrhizae act as a biofertiliser. 
The genus of fungi Glomus forms a mycorrhizal association with plants. 
 
  
 
CBSE XII |  Biology 
Board Paper 2012 – Delhi – Set 2 (Solution) 
 
     
16. Ans.   
(a) The chromosome number is haploid in gametes, whereas there is a diploid 
set of chromosomes in the meiocyte (gamete mother cell). 
(b) Whiptail lizard is said to be parthenogenetic because the female gamete 
undergoes development to form new organisms without fertilisation. 
 
17. Ans. In 1972, Stanley Cohen and Herbert Boyer introduced a piece of gene 
containing foreign DNA into the plasmid of E. coli. They invented the technique 
of DNA cloning which allowed genes to be transplanted between different 
biological species. Boyer had discovered a restriction enzyme which cut DNA 
strands at specific positions, allowing them to be connected to other DNA. 
Combining these techniques allowed them to invent genetic engineering, to 
choose the genes to transplant and to choose the position to clone them.   
 
18.  Ans. Sporopollenin is found in the cell walls of plant spores and the exines of 
pollen grains. It is a complex substance of an oxidative polymer of carotenoids. It 
is the most resistant to biological materials which helps in the fossilisation of 
pollen grains. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Page 5


  
 
CBSE XII |  Biology 
Board Paper 2012 – Delhi – Set 2 (Solution) 
 
     
CBSE 
Class XII Biology (Theory) 
Board Paper 2012 – Delhi (Set 2) 
Solution 
Time: 3 hours  Total Marks: 70 
 
SECTION A 
 
1. Ans. Cucurbits are monoecious as they bear both staminate and pistillate 
flowers on the same plant, while papaya plants are dioecious as the staminate 
and pistillate flowers are borne on two different plants. 
 
2. Ans. Inflated yellow seeds are dominant over constricted green seeds. 
 
3. Ans. Phytophagous insects feed on plant sap and other parts of the plant. 
 
4. Ans. The interaction between Cuscuta and shoe flower bush is called parasitism. 
Cuscuta coils around the host plant and sends its haustoria into the host tissue 
for the absorption of food. 
 
5. Ans. Oogenesis starts during the period of foetal development and completes 
only after the onset of puberty. Spermatogenesis begins at puberty. 
 
6. Ans. Smoking of tobacco releases carbon monoxide in the body, thereby 
depleting the oxygen content which is bound to the haemoglobin. 
 
7. Ans. The study of fossils is significant in evolution as 
(i) Fossil records provide missing links between two groups of organisms. 
(ii) The fossils occur in various strata of rock. The lowest strata carry the fossils 
of primitive groups, whereas the upper strata contain the complex group of 
organisms. 
8. Ans.   
(a) Sonalika is the semi-dwarf variety of wheat which is high-yielding and 
disease resistant. 
(b) Zonkey is an interspecific hybrid mammal which is a cross between zebra 
and donkey. 
 
 
 
 
 
 
  
 
CBSE XII |  Biology 
Board Paper 2012 – Delhi – Set 2 (Solution) 
 
     
 
SECTION B 
9. Ans.        
(a) In the thymus, immature lymphocytes differentiate into antigen-sensitive 
lymphocytes. After maturation in the thymus, they migrate to secondary 
lymphoid organs.   
(b) The cells released from the thymus are called T-lymphocytes. These 
lymphocytes are responsible for cell-mediated immunity which defends the 
body against virus, fungi and some bacteria which have entered the host 
cells. Helper T-cells stimulate B-cells to produce antibodies and killer T-cells 
migrate to the site of infection. 
                                      
10. Ans.  The clown fish protects itself from predators by attaching itself to the body 
of sea anemone which possesses stinging tentacles. The sea anemone does not 
get any benefit from the clown fish. This interaction is called commensalism as 
one species is benefited, whereas the other species is neither harmed nor 
benefited. 
 
11. Ans. 
(a) Cysts formed in bacteria and fungi help them to survive in unfavourable 
conditions and germinate in favourable conditions. 
(b) Higher plants, seeds and vegetative structures germinate to form new plants 
under favourable temperature and moisture conditions, thereby reducing 
metabolic activity. 
(c) Animals stay at favourable conditions by going into hibernation during 
winter and aestivation during summer. For example, bears go into 
hibernation and snails go into aestivation. 
(d) Many zooplankton are known to enter diapause, a stage of suspended 
development under unfavourable conditions. 
 
12. Ans. 
(a) DNA ligase enzyme helps in joining the two ends of fragments, having the 
same kind of sticky ends. 
(b) Meloidogyne incognita is a nematode which infects the roots of tobacco plant. 
If Meloidogyne incognita consumes cells with the RNAi gene, the DNA forms 
sense and antisense RNA in the host cells. These two RNAs, being 
complementary to each other, form double-stranded RNA which binds to and 
prevents translation of the mRNA of the nematode. The parasite could not 
survive in a transgenic host expressing specific interfering RNA and dies. The 
transgenic plant therefore gets protected from the parasite. 
 
 
 
  
 
CBSE XII |  Biology 
Board Paper 2012 – Delhi – Set 2 (Solution) 
 
     
 
13.  Ans.   
 
 
14.  Filariasis is caused by Wuchereria bancrofti and Wuchereria malayi. 
Symptoms:  
(i) Fever 
(ii) Legs may become swollen resembling those of an elephant. 
It is transmitted to a healthy person through the bite of female mosquito vectors. 
 
15. Ans. Streptococcus is used in the production of streptokinase which is used as a 
clot buster for removing clots from blood vessels of heart attack patients. 
 
OR 
 
Mycorrhiza is the symbiotic association between fungal hypha and roots of seed-
bearing plants. The fungal symbiont in these associations absorbs phosphorus 
from soil and passes it to the plant. Thus, mycorrhizae act as a biofertiliser. 
The genus of fungi Glomus forms a mycorrhizal association with plants. 
 
  
 
CBSE XII |  Biology 
Board Paper 2012 – Delhi – Set 2 (Solution) 
 
     
16. Ans.   
(a) The chromosome number is haploid in gametes, whereas there is a diploid 
set of chromosomes in the meiocyte (gamete mother cell). 
(b) Whiptail lizard is said to be parthenogenetic because the female gamete 
undergoes development to form new organisms without fertilisation. 
 
17. Ans. In 1972, Stanley Cohen and Herbert Boyer introduced a piece of gene 
containing foreign DNA into the plasmid of E. coli. They invented the technique 
of DNA cloning which allowed genes to be transplanted between different 
biological species. Boyer had discovered a restriction enzyme which cut DNA 
strands at specific positions, allowing them to be connected to other DNA. 
Combining these techniques allowed them to invent genetic engineering, to 
choose the genes to transplant and to choose the position to clone them.   
 
18.  Ans. Sporopollenin is found in the cell walls of plant spores and the exines of 
pollen grains. It is a complex substance of an oxidative polymer of carotenoids. It 
is the most resistant to biological materials which helps in the fossilisation of 
pollen grains. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
CBSE XII |  Biology 
Board Paper 2012 – Delhi – Set 2 (Solution) 
 
     
SECTION C 
19. Ans. 
(a) The middle piece in human sperm possesses numerous mitochondria which 
produces energy for the movement of the tail that facilitates sperm motility 
essential for fertilisation. 
(b) Tapetum in anthers is the innermost layer and provides nourishment to the 
developing pollen grains. 
(c) Luteinising hormones in males stimulate the Leydig cells to produce 
testosterone. 
 
20. Ans. 
(a) This representation indicates a normal human because glutamic acid is 
present at the sixth position in the respective amino acid chain. 
(b) In the sufferer who exhibits the sickle cell trait, the defect is caused by the 
substitution of glutamic acid (Glu) by valine (Val) at the sixth position of the 
ß-chain of haemoglobin. 
(c) Both males and females suffer equally because sickle cell anaemia is not a 
sex-linked disease. It is an autosomal disease and sickle-shaped RBCs will 
cause equal deficiency of oxygen in both males and females.  
 
21. Ans. 
(a) Two restriction sites – BamHI and PvuII 
(b) Ori and rop genes – Ori is the site of origin of replication. Rop codes for the 
proteins involved in the replication of the plasmid. 
(c) Antibiotic-resistant genes – amp
R
 and tet
R
 
 
 
 
Schematic sketch of plasmid pBR322