CBSE Biology Past year paper Delhi (Set - 1) Solutions - 2011, Class 12 | Additional Study Material for NEET PDF Download

 Page 1


  
 
CBSE XII  |  Biology 
Board Paper 2011 – Delhi – Set 1 (Solution) 
 
     
CBSE 
Class XII Biology (Theory) 
Board Paper 2011 – Delhi (Set 1) 
SOLUTION 
Time: 3 hrs Total Marks: 70 
 
SECTION A 
1. Ans. Meiosis occurs in the zygote of an organism exhibiting the haplontic life cycle 
to produce haploid individuals. 
 
2. Ans. Brewer’s yeast (Saccharomyces cerevisiae) is used for fermenting malted 
cereals and fruit juices. 
 
3. Ans. Dobson unit (DU) is used for measuring ozone thickness. 
 
4. Ans. Aneuploidy is a condition of having fewer or extra chromosomes than the 
normal genome number of the species. Loss of chromosomes is called hypoploidy 
and addition of chromosomes is called heteroploidy. 
 
5. Ans. DNA is enclosed within membranes, so it is released by breaking the cell. DNA 
along with other macromolecules such as RNA, proteins, polysaccharides and lipids 
are released by treating bacterial, plant, fungal or animal cells with enzymes such as 
lysozyme (bacteria), cellulose (plants) and chitinase (fungi). 
 
6. Ans. Cryopreservation is preservation at -196
o
C in liquid nitrogen. It is useful in 
sperms, eggs, cells and embryonic tissues of animals.  
 
7. Ans. AUG is the initiation codon which signals the start of translation, and UGA is the 
termination codon. When UGA comes into register with the A site, the protein-
releasing factors modify the specificity of the peptidyl transferase so that the water 
molecule is added to the peptide instead of another amino acid, and this causes the 
dissociation of ribosomal subunits. 
 
8. Ans. Embryos are developed when the nucellar cells surrounding the embryo sac 
start dividing and protrude into the embryo sac. This condition of occurrence of 
more than one embryo in seed is called polyembryony. Because orange is a citrus 
fruit, it shows the polyembryony stage, i.e. its seeds possess more than one embryo. 
Hence, when an orange seed is squeezed, many embryos of different shapes and 
sizes are seen. 
 
 
Page 2


  
 
CBSE XII  |  Biology 
Board Paper 2011 – Delhi – Set 1 (Solution) 
 
     
CBSE 
Class XII Biology (Theory) 
Board Paper 2011 – Delhi (Set 1) 
SOLUTION 
Time: 3 hrs Total Marks: 70 
 
SECTION A 
1. Ans. Meiosis occurs in the zygote of an organism exhibiting the haplontic life cycle 
to produce haploid individuals. 
 
2. Ans. Brewer’s yeast (Saccharomyces cerevisiae) is used for fermenting malted 
cereals and fruit juices. 
 
3. Ans. Dobson unit (DU) is used for measuring ozone thickness. 
 
4. Ans. Aneuploidy is a condition of having fewer or extra chromosomes than the 
normal genome number of the species. Loss of chromosomes is called hypoploidy 
and addition of chromosomes is called heteroploidy. 
 
5. Ans. DNA is enclosed within membranes, so it is released by breaking the cell. DNA 
along with other macromolecules such as RNA, proteins, polysaccharides and lipids 
are released by treating bacterial, plant, fungal or animal cells with enzymes such as 
lysozyme (bacteria), cellulose (plants) and chitinase (fungi). 
 
6. Ans. Cryopreservation is preservation at -196
o
C in liquid nitrogen. It is useful in 
sperms, eggs, cells and embryonic tissues of animals.  
 
7. Ans. AUG is the initiation codon which signals the start of translation, and UGA is the 
termination codon. When UGA comes into register with the A site, the protein-
releasing factors modify the specificity of the peptidyl transferase so that the water 
molecule is added to the peptide instead of another amino acid, and this causes the 
dissociation of ribosomal subunits. 
 
8. Ans. Embryos are developed when the nucellar cells surrounding the embryo sac 
start dividing and protrude into the embryo sac. This condition of occurrence of 
more than one embryo in seed is called polyembryony. Because orange is a citrus 
fruit, it shows the polyembryony stage, i.e. its seeds possess more than one embryo. 
Hence, when an orange seed is squeezed, many embryos of different shapes and 
sizes are seen. 
 
 
  
 
CBSE XII  |  Biology 
Board Paper 2011 – Delhi – Set 1 (Solution) 
 
     
 
SECTION B 
 
9. Ans. In eukaryotic nucleosomes, DNA packaging is carried out with the help of 
positively charged basic proteins called histones. Histones are low molecular weight 
proteins rich in basic amino acid residues of lysine and arginine which carry 
positive charges in their side chains; therefore, histones are positively charged.  
 
10.  Ans. CuT increases the phagocytosis of sperms in the uterus and copper ions 
released decrease the sperm motility and prevent fertilisation, so it is considered a 
good contraceptive device to space children. 
 
11.  Ans. 
Albuminous seeds Non-albuminous seeds 
(i) The seeds in which the cotyledons 
are thin and membranous and the 
food is stored in the endosperm are 
called endospermic or albuminous 
seeds. 
(ii) Examples: Wheat, maize 
(i) The seeds which are without 
endosperms are called non-
endospermic or non-albuminous 
seeds. 
 
(ii) Examples: Pea, gram 
 
 
12.  Ans. RNA interference (RNAi) is a system within living cells which helps control the 
activity of specific genes and is used as a method of cellular defence against 
parasites. This method involves silencing of a specific mRNA. The introduction of 
DNA produces both sense and antisense RNA in the host cells. These two RNAs, 
being complementary to each other, form a double-stranded RNA which binds to 
and prevents translation of mRNA. 
   
13.  Ans. The tools used in recombinant DNA technology are 
(i) Enzymes: Many kinds of specific enzymes are employed in genetic engineering 
to perform specific functions. These include lysing enzymes, cleaving enzymes, 
synthesising enzymes, joining enzymes and alkaline phosphatases. 
(ii) Vehicle or vector DNA: The DNA used as a carrier for transferring a fragment of 
foreign DNA into a suitable host is called vehicle DNA or vector DNA. 
(iii) Passenger DNA: It is the DNA which is transferred from one organism into 
another by combining it with the vehicle DNA. 
 
 
 
 
 
 
Page 3


  
 
CBSE XII  |  Biology 
Board Paper 2011 – Delhi – Set 1 (Solution) 
 
     
CBSE 
Class XII Biology (Theory) 
Board Paper 2011 – Delhi (Set 1) 
SOLUTION 
Time: 3 hrs Total Marks: 70 
 
SECTION A 
1. Ans. Meiosis occurs in the zygote of an organism exhibiting the haplontic life cycle 
to produce haploid individuals. 
 
2. Ans. Brewer’s yeast (Saccharomyces cerevisiae) is used for fermenting malted 
cereals and fruit juices. 
 
3. Ans. Dobson unit (DU) is used for measuring ozone thickness. 
 
4. Ans. Aneuploidy is a condition of having fewer or extra chromosomes than the 
normal genome number of the species. Loss of chromosomes is called hypoploidy 
and addition of chromosomes is called heteroploidy. 
 
5. Ans. DNA is enclosed within membranes, so it is released by breaking the cell. DNA 
along with other macromolecules such as RNA, proteins, polysaccharides and lipids 
are released by treating bacterial, plant, fungal or animal cells with enzymes such as 
lysozyme (bacteria), cellulose (plants) and chitinase (fungi). 
 
6. Ans. Cryopreservation is preservation at -196
o
C in liquid nitrogen. It is useful in 
sperms, eggs, cells and embryonic tissues of animals.  
 
7. Ans. AUG is the initiation codon which signals the start of translation, and UGA is the 
termination codon. When UGA comes into register with the A site, the protein-
releasing factors modify the specificity of the peptidyl transferase so that the water 
molecule is added to the peptide instead of another amino acid, and this causes the 
dissociation of ribosomal subunits. 
 
8. Ans. Embryos are developed when the nucellar cells surrounding the embryo sac 
start dividing and protrude into the embryo sac. This condition of occurrence of 
more than one embryo in seed is called polyembryony. Because orange is a citrus 
fruit, it shows the polyembryony stage, i.e. its seeds possess more than one embryo. 
Hence, when an orange seed is squeezed, many embryos of different shapes and 
sizes are seen. 
 
 
  
 
CBSE XII  |  Biology 
Board Paper 2011 – Delhi – Set 1 (Solution) 
 
     
 
SECTION B 
 
9. Ans. In eukaryotic nucleosomes, DNA packaging is carried out with the help of 
positively charged basic proteins called histones. Histones are low molecular weight 
proteins rich in basic amino acid residues of lysine and arginine which carry 
positive charges in their side chains; therefore, histones are positively charged.  
 
10.  Ans. CuT increases the phagocytosis of sperms in the uterus and copper ions 
released decrease the sperm motility and prevent fertilisation, so it is considered a 
good contraceptive device to space children. 
 
11.  Ans. 
Albuminous seeds Non-albuminous seeds 
(i) The seeds in which the cotyledons 
are thin and membranous and the 
food is stored in the endosperm are 
called endospermic or albuminous 
seeds. 
(ii) Examples: Wheat, maize 
(i) The seeds which are without 
endosperms are called non-
endospermic or non-albuminous 
seeds. 
 
(ii) Examples: Pea, gram 
 
 
12.  Ans. RNA interference (RNAi) is a system within living cells which helps control the 
activity of specific genes and is used as a method of cellular defence against 
parasites. This method involves silencing of a specific mRNA. The introduction of 
DNA produces both sense and antisense RNA in the host cells. These two RNAs, 
being complementary to each other, form a double-stranded RNA which binds to 
and prevents translation of mRNA. 
   
13.  Ans. The tools used in recombinant DNA technology are 
(i) Enzymes: Many kinds of specific enzymes are employed in genetic engineering 
to perform specific functions. These include lysing enzymes, cleaving enzymes, 
synthesising enzymes, joining enzymes and alkaline phosphatases. 
(ii) Vehicle or vector DNA: The DNA used as a carrier for transferring a fragment of 
foreign DNA into a suitable host is called vehicle DNA or vector DNA. 
(iii) Passenger DNA: It is the DNA which is transferred from one organism into 
another by combining it with the vehicle DNA. 
 
 
 
 
 
 
  
 
CBSE XII  |  Biology 
Board Paper 2011 – Delhi – Set 1 (Solution) 
 
     
 
14.  Ans. The two types of immune system in human body are 
(a) Humoral or antibody-mediated immune system: This immune system operates 
by the production of humoral antibodies, so it is named humoral or antibody-
mediated immune system. The humoral antibodies in blood and lymph react 
with specific foreign substances (antigens) in promoting their destruction. 
(b) Cell-mediated immune system: This immune system operates by the production 
of lymphocytes and macrophages. Hence, it is called cell mediated. The T-
lymphocytes attack the pathogenic microorganisms which have entered the 
host’s body or grafts such as transplanted kidney. It also protects the body from 
its own cells which have become cancerous.  
OR 
 
                  Elephantiasis is caused by the filarial worm Wuchereria (Wuchereria bancrofti  
                  and Wuchereria malayi). It usually affects the lymphatic vessels of the lower  
                  limbs and genital organs.  
                  Ringworm is caused by the fungi Microsporum, Trichophyton and   
                  Epidermophyton. It affects the skin, nails and scalp. 
 
15. Ans. When the Nile Perch, a large predator fish, was introduced in Lake Victoria, it 
started feeding on the native cichlid fish. As a result, the cichlid fish became extinct 
and Nile Perch, not finding any food, died too. 
 
16. Ans. 
A: Antigen-binding site 
D: Light chain 
E: Heavy chain 
F: Disulfide bond 
 
17.  Ans. Discharge of domestic sewage into the river results in the rise of BOD because 
decomposer organisms consume a large amount of oxygen to decompose the 
organic matter. When the amount of organic matter reduces, the amount of 
dissolved oxygen again increases. 
 
 
 
 
 
 
 
 
 
 
Page 4


  
 
CBSE XII  |  Biology 
Board Paper 2011 – Delhi – Set 1 (Solution) 
 
     
CBSE 
Class XII Biology (Theory) 
Board Paper 2011 – Delhi (Set 1) 
SOLUTION 
Time: 3 hrs Total Marks: 70 
 
SECTION A 
1. Ans. Meiosis occurs in the zygote of an organism exhibiting the haplontic life cycle 
to produce haploid individuals. 
 
2. Ans. Brewer’s yeast (Saccharomyces cerevisiae) is used for fermenting malted 
cereals and fruit juices. 
 
3. Ans. Dobson unit (DU) is used for measuring ozone thickness. 
 
4. Ans. Aneuploidy is a condition of having fewer or extra chromosomes than the 
normal genome number of the species. Loss of chromosomes is called hypoploidy 
and addition of chromosomes is called heteroploidy. 
 
5. Ans. DNA is enclosed within membranes, so it is released by breaking the cell. DNA 
along with other macromolecules such as RNA, proteins, polysaccharides and lipids 
are released by treating bacterial, plant, fungal or animal cells with enzymes such as 
lysozyme (bacteria), cellulose (plants) and chitinase (fungi). 
 
6. Ans. Cryopreservation is preservation at -196
o
C in liquid nitrogen. It is useful in 
sperms, eggs, cells and embryonic tissues of animals.  
 
7. Ans. AUG is the initiation codon which signals the start of translation, and UGA is the 
termination codon. When UGA comes into register with the A site, the protein-
releasing factors modify the specificity of the peptidyl transferase so that the water 
molecule is added to the peptide instead of another amino acid, and this causes the 
dissociation of ribosomal subunits. 
 
8. Ans. Embryos are developed when the nucellar cells surrounding the embryo sac 
start dividing and protrude into the embryo sac. This condition of occurrence of 
more than one embryo in seed is called polyembryony. Because orange is a citrus 
fruit, it shows the polyembryony stage, i.e. its seeds possess more than one embryo. 
Hence, when an orange seed is squeezed, many embryos of different shapes and 
sizes are seen. 
 
 
  
 
CBSE XII  |  Biology 
Board Paper 2011 – Delhi – Set 1 (Solution) 
 
     
 
SECTION B 
 
9. Ans. In eukaryotic nucleosomes, DNA packaging is carried out with the help of 
positively charged basic proteins called histones. Histones are low molecular weight 
proteins rich in basic amino acid residues of lysine and arginine which carry 
positive charges in their side chains; therefore, histones are positively charged.  
 
10.  Ans. CuT increases the phagocytosis of sperms in the uterus and copper ions 
released decrease the sperm motility and prevent fertilisation, so it is considered a 
good contraceptive device to space children. 
 
11.  Ans. 
Albuminous seeds Non-albuminous seeds 
(i) The seeds in which the cotyledons 
are thin and membranous and the 
food is stored in the endosperm are 
called endospermic or albuminous 
seeds. 
(ii) Examples: Wheat, maize 
(i) The seeds which are without 
endosperms are called non-
endospermic or non-albuminous 
seeds. 
 
(ii) Examples: Pea, gram 
 
 
12.  Ans. RNA interference (RNAi) is a system within living cells which helps control the 
activity of specific genes and is used as a method of cellular defence against 
parasites. This method involves silencing of a specific mRNA. The introduction of 
DNA produces both sense and antisense RNA in the host cells. These two RNAs, 
being complementary to each other, form a double-stranded RNA which binds to 
and prevents translation of mRNA. 
   
13.  Ans. The tools used in recombinant DNA technology are 
(i) Enzymes: Many kinds of specific enzymes are employed in genetic engineering 
to perform specific functions. These include lysing enzymes, cleaving enzymes, 
synthesising enzymes, joining enzymes and alkaline phosphatases. 
(ii) Vehicle or vector DNA: The DNA used as a carrier for transferring a fragment of 
foreign DNA into a suitable host is called vehicle DNA or vector DNA. 
(iii) Passenger DNA: It is the DNA which is transferred from one organism into 
another by combining it with the vehicle DNA. 
 
 
 
 
 
 
  
 
CBSE XII  |  Biology 
Board Paper 2011 – Delhi – Set 1 (Solution) 
 
     
 
14.  Ans. The two types of immune system in human body are 
(a) Humoral or antibody-mediated immune system: This immune system operates 
by the production of humoral antibodies, so it is named humoral or antibody-
mediated immune system. The humoral antibodies in blood and lymph react 
with specific foreign substances (antigens) in promoting their destruction. 
(b) Cell-mediated immune system: This immune system operates by the production 
of lymphocytes and macrophages. Hence, it is called cell mediated. The T-
lymphocytes attack the pathogenic microorganisms which have entered the 
host’s body or grafts such as transplanted kidney. It also protects the body from 
its own cells which have become cancerous.  
OR 
 
                  Elephantiasis is caused by the filarial worm Wuchereria (Wuchereria bancrofti  
                  and Wuchereria malayi). It usually affects the lymphatic vessels of the lower  
                  limbs and genital organs.  
                  Ringworm is caused by the fungi Microsporum, Trichophyton and   
                  Epidermophyton. It affects the skin, nails and scalp. 
 
15. Ans. When the Nile Perch, a large predator fish, was introduced in Lake Victoria, it 
started feeding on the native cichlid fish. As a result, the cichlid fish became extinct 
and Nile Perch, not finding any food, died too. 
 
16. Ans. 
A: Antigen-binding site 
D: Light chain 
E: Heavy chain 
F: Disulfide bond 
 
17.  Ans. Discharge of domestic sewage into the river results in the rise of BOD because 
decomposer organisms consume a large amount of oxygen to decompose the 
organic matter. When the amount of organic matter reduces, the amount of 
dissolved oxygen again increases. 
 
 
 
 
 
 
 
 
 
 
  
 
CBSE XII  |  Biology 
Board Paper 2011 – Delhi – Set 1 (Solution) 
 
     
18.  Ans. A hereditary disease can be corrected by gene therapy. Treatment of a genetic 
disorder by manipulating genes is called gene therapy. The first clinical gene 
therapy was given in 1990 to a 4-year-old girl with adenosine deaminase (ADA) 
deficiency. 
Gene therapy of ADA deficiency: 
(i) The patient lacks functional T-lymphocytes and therefore fails to fight the 
infecting pathogens.  
(ii) Lymphocytes are extracted from the patient’s bone marrow and a normal 
functional copy of gene coding for ADA is introduced into these lymphocytes 
with the help of retrovirus.  
(iii) The cells so treated are introduced into the patient’s bone marrow.  
(iv) The lymphocytes produced by these cells contain functional ADA gene and 
reactivate the victim’s immune system for life. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
Page 5


  
 
CBSE XII  |  Biology 
Board Paper 2011 – Delhi – Set 1 (Solution) 
 
     
CBSE 
Class XII Biology (Theory) 
Board Paper 2011 – Delhi (Set 1) 
SOLUTION 
Time: 3 hrs Total Marks: 70 
 
SECTION A 
1. Ans. Meiosis occurs in the zygote of an organism exhibiting the haplontic life cycle 
to produce haploid individuals. 
 
2. Ans. Brewer’s yeast (Saccharomyces cerevisiae) is used for fermenting malted 
cereals and fruit juices. 
 
3. Ans. Dobson unit (DU) is used for measuring ozone thickness. 
 
4. Ans. Aneuploidy is a condition of having fewer or extra chromosomes than the 
normal genome number of the species. Loss of chromosomes is called hypoploidy 
and addition of chromosomes is called heteroploidy. 
 
5. Ans. DNA is enclosed within membranes, so it is released by breaking the cell. DNA 
along with other macromolecules such as RNA, proteins, polysaccharides and lipids 
are released by treating bacterial, plant, fungal or animal cells with enzymes such as 
lysozyme (bacteria), cellulose (plants) and chitinase (fungi). 
 
6. Ans. Cryopreservation is preservation at -196
o
C in liquid nitrogen. It is useful in 
sperms, eggs, cells and embryonic tissues of animals.  
 
7. Ans. AUG is the initiation codon which signals the start of translation, and UGA is the 
termination codon. When UGA comes into register with the A site, the protein-
releasing factors modify the specificity of the peptidyl transferase so that the water 
molecule is added to the peptide instead of another amino acid, and this causes the 
dissociation of ribosomal subunits. 
 
8. Ans. Embryos are developed when the nucellar cells surrounding the embryo sac 
start dividing and protrude into the embryo sac. This condition of occurrence of 
more than one embryo in seed is called polyembryony. Because orange is a citrus 
fruit, it shows the polyembryony stage, i.e. its seeds possess more than one embryo. 
Hence, when an orange seed is squeezed, many embryos of different shapes and 
sizes are seen. 
 
 
  
 
CBSE XII  |  Biology 
Board Paper 2011 – Delhi – Set 1 (Solution) 
 
     
 
SECTION B 
 
9. Ans. In eukaryotic nucleosomes, DNA packaging is carried out with the help of 
positively charged basic proteins called histones. Histones are low molecular weight 
proteins rich in basic amino acid residues of lysine and arginine which carry 
positive charges in their side chains; therefore, histones are positively charged.  
 
10.  Ans. CuT increases the phagocytosis of sperms in the uterus and copper ions 
released decrease the sperm motility and prevent fertilisation, so it is considered a 
good contraceptive device to space children. 
 
11.  Ans. 
Albuminous seeds Non-albuminous seeds 
(i) The seeds in which the cotyledons 
are thin and membranous and the 
food is stored in the endosperm are 
called endospermic or albuminous 
seeds. 
(ii) Examples: Wheat, maize 
(i) The seeds which are without 
endosperms are called non-
endospermic or non-albuminous 
seeds. 
 
(ii) Examples: Pea, gram 
 
 
12.  Ans. RNA interference (RNAi) is a system within living cells which helps control the 
activity of specific genes and is used as a method of cellular defence against 
parasites. This method involves silencing of a specific mRNA. The introduction of 
DNA produces both sense and antisense RNA in the host cells. These two RNAs, 
being complementary to each other, form a double-stranded RNA which binds to 
and prevents translation of mRNA. 
   
13.  Ans. The tools used in recombinant DNA technology are 
(i) Enzymes: Many kinds of specific enzymes are employed in genetic engineering 
to perform specific functions. These include lysing enzymes, cleaving enzymes, 
synthesising enzymes, joining enzymes and alkaline phosphatases. 
(ii) Vehicle or vector DNA: The DNA used as a carrier for transferring a fragment of 
foreign DNA into a suitable host is called vehicle DNA or vector DNA. 
(iii) Passenger DNA: It is the DNA which is transferred from one organism into 
another by combining it with the vehicle DNA. 
 
 
 
 
 
 
  
 
CBSE XII  |  Biology 
Board Paper 2011 – Delhi – Set 1 (Solution) 
 
     
 
14.  Ans. The two types of immune system in human body are 
(a) Humoral or antibody-mediated immune system: This immune system operates 
by the production of humoral antibodies, so it is named humoral or antibody-
mediated immune system. The humoral antibodies in blood and lymph react 
with specific foreign substances (antigens) in promoting their destruction. 
(b) Cell-mediated immune system: This immune system operates by the production 
of lymphocytes and macrophages. Hence, it is called cell mediated. The T-
lymphocytes attack the pathogenic microorganisms which have entered the 
host’s body or grafts such as transplanted kidney. It also protects the body from 
its own cells which have become cancerous.  
OR 
 
                  Elephantiasis is caused by the filarial worm Wuchereria (Wuchereria bancrofti  
                  and Wuchereria malayi). It usually affects the lymphatic vessels of the lower  
                  limbs and genital organs.  
                  Ringworm is caused by the fungi Microsporum, Trichophyton and   
                  Epidermophyton. It affects the skin, nails and scalp. 
 
15. Ans. When the Nile Perch, a large predator fish, was introduced in Lake Victoria, it 
started feeding on the native cichlid fish. As a result, the cichlid fish became extinct 
and Nile Perch, not finding any food, died too. 
 
16. Ans. 
A: Antigen-binding site 
D: Light chain 
E: Heavy chain 
F: Disulfide bond 
 
17.  Ans. Discharge of domestic sewage into the river results in the rise of BOD because 
decomposer organisms consume a large amount of oxygen to decompose the 
organic matter. When the amount of organic matter reduces, the amount of 
dissolved oxygen again increases. 
 
 
 
 
 
 
 
 
 
 
  
 
CBSE XII  |  Biology 
Board Paper 2011 – Delhi – Set 1 (Solution) 
 
     
18.  Ans. A hereditary disease can be corrected by gene therapy. Treatment of a genetic 
disorder by manipulating genes is called gene therapy. The first clinical gene 
therapy was given in 1990 to a 4-year-old girl with adenosine deaminase (ADA) 
deficiency. 
Gene therapy of ADA deficiency: 
(i) The patient lacks functional T-lymphocytes and therefore fails to fight the 
infecting pathogens.  
(ii) Lymphocytes are extracted from the patient’s bone marrow and a normal 
functional copy of gene coding for ADA is introduced into these lymphocytes 
with the help of retrovirus.  
(iii) The cells so treated are introduced into the patient’s bone marrow.  
(iv) The lymphocytes produced by these cells contain functional ADA gene and 
reactivate the victim’s immune system for life. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
CBSE XII  |  Biology 
Board Paper 2011 – Delhi – Set 1 (Solution) 
 
     
SECTION C 
19.  Ans.   
(a)   
 
 
(b) Sporopollenin is considered the most resistant organic material because it can 
withstand high temperatures, strong acids and alkalis and cannot be degraded 
by any enzyme. 
 
20.  Ans. 
Dominance Co-dominance Incomplete 
dominance 
When two different 
factors or a pair of 
contrasting forms of a 
character are present 
in an organism, only 
one expresses itself in 
the F 1 generation and 
is termed dominant, 
while the other 
remains unexpressed 
and is called recessive. 
When both alleles are 
present together in a 
heterozygous organism 
and express their traits 
independently instead 
of showing a dominant–
recessive relationship, 
they are called co-
dominant alleles and 
the phenomenon is 
called co-dominance. 
Incomplete 
dominance is the 
phenomenon where 
none of the two 
contrasting genes or 
factors is dominant 
and the expression of 
the character in a F 1 
hybrid individual is 
the intermediate 
type.