MARKING SCHEME (2023-24
Class XII
Biology (Subject Code-044)
Q. Answer Marks
No.
Section - A
1 d) black pepper 1
2 d) tapetum 1
3 d) 7 1
4 a) males and females, respectively 1
5 a) 0.32 1
6 a) random and directionless 1
7 d) Nucleotide 1
8 d) aa 1
9 c) Cyclosporin A produced from Trichoderma polysporum 1
10 d) 1
11 b) Reduce pesticide accumulation in food chain 1
12 d) Soil Sample C 1
13 d) A is false but R is true 1
14 c) A is true but R is false 1
15 a) Both A and R are true and R is the correct explanation of A. 1
16 a) Both A and R are true and R is the correct explanation of A. 1
Section – B
17 Spermatogenesis starts at the age of puberty due to significant increase in the secretion of 2
gonadotropin releasing hormone (GnRH). This is a hypothalamic hormone. [0.5]
The increased levels of GnRH then act at the anterior pituitary gland and stimulate secretion of
two gonadotropins – luteinising hormone (LH) and follicle stimulating hormone (FSH). [0.5]
LH acts at the Leydig cells and stimulates synthesis and secretion of androgens. Androgens, in
turn, stimulate the process of spermatogenesis. [0.5]
FSH acts on the Sertoli cells and stimulates secretion of some factors which help in the process of
spermiogenesis. [0.5]
18 a) CTT would become CAT which codes for valine. Thus, valine would replace glutamic acid at 2
that point. [0.5]
b) Sickle cell anaemia [0.5], the mutant haemoglobin molecule undergoes polymerization [0.5]
leading to the change in the shape of the RBC from biconcave disc to elongated sickle like
structure. [0.5]
1
, 19 On administration of the first dose of the vaccine (L), the body shows a response of low 2
intensity (X) as the immune system comes in contact with the antigenic protein of the
weakened/inactivated pathogen for the first time. This is called primary immune response. [1]
On subsequent encounter with the same antigenic protein in the second dose (M), the body
elicits a highly intensified secondary response (Y). Because of the memory of the first contact
with the antigen, the secondary immune response is faster and stronger, leading to more
effective pathogen elimination in comparison to the primary immune response. [1]
20 a) Plate 1, b-galactosidase enzyme is responsible for blue colour. Gene is inserted in the 2
b-galactosidase site of the plasmid thereby causing insertional inactivation of the enzyme,
so no blue colour is made. [1]
b) Plate II - Gene of interest not inserted in the plasmid [0.5]
Plate III - No plasmid [0.5]
21 2
OR
a) Gross Primary Productivity is 45000 + 40367 = 85367 KJm-2y-1 [1]
b) Net production is gradually reducing as we move from producers to consumers due to heat
loss/respiration /10% law. [1]
Section – C
22 a) Sperm A [0.5] 3
b) In the figure given, Sperm ‘A’has come in contact with the zona pellucida layer (P) of the
ovum (Q), it will induce changes in the membrane that will block the entry of additional
sperms (B and C). Thus, it ensures that only one sperm can fertilise the ovum. [0.5]
The secretions of the acrosome of sperm A will help it to enter into the cytoplasm of the
ovum (Q) through the zona pellucid (P) and the plasma membrane, this will induce the
completion of the meiotic division of the secondary oocyte (Q). [1]
The second meiotic division in Q being unequal will result in the formation of a second
polar body and a haploid ovum. Then, the haploid nucleus of the sperm ‘A’ and that of the
ovum (Q) will fuse together to form a diploid zygote. [1]
23 The embryo with 8 to 16 blastomeres is called a morula. 3
The morula continues to divide and transforms into blastocyst as it moves further into the
uterus.
The blastomeres in the blastocyst are arranged into an outer layer called trophoblast and
An inner group of cells attached to trophoblast called the inner cell mass.
The trophoblast layer then gets attached to the endometrium and the inner cell mass gets
differentiated as the embryo.
After attachment, the uterine cells divide rapidly and covers the blastocyst.
As a result, the blastocyst becomes embedded in the endometrium of the uterus. This is
called implantation and it leads to pregnancy. [0.5X6=3]
2
Class XII
Biology (Subject Code-044)
Q. Answer Marks
No.
Section - A
1 d) black pepper 1
2 d) tapetum 1
3 d) 7 1
4 a) males and females, respectively 1
5 a) 0.32 1
6 a) random and directionless 1
7 d) Nucleotide 1
8 d) aa 1
9 c) Cyclosporin A produced from Trichoderma polysporum 1
10 d) 1
11 b) Reduce pesticide accumulation in food chain 1
12 d) Soil Sample C 1
13 d) A is false but R is true 1
14 c) A is true but R is false 1
15 a) Both A and R are true and R is the correct explanation of A. 1
16 a) Both A and R are true and R is the correct explanation of A. 1
Section – B
17 Spermatogenesis starts at the age of puberty due to significant increase in the secretion of 2
gonadotropin releasing hormone (GnRH). This is a hypothalamic hormone. [0.5]
The increased levels of GnRH then act at the anterior pituitary gland and stimulate secretion of
two gonadotropins – luteinising hormone (LH) and follicle stimulating hormone (FSH). [0.5]
LH acts at the Leydig cells and stimulates synthesis and secretion of androgens. Androgens, in
turn, stimulate the process of spermatogenesis. [0.5]
FSH acts on the Sertoli cells and stimulates secretion of some factors which help in the process of
spermiogenesis. [0.5]
18 a) CTT would become CAT which codes for valine. Thus, valine would replace glutamic acid at 2
that point. [0.5]
b) Sickle cell anaemia [0.5], the mutant haemoglobin molecule undergoes polymerization [0.5]
leading to the change in the shape of the RBC from biconcave disc to elongated sickle like
structure. [0.5]
1
, 19 On administration of the first dose of the vaccine (L), the body shows a response of low 2
intensity (X) as the immune system comes in contact with the antigenic protein of the
weakened/inactivated pathogen for the first time. This is called primary immune response. [1]
On subsequent encounter with the same antigenic protein in the second dose (M), the body
elicits a highly intensified secondary response (Y). Because of the memory of the first contact
with the antigen, the secondary immune response is faster and stronger, leading to more
effective pathogen elimination in comparison to the primary immune response. [1]
20 a) Plate 1, b-galactosidase enzyme is responsible for blue colour. Gene is inserted in the 2
b-galactosidase site of the plasmid thereby causing insertional inactivation of the enzyme,
so no blue colour is made. [1]
b) Plate II - Gene of interest not inserted in the plasmid [0.5]
Plate III - No plasmid [0.5]
21 2
OR
a) Gross Primary Productivity is 45000 + 40367 = 85367 KJm-2y-1 [1]
b) Net production is gradually reducing as we move from producers to consumers due to heat
loss/respiration /10% law. [1]
Section – C
22 a) Sperm A [0.5] 3
b) In the figure given, Sperm ‘A’has come in contact with the zona pellucida layer (P) of the
ovum (Q), it will induce changes in the membrane that will block the entry of additional
sperms (B and C). Thus, it ensures that only one sperm can fertilise the ovum. [0.5]
The secretions of the acrosome of sperm A will help it to enter into the cytoplasm of the
ovum (Q) through the zona pellucid (P) and the plasma membrane, this will induce the
completion of the meiotic division of the secondary oocyte (Q). [1]
The second meiotic division in Q being unequal will result in the formation of a second
polar body and a haploid ovum. Then, the haploid nucleus of the sperm ‘A’ and that of the
ovum (Q) will fuse together to form a diploid zygote. [1]
23 The embryo with 8 to 16 blastomeres is called a morula. 3
The morula continues to divide and transforms into blastocyst as it moves further into the
uterus.
The blastomeres in the blastocyst are arranged into an outer layer called trophoblast and
An inner group of cells attached to trophoblast called the inner cell mass.
The trophoblast layer then gets attached to the endometrium and the inner cell mass gets
differentiated as the embryo.
After attachment, the uterine cells divide rapidly and covers the blastocyst.
As a result, the blastocyst becomes embedded in the endometrium of the uterus. This is
called implantation and it leads to pregnancy. [0.5X6=3]
2
