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Directional Academy
1
Class 12 Biology Solved Paper
Time: 3 Hours
Total Marks: 70
General Instructions:
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1
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2
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Section A contains 5
questions of one mark each, Section B is of 5 questions of two marks each, Section C
is of 12 questions of three marks each, Section D is of 1 question of four marks and
Section E is of 3 questions of five marks each
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There is no overall choice
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A student has to attempt only one of the alternatives in such questions
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Wherever necessary, the diagrams drawn should be neat and properly labelled
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What is the main function of gel electrophoresis?
[1]
3
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Name two lymphoid organs
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Why is Gambusia introduced into drains and ponds?
[1]
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1
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In a cross between a black and a white guinea pig, all F1 members are black
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[2]
(a) What are the possible genotypes at each level?
(b) What will the offspring be like if two F2 whites are mated?
8
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If tall and red flower (heterozygous) for both
characters is crossed with dwarf and white flower, then what will be the
probability of the offspring?
[2]
9
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[2]
Mention any two symptoms of AIDS
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Name two commonly used bioreactors
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[2]
Section C
11
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What is ovulation? What happens to the Graafian follicles after ovulation?
[3]
13
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On selfing, these plants produced
470 plants with purple flowers and 162 with white flowers
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What acts as an inducer in lac operon? How does it switch on the operon?
15
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[3]
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(a) Is this representation indicating a normal human or a sufferer from a certain
related genetic disease? Give reason in support of your answer
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Name the pathogen, vector and symptoms of the disease Elephantiasis (Filariasis)
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(a) Explain how to overcome inbreeding depression in cattle
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(c) Name an improved breed of cattle
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How are red algae more successful to live in deep water?
[3]
20
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Do eukaryotic cells have restriction endonucleases? Justify you answer
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What are the effects of noise pollution?
[3]
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22
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Give an example of the first
successful attempt made towards correction of such diseases
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Anand, a 14-year-old boy, thinks smoking makes him more energetic and feels like
an adult and thus a more responsible citizen
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As a friend, you have to educate him on
[4]
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(a) Why he feels more energetic while smoking
(b) The effects of CO in smoke
(c) Other ill effects on the body
(d) What values are reflected here?
Section E
24
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S
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[5]
OR
What are the major functions of male accessory ducts and glands?
25
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[5]
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Write the full names of the different types of RNA
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26
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Explain the simplified model of the
carbon cycle in nature
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Ans
Banana is an underground modified stem (rhizome)
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It is recognised by its well-marked nodes and internodes
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2
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3
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It
is self-replicating and carries the genes for sex factor or fertility factor
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Ans
Spleen and tonsils
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So, it is introduced into drains
and ponds
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Ans
Syngamy is the fusion of male and female gametes
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The term syngamy means ‘fusion of gametes’ and describes the event which occurs
when two gametes of opposite sexes come close to each other and fuse
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The genotype at the F2
level will be BB, Bb, Bb, bb
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8
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Tall and Red × Dwarf and White
Genes
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TR, Tr, tR, tr × tr
These gametes fuse as follows:
Tr
Ttrr
(Tall plant
with white
flowers)
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tr
TR
TtRr
(Tall plant with
red flowers)
tR
ttRr
(Dwarf plant
with red
flowers)
tr
Ttrr
(Dwarf plant
with white
flowers)
Result: 1:1:1:1
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It generates heat which
results in fever
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OR
Symptoms of AIDS:
(i) Swollen lymph nodes and fever
(ii) Sweating at night and weight loss
10
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The importance of using bioreactors is
(i) It provides large volume for cultures
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(ii) It also provides the optimal conditions for achieving the growth of the desired
product such as temperature, pH, vitamins and oxygen
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Ans
Significance of parthenogenesis:
(i) It helps in determining the sex of an animal as in honey bee
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(iii) It rapidly increases the number of animals in a population
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Ans
Ovulation: It is the process of release of the mature ovum from the ovary in the
abdominal cavity
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The corpus luteum secretes progesterone
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If there is no fertilisation, then the corpus
luteum undergoes degeneration and progesterone secretion declines leading to a
fresh start of the menstruation cycle
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Ans
In the F1 generation, only plants producing purple flowers appeared
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In
the F2 generation, purple and white-coloured flowers were produced in the ratio of
3:1
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This occurs because of the segregation of genes during gamete formation
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14
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The inducer lactose binds to the
repressor and forms a complex which remains unable to bind to the operator
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This initiates the transcription of the structural genes,
producing the three polypeptides (enzymes)
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15
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(b) In a person who exhibits sickle cell trait, the defect is caused by the substitution
of glutamic acid (Glu) by valine (Val) at the sixth position of the β-chain of
haemoglobin
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It is an autosomal disease and sickle-shaped RBCs will cause
equal deficiency of oxygen in both males and females
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Ans
Pathogen: Filarial worm (Wuchereria bancrofti)
Vector: Culex sp
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(ii) Pathogen blocks the lymphatic system and lymph accumulates in other parts of
the body, resulting in enlargement of these parts of the body
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It is a strong analgesic and has a
sedative and calming effect
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(ii) Cocaine: It is obtained from the coca plant (Erythroxylum coca)
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It has a potent
stimulating action on CNS, producing a sense of euphoria and increased energy
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(iii) Marijuana: It is obtained from the direct inflorescence and the top leaves of the
female plant of Cannabis sativa
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It lowers the levels of sex hormones, suppresses the immune
system and may cause psychosis
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Ans
(a) The selected animals of the breeding population should be mated with superior
animals of the same breed but unrelated to the breeding population
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(b) Advantages of inbreeding:
(i) It helps in the accumulation of superior genes and the elimination of
undesirable genes
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(iii) It exposes harmful recessive genes for undesirable characters which are
eliminated by selection
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18
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All the
restriction endonucleases have been isolated from the various strains of bacteria,
and they are also named according to the genus and species of prokaryotes
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For example,
motility of sperms after ejaculation and flavin gives semen a strong fluorescence
in ultraviolet light
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(ii) Prostate gland: It is the largest auxiliary gland with a chestnut-like shape
situated around the 1st part of the urethra below the urinary bladder
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It secretes milky, thin and alkaline
fluid containing citric acid, bicarbonate ions, lipids and acid phosphatase which
gives characteristic seminal order and alkalinity to the ejaculate
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It constitutes
approximately 5–30% of the ejaculate
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They are about the size of a pea and form the floor of the pelvis
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In prokaryotic
cells, there is a single origin of replication, whereas in eukaryotic cells, there are
numerous origins which merge during replication
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Unwinding of DNA leads to the formation of a Y-shaped structure of the two
strands of the DNA duplex
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(iii) Synthesis of primer: It is a stretch of RNA formed on the DNA where synthesis
of new DNA starts
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New strands grow from the fork,
and as replication proceeds, it appears as if the point of divergence at the fork is
moving
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This process occurs in the presence of DNA polymerase and ATP
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(v) Formation of lagging (discontinuous) stand: In the second parental strand, the
enzyme primase forms the RNA primer
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These short DNA segments, consisting of
numerous nucleotides, are called Okazaki fragments
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This newly synthesised second
DNA strand is called the lagging strand because it is formed later on in reference
to the first continuous strand
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t-RNA has a cloverleaf
structure in two dimensions:
(i) r-RNA: It forms approximately 80% of the total cellular RNA and is a component
of the ribosomes
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Role: It serves to release mRNA from DNA
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(ii) mRNA: It is formed by the DNA template in the nucleus and moves to the
cytoplasm within two subunits of ribosomes
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It forms 5–10% of the total RNA
in a cell
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It has a cap structure as 5′ end and poly A tail at the 3′ end
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(iii) t-RNA: It is the smallest of all the RNA with molecular weight ranging from 25 to
30 thousand Daltons
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Role: It picks up activated amino acid from the cytoplasm and supplies it to
mRNA in the ribosome according to the message expressed by the codon
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Carbon cycle in nature:
(i) The main source of carbon in the Universe is CO2 which is dissolved in water and
present in air (0
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04%)
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These organic compounds are transferred to
animals as their food
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(iv) The organic compounds of plants and animals are buried in the deep soil where
they are acted by decomposers to change them in petroleum, coal, oil and
carbonate rocks
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(v) Some carbon dioxide is found in dissolved state in water
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Weathering and combustion of carbonatecontaining rocks or treatment of their minerals give CO2
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(a) Commensalism: It is an interspecific interaction between individuals of two
species where one species is benefited and other is not affected
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Example: Malarial parasite and human beings
(c) Camouflage: It is the ability of animals to blend with the surroundings or
background, and thus, they remain unnoticed for protection or aggression
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Example:
Pollination in plants by animals
(e) Interspecific competition: It is an interspecific interaction between individuals of
two species where both interacting species are affected