Pre-Board Examination

Academic Year 2024 – 25

Class: XII Max. Marks: 70
Subject: BIOLOGY Duration: 3 hrs
Date: 06-12-2024 Day: Friday

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 A. Chromosome 21 and Y
B. Chromosome 1 and X
C. Chromosome 1 and Y
D. Chromosome X and Y
5 Gregor Mendel, conducted hybridisation experiments on garden peas. Consider a 1
test cross between two garden pea plants, one with green seeds and the other
plant having an unknown seed type. 50% of the offsprings in F1 generation have
yellow seeds and 50% have green seeds.
Which of the following statements is/are TRUE about the cross?
A. The unknown seed is homozygous for yellow seeds.
B. The unknown seed is heterozygous for yellow seeds.
C. The unknown seed is homozygous for green seeds.

D. The unknown seed is heterozygous for green seeds.

6 Identify the mistake in the illustration 1
depicting the formation of poly peptide of
beta chain of haemoglobin given below.

A. In the first position it should be Glutamine

(Glu) instead of Valine (Val)
B. GAG codes for Glutamine (Glu) and not
Valine (Val)
C. The codon in the mRNA should be GCG
instead of GAG.
D. In the first position it should be Leucine
(Leu) instead of Valine (Val)
7 Occasionally, a single gene product may produce more than one effect. A single 1
gene controls the size of starch grain and seed shape in pea plants.
BB (round seeds with big starch grains) and bb (wrinkled seeds with small starch
grains).

What is the phenotype of a plant with genotype Bb?

A. round seeds with intermediate starch grains
B. round seeds with big starch grains
C. round seeds with small starch grains
D. wrinkled seeds with intermediate starch grains
8 Which one of the images of the replicating fork given below represent the process 1
correctly?

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 A. Figure 1
B. Figure 2
C. Figure 3
D. Figure 4
9 Which of the following organic acids is produced by fermentation activity of 1
Aspergillus niger?
A. Acetic acid
B. Butyric acid
C. Citric acid
D. Pyruvic acid
10 Darwin judged the fitness of individuals by 1
A. ability to defend itself
B. strategy to obtain food
C. number of offsprings produced
D. dominance over other individuals
11 Raghav listed his observations while performing Recombinant DNA technology, 1
ligating a foreign DNA at the BamH I site of tetracycline resistance gene in the
vector pBR322.
Identify the correct observation listed by Raghav.

A. The recombinant plasmids lose ampicillin resistance

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 B. The recombinants will grow in ampicillin containing medium but not on that
containing tetracycline.
C. The transformants will grow in tetracycline containing medium but not on that
containing ampicillin.
D. The transformants lose ampicillin resistance

12 BOD of waste water is estimated by measuring the amount of 1

A. total organic matter
B. biodegradable organic matter
C. oxygen evolution
D. oxygen consumption

Question No. 13 to 16 consist of two statements – Assertion (A) and Reason (R).
Answer these questions selecting the appropriate option given below:
A. Both A and R are true and R is the correct explanation of A.
B. Both A and R are true and R is not the correct explanation of A.
C. A is true but R is false.
D. A is False but R is true
13 Assertion: Apomictic embryos are genetically identical to the parent plant. 1
Reason: Apomixis is the production of seeds without fertilization.
14 Assertion : Hershey and Chase grew some viruses on a medium that contained 1
radioactive phosphorus and some others on medium that contained radioactive
sulphur.
Reason : The bacteriophage attaches to the bacteria and its genetic material then
enters the bacterial cell.
15 Assertion: A high BOD indicates the presence of large number decomposer 1
microbes in the water body.
Reason: BOD is the measure of oxygen utilized by the microbes to decompose the
organic matter wastes in the water body
16 Assertion : Restriction endonucleases cut the strand of DNA a little away from the 1
centre of the palindrome sites, but between the same two bases on the opposite
strands.
Reason: Overhanging stretches called sticky ends are formed which facilitates the
action of the enzyme DNA ligase.
SECTION B
17 Attempt either option A or B. 2
A i) How is primary spermatocyte different from a secondary spermatocyte?

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 ii) Write the effect of high concentration of LH on mature Graafian follicle
OR
B i) State the role of Oxytocin in parturition? Name the gland which releases
Oxytocin.
ii) Placenta acts as an endocrine tissue. Justify

18 Attempt either option A or B. 2

A. Alec Jeffreys developed a technique that has immense applications in the field
of forensic science. Identify the technique and name the type of satellite DNA,
which he used as a probe in this technique.
OR
B. Identify the sex of organism as male or female in which the sex chromosome are
found as :

i. ZW in bird
ii. XY in Drosophila
iii. ZZ in birds
iv. XO in grasshopper.

19 A time bond vaccination is followed for the children in our country from their birth 2
up to ten years of age. A graph plotted below shows the effect of the vaccination
by infection by the same pathogen, and the antibody concentration in the blood of
the child.

A) Explain why the administration of the vaccine causes an increase in the antibody
concentration
B) If the child is infected with same pathogen almost four months later, the
antibody concentration in his/her blood increases very fast. Explain why?

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20 Amplification of gene of interest is done using PCR. Highlight the role of any two of 2
the following in the process and mention the step in which they are involved.

a. Primers
b. deoxynucleotides
c. Taq polymerase
21 Attempt either option A or B.
2
Use the information in the
table given below to answer
the following questions :

A. i) Calculate the gross

primary productivity.
ii) Analyse the trend in the
Net Production from
Producers to Top
Carnivore.Give a reason for
your observation.
OR
B. i) Pyramids of Biomass of two
types are shown in the diagram
given above. Answer the
following questions.
(a) Identify the type of
ecosystems in which the
pyramid of biomass A and B
occur, respectively.
(b) Why is the pyramid A
inverted and B upright?
ii) Differentiate between humification and mineralization
SECTION C
22 List three strategies that a bisexual chasmogamous flower can evolve to prevent 3
self-pollination (autogamy).
23 Explain the events in a normal woman during her menstrual cycle on the 3
following days:
a) Ovarian events from 13-15 days
b) Ovarian hormones level from 16-23 days
c) Uterine events from 24-29 days (if fertilization has not occurred)

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24 Study the representation of the Central Dogma of 3
Molecular Biology given below.

a. Identify the process S.

b. Schematically represent the steps involved in
the process Q in Eukaryotes which is not
found in prokaryotes.

25 In prokaryotes, control of the rate of transcriptional initiation is the predominant 3

site for control of gene expression. In a transcription unit, the activity of RNA
polymerase at a given promoter is in turn regulated by interaction with accessory
proteins, which affect its ability to recognise start sites.

a. The given diagram illustrates lac operon in the presence of inducer. Identify the
error in this diagram, which can be rectified using one of the options given
below.
(i) The repressor should be marked as active.
(ii) The gene ‘a’ codes for transacetylase and ‘y’ codes for permease.
(iii) The operator should be blocked by repressor.
(iv) The gene ‘z’ codes for permease and ‘a’ codes for beta galactosidase.
b. Explain the regulation of lac operon in the absence of inducer.
26 What are methanogens? Name the animals they are present in and the role they 3
play.
27 The cutting of DNA by restriction endonucleases results in the fragments of DNA. 3
These fragments can be separated by a technique known as gel electrophoresis.
Highlight the role of Agarose gel and Ethidium bromide in this technique.
28 A. Identify the Interspecific interactions in the pictures A, B, C, D given below. 3

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A.

B.

B. In a pond there are 100 frogs.20 more were born in a year. Calculate the birth
rate of this population. How will you measure the population density of fish in a
lake?

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 SECTION D
29 Read the following passage and answer the questions that follow: 4
According to Hardy-Weinberg principle, the allele frequencies in a population are
stable and remain constrict through generations. When the frequency differs from
the expected values, the difference indicates the extent(direction)of evolutionary
change. Disturbance in the genetic equilibrium or Hardy-Weinberg in a population
can be interpreted as resulting in evolution.
A) Write the algebraic equation that represents the Hardy-Weinberg equilibrium.
B) What does the disturbance in the genetic equilibrium of a population indicate?
Attempt either subpart C or D
C) Natural selection is one of the factors that disturbs genetic equilibrium. Identify
and describe the types of natural selection operating in A and B in the figure given
below
OR
D) Explain the type of natural selection that was obvious in the increase/evolution
of melanic form of moths in England post-industrial revolution.

30 The diagram shows the life cycle of a pathogenic protozoan 4

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 A) Name the parasitic stage that is being transferred from host X to host Y
B) Write the changes the parasite undergoes when it enters in the liver and RBC
Attempt either subpart C or D
C) Trace the changes the parasite undergoes when the host X takes its blood meal
from infected host Y
OR
D)At what stage during the life cycle of the pathogen does the host Y experience
the symptoms of the disease? Name the toxic substance responsible for these
symptoms
SECTION E
31 Attempt either option A or B. 5
A.
The following is the illustration of the sequence of ovarian events ‘a’ to ‘i’ in a
human female:

a) Identify the figure that illustrates corpus luteum and name the hormone that
influences its formation.
b) Specify the endocrine function of corpus luteum. How does it influence the
uterus? why is it essential?
c)What is the difference between “d” and “e”
d)Draw a neat, labelled sketch of Graafian follicle.

OR
B.
The given diagram shows Fertilized embryo sac of a
plant with diploid number 24.

a. Name and write the chromosome number of the

parts labeled 2 and 5.
b. Identify and name the triploid tissue in this
diagram.
c. Explain double fertilization in angiosperms.

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32 Attempt either option A or B. 5
A.
The main challenge for production of insulin using rDNA techniques was getting
insulin assembled into a mature form. Comment on this statement. Mention the
role of Eli Lilly an American company in overcoming this challenge.
OR
B.
Correction of a genetic defect involves delivery of a normal gene into the
individual or embryo to take over the function of and compensate for the non-
functional gene. Explain with an example.

33 Attempt either option A or B. 5

A.
There are many animals which have become extinct in the wild but continue to be
maintained in zoological parks.
(i) What type of biodiversity conservation is observed in this case?
(ii) Name and explain any two causes that are responsible for the loss of
biodiversity
(iii) Explain any other two ways which help in this type of conservation.
OR
B.
(i) Compare narrowly utilitarian and broadly utilitarian approaches to conserve
biodiversity, with the help of suitable examples
(ii) Enlist criteria that are used to identify a region for maximum protection as
Biodiversity hot spot
(iii)Explain the concept of endemism.

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