Class 12 Pre-Board Sample Paper 2025 Biology

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Pre-Board Exam 2025 Sample Question Paper

BIOLOGY (SUBJECT CODE -044)
Maximum Marks: 70 Time: 3 hours
Class XII
General Instructions:
(i) All questions are compulsory.
(ii) The question paper has five sections and 33 questions. All questions are compulsory.
(iii) Section–A has 16 questions of 1 mark each;
Section–B has 5 questions of 2 marks each;
Section–C has 7 questions of 3 marks each; Section– D has 2 case-based questions of 4 marks each;
and Section–E has 3 questions of 5 marks each.
(iv) There is no overall choice. However, internal choices have been provided in some questions. A
student has to attempt only one of the alternatives in such questions.
(v) Wherever necessary, neat and properly labeled diagrams should be drawn.

Q.N SECTION A MARK
o S

1. 10 Oogonia yield 10 primary oocytes, then how many ova are produced on completion 1
of Oogenesis?
(a) 5 (b) 10
(c) 20 (d) 40

2. How many nucleosomes are present in a DNA having 125800 bp 1
(a)12580 (b)1258
(c) 629 (d)6290

3. Control of gene expression in prokaryotes take place at the level of 1
(a) DNA replication (b)Transcription
© Translation (d)None of the above

4. Which of the following correctly represents the manner of replication of DNA 1

(a) (b) (c) (d)

5. An interesting modification of flower shape for insect pollination occurs in some 1
orchids in which a male insect mistakes the pattern on the orchid flower for the female
species and tries to copulate with it, thereby pollinating the flower. This phenomenon is
called
(a) pseudo pollination (b) pseudo parthenocarpy

(c) mimicry (d) pseudo copulation.

6. A Polypeptide chain consist of sequence of 1500 amino acids .Can you guess how 1
many nucleotide bases must there be present in the processed mRNA of an eukaryotic
cell to message for it .
(a)500 (b)1500
© 4500 (d)None of the above
7. Which one of the following ancestors of Man used hides to protect their body and 1
buried their dead?
(a) Neanderthal Man (b) Homo habilis
(c) .Homo erectus (d) .Ramapithecus

8. If the maternal grandfather of a boy is haemophilic, maternal grandmother is normal 1
and father is normal then what are the chances that this boy could have haemophilia
disease?
(a) 25 % (b) 50%
(c) 75% (d) 0%

9. Match the items in column ‘A’ and Column ‘B’ and choose the correct answer. 1
COLUMN A COLUMN B
A Lady bird i) Methanobacterium
B Mycorrhiza ii) Trichoderma
C Biological control iii) Aphids
D Bio gas iv) Glomus
(a) A-(ii), B-(iv), C-(iii), D-(i)
(b) A-(iii), B-(iv), C-(ii), D-(i)
(c) A-(iv), B-(i), C-(ii), D-(iii)
(d) A-(iii), B-(ii), C-(i), D-(iv)

10. While isolating DNA from bacteria , which of the following enzymes are not required? 1
(a) Lysozyme (b)Ribonuclease
( c ) Protease (d)Deoxyribonuclease
11. Which of the following statements does not hold true for restriction enzymes? 1
(a) It recognizes a palindromic sequence
(b) Its an endonuclease
(c ) Its isolated from bacteria
( d) It can produce the different kind of sticky ends in different DNA molecules.

12. Which of the following structures are haploid in nature? 1
(a) Nucellus and Antipodals
(b) MMC and Antipodals

(c) Egg cell and Antipodals
(d) Micropore and Central cell

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 (A) : Genetic Drift refers to changesin allele frequency. 1
Reason (R) : Heritable variations enable survival of the fittest.

14. Assertion (A) : Second infection of the same pathogen is quickly eliminated. 1
Reason (R) : Pre -formed memory B and T cells elicit a quick and vigorous attack on
pathogen.

15. Assertion (A) : “Saheli” is an oral contraceptive pill for females containing nonsteroidal 1
preparation.
Reason (R) : It is “once in a week” pill with high contraceptive value and side effects.

16. Assertion (A) : Human Insulin is produced in E. coli. 1
Reason (R) : In mammals , insulin is synthesized as a pro- hormone which contains an
extra non- protein part.

SECTION B

17. Explain with the help of an example the relationship between restriction Endonuclease 2
and a Pallindromic nucleotide sequence.

18. (A) Mention the type of evolution that has brought the similarity as seen in potato tuber 2
and sweet potato.
(B) According to Hardy Weinberg’s principle the allele frequency of a population
remains constant. How do you interpret the change of frequency of alleles in a
population?

19 Given below is an enlarged view of one microsporangium of a mature anther. 2
(i) Identify and name R, S &T wall layers.
(ii) Mention the characterstics and function of the cell forming wall layer “T”

20 Write the source and the effect on the human body of the following Drugs. 2
a) Morphine
b) Cocaine

21. What is meant by “alien species” invasion? Name one plant and one animal alien 2
species that are a threat to our Indian native species.

SECTION C

22. A schematic representation of Polymerase chain reaction (PCR) is given below. Answer 3
the questions that follows:

a) Name the process ‘a’ and identify ‘b’.
b) Identify ‘c’ and mention its importance in PCR.
c) For what purpose PCR technique is used?

23. (a) Mention any 2 problems that are taken care of by Reproduction and Child Health 3
Care programme.
(b) What is amniocentesis and why there is a statutory ban on it?

24. Trace the development of a megaspore to the formation of mature embryo sac in a 3
flowering plant with the help of labeled diagram.

25. Name a disorder and give its karyotype and write the symptoms which a human male 3
suffer as a result of an additional X chromosome.

26. A)Draw the structure of t-RNA having anticodon UAC. 3
B) How is degeneracy different from unambiguous characterstic of codon.

27. Study the age pyramids A, B & C of the Human population given below and answer 3
the question that follows.

i) Identify the population pyramid which is more appropriate and name it .
ii) What would be the growth rate pattern when the resources are unlimited?
iii) What is unique about population pyramid “C” ?

28. Given below is a figure of a biogas plant 3

i) Name the group of organisms and the substrate they act on to produce
biogas.
ii) Identify the products A ,B,D, E and discuss their significance.
OR
Explain how do Flocs& activated sludge help in sewage treatment .

SECTION D CASE BASED QUESTION)

29. Study the figure given below of a biomolecule 4

i) What does the above diagram depicts ?
ii) Identify the strand “A” mentioned in the above figure.
iii) Write the main steps involved for the formation of mature insulin with the
help of Genetic Engineering.

30. Study the graph given below and answer the questions that follows . 4

i) Name the naturalist who studied the kind of relationship shown in the graph
.write the observation made by him.
ii) When would the slope of the line “b’ become stepper?
iii) Write the situations as discovered by ecologists when the value of “Z” lies
between
0.1 and 0.2

SECTION E

31. The following is the illustration of the sequence of ovarian events 1 TO 13 in human 5
female:

a) Identify the figure that illustrates corpus luteum and name the pituitary hormone
that influences its formation.
b) Specify the endocrine function of corpus luteum. Why is it essential?
c) Draw a neat sketch of ovum with following labels: zonapellucida, corona radiata
and perivitelline space
OR
a) Write the type of and location of the genes causing thalassemia in human.
b) State the cause and symptoms of the disease.
c) Why are colour blindness and thalassemia categorized as Mendelian disorders?
d) About 8% of human male population suffers from colour blindness whereas only
about 0.4% of human female population suffers from this disease. Write an explanation
to show how it is possible

32. Answer the following questions based on Meselson and Stahl’s experiment: 5
(i) Write the name of the chemical substance used as source of nitrogen in the
experiment by them.
(ii) Why did the scientists synthesize the light and the heavy DNA molecules in the
organism used in the experiment?
(iii) How did the scientists make it possible to distinguish the heavy DNA molecule
from the light DNA molecule? Explain.
(iv) Write the conclusion the scientists arrived at, after completing the experiment.
OR
Study the diagram showing replication of HIV in Humans and answer the questions that

follows

i) What type of viruses causes AIDS? Name its Genetic Material. Or the group
name of such viruses which possesses this type of genetic material.
ii) Does this virus follows central dogma or it deviates from it ?
iii) Name the enzyme “B” acting on “X” to produce molecule “C”.
iv) What does NACO means and write its role in preventing AIDS?
v) What do you mean by the statement that “ Incubation period for AIDS may
vary from one month to ten years”.

33. a) IVF is becoming more popular in current scenario that is helping childless couples to 5
bear a child. Describe the different steps that are carried out in this technique.
b) Would you consider Gamete Intrafallopian Transfer (GIFT) as an IVF ? Give reason
to support your answer.
OR

x------x

SUBJECT: BIOLOGY THEORY (044)
MARKING SCHEME
Q. NO. MM

SECTION A
1. b 1

2. c 1

3. b 1

4. d 1

5. d 1

6. c 1

7. a 1

8. b 1

9. b 1

10. d 1

11. d 1

12. c 1

13. b 1

14. a 1

15. c 1

16. c 1

SECTION B 2

17. Restriction endonucleases recognizes a specific palindromic sequence in DNA& it cut 1
the DNA a little away from the centre of palindromic nucleotide sequence but between
the same two bases on the opposite strand making an overhang or called sticky ends .

(1/2

+1/2)

18 A) The potato tuber and sweet potato are analogous hence show convergent 1+
evolution.
B) Natural selection, genetic drift, and gene flow , migration are the mechanisms
that cause changes in allele frequencies over time. When one or more of these
forces are acting in a population, the population violates the Hardy-Weinberg
principle, and evolution occurs.

19 i) R =Middle layer (½+1/2
S = Microspore mothers cell +1/2+1/2)
T= Tapetum
ii) “ T” wall layer help in providing nutrition to microspore and synthesis of
sporopollenin in exine

20. a) It is obtained from Poppy plant Papaversomniferum . it binds to specific opiod (½+ ½)
receptors present in central nervous system and Gastrointestional tract.
(Any other correct point ) (1/2
b) Its obtained from coca plant Erythroxylum coca .
it interferes with the transport of the Neurotransmitter dopamine. + ½)
(Any other correct point )

21. alien species invasion means when some alien species introduced unintentionally or 1
deliberately, becomes invasive and cause harmful impact resulting in extinction of
indigenous species (1/2
Example PLANT; Parthenium, Lantana (any one)
Animal; Clariasgariepinus (African Catfish)/ Nile Perch (any one) +1/2)
SECTION C 3
22. a) Denaturation , primer ½+1/2
b) Taq polymerase it is thermo table polymerase 1+
c) To make many copies of (amplify) small sections of DNA or a gene OR 1
Amplifying DNA content
23. a) To improve the health of women and children to guarantee safe maternity and child 1
survival and reproductive health.
b) Amniocentesis is a test on the foetus carried out during pregnancy to check for and 1+1
to detect chromosomal abnormalities and other defects or disorders in the foetus.

Amniocentesis can lead to female foeticide as it detects the sex of the foetus which
decreases the gender ratio. So, it has a statutory ban to avoid female foeticide.

24.

1+
1+
1

Consider main 3 diagram step for evaluation
25. Klinefelter’s syndrome 1+1+1
Correct definition and symptoms

26. Diagram 1
+
The genetic code is unambiguous because each triplet specifies only a single amino 1
acid. +
1
Degeneracy means the coding of a particular amino acid by more than one codon. Since
numerous distinct codons define the same amino acid, the genetic code degenerates.
27. i) B stable population pyramid. ½ +1/2
ii) Exponential growth rate 1
iii)Its Declining pyramid and indicating population is in regression 1

28 i) Methanogens acts on cellulosic materials and agricultural waste. 1
ii) A =the biomass is mixed with water and ½+1/2
D= then is decomposed by the anaerobic bacteria
½+1/2
E=into the products like gasses (methane, hydrogen, carbon dioxide) and

B= the other side products (manure, fertilizers)
or
Correct explanation

SECTION D (CASE BASED QUESTIONS) 4
29. I) Its showing Proinsulin is the prohormone precursor to insulin and how cleavage of ½
polypeptide chain is creating functional insulin.
ii) c peptide chain ½
iii) The recombinant human insulin can be produced by following steps:
1. The human insulin is extracted from pancreatic cells of humans and two genes are ½
extracted that are responsible for insulin chain A and chain B production.
2. In the second step we extract a plasmid DNA from a bacteria and form a plasmid ½
vector.
3. Then insert the human insulin chain A and B producing genes into this plasmid vector.
This results in the formation of recombinants DNA. ½
4. The next step is introduction of recombinant DNA again into the bacterial cell. This
results in the formation of the recombinant bacterium. ½
5. Then put the recombinant bacteria into the large fermentation tank where it
multiplies. Each bacteria will produce human insulin chain A and chain B. ½
6. These A and B insulin chains are then extracted, purified and combined by creating
disulfide bonds to form human insulin. ½
30. i) Alexander Von Humbolt (1+1)+
He observed that within a region , species richness increased with increasing explored 1+1
area.
ii)If species richness is more
iii)The slope regression lines are similar indicating unaffected distribution in an area is
analysed.
SECTION E 5

31.
a) 9, LH 1
b) Corpus luteum is the structure which is formed by the follicles after the egg is
released from the Graafian follicle. This is a yellow coloured structure which is
2
present in the ovary. The corpus luteum is the structure which is responsible for
the release of the hormone progesterone. This is known as the pregnancy
hormone which causes changes in the ovary and increasing the cell lining in the
uterus. The hormone helps in maintaining pregnancy. 2
c) LABELLED DIAGRAM

OR
a) Autosomal recessive gene. gene for alpha thalassemia is on chromosome 16 and for
Beta thalassemia it is on chromosome 11. 1
b) Cause and symptoms-Mutation or deletion of the gene / genes resulting in reduced

rate of synthesis of one of the globin chains / alpha or beta chains. 1
c) Colour blindness and thalassaemia are categoried as Mendelian disorders because
they are caused by mutation in a single gene. Their mode of inheritance follows the 1
principles of Mendelian genetics.

d) Colour blindness is a X-linked recessive disorder. Males have higher chances of
getting affected in comparison to females because males have only one X with Y
chromosome while females have two X chromosomes (XX). Thus, for a female to get 2
affected by colour blindness, she has to have the mutant gene on both the X
chromosomes while males can be affected if they carry it on the single X chromosome
32. I) Retrovirus , RNA ½
II) No , this virus deviates from central Dogma as it shows reverse transcription. ½
iii) B = Reverse Transcriptase ; C= DNA ½
iv) NACO is the National Aids Control Organization. It is a government ½
organization of India, set up to monitor HIV+ individuals' healthcare ½+1/2
coverage and to safeguard and uphold their human rights.aims at halting
1
and reversing HIV epidemic in India.
v) It depends on immunity and life style of an individual too. 1

33. a) Assisted Reproductive Technology (ART) ½
In Vitro Fertilization (IVF)
GIFT. ½
ZIFT. ½
Intracytoplasmic sperm injection (ICSI) ½
Intrauterine Insemination (IUI) ½
½

b) NO, GIFT cannot be considered as an IVF Technique because in this method 1+1
fertilization takes place in the female body.

OR

A) Any two point of differences for each (1+1)
B)
(i) A is female Anopheles mosquito, this mosquito acts as a vector and transmits the 1
disease from patients to healthy individuals.
(ii) Fertilisation The event C occurs in the intestinal wall of mosquito and is called as (½ + ½)
fertilisation. 1
(iii) B is the salivary glands from where sporozoites of Plasmodium are released.
=5

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