Class 12 Question Paper 2023-24 Biology (Half Yearly)

2023-24
HALF YEARLY
EXAM
NCERT BASED
SYLLABUS
DOWNLOAD PDF

FOR
CBSE BOARD
AND
STATE BOARDS

HALF YEARLY EXAMINATION, 2023-24
SUBJECT – BIOLOGY
CLASS - XII
TIME : 3 hrs MM : 70
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 questions of 2 marks each; section-C
has 7 questions of 3marks 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 alternative in such questions.
v. Wherever necessary, neat and properly labeled diagrams should be drawn .

Section -A
1. Remnants of nucleus are persistent during Seed development in:
a) Black pepper
b) Wheat
c) Pea
d) Groundnut
2. In a fertilised embryo sac , the haploid, diploid and triploid structures are
a) Synergid, zygote and primary endosperm nucleus
b) Synergid , antipodal and polar nuclei.
c) Antipodal, synergid and primary endosperm nucleus.
d) Synergid, polar nuclei and zygote .
3. At a particular locus ,the frequency of allele A is 0.8 and that of allele a is 0.2 . What
would be the frequency of heterozygous in a random mating population at equilibrium?
a) 0.32
b) O.48
c) 0.16
d) O.24
4. The average Guanine content in yeast is found to be 18%.
Which of the following represents the nitrogeneous base content percentages correctly
from the above data?
a) A:18%; T: 18%; C : 36%
b) A:36%; T: 32%; C : 32%
c) A:32%; T: 32%; C : 18%
d) A:18%; T: 18%; C : 18%
5. In a certain taxon of insects some have 17 chromosomes and the other have 18
chromosomes. The 17 and 18 chromosome bearing organisms are
a) Males and females respectively
b) Females and males respectively

c) All males
d) All females
6. All genes located on the same chromosome
a) Form different groups depending upon their relative distance
b) Form one linkage group
c) Will not form any linkage groups
d) Form interactive group that affect the phenotype
7. How many types of gametes would be produced if the genotype of a parent is AaBB?
a) 1
b) 2
c) 3
d) 4
8. Study the pedigree given below and select the probable mode of inheritance and a
human trait that follows this pattern of inheritance.

a) Autosomal recessive, sickle cell anaemia
b) Sex linked recessive, haemophilia
c) Autosomal dominant, myotonic dystrophy
d) Sex linked dominant, colour blindness
9. Shown here is how the levels of hormones estrogen and progesterone change during
the menstrual cycle .

Which of these correctly show the levels of lutenising hormone (LH) and follicle
stimulating hormone ( FSH) change during the same cycle ?

10. Intensely lactating mothers do not generally conceive due to the
a) Suppression of gonadotropins
b) Hypersecretion. Of gonadotropins
c) Suppression of gametic transport
d) Suppression of fertilisation
11. Select the option that gives the correct description of the process of natural selection
with respect to the length of the neck of giraffe.

a) Stabilizing selection as giraffes with loner neck lengths are selected further.
b) Disruptive selection as giraffes with smaller and longer neck lengths are
selected.
c) Directional selection as giraffes with longer neck length are selected

d) Stabilizing selection as giraffes with medium neck lengths are selected .
12. Given below are two columns. In column I the names of four contraceptive devices are
given and in column II the modes of action of the contraceptives are given .select the
option where the contraceptive devices are correctly matched with their respective
modes of action.

Questions 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 : the human genome comprises of a large amount of repetitive sequences.
Reason :The repetitive sequences in the genome do not have direct coding functions.
14. Assertion: Genetic drift refers to change in allele frequency.
Reason : heritable variation enable survival of the fittest .
15. Assertion: The maximum frequency of recombination that results from crossing over of
linked gene is 50 percent.
Reason: if distance between linked genes is longer, they show higher frequency of
crossing over.
16. Assertion: In human beings, ovum is released from the ovary in the ootid stage.
Reason : The secondary oocytes divides into unequal daughter cells , a large ootidand a
small polar body.
Section -B
17. Branching descent and natural selection are the two key concepts of Darwinian theory
of evolution. Explain each concept with the help of a suitable example.
18. Answer the following question:

a) List any two characteristics features of wheat flowers that make it a good
example of wind pollination.
b) It is observed that plant breeders carrying out wheat hybridisation often taken
pollen grains from the ‘pollen banks'. Do you agree? Give one reason in support
of your answer.
19. Answer the following questions
a) Recently a baby girl has been reported to suffer from haemophilia. How is it
possible? Explain with the help of a cross.
b) Sickle cell anaemia in humans is a result of point mutation Explain.
20.
a) Draw a labelled diagram of a replication fork showing continuous and
discontinuous replication of DNA stands.
b) State a reason why is the replication continuous and discontinuous in the
diagram drawn.
21. A pregnant human female was advised to undergo MTP. It was diagnosed that the
foetus she was carrying had developed from a zygote having 45 chromosomes with only
one X chromosome.
a) What is this condition called and how does it arise?
b) Why was she advised to undergo MTP?

SECTION - C

22. Answer the following question:
a) Explain the development of a secondary oocyte (ovum) in human female from
the embryonic stage upto its ovulation.
b) Describe the post zygotic events leading to implantation and placenta formation
in humans. Mention any two functions of placenta.
23. Answer the following question:
a) Describe the endosperm development in coconut.
b) How are pea seeds different from castor seeds with respect to endosperm?
c) Give reason why apple and cashew are not called true fruits.
24. Answer the following question:
a) Describe the mechanism of inheritance of ABO system of blood group,
highlighting the principles of genetics involved in it.
b) In one family, the four children each have a different blood group. Their
mother has blood group A and their father has blood group B. work out a cross
to explain how it is possible.
25. Explain the process of transcription in prokaryotes. How is the process different in
eukaryotes.
26. Answer the following questions:
a) Differentiate between analogous and homologous organ giving one example
each of plant and animal respectively.
b) How they are considered as an evidence in support of evolution?
27. Answer the following questions
a) A true breeding pea plant, homozygous for inflated green pods are

crossed with another pea plant with constricted yellow pods (ffgg).what
would be the phenotypeand genotype of F1 and F2 generations? Give
the phenotype ratio of generation.
b) Explain the chromosomal theory of Inheritance.
28. Why did Hershey and chase use radioactive Sulphur and radioactive
phosphorous in theirexperiment?
SECTION – D
29. A biology student Advik, read an article on apple being a false fruit. He asked his
teacher about how fruit can be called false fruit and was explained about the
development of fruits.
(i) A true fruit is formed from
(a) ovary
(b) ovary and thalamus
(c) ovary and calyx
(d) ovary and receptacle
(ii) Fruit is a
(a) post fertilisation product of pistel
(b) product of flower
(c) body having seeds
(d) product of ovary
(iii) Parthenocarp is a fruit
(a) formed from superior ovary
(b) formed from inferior ovary
(c) consisting of ripened ovary and thalamus
(d) which does not possess seeds
(iv) Schizocarpic fruit splits up into
(a) Achenial fruit
(b) Capsular
(c) Schizocarpic
(d) Drupe
30. Darwin found the varieties of finches that in travelled to Galapagos Islands
and observed variations in them.

(i) What role does an individual organism play as per Darwin’s theory
of natural selection?
(ii) How did Darwin explain the existence of different varieties of

finches on Galapagos Islands?
(iii) What is “fitness of an individual” according to Darwin?
SECTION - E
31. Placed below are case studies of some couples who were not able to have kids. These
couples are not ready for adoption or taking gametes from donors. After thoroughly
examining the cases, which Assisted Reproductive Technology will you suggest to these
couples as a medical expert? Explain briefly with justification of each case.

32. Given below is a stretch of DNA showing the coding strand of a structural gene of a
transcription unit? 5’--ATG ACC GTA TTT TCT GTA GTG CCC GTA CTT CAG GCA TAA—3’
a) Write the corresponding template strand and the mRNA strand that will be
transcribed, along with its polarity.
b) If GUA of the transcribed mRNA is an intron, depict the sequence involved in the
formation of mRNA /the mature processed hnRNA strand.
i. In a bacterium
ii. In humans
c) Upon translation, how many amino acids will the resulting polypeptide have? Justify.
33. Study the graph given below and answers the questions that follow:

a) Name the hormone X and Y.
b) Identify the ovarian phases during a menstrual cycle
i. 5th day to 12th day of the cycle
ii. 14th day of the cycle
iii. 16th day to 25th day of the cycle
c) Explain the ovarian event (i). (ii) and (iii) under the influence of hormone X
and Y.