biology (code-a) sample question paper for class xii

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Biology (Code-A) Sample Question Paper for Class XII

Time : 3 Hours Max. Marks : 70

General Instructions :

(i) All questions are compulsory.

(ii) Questions number 1 to 8 are very short answer questions and carry 1 marks each.

(iii) Questions number 9 to 18 are short answer type questions and carry 2 mark each.

(iv) Questions number 19 to 27 are also short answer type questions and carry 3 marks each.

(v) Questions number 28 to 30 are long answer type questions and carry 5 marks each.

(vi) There is no overall choice. However, an internal choice has been provided in one question of 2 marks,

one question of 3 marks and all three questions of 5 marks each. You have to attempt only one of the given

choices in such questions.

(vii) Use log tables if necessary, use of calculator is not allowed.

SAMPLE QUESTION PAPERBiology (Theory) - Class XII (Code-A)

SECTION-A

Very Short Answer Type Questions :

1. Name the anther wall layer which nourishes the developing pollen grains. [1]

2. What is spermiogenesis? [1]

3. What is Punnett square? [1]

4. What do you mean by Adaptive radiation? [1]

5. Name the linkage between nitrogenous base and pentose sugar in a nucleic acid. [1]

6. Name the pathogen which causes amoebiasis (amoebic dysentery). [1]

7. What is meant by flocs? [1]

8. Name an organism that produces Cry proteins. [1]

SECTION-B

Short Answer Type Questions :

9. Draw a labelled diagram of the mature embryo sac. [2]

10. (a) What do you mean by spermiation? [2]

(b) What is the importance of Sertoli cells in the process of spermatogenesis?

11. What are the factors that affect the primary productivity of a natural ecosystem? [2]

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Sample Question Paper for Class XII Biology (Code-A)

12. (a) When did India initiate the family planning programmes? [2]

(b) Do you think that statutory ban on amniocentesis is justified, if so how?

(c) What is the contribution of CDRI, Lucknow in the field of reproductive health?

13. Name the microbes that are the source for bioactive molecule cyclosporin A and statin respectively. [2]

14. (a) What is Lippes loop known for? [2]

(b) What does the term Panspermia stand for?

15. What do you mean by convergent evolution? [2]

OR

Define biofortification. Write the name of wheat variety with high protein content.

16. Why do we consider present day mammals more closely related to present day turtles & lizards? [2]

17. Discuss briefly eutrophication. [2]

18. (a) What are interferons? [2]

(b) What do you mean by passive immunisation?

SECTION-C

Short Answer Type Questions :

19. Explain Chargaff’s rule for a double stranded DNA. [3]

20. What is oogenesis? Give a brief account of oogenesis. [3]

21. What is predation and its role in a biotic community? [3]

22. Expand the following [3]

(a) IVF

(b) ICSI

(c) GIFT

(d) ZIFT

(e) AI

(f) IUI

23. Write briefly about genetic diversity. [3]

24. Draw a well-labelled diagram of an antibody molecule. [3]

25. What is apomixis and its importance? [3]

OR

Write down the chromosomal constitution and one important symptom of following syndromes.

(a) Down’s syndrome

(b) Klinefelter’s syndrome

(c) Turner’s syndrome

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Biology (Code-A) Sample Question Paper for Class XII

26. You overheard your mother telling an expecting mother to avoid breastfeeding the newly born for first two three

days after birth as the yellowish fluid secreted by the mother is a waste fluid and should be discarded. Will

you support your mother’s opinion? [3]

27. Explain PCR with suitable diagram/ [3]

SECTION-D

Long Answer Type Questions :

28. Describe the various methods of outbreeding devices giving suitable examples. [5]

OR

Describe in brief

(a) Co-dominance

(b) Pleiotropy

(c) Sickle cell anaemia

29. Explain the mode of entry of AIDS virus into host cell and its release from it. Support your answer with a

neat and labelled diagram. [5]

OR

(a) What do you mean by metastasis? How is loss of contact inhibition and loss of adhesiveness related to

cancerous cells?

(b) Mention the genes that are associated with development of cancer.

(c) How is cancer detected?

30. Give salient features of Human Genome Project (HGP). [5]

OR

Describe Verhulst- Pearl logistic growth.

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Biology (Code-A) Solutions of Sample Question Paper for Class XII

SECTION-A

1. Tapetum

2. Transformation of spermatids into sperm is called spermiogenesis.

3. Graphical representation to calculate the probability of all possible genotypes of progeny in a genetic cross.

4. Evolution of different species in a given geographical area starting from a point a common ancestor and literally

radiating to other areas of geography (habitats) is called adaptive radiation.

5. N-glycosidic linkage

6. Entamoeba histolytica

7. Flocs : Masses of bacteria associated with fungal filaments to form mesh-like structures in aeration tank during

sewage treatment.

8. Bacillus thuringiensis

SECTION-B

9. Chalazal end

Antipodals

Polar nuclei

Central cell

Egg

Synergids

Micropylar end

Filiform apparatus

10. (a) Spermiation : After spermiogenesis, sperm head become embedded in Sertoli cells and are finally released

from seminiferous tubules by the process called spermiation.

(b) Sertoli cells secrete androgen-binding protein that helps in maintaining high concentration of testosterone in

the seminiferous tubules required for normal spermatogenesis. It also provides nutrition to germ cells.

Biology (Theory) - Class XII (Code-A)

SOLUTIONS

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Solutions of Sample Question Paper for Class XII Biology (Code-A)

11. Factors affecting primary productivity of a natural ecosystem are

(i) Plant species inhabiting the ecosystem

(ii) Variety of environmental factors

(iii) Availability of nutrients

(iv) Photosynthetic capacity of plants.

12. (a) India initiated ‘family planning programmes’ in 1951.

(b) Statutory ban on amniocentesis ; a test based on the study of the chromosomal pattern of the cells present in

the amniotic fluid surrounding the developing embryo, since it is being used by people as a sex-determination

test. The ban on this test is aimed at legally checking the female foeticide.

(c) ‘Saheli’ a non-steroidal oral contraceptive for females was developed by scientists at CDRI, Lucknow.

13. Cyclosporin A – Trichoderma polysporum

Statin – Monascus purpureus

14. (a) Lippes loop is a non-medicated type of IUD.

(b) Panspermia is one of the theory to explain origin of life on earth. It advocates that life on earth and other planets

started from units of life called spores transferred to them from outer space.

15. Evolutionary changes that lead to formation of structures that are different in origin but similar in function in response

to common demands from environment is known as convergent evolution.

OR

Biofortification : Breeding crops with higher levels of vitamins and minerals or higher proteins and healthier fats.

Wheat variety with high protein content is Atlas-66.

16. Present day mammals and turtles and lizards, arose from common ancestors i.e., early extinct reptiles

350 mya, hence, the two are more closely related.

17. Eutrophication : It is natural ageing of lake by biological enrichment of water, nutrients like nitrogen and phosphorus

encourage the growth of aquatic organisms. The dead remains of organisms deposit in lake and over years the lake

becomes shallower and warmer. Overgrowth of algae causes the algal bloom and finally lake is choked to death.

18. (a) Interferons are glycoproteins that are secreted by virus-infected cell in response to viral infection. As they

check viral replication they are said to prevent spread of virus to adjacent cells (non-infected cell). They are a

part of cytokine barrier belonging to innate immunity.

(b) When preformed antibodies are injected into the body of the host to protect the body against foreign agents is

passive immunisation.

SECTION-C

19. Chargaff’s rule

(i) Molar concentration of purines equals pyrimidines.

(ii) A pairs T and G pairs C.

(iii) A+ T/G+C ratio is constant for a species.

(iv) Molar concentration of A equals T and that of G equals C.

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20. The process of formation of mature female gamete is called oogenesis. Oogenesis is initiated during the embryonic

development when a couple of million gamete mother cells (oogonia) are formed within each fetal ovary, no more

oogonia are formed and added after birth. These cells start division and enter into prophase-1 of the meiotic division

and get temporarily arrested at that stage called primary oocyte. Each primary oocyte then gets surrounded by

a layer of granulosa cells and is called the primary follicles. A large no. of these follicles degenerate during the

phase from birth to puberty. Therefore, at puberty only 60,000-80,000 primary follicles are left in each ovary. The

primary follicles get surrounded by more layers of granulose cells and a new theca and are called secondary

follicles. The secondary follicle soon transforms into a tertiary follicle which is characterised by a fluid-filled cavity

called antrum. The theca layer is organised into an inner theca interna and an outer theca externa. At this stage

that the primary oocyte within the tertiary follicle grows in size and completes its first meiotic division and forming

large haploid secondary oocyte and tiny first polar body. The tertiary follicle further changes into the mature follicle

or Graafian follicle. The secondary oocyte forms a new membrane called zona pellucida. The Graafian follicle now

ruptures to release the secondary oocyte from the ovary by the process called ovulation.

21. Interspecifc interaction in which one species is benefited (predator) and the other is harmed (prey).

Role of predator :

(i) Energy transfer to a higher trophic level

(ii) Keeps population of prey under control

(iii) Maintains species diversity in ecosystem

22. (a) IVF – ‘In vitro fertilization’

(b) ICSI – ‘Intra cytoplasmic sperm injection’

(c) GIFT – ‘Gamete intra fallopian transfer’

(d) ZIFT – ‘Zygote intra fallopian transfer’

(e) AI – ‘Artificial insemination’

(f) IUI – ‘Intra uterine insemination’

23. Genetic diversity : A single species may have high diversity at gene level over its distributional range. Higher

is the genetic diversity more is adaptability in wide range of habitat and hence helps in ecotype formation and

speciation.

24.

N N

N

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25. Apomixis : Formation of seeds without fertilisation is called apomixis. It is a form of asexual reproduction that

mimics sexual reproduction. It has its importance in hybrid seed industry because segregation of characters

is avoided in hybrid seeds if developed apomictically.

OR

(a) Chromosome constitution : AA + 1 + XX or AA + 1 + XY

Important symptoms : It is due to trisomy in 21st chromosome, may be male or female, short statured,

small round head, furrowed tongue and partially opened mouth.

(b) Chromosome composition : AA + XXY

Important symptom : Males with gynaecomastia

(c) Chromosome composition : AA + XO

Important symptoms : Sterile females with rudimentary ovaries and lack secondary sexual characters.

26. No, it is wrong to say that yellowish fluid discharged during first 2-3 days of lactation is waste. It is actually

colostrum. It is pale coloured and highly nutritious. It has abundant antibodies (IgA) to develop resistance for

the newborn babies, providing them with passive immunisty. As the immune system of the newly born is not

fully developed therefore these maternal antibodies passing via milk will provide protection against the pathogens.

27. The basic requirements of a PCR reaction are the following :

(i) DNA Template : One or more target DNA molecules to be amplified can be taken as template.

(ii) Primers : These are oligonucleotides, usually 10-18 nucleotides long that hybridize to the target DNA region,

one to each strand of the double helix. Two primers are required and these primers are oriented with their ends

facing each other allowing synthesis of the DNA towards one another.

(iii) Enzyme : DNA polymerase which is stable at high temperature (>90°) is required to the synthesis of new

DNA. The enzyme generally used in PCR reaction is Taq polymerase isolated from bacteria Thermus aquaticus.

Working Mechanism of PCR

A single PCR amplification cycle involves three basic steps

(i) Denaturation : In denaturation step, the target DNA is heated to a high temperature (usually 94°C) for breaking

of hydrogen bonds of two strands.

(ii) Annealing : In this step, the two primers anneal to each of the single-stranded template DNA since the

sequence of the primers is complementary to the 3’ ends of the template DNA.

(iii) Primer Extension (Polymerisation) : The optimum temperature for this polymerization step is 72°C. In the

presence of Taq DNA polymerase, dNTPs and Mg2+ the primers are extended towards each other so that the

DNA segment lying between the two primers is copied.

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SECTION-D

28. Outbreeding devices

(i) Dioecy : If both male and female flowers are present on different plants, they show cross pollination. It

prevents both autogamy and geitonogamy e.g., Papaya.

(ii) Dichogamy : Maturity of the stamens and carpels in a bisexual flower is not synchronised i.e., male or

female flowers mature at different time e.g., Cotton, Ficus etc.

(iii) Self-incompatibility : This is a genetic mechanism in which the germination of pollen on stigma of the same

flower is inhibited to avoid fertilisation of ovule. e.g., Tobacco.

(iv) Herkogamy : Natural barrier present between two sex organs avoids contact of pollen with stigma of same

flowers. e.g., Calotropis.

(v) Heterostyly : Length of stamen and carpel (style) are different thus preventing self-pollination e.g., Primula.

OR

(a) Co-dominance – The two alleles of the gene express equally i.e., there is no dominant-recessive relationship.

The F1 generation resembles the phenotype of both the parents. e.g., AB blood group in human beings.

(b) Pleiotropy – A single gene product may produce more than one effect. Both the effects may not be equal.

e.g., Gene B in pea controls both starch grain size (incomplete dominance) and shape of the seeds (complete

dominance)

(c) Sickle cell anaemia – An autosomal recessive disorder in which 6th amino acid glutamic acid is replaced

by valine due to single nucleotide mutation (Transversion). The RBC becomes sickle-shaped due to

polymerisation under low oxygen.

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29. After getting into the body of host the virus enters into macrophages by binding to their CD4 receptors with the

help of GP120

part of its glycoprotein spike. Inside the macrophage its RNA genome replicates to form viral DNA

with the help of enzyme reverse transcriptase. This viral DNA gets incorporated into host cells DNA and directs

the infected cells to produce virus and in this way acts like an HIV factory. Simultaneously, HIV enters into

helper T-lymphocytes, replicates and produces progeny viruses. The progeny viruses released in the blood attack

other helper T-lymphocytes. This is repeated leading to a progressive decrease in the number of helper T-

lymphocytes in the body of the infected person.

OR

(a) Metastasis, the most feared property of cancerous cells, deals with migration of cancerous cells from one body

part to another. The cells that lose their ability to stop division on coming in contact with each other are said to

have gone cancerous. Similarly cancerous cells lose their ability to remain stuck with cells of their own type.

(b) Genes associated with cancer are

(i) Cellular oncogenes or Proto-oncogenes

(ii) Tumour suppressor genes

(iii) Genes for programmed cell death or apoptosis.

The mutation in any one type of these genes leads to cancer.

(c) Cancer is detected by biopsy, MRI, CT scanning or by cancer-specific antibodies.

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30. Salient features of HGP

(i) Number of nucleotide bases 3164.7 million.

(ii) Average gene consists 3000 bases, but size varies considerably.

(iii) Total number of genes estimated is 30,000.

(iv) Functions are unknown for over 50% of discovered genes.

(v) Less than 2% of genome has coding sequence.

(vi) Repeated sequences make very large portion of human genome.

(vii) Chromosome 1 has most genes (2968) and the Y has fewest (231).

(viii) 1.4 million locations have SNPs (Single nucleotide polymorphism) pronounced as snips. This can throw light

on evolution of human.

OR

Verhulst-Pearl logistic growth Curve.

A population growing in habitat of limited resources show initially a lag phase, followed by phase of acceleration

and deceleration and finally reaches an asymptote, when the population density reaches the carrying capacity. A

plot of population density (N) in relation to time gives a sigmoid growth curve. It is represented mathematically as

dN K –NrN

dt K

⎛ ⎞ ⎜ ⎟⎝ ⎠

where

N = Population density at time t

r = Intrinsic rate of natural increase

K = Carrying capacity

dN

dt= rN

K – N

K

Time (t)

Popula

t io

n d

ensity (

N)

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biology (code-a) sample question paper for class xii

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