Model Paper 1
Max Marks: 70
Time allowed : 3 hrs
Q1. At what stage is the embryo implanted in the uterus of the mother
in case of a test tube baby?(1 mark)
Ans1. 32-celled Morula.
Q.2 Write the full form of TRNA.(1 mark)
Ans2. Transfer Ribosenucleic Acid
Q3. Which of the following diseases could be avoided by analysing
the pedigree of parents -
Klinefelter's syndrome, Haemophilia, Amoebiasis.(1 mark)
Q4. The venous blood in the lung has a PCO2 of 46 mm Hg.
Should the alveolar PCO2 exceed or be less than 46 mm Hg to
result in diffusion of CO2 from the blood into the alveolus?(1
Ans4. It should be less than 46 mm Hg.
Q5. What forms the cambial ring in a dicot stem during the secondary
Ans5. The cambial rings are formed by alternately forming secondary
Q 6. When is a tumour referred to as malignant? (1 mark)
Ans6. A tumour is called malignant, if it has the capacity to undergo
Q 7. What are the two functions of DNA polymerase? (1 mark)
Ans7. DNA Polymerase is responsible for
(i) binding the deoxynucleotide bases after they have arranged on the
(ii) proofreading the formed sequence for errors.
Q.8 Name any two structures in our body, which bear ciliated epithilium.(1
Ans8. (i) Kidney tubules, and
(ii) Fallopian tubes
Q9. Why is the cleavage in mammals referred to as simple holoblastic?(2
Ans9.Cleavage in mammals is referred to as simple holoblastic because
in the absence of any yolk in the mammalian egg, it divides completely.
This means the cleavage furrow divides the egg or blastoderms completely.
Q.10. Amongst pea tendrils, opuntia spines, lemon thorns and cucurbit
tendril, which ones are homologous structures? Give reasons.(2 marks)
Ans10. Pea tendrils are homologous to Opuntia spines because both
are modifications of leaves; Lemon thorns are homologous to Cucurbit tendril
because both are modified stems.
Q.11 How is growth measured in animals?(2 marks)
Ans 11. In animals two main patterns of the growth occur:
(A) Isometric growth:
- when an organ grows at the same mean rate as the rest of the body.
- Isometric growth is seen in fish an certain insects.
(B) Allometric growth:
- an organ grows at the different rate from the rest of the body.
This produces the change in size of the organism, which is accompanied
by a change in the shape of the organism, eg in human beings.
Q.12 Give any four examples of human reflexes (2 marks)
Ans12. (1) Salivation on the sight or smell of a tasty food,
(2) constriction of pupils on the illumination with bright light,
(3) Blinking of eye lids on the approach of an object close to the eyes,
(4) Jerk in the legs when a pin pricks sole.
Q 13. What was Emerson's experiment? What is Emerson's enhancement
Ans. 13 Emerson's experiment: When the quantum yield (number of
oxygen evolved per quanta of light absorbed) is plotted with respect to
the wave length of the light used for photosynthesis, the plot indicated
that beyond 680nm there is a drop in the rate of photosynthesis. This
drop is known as 'red drop' or 'Emerson effect' i.e. far red light (690-700nm)
is inefficient for photosynthesis. If, along with 690-700nm light a light
of shorter wavelength i.e. 660nm is provided, the rate of photosynthesis
shows a rise again (Emerson enhancement effect).
Q 14. Differentiate between morula and blastula of mammals. (2 marks)
Ans14. Morula is a solid ball of cells and looks like a mulberry.
Often zona pellucida remains intact around the morula.
Blastula is like a hollow tennis ball where a cavity called 'Blastocoel'
forms due to rearrangement of blastomeres. The zona pellucida envelope
disintegrates as the blastula develops.
Q 15. What is the biological significance of Azolla pinnata in agriculture?
Ans15.Azolla pinnata is a small, fast-growing fern that occurs
floating on water. Anabaena azollae, a cyanobacterium lives in cavities
of Azolla leaves. It fixes nitrogen from air and excretes the nitrogenous
compounds into the leaf cavity of the fern. Thus Azolla pinnata serves
as an excellent biofertilizer when grown in association with rice.
Q 16. An animal should possess at least one out of the three possible
to enable it to function as a ureotelic organism. List these characteristics.(2
Ans16.Ureotelism is the urinary elimination of nitrogen mainly
as urea. An animal can be ureotelic only if the animal can afford to:
(i) excrete sufficient volumes of water,
(ii) concentrate urea considerably in the urine,
(iii) retain considerable amounts of urea in the blood and body fluids.
Whale, camel, toad, and shark are all ureotelic.
Q17. How a sickle-cell carrier has an advantage over the rest of the
human population in a Malaria ridden area? (2 marks)
Ans17. A defective form of haemoglobin is found in the RBCs of the
Sickle-cell carrier. They have sickle-shaped RBCs, which are highly inefficient
in binding oxygen. However, a sickle shaped RBC effectively kills the
malaria parasite too, which harbors in it. Thus individuals homozygous
for Sickle-cell trait have a better survivability in the event of malaria
epidemics and thus natural selection has not eliminated this trait in
those geographical locations in the world, where there is a prevalence
Q 18. Explain the structural and functional significance of fovea
in the human eye.(2 marks)
Ans18.Fovea is a depressed area of the retina, which contains only
cones and no rods. Ability for vision is highest in the fovea. When eyes
are fixed on an object, its image is focussed on the fovea and is consequently
seen most accurately.
Q.19 Distinguish between bacterial transduction and bacterial transformation.
Ans19. Transduction: Transfer of the DNA from one bacterium to
the other, mediated through a bacteriophage. The carried DNA bestows some
of the properties of the donor to the acceptor bacterium.
Transformation: Transfer of the DNA from one bacterium to the other through
the solution phase, after which the acceptor bacterium gets the properties
of the donor bacterium.
Q20. Define Cancer. How are cancers broadly classified pathologically?
Name one major cancer in women and one major cancer in men in India.(3
Ans20. Pathologically, cancers may be broadly classified into three
(i) Carcinomas, which are malignant growths of the epithelial (ectodermal)
(ii) Sarcomas, which are malignant growths of the mesodermal tissues such
as bone, muscle,
lymph nodes etc.
(iii) Leukaemias, which are unchecked proliferation of blood cells, and
there precursors in the bone marrow.
In India the major form of cancer in women is the uterine-cervical cancer
and it is the cancer of the mouth and throat in men.
Q21. Human skin colour is believed to be controlled by at least three
What do you call this type of inheritance?(3 marks)
i Suppose the genes are designated as A, B, and C and darkness is dominant
over fairness, what shall be the genotypes of the darkest, fairest and
intermediate skin colour?
ii What will be the total number of allele combinations in the gametes
of a person
heterozygous,all the three genes.
Ans21.(i) This inheritance is called Quantitative Inheritance and
individual genes show Incomplete Dominance.
(ii) The genotype of the darkest will be AABBCC, that of the intermediate
will be AaBbCc; and that of the fairest will be aabbcc.
(iii) The number of possible allele combinations in the gametes
is eight for
such a three-gene combination (23)
Q22. If abiotic origin of life were in progress on a planet other than
the earth, what should be the conditions there? (3 marks)
Ans 22. (i)If abiotic origin of life is in progress on a planet
other than the earth, the conditions there should be same as the one prevalent
on the primitive earth. Thus the following conditions would be required:
Solids, liquids, and gases coexist.
(ii)The atmosphere should be reducing.
(iii)Hydrogen, nitrogen, water vapour, carbon dioxide, methane,
and ammonia should be present. Sources of energy such as thermal energy,
radiation, and lightning should be present.
Q 23. An mRNA strand has a series of codons out of which three are
(i) AUG, (ii) UUU and (iii) UAG
(a) What will these codons be translated into?
(b) What are the DNA codons that would have transcribed these RNA codons?
(a) (i) AUG and (ii) UUU will be translated. (iii) UAG is a stop
codon which will not be translated.
RNA codon DNA codon
Q24. Describe the role of red blood cells in the transport of oxygen
and carbon dioxide by blood.(3 marks)
Ans24. Blood transports oxygen with the help of haemoglobin in RBCs
and carbon dioxide with the help of cytoplasm of red blood cells. Oxygen
diffuses into the RBCs and combines loosely with the Fe2+ ions of hemoglobin
to form oxyhaemoglobin. A lower PO2 and higher PCO2 in the tissues causes
dissociation of oxyhaemoglobin to deoxyhaemoglobin (reduced haemoglobin)
and molecular oxygen.
Carbon dioxide diffuses into RBCs and reacts with water in the cytoplasm,
to form Carbonic acid:
CO2 + H2O = H2CO3, The reaction is catalysed by zinc containing Carbonic
In RBCs carbonic acid forms bicarbonate:
Some of the bicarbonate remains in the RBCs but most of it comes out in
plasma. Some of the CO2 reacts with globin of deoxyhaemoglobin to form
Carbaminohaemoglobin in RBCs.
Q 25. Answer the following with reference to the anatomy of dicot
(i) Where exactly are the cambial cells located in the vascular bundles?
(ii) What is the name given to such a bundle?
(iii) How are the xylem vessels arranged?
(iv) What type of cells constitute the pith? (3 marks)
Ans25. (i) The cambial cells are located in the vascular bundles
of the young dicotyledonous stem, between xylem and phloem.
(ii) It is called Fascicular Cambium.
(iii) Xylem vessels are arranged towards the center, protoxylem
innermost and metaxylem next.
(iv) Parenchymatous cells constitute the pith.
Q26. Give one reason why lysozyme is considered an enzyme and not
a hormone? How does it defend the body? Name any two secretions in humans,
which contain lysozyme.(3 marks)
Ans26. Lysozyme is not a hormone because it does not satisfy the following
required for a protein to become a hormone:
(i) It is not secreted in response to any change in the internal or external
environment of the body,
(ii) It is not transported by blood,
(iii)It has no specific target organ of its own,
(iv) It does not stimulate or inhibit specific biological processes in
the targeted organs to modify their activity.
Lysozyme destroys the cell wall of many bacteria and thus prevents many
Q27. Sometimes natural selection is not operative if the abnormal
allele is somewhat advantageous to the individual. Explain this mechanism
with a suitable example. (3 marks)
Ans27.Sometimes natural selection is not operative if the abnormal
is advantageous to the individual because the abnormality offers better
survivability due to its advantages over the normality. Sickle cell anaemia
is a good example of this phenomenon, where a defective form of haemoglobin
is found in the RBCs. Individual homozygous for this trait die at an early
age. Even those homozygous for this trait have sickle-shaped RBCs, which
are highly inefficient in binding oxygen. However, natural selection has
not eliminated this trait in those geographical locations in the world,
where there is a prevalence of malaria. This has happened because a sickle
shaped RBC effectively kills the malaria parasite, which harbours in it.
Thus individuals homozygous for Sickle-cell trait have a better survivability
in the event of malaria epidemics and are favoured during the natural
selection despite of their abnormal trait.
Question Nos. 28 - 30 are long answer questions carrying 5 marks
It is appropriate to answer them in about 80 - 120 word each.
Q 28. In the case of snapdragon (Antirrhinum majus) a plant with red
flowers was crossed with another plant with white flowers. Trace the inheritance
of flower colour up to the F2 generation indicating the genotypesand phenotypes
at each level. What special feature do you note in the genotypic ratios
in F2 generation? (5 marks)
Ans28.When homozygous red (RR) Antirrhinum majus is crossed with homozygous
white (rr), the F1 heterozygous (Rr) bears pink flowers. These heterozygous
pink- flowered A. majus give homozygous red (RR), heterozygous pink (Rr)
and homozygous white (rr) in a ratio of 1:2:1in their F2 generation when
underwent self pollination. This is an example of 'Incomplete Dominance'.
The phenotypic and genotypic ratios are the same In case of Incomplete
Dominance except for the fact that unlike in Complete Dominance, the homozygote
and heterozygote for the dominant allele differ in their phenotypes.
Q 29. Name the hormone that regulates each of the following and mention
the source of it:
(i) Urinary elimination of water
(ii) Storage of glucose as glycogen
(iii) Sodium and potassium ion metabolism
(iv) Basal metabolic rate
(v) Descent of testes into the scrotum (5 marks)
|(i) Vasopressin (ADH)
|| Islets of Langerhans in the Pancreas
|(iv) Thyroid hormones
|(v) Follicle Stimulating Hormone (FSH)
Q30. What is a synapse? How is the nerve impulse transmitted across
a synapse? (5 marks)
Ans30. Synapse is the junction between two neurons, across which the
impulse has to pass from one neuron to the next. Synapses are formed between
the axon terminals of one neuron and the dendrites, the cell body or even
sometimes the axon of one or more neurons. There is no actual continuity
between neurons at the synapse. The axon of a neuron divides near its
termination into many branches, each branch losing its myelin sheath before
termination. These axon terminals of a neuron then end in expanded feet-like
forms on the dendrites or the cell body of another neuron; there is a
narrow fluid-filled space, called Synaptic cleft, separating the membranes
of the two neurons at the synapse. The axon terminal contains many membrane-bound
vesicles, called Synaptic Vesicle, in its cytoplasm. Within these vesicles,
chemical substances, such as adrenaline and acetylcholine remain stored.
When a nerve impulse passes the axon terminal, its synaptic vesicles release
their stored chemicals to the synaptic cleft. These diffuse through the
cleft to reach the membrane of the next neuron, and stimulating the latter.
This causes the nerve impulse to be transmitted along the next neuron.