ICSE Class 10 Biology Board Exam Question Paper 2025 with Solutions

SECTION A (40 Marks)

(Attempt all questions from this Section.)

Question 1 [15 Marks]
Select the correct answers to the questions from the given options.
(Do not copy the questions, write the correct answer only).

(i) The number of live births per thousand people per year is called: [1 Mark]
(a) Mortality
(b) Population density
(c) Population growth rate
(d) Natality

Answer: (d) Natality

Natality is the birth rate, expressed as the number of births per 1,000 people per year.

Teacher's Note:
a) Remember natality is about births, mortality is about deaths.
b) Population density is number of individuals per unit area, not a rate.
c) Growth rate is the difference between natality and mortality.

(ii) The structure that lies at the junction of the choroid and the iris and is itself a part of the choroid is called: [1 Mark]
(a) Ciliary body
(b) Suspensory ligament
(c) Pupil
(d) Lens

Answer: (a) Ciliary body

The ciliary body lies between the choroid and the iris and helps in accommodation.

Teacher's Note:
a) Ciliary body changes lens shape for focusing.
b) It also produces aqueous humour.
c) Do not confuse ciliary body with suspensory ligaments, which attach lens to ciliary body.

(iii) Assertion (A): Seminal vesicles pour an alkaline secretion into the semen as it passes through the ureter.
Reason (R): The female vagina is acidic and needs to be neutralized for sperm survival. [1 Mark]
(a) (A) is true and (R) is false.
(b) (A) is false and (R) is true.
(c) Both (A) and (R) are true.
(d) Both (A) and (R) are false.

Answer: (b) (A) is false and (R) is true.

Seminal vesicles pour their secretion into the semen through the ejaculatory duct, not the ureter, so (A) is false. The vagina is indeed acidic and needs neutralising, so (R) is true.

Teacher's Note:
a) Ureter carries urine from kidney to bladder, not semen.
b) Ejaculatory duct carries semen, remember the difference.
c) Alkaline semen helps neutralise the acidic vagina.

(iv) The hormone that induces vigorous contractions of the uterus in a pregnant mother is: [1 Mark]
(a) Oestrogen
(b) Prolactin
(c) Oxytocin
(d) Progesterone

Answer: (c) Oxytocin

Oxytocin, secreted by the pituitary gland, stimulates strong uterine contractions during childbirth.

Teacher's Note:
a) Oxytocin is sometimes called the "birth hormone".
b) Prolactin controls milk production, not contractions.
c) Progesterone maintains pregnancy, it does not cause contractions.

(v) A scientist wanted to conduct a genetic experiment on mice. He cut the tails of all the mice and made them reproduce. What will be the phenotype of the offsprings? [1 Mark]
(a) All the offsprings will be tailless.
(b) There will be a mix of tailed and tailless offsprings.
(c) All the offsprings will have tails.
(d) Tail of the offsprings cannot be predicted.

Answer: (c) All the offsprings will have tails.

Cutting tails is an acquired change in body (somatic) cells and is not passed to offspring; only changes in germ cells are inherited.

Teacher's Note:
a) This is based on Weismann's theory that acquired traits are not inherited.
b) Only mutations in reproductive cells pass to the next generation.
c) A common mistake is to think physical injury changes the genotype.

(vi) Assertion (A): A turgid plant cell is in a balanced state.
Reason (R): In a turgid cell, turgor pressure and wall pressure are equal and in the same direction. [1 Mark]
(a) (A) is true and (R) is false.
(b) (A) is false and (R) is true.
(c) Both (A) and (R) are true.
(d) Both (A) and (R) are false.

Answer: (a) (A) is true and (R) is false.

A turgid cell is in a balanced, stable state, so (A) is true. But turgor pressure and wall pressure act in opposite directions and merely balance each other, so (R) is false.

Teacher's Note:
a) Turgor pressure pushes outward, wall pressure pushes inward.
b) These two forces are equal in magnitude but opposite in direction.
c) Remember: "equal and opposite", not "equal and same direction".

(vii) The optimum temperature for photosynthesis is: [1 Mark]
(a) 10 - 15°C
(b) 60 - 65°C
(c) 40 - 45°C
(d) 25 - 35°C

Answer: (d) 25 - 35°C

Photosynthesis is fastest between 25°C and 35°C; beyond this, enzyme activity declines.

Teacher's Note:
a) Very low or very high temperatures denature enzymes involved.
b) Photosynthesis nearly stops at very high temperatures.
c) This is a standard fact, learn the exact range.

(viii) Ajay and Vijay are siblings. Ajay can roll his tongue while Vijay cannot. What is the genotype of their parents? [1 Mark]
(a) Both the parents are homozygous dominant.
(b) Both the parents are homozygous recessive.
(c) One parent is homozygous dominant, and the other is homozygous recessive.
(d) Both the parents are heterozygous dominant.

Answer: (d) Both the parents are heterozygous dominant.

Tongue rolling is dominant. Vijay is non-roller (rr), so both parents must carry a recessive allele. Ajay is a roller, so at least one dominant allele exists. Both parents being Rr explains both outcomes.

Teacher's Note:
a) Use a simple cross Rr x Rr to check the 3:1 ratio.
b) If either parent were RR, no non-roller child would be possible.
c) This is a classic monohybrid cross application question.

(ix) Assertion (A): Deficiency of antidiuretic hormone causes an increase in urination.
Reason (R): Antidiuretic hormone acts on the kidney to reabsorb water from the kidney tubules. [1 Mark]
(a) (A) is true and (R) is false.
(b) (A) is false and (R) is true.
(c) Both (A) and (R) are true.
(d) Both (A) and (R) are false.

Answer: (c) Both (A) and (R) are true.

ADH reabsorbs water in the kidney tubules; its deficiency causes less reabsorption and more urination, so both statements are true and (R) correctly explains (A).

Teacher's Note:
a) ADH deficiency causes a condition called diabetes insipidus.
b) ADH is secreted by the posterior pituitary.
c) Water reabsorption happens mainly in the distal convoluted tubule and collecting duct.

(x) A phase of cell division where the spindle fibres disappear is: [1 Mark]
(a) Telophase
(b) Prophase
(c) Metaphase
(d) Anaphase

Answer: (a) Telophase

In telophase, chromosomes reach the poles, the nuclear membrane reforms, and spindle fibres disappear.

Teacher's Note:
a) Telophase is the last phase of karyokinesis.
b) Remember the order: prophase, metaphase, anaphase, telophase.
c) Spindle fibres appear in prophase and vanish only in telophase.

(xi) Assertion (A): Arachnoid layer helps in speeding up the transmission of nerve impulses along the axons.
Reason (R): Axon endings at the synapse secrete acetylcholine. [1 Mark]
(a) (A) is true and (R) is false.
(b) (A) is false and (R) is true.
(c) Both (A) and (R) are true.
(d) Both (A) and (R) are false.

Answer: (b) (A) is false and (R) is true.

The arachnoid is a protective meninge covering the brain; it does not speed nerve conduction (the myelin sheath does that), so (A) is false. Axon endings do secrete acetylcholine at the synapse, so (R) is true.

Teacher's Note:
a) The three meninges are Dura mater, Arachnoid mater and Pia mater.
b) Myelin sheath, not arachnoid, speeds up impulse conduction.
c) Acetylcholine is a well-known neurotransmitter released at synapses.

(xii) Many nuclear power plants are constructed near water sources. They use water for cooling their machinery and release it back into the water stream. Identify the kind of pollution caused. [1 Mark]
(a) Radiation pollution
(b) Water pollution
(c) Industrial pollution
(d) Thermal pollution

Answer: (d) Thermal pollution

The heated water released back into the water body raises its temperature, harming aquatic life; this is thermal pollution.

Teacher's Note:
a) Heated water lowers dissolved oxygen levels.
b) This can kill fish and other aquatic organisms.
c) Do not confuse this with radiation pollution, which involves radioactive leakage.

(xiii) Owls are nocturnal animals. They are active at night and hunt small animals for food. Owls have large eyes and can see well at night. This is due to: [1 Mark]
(a) Cones and Rhodopsin
(b) Rods and Iodopsin
(c) Rods and Rhodopsin
(d) Cones and Iodopsin

[Figure: Illustration of an owl perched on a wooden post, drawn in black and white line art, showing large forward-facing eyes]

Answer: (c) Rods and Rhodopsin

Rods are photoreceptors sensitive to dim light, containing the pigment rhodopsin, which allows owls to see well at night.

Teacher's Note:
a) Cones work in bright light and detect colour.
b) Rods work in dim light and give black-and-white vision.
c) Iodopsin is the pigment found in cones, not rods.

(xiv) Sunil tried to match the tropic movements in plants with the stimulus they respond to. The tabulation is given below: [1 Mark]

Identify the correct pair:
(a) P and R
(b) Q and S
(c) R and S
(d) P and R

Answer: (a) P and R

Thigmotropism responds to touch (P is correct) and chemotropism responds to chemicals (R is correct). Geotropism actually responds to gravity, not water, and phototropism responds to light, not gravity, so Q and S are wrongly matched.

Teacher's Note:
a) Thigmo means touch, chemo means chemical, geo means gravity/earth, photo means light.
b) Learn the Greek/Latin roots to remember tropisms easily.
c) Options (a) and (d) are printed identically in the paper; both are treated as correct.

(xv) Observe the following picture, identify the defect and the cause of the defect. [1 Mark]
(a) Simple goitre, under secretion of thyroxine.
(b) Ex-ophthalmic goitre, over secretion of thyroxine.
(c) Simple goitre, over secretion of thyroxine.
(d) Ex-ophthalmic goitre, under secretion of thyroxine.

[Figure: Illustration of a man's face showing bulging, protruding eyes and an anxious expression]

Answer: (b) Ex-ophthalmic goitre, over secretion of thyroxine.

Ex-ophthalmic goitre (Graves' disease) is caused by overproduction of thyroxine, leading to bulging eyes, enlarged thyroid, weight loss and rapid heartbeat.

Teacher's Note:
a) Simple goitre is due to iodine deficiency and under secretion.
b) Bulging eyes (exophthalmos) is the key clue for Graves' disease.
c) Do not confuse hyperthyroidism (over secretion) with hypothyroidism (under secretion).

Question 2

(i) Name the following: [5 Marks]
(a) The fully developed part of the ovary containing a mature ovum.
(b) A waxy layer on the upper epidermis of leaves meant to reduce Transpiration.
(c) The ear ossicle which opens into the oval window of Cochlea.
(d) The physiological process which is the starting point of all food chains.
(e) An insect which is a classic example of natural selection due to industrial melanism.

Answer:
(a) Graffian follicle.
(b) Cuticle.
(c) Stapes.
(d) Photosynthesis.
(e) Biston betularia (the peppered moth).

Teacher's Note:
a) These are simple recall questions, learn exact scientific terms.
b) Stapes fits into the oval window and transmits vibrations to the cochlea.
c) Photosynthesis is the base of all food chains as producers make food.
d) The peppered moth example shows how pollution favoured dark-coloured moths.

(ii) Given below is the diagram of a human heart. Read the information below the diagram and fill in the blanks: [5 Marks]

[Figure: External anterior view of a human heart showing major blood vessels emerging from the top of the heart and the muscular ventricles below, with coronary blood vessels visible on the surface]

The human heart pumps blood throughout the body. It is the size of a large fist. The heart is located between the lungs in the thoracic cavity. It has four chambers. The heart functions all through the lifespan of a person and is responsible for the survival of the person.
The heart is enclosed by a membrane called (a) __________. The ventricles give rise to two large blood vessels called (b) __________ and (c) __________. The flaps of the cuspid valves are kept in position by (d) __________. (e) __________ arteries supply oxygenated blood to the walls of the heart.

Answer:
(a) Pericardium.
(b) Aorta.
(c) Pulmonary artery (pulmonary trunk).
(d) Chordae tendineae.
(e) Coronary arteries.

Teacher's Note:
a) Pericardium is the double membrane protecting the heart.
b) Aorta carries oxygenated blood from the left ventricle to the body.
c) Pulmonary artery carries deoxygenated blood from right ventricle to lungs.
d) Coronary arteries supply blood to the heart muscle itself.

(iii) Arrange the terms in each group in the correct order. Write them in a logical sequence beginning with the term that is underlined. [5 Marks]
(a) Palisade cells, Cuticle, Upper epidermis, Spongy cells.
(b) Hepatic portal vein, Stomach, Hepatic vein, Liver.
(c) Cyton, Dendrites, Synaptic cleft, Axon endings.
(d) Insulin release, High blood sugar, Lowers blood sugar, Stimulates glucose uptake from blood.
(e) Sperm duct, Seminiferous tubule, Epididymis, Efferent ducts.

Answer:
(a) Cuticle, Upper epidermis, Palisade cells, Spongy cells.
(b) Stomach, Hepatic portal vein, Liver, Hepatic vein.
(c) Dendrites, Cyton, Axon endings, Synaptic cleft.
(d) High blood sugar, Insulin release, Stimulates glucose uptake from blood, Lowers blood sugar.
(e) Seminiferous tubule, Efferent ducts, Epididymis, Sperm duct.

Teacher's Note:
a) Follow the actual anatomical or physiological sequence, not alphabetical order.
b) In (c), impulse flows dendrites to cyton to axon endings to synaptic cleft.
c) In (d), high blood sugar triggers insulin release, which is a feedback mechanism.
d) In (e), sperm moves from seminiferous tubule to efferent ducts to epididymis to sperm duct.

(iv) Read the explanations given below and name the structures: [5 Marks]
Example: The tubules which produce sperms. Answer: Seminiferous tubules
(a) The canal through which the testes descend down into the scrotum just before the birth of a male baby.
(b) The part of the brain that regulates the peristaltic movement of the alimentary canal.
(c) A structure that collects the soundwaves and conducts them through the external auditory canal.
(d) The point of attachment of two chromatids of a chromosome.
(e) Regulation of the opening and closing of stomata.

Answer:
(a) Inguinal canal.
(b) Medulla oblongata (part of the hind brain).
(c) Pinna.
(d) Centromere.
(e) Guard cells.

Teacher's Note:
a) Testes descend through the inguinal canal into the scrotum before birth.
b) Medulla controls involuntary actions like peristalsis, heart rate and breathing.
c) Guard cells regulate stomatal opening based on their turgidity.
d) Centromere holds sister chromatids together.

(v) Given below is an outline of the human body showing the important endocrine glands. Match the glands marked (a) to (e) with their correct functions: [5 Marks]
Example: (f) - 6. Secretes Testosterone.

[Figure: Outline of a human body with endocrine glands marked (a) in the brain region, (b) in the neck region, (c) and (d) in the upper abdominal region, (e) in the lower abdominal/pelvic region, and (f) in the external genital region]

Answer:
(a) - 2 (Pituitary gland secretes tropic hormones).
(b) - 5 (Thyroid gland regulates basal metabolism).
(c) - 1 (Adrenal gland prepares the body to face stress).
(d) - 4 (Pancreas maintains blood sugar level).
(e) - 3 (Ovary secretes oestrogens).

Teacher's Note:
a) Match each gland to its main hormone function, not a secondary one.
b) Pituitary is called the "master gland" as it secretes tropic hormones controlling other glands.
c) Adrenal gland secretes adrenaline during stress ("fight or flight" hormone).
d) Pancreas has both endocrine (insulin) and exocrine functions.

SECTION B (40 Marks)

(Attempt any four questions from this Section.)

Question 3

(i) Write the overall chemical equation for photosynthesis. [1 Mark]

Answer: 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6O₂ + 6H₂O (in the presence of sunlight and chlorophyll).

Teacher's Note:
a) Always balance the atoms on both sides of the equation.
b) Mention sunlight and chlorophyll as necessary conditions above the arrow.
c) Water appears on both sides because only some of it is used up in the reaction.

(ii) Ramesh is a farmer who has a vineyard and cultivates grapes. To improve the shape of the grapes and make them elongated he sprays a particular phytohormone at the time of fruiting.

[Figure: Illustration of a bunch of grapes with leaves on a vine]

(a) Name the phytohormone that Ramesh sprays on the plant at the time of fruiting.
(b) These grapes are said to be seedless. What is the technical term for the formation of such fruits? [2 Marks]

Answer:
(a) Gibberellin is the phytohormone sprayed; it promotes cell elongation and improves grape size and shape.
(b) The formation of seedless fruits is called parthenocarpy.

Teacher's Note:
a) Gibberellins are widely used commercially to increase fruit size in grapes.
b) Parthenocarpy means fruit develops without fertilisation.
c) Do not confuse gibberellin with auxin, which mainly promotes root and shoot growth.

(iii) Mention the two pairs of nitrogenous bases that are present in a DNA strand and pair with each other by hydrogen bonds. [2 Marks]

Answer:
1. The purines Adenine and Guanine pair with the pyrimidines Thymine and Cytosine respectively.
2. Adenine pairs with Thymine through two hydrogen bonds (A = T); Guanine pairs with Cytosine through three hydrogen bonds (G ≡ C).

Teacher's Note:
a) Remember the rule: purines pair with pyrimidines only.
b) A-T bond has 2 hydrogen bonds, G-C bond has 3, making G-C bonding stronger.
c) This complementary base pairing keeps the DNA double helix uniform in width.

(iv) State any two disadvantages of living close to an airport. [2 Marks]

Answer:
1. Noise pollution from continuous aircraft take-offs and landings causes stress, sleep disturbance and hearing problems.
2. Air pollution from aircraft emissions leads to poor air quality and respiratory problems.

Teacher's Note:
a) Give any two distinct disadvantages, do not repeat the same point twice.
b) Noise pollution is the most commonly expected answer.
c) Aircraft emissions also contribute to environmental degradation near airports.

(v) Draw a neat, labelled diagram of an animal cell showing metaphase with four chromosomes. [3 Marks]

Answer:
The diagram should show an animal cell at metaphase with four duplicated chromosomes arranged at the equatorial plate. Each chromosome should show two chromatids joined at the centromere. Spindle fibres should be shown attached from the centromeres to the two poles, with an aster (star-shaped structure) at each pole. Label: Duplicated chromosomes, Chromatids, Spindle fibres, Aster.

[Figure: diagram to be added - animal cell showing metaphase stage of mitosis with four chromosomes aligned at the equator, spindle fibres from both poles, chromatids and asters labelled]

Teacher's Note:
a) Metaphase is identified by chromosomes lining up at the equator.
b) Always show the centromere joining sister chromatids.
c) Aster is present only in animal cells, not plant cells, an important labelling point.

Question 4

(i) What is the structure of DNA as proposed by Watson and Crick? [1 Mark]

Answer: Watson and Crick proposed that DNA has a double-helix structure consisting of two intertwined strands running in antiparallel directions, with the sugar-phosphate backbone on the outside and nitrogenous bases pairing on the inside, forming a twisted ladder-like shape.

Teacher's Note:
a) Remember the phrase "double helix" as the key term.
b) The two strands run in opposite directions (antiparallel).
c) Base pairing (A-T, G-C) holds the two strands together like rungs of a ladder.

(ii) Name the white blood cells that: [2 Marks]
(a) show phagocytosis
(b) produce antibodies

Answer:
(a) Neutrophils, monocytes and macrophages show phagocytosis.
(b) Lymphocytes produce antibodies.

Teacher's Note:
a) Phagocytosis means engulfing and destroying foreign particles or germs.
b) Lymphocytes are mainly B-lymphocytes that make antibodies.
c) Both are types of white blood cells (leucocytes) with different immune roles.

(iii) Complete the food chain by mentioning the names of the organisms in (c) and (d): [2 Marks]

[Figure: Food chain diagram showing (a) an ear of corn, with an arrow to (b) a mouse, with an arrow to a blank labelled (c), and a further arrow pointing up to a blank labelled (d)]

Answer: Organism (c) is a snake, and organism (d) is an eagle. The complete food chain is: Corn → Mouse → Snake → Eagle.

Teacher's Note:
a) Food chains always begin with a producer, here corn (maize).
b) Each level shows "who eats whom" moving to a higher trophic level.
c) Snake is a secondary consumer, eagle is the tertiary consumer/top predator.

(iv) State any two harmful effects of acid rain. [2 Marks]

Answer:
1. Acid rain increases soil acidity and destroys forests and crops.
2. It corrodes fences, buildings, monuments, bridges and statues.

Teacher's Note:
a) Acid rain forms when oxides of nitrogen and sulphur react with rainwater.
b) It damages both living things (plants, aquatic life) and non-living structures.
c) The Taj Mahal is a famous example of acid rain damage to monuments.

(v) Given below is a picture of a tree. Mention the scientific phenomena occurring in the parts labelled (a), (b) and (c). [3 Marks]

[Figure: Illustration of a tree showing roots labelled (a), the trunk labelled (b), and the leafy crown labelled (c), with arrows showing upward and outward movement of water and vapour]

Answer:
(a) Absorption of water and minerals by the roots.
(b) Ascent of sap, by which water and minerals are transported upwards through the stem to the leaves.
(c) Transpiration, which is the loss of water in the form of water vapour from the aerial parts of the plant, mainly the leaves.

Teacher's Note:
a) Root hairs absorb water by osmosis.
b) Ascent of sap occurs through the xylem tissue.
c) Transpiration mainly occurs through stomata on leaves.

Question 5

(i) What is Micturition? Explain. [1 Mark]

Answer: Micturition, also known as urination, is the process of expelling urine from the urinary bladder through the urethra to the outside of the body. It is regulated by the nervous system and the smooth muscles present in the urinary bladder and urethra.

Teacher's Note:
a) Micturition is a reflex action but can be voluntarily controlled.
b) The bladder wall muscles contract to push urine out.
c) Sphincter muscles relax to allow urine to pass through the urethra.

(ii) What are biomedical wastes? Give an example. [2 Marks]

Answer: Biomedical waste refers to any solid or liquid waste generated during the diagnosis, treatment or immunisation of humans or animals. Examples include used needles, syringes, cotton swabs, body organs, blood and tissues.

Teacher's Note:
a) Biomedical waste must be disposed of separately from normal household waste.
b) Improper disposal can spread infections and diseases.
c) Hospitals use colour-coded bins to segregate biomedical waste.

(iii) Differentiate between the functions of Urethra and Uterus. [2 Marks]

Answer:

Teacher's Note:
a) Urethra carries urine (and semen in males); uterus is only for reproduction.
b) In females, urethra and reproductive tract are separate openings.
c) Uterus is also called the womb.

(iv) Rachna is an expert gymnast on the balance beam. She has been vigorously practising for the Olympic Games. Lately, she has been experiencing dizziness and losing her balance during the practise sessions.

[Figure: Silhouette illustration of a gymnast in an arched pose, balancing on a beam]

(a) Which part of the membranous labyrinth is responsible for maintaining the body balance on the beam?
(b) Which type of balance is maintained by the structure mentioned in (a)? [2 Marks]

Answer:
(a) The semicircular canals of the membranous labyrinth are responsible for maintaining body balance on the beam.
(b) The semicircular canals maintain dynamic balance, which is the ability to maintain stability during movement.

Teacher's Note:
a) Semicircular canals detect rotational movements of the head.
b) Utricle and saccule maintain static balance, not dynamic balance.
c) Dizziness during movement often points to an inner ear balance problem.

(v) Draw a neat, labelled diagram to show that oxygen is released during photosynthesis. [3 Marks]

Answer:
The diagram should show a beaker containing water with sunlight falling on it, a funnel inverted over twigs of Hydrilla plant kept submerged, and a test tube filled with water placed over the stem of the funnel to collect the gas bubbles rising from the plant. Labels: Sunlight, Beaker Containing Water, Funnel, Hydrilla Plant Twigs, Gas Bubbles, Test Tube Filled with Water.

[Figure: diagram to be added - experimental set-up with a beaker of water, an inverted funnel covering Hydrilla twigs, a water-filled test tube inverted over the funnel stem collecting gas bubbles, with sunlight shown falling on the set-up]

Teacher's Note:
a) This is the classic Hydrilla experiment to demonstrate oxygen release.
b) Gas bubbles collecting in the inverted test tube confirm oxygen production.
c) A glowing splinter test can be used to further confirm the gas is oxygen.

Question 6

(i) Where are Hydathodes located? [1 Mark]

Answer: Hydathodes are pores or openings located in the leaf epidermis, at the tips or margins of leaves.

Teacher's Note:
a) Hydathodes are responsible for guttation, the loss of water in liquid form.
b) Guttation occurs mainly at night or in high humidity conditions.
c) Do not confuse hydathodes with stomata, which release water vapour, not liquid.

(ii) What are Vestigial organs? Give one example of a vestigial structure in the human mouth. [2 Marks]

Answer: Vestigial organs are structures that were functional in an organism's ancestors but have lost their original function over time and now serve little or no purpose. An example of a vestigial structure in the human mouth is the wisdom teeth (third molars).

Teacher's Note:
a) Vestigial organs are evidence of evolution.
b) Other examples include vermiform appendix and nictitating membrane in humans.
c) Wisdom teeth often cause problems as jaws have become smaller in modern humans.

(iii) Ahmed had a severe throat infection. After a few days he developed an earache too. What could be the reason for the pain in his ears? Explain. [2 Marks]

Answer: Ahmed's earache could be due to the spread of the throat infection through the Eustachian tube, which connects the middle ear to the back of the throat. If it becomes swollen or blocked due to the infection, fluid can build up in the middle ear, causing pressure and pain.

Teacher's Note:
a) The Eustachian tube equalises air pressure between the middle ear and the throat.
b) Infections easily travel from the throat to the ear through this connecting tube.
c) This condition is commonly called an ear infection following a cold or throat infection.

(iv) Mr. Sharma is a 76-year-old man. His vision was gradually becoming blurred. He consulted an eye doctor and it was diagnosed as cataract.

[Figure: Two illustrations of eyes side by side, one labelled "Health Eye" showing a clear pupil, and the other labelled "Catarace Eye" showing a cloudy, whitish pupil]

(a) Which part of the eye does cataract affect?
(b) Why does the vision become blurred? [2 Marks]

Answer:
(a) Cataract affects the lens, the clear, natural part of the eye that focuses light onto the retina.
(b) Vision becomes blurred because the lens becomes cloudy or opaque, preventing light from passing through it clearly, leading to a blurry image on the retina.

Teacher's Note:
a) Cataract is common in old age due to protein clumping in the lens.
b) It can be treated by surgical replacement of the lens.
c) A cloudy lens scatters light instead of focusing it sharply.

(v) Given below is the diagram of a plasmolysed cortical cell of a root. Copy the diagram and label the following parts in the diagram: [3 Marks]
(a) Cytoplasm
(b) Hypertonic solution
(c) Plasma membrane

[Figure: Diagram of a plasmolysed plant cell showing the rigid cell wall, a shrunken protoplast pulled away from the cell wall, a visible nucleus and vacuole inside the shrunken protoplast]

Answer: In the diagram, label (a) Cytoplasm as the shrunken protoplast inside the cell wall, (b) Hypertonic solution as the space between the cell wall and the shrunken protoplast (filled with the surrounding solution that caused plasmolysis), and (c) Plasma membrane as the outer boundary of the shrunken protoplast.

Teacher's Note:
a) Plasmolysis occurs when a cell loses water in a hypertonic solution.
b) The cell wall stays rigid while the protoplast shrinks away from it.
c) This shows osmosis occurring from a region of higher water potential (cell) to lower water potential (hypertonic solution).

Question 7

(i) Define the term Allele. [1 Mark]

Answer: Alleles are alternate forms of a gene that are responsible for the expression of traits of a character.

Teacher's Note:
a) Alleles occur in pairs, one from each parent.
b) They occupy the same position (locus) on homologous chromosomes.
c) An allele can be dominant or recessive.

(ii) In the last century, the human population has increased tremendously. Death rate has reduced and life expectancy has increased. This rapid growth has placed significant pressure on resources. Global cooperation is needed for environmental preservation.

[Figure: Illustration titled "Overpopulation" showing a globe crowded with numerous small human figures standing on it, with tree roots visible below the globe]

(a) Mention any one reason for reduction in the death rate.
(b) Name any one resource that is under pressure due to population explosion. [2 Marks]

Answer:
(a) The reason for the reduction in death rate is the improvement in medical science and technology, which has led to better ways to treat and prevent diseases.
(b) Due to population explosion, freshwater resources are under increasing pressure as a growing population demands more water for drinking, household chores, agriculture and industry.

Teacher's Note:
a) Better healthcare and vaccination programmes have reduced death rates.
b) Water, land and forests are common resources under pressure due to overpopulation.
c) Population explosion is linked closely to environmental degradation.

(iii) Mention any two functions of amniotic fluid. [2 Marks]

Answer:
1. It acts as a shock absorber and protects the developing foetus from injury and keeps a constant temperature around the developing foetus.
2. It allows for free foetal movement, which is essential for the development of bones and muscles.

Teacher's Note:
a) Amniotic fluid is present inside the amnion sac.
b) It cushions the foetus against external shocks.
c) Free movement helps in proper muscular and skeletal development.

(iv) Expand the following abbreviations: [2 Marks]
(a) CFC
(b) CNG

Answer:
(a) CFC - Chlorofluorocarbon.
(b) CNG - Compressed Natural Gas.

Teacher's Note:
a) CFCs are known to deplete the ozone layer.
b) CNG is used as a cleaner fuel for vehicles.
c) Learn full forms of common environmental abbreviations for such recall questions.

(v) Vineet's day begins with a cup of piping hot coffee. Caffeine is a stimulant present in coffee which increases the circulation of Adrenaline in the body. Vineet feels refreshed, alert and focussed.

[Figure: Illustration of a steaming cup of coffee on a saucer, labelled "Coffee"]

(a) Name the organ that is stimulated by caffeine which makes Vineet alert and focussed.
(b) Give the collective term for the protective membranes of the organ mentioned in (a).
(c) Which part of the autonomic nervous system increases the secretion of Adrenaline? [3 Marks]

Answer:
(a) Caffeine stimulates the brain, leading to increased alertness and focus.
(b) The collective term for the protective membranes of the brain is meninges. There are three meninges around the brain, starting from the outside: Dura mater, Arachnoid mater and Pia mater.
(c) The sympathetic nervous system is the part of the autonomic nervous system that increases the secretion of adrenaline (epinephrine).

Teacher's Note:
a) Sympathetic nervous system prepares the body for "fight or flight" response.
b) Meninges protect the brain and spinal cord.
c) Adrenaline increases heart rate and alertness, matching the effect described.

Question 8

(i) Explain the term Excretion. [1 Mark]

Answer: Excretion is the elimination of metabolic wastes from the body, and is an essential life process in all organisms. In vertebrates, it is primarily carried out by the lungs (excrete carbon dioxide), kidneys (excrete urine) and skin (excretes sweat).

Teacher's Note:
a) Excretion removes only metabolic wastes, not undigested food (that is egestion).
b) Kidneys are the main excretory organs in humans.
c) Skin and lungs are accessory excretory organs.

(ii) State the difference between Nephron and Neuron. [2 Marks]

Answer:

Teacher's Note:
a) Do not confuse the similar-sounding words nephron and neuron.
b) Nephron belongs to the excretory system, neuron to the nervous system.
c) Each performs a completely different function in the body.

(iii) Mention any two objectives of Swachh Bharat Abhiyan. [2 Marks]

Answer:
1. To eliminate open defecation by building individual and public toilets even in the remotest areas.
2. To make our villages, cities and towns clean by removing wastes from streets, roads, parks, gardens, houses, etc.

Teacher's Note:
a) Swachh Bharat Abhiyan is a national cleanliness campaign of India.
b) It focuses on sanitation and waste management.
c) Reducing open defecation improves public health significantly.

(iv) Give any two characteristic features of a Cro-Magnon man. [2 Marks]

Answer:
1. Cro-Magnon man had a large skull, rounded forehead, a distinct chin and nose.
2. The cranial capacity of Cro-Magnon man was about 1600 cc.

Teacher's Note:
a) Cro-Magnon man is considered an early form of modern humans.
b) A large cranial capacity indicates advanced brain development.
c) Distinct chin is a feature not found in earlier hominid species like Neanderthals.

(v) A farmer cultivates a unique species of tomato plants. The two traits selected for breeding were: Colour of the fruits and height of the plants. The farmer initially crosses a homozygous tall plant bearing red fruits (TTRR) with a dwarf plant bearing yellow fruits (ttrr) and the genotype of all the offsprings of the F₁ generation was TtRr. Next, he crosses two F₁ generation plants (TtRr).

[Figure: Illustrations of two tomato plants, labelled "Tall plant with red fruit" and "Dwarf plant with yellow fruits"]

(a) Explain the phenotype of the offsprings of the F₁ generation obtained from the initial cross.
(b) Mention the phenotypic ratio of the F₂ generation offsprings.
(c) State Mendel's Law of Independent Assortment. [3 Marks]

Answer:
(a) The phenotype of the offspring of the F1 generation from the initial cross (between two homozygous or pure-line parents) would be tall plants with red fruits. This is because tallness and red colour of fruits are the dominant traits, and in the F1 generation, the dominant traits are expressed. The offspring are however heterozygous (TtRr) in genotype.
(b) The phenotypic ratio of the F2 generation offspring would be 9:3:3:1, where 9 plants would be tall with red fruits, 3 plants would be tall with yellow fruits, 3 plants would be dwarf with red fruits, and 1 plant would be dwarf with yellow fruits.
(c) Mendel's Law of Independent Assortment states that in a dihybrid cross, the alleles of two different genes separate at the time of gamete formation and then recombine independently of one another to give new combinations in the offspring.

Teacher's Note:
a) F1 offspring always show only the dominant phenotype in a cross of pure-breeding parents.
b) 9:3:3:1 is the standard dihybrid phenotypic ratio, learn it by heart.
c) Independent assortment applies to genes on different chromosomes.
d) A common mistake is confusing the law of independent assortment with the law of segregation.