ICSE Biology 2026 Prediction Paper

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ICSE CLASS X - BIOLOGY (SCIENCE Paper 3)

HIGH-PROBABILITY PREDICTION PAPER FOR 13 MARCH 2026

Maximum Marks: 80
Time allowed: Two hours

Answers to this Paper must be written on the paper provided separately.
You will not be allowed to write during the first 15 minutes.
This time is to be spent in reading the question paper.
The time given at the head of this Paper is the time allowed for writing the answers.

Attempt all questions from Section A and any four questions from Section B.
The intended marks for questions or parts of questions are given in brackets [ ].

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SECTION A (40 Marks)

Attempt all questions from this Section.

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Question 1

Choose the correct answers to the questions from the given options. [15]

(i) The phase of mitosis during which the centromere splits and chromatids move to opposite poles is:
- (a) Prophase
- (b) Metaphase
- (c) Anaphase
- (d) Telophase

(ii) In a monohybrid cross between a homozygous tall plant (TT) and a homozygous dwarf plant (tt), the phenotypic ratio in the F₂ generation is:
- (a) 1 : 1
- (b) 1 : 2 : 1
- (c) 3 : 1
- (d) 9 : 3 : 3 : 1

(iii) A cell placed in a hypertonic solution will:
- (a) Swell up and burst
- (b) Undergo plasmolysis
- (c) Remain unchanged
- (d) Become turgid

(iv) The instrument used to measure the rate of transpiration is:
- (a) Auxanometer
- (b) Ganong's potometer
- (c) Photometer
- (d) Barometer

(v) The dark reaction of photosynthesis takes place in the:
- (a) Grana of the chloroplast
- (b) Stroma of the chloroplast
- (c) Cytoplasm
- (d) Cell membrane

(vi) Study the diagram below representing a cross-section of the human heart. The chamber marked 'X' that receives deoxygenated blood from the superior vena cava is the:
- (a) Left atrium
- (b) Right atrium
- (c) Left ventricle
- (d) Right ventricle

(vii) The functional unit of the kidney is:
- (a) Neuron
- (b) Nephron
- (c) Nephridia
- (d) Ureter

(viii) The part of the brain responsible for maintaining balance and posture is the:
- (a) Cerebrum
- (b) Cerebellum
- (c) Medulla oblongata
- (d) Hypothalamus

(ix) Assertion (A): Insulin is secreted by the beta cells of the Islets of Langerhans in the pancreas.
Reason (R): Insulin converts excess glucose in the blood into glycogen stored in the liver.
- (a) Both A and R are true, and R is the correct explanation of A
- (b) Both A and R are true, but R is not the correct explanation of A
- (c) A is true but R is false
- (d) A is false but R is true

(x) The hormone responsible for the development of secondary sexual characteristics in males is:
- (a) Oestrogen
- (b) Progesterone
- (c) Testosterone
- (d) Thyroxine

(xi) The correct sequence of parts in a reflex arc is:
- (a) Receptor → Motor neuron → Spinal cord → Sensory neuron → Effector
- (b) Receptor → Sensory neuron → Spinal cord → Motor neuron → Effector
- (c) Effector → Sensory neuron → Spinal cord → Motor neuron → Receptor
- (d) Receptor → Spinal cord → Sensory neuron → Motor neuron → Effector

(xii) Assertion (A): Meiosis is called reduction division.
Reason (R): In meiosis, the chromosome number is reduced to half in the daughter cells.
- (a) Both A and R are true, and R is the correct explanation of A
- (b) Both A and R are true, but R is not the correct explanation of A
- (c) A is true but R is false
- (d) A is false but R is true

(xiii) The part of the female reproductive system where fertilization normally occurs is:
- (a) Uterus
- (b) Ovary
- (c) Fallopian tube (Oviduct)
- (d) Cervix

(xiv) Which of the following is a greenhouse gas primarily responsible for global warming?
- (a) Nitrogen
- (b) Oxygen
- (c) Carbon dioxide
- (d) Hydrogen

(xv) The plant hormone that promotes cell elongation and is responsible for phototropism is:
- (a) Gibberellin
- (b) Auxin
- (c) Cytokinin
- (d) Ethylene

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Question 2

(i) The diagram below represents the longitudinal section of the human kidney. Study the diagram and answer the questions that follow: [5]

(Diagram of L.S. of human kidney showing: A — Cortex, B — Medulla, C — Renal pelvis, D — Renal artery, E — Ureter)

• (a) Identify the parts labelled A, B, and C. [3]
• (b) Name the structural and functional unit found within part A and part B. [1]
• (c) What is the function of the part labelled E? [1]

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(ii) Give the biological/technical term for the following: [5]

• (a) The process by which water molecules pass through a semi-permeable membrane from a region of high water concentration to a region of low water concentration.
• (b) The type of cell division that produces four haploid daughter cells from a single diploid parent cell.
• (c) The condition in which a person's blood sugar levels remain persistently high due to insufficient insulin production.
• (d) The automatic, involuntary, and immediate response of the body to a stimulus.
• (e) The loss of water in the form of water vapour from the aerial parts of a living plant.

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(iii) Fill in the blanks by choosing the correct option from the brackets: [5]

• (a) The __ is the longest phase of the cell cycle. (S-phase / Interphase / Prophase)
• (b) The blood vessel that carries oxygenated blood from the lungs to the left atrium is the __. (pulmonary artery / pulmonary vein / aorta)
• (c) The __ lobe of the cerebrum is associated with vision. (frontal / temporal / occipital)
• (d) The process of conversion of glucose to pyruvic acid in the cytoplasm is called __. (glycolysis / Krebs cycle / oxidative phosphorylation)
• (e) The movement of a plant part in response to gravity is called __. (phototropism / geotropism / hydrotropism)

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(iv) Match the items in Column A with the most appropriate items in Column B. There are two extra items in Column B. [5]

	Column A	Column B
(a)	Bowman's capsule	(i) Carries impulses away from the cell body
(b)	Axon	(ii) Increases heart rate and blood pressure
(c)	Corpus luteum	(iii) Ultrafiltration
(d)	Adrenaline	(iv) Secretes progesterone
(e)	Synapse	(v) Stores bile
		(vi) Junction between two neurons
		(vii) Carries impulses towards the cell body

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(v) Differentiate between the following pairs on the basis given in brackets: [5]

• (a) Mitosis and Meiosis (number of daughter cells produced)
• (b) Artery and Vein (direction of blood flow)
• (c) Transpiration and Guttation (state of water lost)
• (d) Cerebrum and Cerebellum (main function)
• (e) Diabetes mellitus and Diabetes insipidus (hormone involved)

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SECTION B (40 Marks)

Attempt any four questions from this Section.

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Question 3 — Cell Division and Genetics [10]

(i) Study the following diagram of a stage of mitosis and answer the questions: [3]

(Diagram showing anaphase of mitosis — chromosomes being pulled apart to opposite poles by spindle fibres)

• (a) Identify the stage shown in the diagram. Give one reason for your answer.
• (b) Name the structure that connects the chromatid to the spindle fibre.
• (c) Draw a neat labelled diagram of the stage that follows the one shown above.

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(ii) In pea plants, the gene for round seed (R) is dominant over the gene for wrinkled seed (r). A cross is carried out between a heterozygous round-seeded plant and a wrinkled-seeded plant. [3]

• (a) Write the genotypes of the two parent plants.
• (b) Draw a Punnett square to show the possible genotypes of the offspring.
• (c) State the phenotypic ratio of the offspring obtained.

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(iii) (a) With the help of a suitable cross, explain the mechanism of sex determination in human beings. Show the possible combinations of sex chromosomes in the offspring when a normal man and woman have children. [2]

(b) A heterozygous tall plant with round seeds (TtRr) is crossed with a dwarf plant with wrinkled seeds (ttrr). Work out the cross and state the phenotypic ratio of the offspring. [2]

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Question 4 — Plant Physiology [10]

(i) (a) Define plasmolysis. [1]

(b) Describe an experiment to demonstrate plasmolysis in a plant cell using a peeled section of an onion (Rhoeo leaf). Include the observation and conclusion. [2]

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(ii) (a) List any three factors that affect the rate of transpiration. [1½]

(b) Briefly explain the role of guard cells in opening and closing of stomata. [1½]

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(iii) (a) Write the balanced chemical equation for photosynthesis. [1]

(b) Explain the two main phases of photosynthesis — the Light Reaction and the Dark Reaction (Calvin Cycle). State where each phase occurs in the chloroplast. [2]

(c) Describe an experiment to prove that sunlight is necessary for photosynthesis. [1]

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Question 5 — Nervous System and Endocrine System [10]

(i) The diagram below represents the human brain in longitudinal section. [4]

(Diagram of L.S. of human brain showing: P — Cerebrum, Q — Cerebellum, R — Medulla oblongata, S — Hypothalamus)

• (a) Identify the parts labelled P, Q, R, and S. [2]
• (b) State one function of each of the parts P and R. [1]
• (c) What is the role of the part labelled S in the endocrine system? [1]

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(ii) (a) Draw a neat labelled diagram of a reflex arc. [2]

(b) Explain the pathway of a nerve impulse in a spinal reflex action using the example of withdrawing your hand on touching a hot object. [1]

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(iii) Give the name of the following: [3]

• (a) The hormone secreted by the thyroid gland and its function.
• (b) The disorder caused by over-secretion of growth hormone in adults.
• (c) The gland that acts as both an endocrine and exocrine gland. Name one hormone it secretes and its role.

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Question 6 — Circulatory System and Excretory System [10]

(i) (a) Draw a neat labelled diagram of the internal structure of the human heart. Label the following: left ventricle, right atrium, aorta, bicuspid (mitral) valve. [2]

(b) Trace the path of blood through the pulmonary circulation starting from the right ventricle. [1]

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(ii) Study the diagram of a nephron given below and answer the questions: [4]

(Diagram of a nephron showing: A — Bowman's capsule, B — Glomerulus, C — Proximal convoluted tubule, D — Loop of Henle, E — Collecting duct)

• (a) Identify the parts labelled A, B, and D. [1½]
• (b) Name the process that takes place in part A. What is the fluid formed called? [1]
• (c) What is the importance of the part labelled D in the formation of urine? [½]
• (d) Name the substance reabsorbed by the part labelled C. [1]

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(iii) Differentiate between the following: [3]

• (a) White blood cells (WBC) and Red blood cells (RBC) — (presence of nucleus)
• (b) Arteries and Veins — (thickness of wall)
• (c) Plasma and Serum — (presence of fibrinogen)

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Question 7 — Reproductive System and Population [10]

(i) (a) Draw a neat labelled diagram of the female reproductive system and label: ovary, fallopian tube, uterus, and cervix. [2]

(b) State the function of the fallopian tube and the uterus. [1]

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(ii) (a) Explain the four phases of the menstrual cycle. [2]

(b) Define the following terms: [1]
- Fertilization
- Implantation

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(iii) (a) State any three causes of the rapid increase in population in India. [1½]

(b) Mention three effects of overpopulation on the environment and resources. [1]

(c) Suggest any three measures to control population growth. [1½]

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Question 8 — Pollution and Mixed Topics [10]

(i) (a) Define pollution. Name the three main types of pollution. [1]

(b) State two harmful effects of air pollution on human health. [1]

(c) Suggest one measure to reduce water pollution. [1]

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(ii) (a) What are tropic movements? Name any two types with examples. [2]

(b) Explain the role of auxin in phototropism. How does unequal distribution of auxin cause bending of a plant shoot towards light? [2]

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(iii) (a) What is meant by the term "synapse"? How is a nerve impulse transmitted across a synapse? [1½]

(b) State the function of the following: [1½]
- Eustachian tube
- Renal artery
- Placenta

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ANSWER KEY

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Question 1 — MCQ Answers

Q	Answer	Explanation
(i)	(c) Anaphase	During anaphase, the centromere splits and sister chromatids are pulled apart to opposite poles by shortening spindle fibres.
(ii)	(c) 3 : 1	In a monohybrid cross (TT × tt), F₁ is all Tt (tall). F₂ (Tt × Tt) gives TT : Tt : tt = 1 : 2 : 1 genotypic and 3 tall : 1 dwarf phenotypic ratio.
(iii)	(b) Undergo plasmolysis	In a hypertonic solution, water moves out of the cell by exosmosis, causing the protoplasm to shrink away from the cell wall (plasmolysis).
(iv)	(b) Ganong's potometer	Ganong's potometer is specifically designed to measure the rate of water absorption (as an indirect measure of transpiration).
(v)	(b) Stroma of the chloroplast	The dark reaction (Calvin Cycle) occurs in the stroma, where CO₂ is fixed into glucose using ATP and NADPH from the light reaction.
(vi)	(b) Right atrium	The right atrium receives deoxygenated blood from the body via the superior and inferior vena cava.
(vii)	(b) Nephron	The nephron is the structural and functional unit of the kidney, responsible for filtration, reabsorption, and secretion.
(viii)	(b) Cerebellum	The cerebellum coordinates muscular activity, maintains body balance, posture, and equilibrium.
(ix)	(a) Both A and R are true, and R is the correct explanation of A	Insulin is produced by beta cells of the Islets of Langerhans. It lowers blood glucose by converting excess glucose to glycogen (glycogenesis) in the liver.
(x)	(c) Testosterone	Testosterone is the male sex hormone produced by the testes. It controls development of secondary sexual characteristics such as facial hair, deep voice, and muscular build.
(xi)	(b) Receptor → Sensory neuron → Spinal cord → Motor neuron → Effector	This is the correct sequence of a spinal reflex arc from stimulus detection to response.
(xii)	(a) Both A and R are true, and R is the correct explanation of A	Meiosis is termed reduction division because the diploid (2n) parent cell produces haploid (n) daughter cells, reducing the chromosome number by half.
(xiii)	(c) Fallopian tube (Oviduct)	Fertilization (fusion of sperm and ovum) normally occurs in the ampulla of the fallopian tube (oviduct).
(xiv)	(c) Carbon dioxide	CO₂ is a major greenhouse gas. Its increased concentration due to burning fossil fuels traps heat in the atmosphere, causing global warming.
(xv)	(b) Auxin	Auxin (Indole-3-acetic acid / IAA) promotes cell elongation. In phototropism, auxin accumulates on the shaded side, causing differential growth and bending towards light.

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Question 2 — Answers

(i) Kidney Diagram [5]

• (a) A — Cortex (outer region of the kidney containing Bowman's capsules and convoluted tubules); B — Medulla (inner region containing loops of Henle and collecting ducts); C — Renal pelvis (funnel-shaped cavity that collects urine).
• (b) Nephron — the structural and functional unit of the kidney, found spanning both the cortex and medulla.
• (c) Part E (Ureter) — carries urine from the renal pelvis of the kidney to the urinary bladder by peristalsis.

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(ii) Biological Terms [5]

• (a) Osmosis
• (b) Meiosis
• (c) Diabetes mellitus
• (d) Reflex action
• (e) Transpiration

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(iii) Fill in the Blanks [5]

• (a) Interphase — Interphase is the longest phase of the cell cycle, during which DNA replication and cell growth occur.
• (b) Pulmonary vein — The pulmonary vein is the only vein that carries oxygenated blood, transporting it from the lungs to the left atrium.
• (c) Occipital — The occipital lobe at the back of the cerebrum is the visual processing centre.
• (d) Glycolysis — Glycolysis is the anaerobic breakdown of glucose into two molecules of pyruvic acid in the cytoplasm.
• (e) Geotropism — Geotropism (gravitropism) is the directional growth response of a plant in response to gravity. Roots show positive geotropism.

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(iv) Match the Following [5]

Column A	Column B
(a) Bowman's capsule	(iii) Ultrafiltration
(b) Axon	(i) Carries impulses away from the cell body
(c) Corpus luteum	(iv) Secretes progesterone
(d) Adrenaline	(ii) Increases heart rate and blood pressure
(e) Synapse	(vi) Junction between two neurons

(Extra options: (v) Stores bile and (vii) Carries impulses towards the cell body — not used)

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(v) Differences [5]

	Term 1	Term 2
(a)	Mitosis — produces 2 identical diploid daughter cells	Meiosis — produces 4 non-identical haploid daughter cells
(b)	Artery — carries blood away from the heart	Vein — carries blood towards the heart
(c)	Transpiration — water is lost as water vapour (gaseous state)	Guttation — water is lost as liquid droplets (liquid state)
(d)	Cerebrum — seat of intelligence, memory, thinking, and voluntary actions	Cerebellum — maintains body balance, posture, and coordination of movements
(e)	Diabetes mellitus — caused by deficiency of insulin (from pancreas)	Diabetes insipidus — caused by deficiency of ADH / vasopressin (from posterior pituitary)

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Question 3 — Cell Division and Genetics

(i) Mitosis Diagram [3]

• (a) The stage shown is Anaphase of mitosis. Reason: The centromeres have split and the chromatids (now called daughter chromosomes) are being pulled to opposite poles of the cell by shortening spindle fibres.
• (b) The structure connecting the chromatid to the spindle fibre is the centromere (or kinetochore).
• (c) The next stage is Telophase:
• Daughter chromosomes reach the opposite poles and uncoil to form chromatin.
• The nuclear membrane and nucleolus reappear around each set of chromosomes.
• The spindle fibres disappear.
• Cytokinesis (division of the cytoplasm) begins, forming a cell plate in plant cells or a cleavage furrow in animal cells.

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(ii) Monohybrid Cross [3]

• (a) Parent genotypes: Heterozygous round-seeded plant = Rr; Wrinkled-seeded plant = rr
• (b) Punnett Square (Rr × rr):

	r	r
R	Rr (Round)	Rr (Round)
r	rr (Wrinkled)	rr (Wrinkled)

• (c) Phenotypic ratio: 1 Round : 1 Wrinkled (i.e., 50% round, 50% wrinkled). This is a test cross.

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(iii) Sex Determination and Dihybrid Cross [4]

(a) Sex Determination in Humans:

• Human females have sex chromosomes XX and males have XY.
• All ova carry the X chromosome. Sperms are of two types: 50% carry X and 50% carry Y.

	X (from father)	Y (from father)
X (from mother)	XX (Girl)	XY (Boy)
X (from mother)	XX (Girl)	XY (Boy)

• Ratio: 1 Girl : 1 Boy (50% chance each). The sex of the child is determined by the father's sperm.

(b) Dihybrid Test Cross (TtRr × ttrr):

Gametes of TtRr: TR, Tr, tR, tr
Gametes of ttrr: tr only

	tr
TR	TtRr (Tall, Round)
Tr	Ttrr (Tall, Wrinkled)
tR	ttRr (Dwarf, Round)
tr	ttrr (Dwarf, Wrinkled)

Phenotypic ratio: 1 Tall Round : 1 Tall Wrinkled : 1 Dwarf Round : 1 Dwarf Wrinkled (1 : 1 : 1 : 1)

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Question 4 — Plant Physiology

(i) Plasmolysis [3]

• (a) Plasmolysis is the shrinkage of the protoplasm of a cell away from its cell wall when placed in a hypertonic solution due to exosmosis (loss of water).

• (b) Experiment:

• Materials: Rhoeo leaf peel, concentrated sugar/salt solution, glass slide, cover slip, microscope, dropper.
• Procedure: Mount a thin peel of Rhoeo leaf on a glass slide in water. Observe the uniformly coloured cells under a microscope. Now add a few drops of concentrated sugar solution at one edge of the cover slip while drawing it in from the other side using blotting paper.
• Observation: The coloured protoplasm (cell sap) shrinks and pulls away from the cell wall. Gaps appear between the cell wall and the shrunken protoplasm.
• Conclusion: The concentrated sugar solution is hypertonic to the cell sap. Water moves out of the cell by exosmosis, causing the protoplasm to shrink — this confirms plasmolysis. Plasmolysis can be reversed (deplasmolysis) by placing the cell back in water (hypotonic solution).

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(ii) Transpiration [3]

• (a) Three factors affecting the rate of transpiration:
• Temperature — Higher temperature increases the rate of transpiration as it increases the rate of evaporation.
• Humidity — Low humidity increases transpiration; high humidity decreases it as the diffusion gradient is reduced.

• Wind velocity — Increased wind speed removes water vapour from around the leaf surface, increasing transpiration rate.

• (b) Role of guard cells: Guard cells are bean-shaped cells surrounding each stoma. When guard cells absorb water (become turgid), their thin outer walls bulge outward, pulling the thick inner walls apart — the stoma opens. When guard cells lose water (become flaccid), the inner walls come together — the stoma closes. This opening and closing regulates transpiration and gas exchange.

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(iii) Photosynthesis [4]

• (a) Balanced equation:

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

• (b) Two phases of photosynthesis:

Light Reaction (Photochemical phase):
- Occurs in the grana (thylakoids) of the chloroplast.
- Chlorophyll absorbs light energy and water molecules are split (photolysis of water): 2H₂O → 4H⁺ + 4e⁻ + O₂
- ATP and NADPH are produced. Oxygen is released as a by-product.

Dark Reaction (Calvin Cycle / Biosynthetic phase):
- Occurs in the stroma of the chloroplast.
- CO₂ is fixed by the enzyme RuBisCO and reduced using ATP and NADPH from the light reaction.
- Glucose (C₆H₁₂O₆) is synthesized. This phase does not directly require light but depends on the products of the light reaction.

• (c) Experiment to prove sunlight is necessary:
• Take a potted plant and destarch it by placing it in a dark cupboard for 48 hours.
• Cover a portion of a leaf with black paper (on both sides) using clips, leaving the rest exposed.
• Place the plant in sunlight for several hours.
• Pluck the leaf, remove the black paper, boil it in water, then in alcohol (to remove chlorophyll).
• Wash with water and test with iodine solution.
• Observation: The exposed part turns blue-black (starch present) while the covered part remains brown (no starch).
• Conclusion: Sunlight is essential for photosynthesis, as starch was produced only in the portion exposed to light.

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Question 5 — Nervous System and Endocrine System

(i) Brain Diagram [4]

• (a) P — Cerebrum; Q — Cerebellum; R — Medulla oblongata; S — Hypothalamus
• (b) Functions:
• P (Cerebrum) — It is the seat of intelligence, memory, consciousness, will power, and voluntary actions. It also receives and interprets sensory impulses (sight, hearing, taste, smell, touch).
• R (Medulla oblongata) — Controls involuntary actions such as breathing, heart rate, blood pressure, swallowing, coughing, sneezing, and vomiting.
• (c) The hypothalamus (S) acts as the link between the nervous system and the endocrine system. It controls the pituitary gland (master gland) by secreting releasing and inhibiting hormones, thereby regulating the activity of many other endocrine glands.

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(ii) Reflex Arc [3]

• (a) Diagram of a reflex arc should include: Receptor (in skin) → Sensory (afferent) neuron → Relay (intermediate) neuron in the spinal cord (grey matter) → Motor (efferent) neuron → Effector (muscle/gland). Labels: dendrites, cell body, axon, synapse, dorsal root ganglion, spinal cord (grey and white matter).

• (b) Pathway of reflex action (withdrawing hand from a hot object):

• The receptor (heat receptor in the skin of the finger) detects the hot stimulus.
• The sensory neuron carries the impulse from the receptor to the spinal cord (relay centre).
• The relay neuron in the spinal cord processes the impulse and transmits it to the motor neuron.
• The motor neuron carries the impulse from the spinal cord to the effector (muscles of the hand).
• The effector (arm muscle) contracts, pulling the hand away from the hot object.
• This entire process is involuntary, automatic, and takes a fraction of a second.

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(iii) Hormones and Glands [3]

• (a) The thyroid gland secretes thyroxine (T₃ and T₄). Function: Thyroxine regulates the basal metabolic rate (BMR) of the body. It controls the rate of metabolism of carbohydrates, fats, and proteins, and is essential for normal physical and mental growth.

• (b) Over-secretion of growth hormone (GH/STH) in adults causes Acromegaly — a condition characterised by abnormal enlargement of the bones of the hands, feet, lower jaw, and facial bones.

• (c) The Pancreas acts as both an endocrine and exocrine gland.

• As an endocrine gland, it secretes insulin (from beta cells of Islets of Langerhans). Insulin lowers blood glucose levels by promoting the conversion of excess glucose to glycogen in the liver (glycogenesis).
• As an exocrine gland, it secretes pancreatic juice containing digestive enzymes (trypsin, lipase, amylase) into the duodenum via the pancreatic duct.

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Question 6 — Circulatory System and Excretory System

(i) Heart [3]

• (a) Diagram of internal structure of the human heart should show: four chambers (left atrium, right atrium, left ventricle, right ventricle), interventricular septum, bicuspid (mitral) valve, tricuspid valve, semilunar valves, aorta, pulmonary artery, pulmonary vein, superior and inferior vena cava. Labels required: left ventricle, right atrium, aorta, bicuspid (mitral) valve.

• (b) Pulmonary circulation:
  Right ventricle → Pulmonary artery → Lungs (where CO₂ is released and O₂ is absorbed) → Pulmonary vein → Left atrium.

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(ii) Nephron [4]

• (a) A — Bowman's capsule (cup-shaped structure enclosing the glomerulus); B — Glomerulus (a tuft/knot of capillaries formed from the afferent arteriole); D — Loop of Henle (U-shaped portion of the renal tubule between the proximal and distal convoluted tubules).
• (b) The process in part A is ultrafiltration (glomerular filtration). Blood under high pressure in the glomerulus forces water, glucose, salts, urea, and other small molecules through the walls of the capillaries and Bowman's capsule. The fluid formed is called glomerular filtrate (nephric filtrate).
• (c) The Loop of Henle (D) plays an important role in the concentration of urine by reabsorbing water (in the descending limb) and sodium/chloride ions (in the ascending limb), creating a concentration gradient in the medulla.
• (d) The proximal convoluted tubule (C) reabsorbs glucose, amino acids, sodium ions, water, and other useful substances by selective reabsorption back into the blood.

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(iii) Differences [3]

Basis	Term 1	Term 2
(a) Presence of nucleus	WBC — possess a nucleus (nucleated)	RBC — mature RBCs are enucleated (no nucleus) in humans
(b) Thickness of wall	Artery — has thick, muscular, elastic walls to withstand high blood pressure	Vein — has thin walls with less muscle and elastic tissue as blood pressure is low
(c) Presence of fibrinogen	Plasma — contains fibrinogen (clotting protein)	Serum — lacks fibrinogen (serum = plasma - clotting factors)

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Question 7 — Reproductive System and Population

(i) Female Reproductive System [3]

• (a) Diagram of the female reproductive system should show: a pair of ovaries, fallopian tubes (oviducts) with fimbriae, uterus, cervix, and vagina. Labels required: ovary, fallopian tube, uterus, cervix.

• (b) Functions:

• Fallopian tube (Oviduct): It receives the ovum released from the ovary (with the help of fimbriae) and is the site of fertilization. It also transports the fertilized egg (zygote) to the uterus through peristaltic movements and ciliary action.
• Uterus (Womb): It is the site of implantation of the embryo. The uterus provides nourishment and protection to the developing foetus throughout pregnancy. Its muscular wall contracts during childbirth to expel the baby.

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(ii) Menstrual Cycle and Key Terms [3]

• (a) Four phases of the menstrual cycle (average 28 days):

• Menstrual phase (Days 1-5): The uterine lining (endometrium) breaks down and is shed along with blood and the unfertilised ovum through the vagina. This is menstruation.

• Follicular phase / Proliferative phase (Days 6-13): Under the influence of FSH from the pituitary gland, a Graafian follicle matures in the ovary. Oestrogen from the follicle stimulates the thickening and repair of the uterine lining.
• Ovulatory phase (Day 14): A surge of LH from the pituitary causes the mature Graafian follicle to rupture, releasing the ovum into the fallopian tube. This is ovulation.

• Luteal phase / Secretory phase (Days 15-28): The ruptured follicle transforms into the corpus luteum, which secretes progesterone. Progesterone further thickens the endometrium and makes it spongy, preparing it for the implantation of a fertilised egg. If fertilization does not occur, the corpus luteum degenerates, progesterone levels drop, and menstruation begins again.

• (b) Definitions:

• Fertilization: The fusion of the male gamete (sperm) with the female gamete (ovum) to form a diploid zygote. It normally occurs in the fallopian tube.
• Implantation: The embedding of the developing blastocyst (early embryo) into the thick, vascular endometrium (uterine lining) for further development and nourishment.

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(iii) Population [4]

• (a) Three causes of rapid population increase in India:
• Decline in death rate due to advances in medical facilities, better nutrition, and improved sanitation, without a corresponding decline in birth rate.
• Early marriage leading to a longer reproductive span and more children per couple.

• Illiteracy and lack of awareness about family planning methods, particularly in rural areas.

• (b) Three effects of overpopulation:

• Depletion of natural resources — Increased demand for food, water, fuel, and land leads to overexploitation and deforestation.
• Environmental pollution — More people generate more waste, vehicular emissions, and industrial pollutants, degrading air, water, and soil quality.

• Unemployment and poverty — The economy cannot provide sufficient jobs for the rapidly growing population, leading to poverty, poor living standards, and inadequate education.

• (c) Three measures to control population growth:

• Education and awareness — Promoting literacy, especially female education, and spreading awareness about family planning and contraception.
• Raising the age of marriage — Enforcing the legal minimum age for marriage (18 for women, 21 for men) to reduce the reproductive span.
• Government incentives and family planning programs — Encouraging small families through tax benefits, free contraception, and accessible reproductive healthcare services.

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Question 8 — Pollution and Mixed Topics

(i) Pollution [3]

• (a) Pollution is the undesirable change in the physical, chemical, or biological characteristics of air, water, or soil that adversely affects living organisms and the environment.
  Three main types: Air pollution, Water pollution, and Soil (Land) pollution.

• (b) Two harmful effects of air pollution on human health:

• Respiratory diseases — Pollutants such as SO₂, NO₂, and particulate matter cause bronchitis, asthma, emphysema, and lung cancer.

• Allergies and eye irritation — Smog and pollen particles can trigger allergic reactions, watering of eyes, and irritation of the respiratory tract.

• (c) One measure to reduce water pollution: Setting up proper sewage treatment plants (effluent treatment plants) to treat domestic and industrial wastewater before discharging it into rivers, lakes, or oceans. This removes harmful chemicals, pathogens, and organic matter from the water.

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(ii) Chemical Coordination in Plants [4]

• (a) Tropic movements are directional growth movements of a plant (or plant part) in response to an external unidirectional stimulus. The growth may be towards the stimulus (positive) or away from it (negative).

Two types with examples:
1. Phototropism — Growth movement in response to light. Example: The stem of a plant bends towards a light source (positive phototropism), while roots grow away from light (negative phototropism).
2. Geotropism (Gravitropism) — Growth movement in response to gravity. Example: Roots grow downwards towards gravity (positive geotropism), while stems grow upwards against gravity (negative geotropism).

• (b) Role of auxin in phototropism:
• Auxin (IAA) is synthesised at the tip of the shoot and moves downward.
• When light falls on one side of the shoot, auxin migrates from the illuminated (lit) side to the shaded (dark) side.
• The higher concentration of auxin on the shaded side stimulates greater cell elongation on that side.
• The cells on the shaded side grow faster and become longer than those on the illuminated side.
• This differential (unequal) growth causes the shoot to bend towards the light source (positive phototropism).
• This was demonstrated by the Cholodny-Went model of auxin redistribution.

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(iii) Mixed Topics [3]

• (a) A synapse is the microscopic gap (junction) between the axon terminal of one neuron and the dendrite of the next neuron. Transmission across a synapse: When a nerve impulse reaches the synaptic knob (end of the axon), it triggers the release of a chemical neurotransmitter (e.g., acetylcholine) from synaptic vesicles into the synaptic cleft. The neurotransmitter diffuses across the cleft and binds to receptors on the membrane of the next neuron, generating a new electrical impulse. This ensures one-way transmission of the nerve impulse.

• (b) Functions:

• Eustachian tube: Connects the middle ear to the pharynx (throat). It equalises the air pressure on both sides of the eardrum (tympanic membrane), preventing damage to the eardrum due to pressure differences.
• Renal artery: Carries oxygenated blood (containing urea and other metabolic wastes) from the aorta to the kidney for filtration and purification.
• Placenta: A disc-shaped structure that connects the foetus to the uterine wall of the mother. It facilitates the exchange of nutrients, oxygen, and waste products between the mother's blood and the foetal blood without direct mixing. It also secretes hormones (oestrogen, progesterone, HCG) to maintain pregnancy.

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TOPIC-WISE PROBABILITY ANALYSIS

Topic	Probability	Level
Nervous System (Brain, Reflex Arc, Neuron)	⬛⬛⬛⬛⬛⬛⬛⬛⬛⬛	Very High
Endocrine System (Hormones, Glands, Disorders)	⬛⬛⬛⬛⬛⬛⬛⬛⬛⬛	Very High
Genetics (Monohybrid Cross, Sex Determination)	⬛⬛⬛⬛⬛⬛⬛⬛⬛⬛	Very High
Cell Division (Mitosis, Meiosis, Stages)	⬛⬛⬛⬛⬛⬛⬛⬛⬛	Very High
Excretory System (Nephron, Urine Formation)	⬛⬛⬛⬛⬛⬛⬛⬛⬛	Very High
Circulatory System (Heart, Blood Vessels, Blood)	⬛⬛⬛⬛⬛⬛⬛⬛⬛	Very High
Photosynthesis (Equations, Light/Dark Reactions)	⬛⬛⬛⬛⬛⬛⬛⬛	High
Transpiration (Factors, Stomata, Potometer)	⬛⬛⬛⬛⬛⬛⬛⬛	High
Reproductive System (Menstrual Cycle, Organs)	⬛⬛⬛⬛⬛⬛⬛⬛	High
Absorption by Roots (Osmosis, Plasmolysis)	⬛⬛⬛⬛⬛⬛⬛	High
Pollution (Types, Effects, Control)	⬛⬛⬛⬛⬛⬛⬛	High
Chemical Coordination in Plants (Auxins, Tropisms)	⬛⬛⬛⬛⬛⬛	Medium
Population (Causes, Effects, Control Measures)	⬛⬛⬛⬛⬛⬛	Medium
Human Evolution	⬛⬛⬛	Medium

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KEY TOPICS TO REVISE

1. Nervous System — Draw and label the brain (L.S.), reflex arc, neuron structure. Know functions of cerebrum, cerebellum, medulla oblongata, and hypothalamus. Understand synapse and nerve impulse transmission.

2. Endocrine System — Learn all glands, their hormones, functions, and associated disorders (e.g., diabetes mellitus, acromegaly, cretinism, goitre, Addison's disease). Understand the difference between diabetes mellitus and diabetes insipidus.

3. Genetics and Cell Division — Practice monohybrid and dihybrid crosses with Punnett squares. Know the mechanism of sex determination in humans (XX/XY). Draw and describe all stages of mitosis and meiosis. Know significance and differences.

4. Excretory System — Draw and label the nephron. Explain ultrafiltration, selective reabsorption, and tubular secretion. Understand urine formation step by step. Know kidney structure (L.S.).

5. Circulatory System — Draw the internal structure of the heart. Trace pulmonary and systemic circulation. Differentiate arteries, veins, and capillaries. Know blood composition (RBC, WBC, platelets, plasma).

6. Photosynthesis — Write the balanced equation. Differentiate light and dark reactions. Know where each occurs. Practice experiments proving necessity of light, CO₂, and chlorophyll.

7. Transpiration and Absorption — Explain stomatal mechanism. Describe Ganong's potometer. Know factors affecting transpiration. Understand osmosis, diffusion, active transport, and plasmolysis with experiments.

8. Reproductive System and Population — Draw male and female reproductive systems. Explain all four phases of the menstrual cycle. Define fertilization, implantation. Know causes, effects, and control measures for population growth.

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Prepared by BrightTutorials.in — For personal study use only. This is a prediction paper based on syllabus analysis and previous year trends. It does not claim to represent the actual ICSE 2026 examination paper.

Topic-Wise Probability Analysis

Based on 10+ years of ICSE board paper analysis and syllabus weightage:

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Key Revision Tips for ICSE Biology 2026

1. Diagrams are crucial — Practise drawing and labelling the brain (L.S.), heart, nephron, reflex arc, neuron, and reproductive system. Neat diagrams with correct labels can fetch full marks.
2. Master Genetics crosses — Solve monohybrid, dihybrid, and sex determination crosses using Punnett squares. Show gametes, genotypic ratio, and phenotypic ratio clearly.
3. Memorise all hormones — Create a table of glands, hormones, functions, and deficiency disorders for the endocrine system. This is one of the most frequently tested topics.
4. Learn experiments thoroughly — Be ready to describe experiments on plasmolysis, photosynthesis (sunlight, CO2, chlorophyll), transpiration (potometer), and osmosis with procedure, observation, and conclusion.
5. Differentiation tables — Prepare comparison tables (mitosis vs meiosis, artery vs vein, transpiration vs guttation, etc.) as these are commonly asked.
6. Answer in points — Use numbered or bulleted points with keywords underlined. Examiners can quickly find marking points this way.
7. Time management — Spend first 15 min reading. Allocate ~48 min for Section A, ~48 min for Section B (4 questions). Leave 4 min for review.
8. Don’t skip Population & Pollution — These are easier topics with guaranteed marks. Know causes, effects, and control measures.

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Prepared by Bright Tutorials — brighttutorials.in

This is a prediction paper based on syllabus analysis and previous year trends. It does not claim to represent the actual ICSE 2026 examination paper.