2020 Biology Science Paper - 3
Complete biology examination paper with Section I (40 marks) covering basic concepts and Section II (40 marks) with detailed questions on photosynthesis, circulation, human eye, nephron, transpiration, genetics, and human reproduction.
ICSE Biology Exam Analysis
Prediction of ICSE Biology Question Papers Based on the Trends
Created by Titas Mallick
Biology Teacher • M.Sc. Botany • B.Ed. • CTET (CBSE) • CISCE Examiner
Complete solution guide for ICSE Biology 2026 examination
Four friends P, Q, R and S discussed genetic disorders. Their examples:
Who gave the correct examples?
| Option | Choice |
|---|---|
| (a) | P and Q |
| (b) | R and S ✅ |
| (c) | P and R |
| (d) | Q and S |
Answer: (b) R and S
Reason: Haemophilia, Colour blindness, and Albinism are all genetic disorders. Malaria is caused by a protozoan (Plasmodium) and Cholera by bacteria — both are infectious diseases, not genetic disorders.
During ventricular systole, the atrioventricular valves (P) _______ and the semilunar valves (Q) _______.
| Option | Choice |
|---|---|
| (a) | P - close and Q - open ✅ |
| (b) | P - close and Q - close |
| (c) | P - open and Q - close |
| (d) | P - open and Q - open |
Answer: (a) P - close and Q - open
Reason: During ventricular systole (contraction), the AV valves (mitral and tricuspid) close to prevent backflow into the atria. Simultaneously, the semilunar valves (aortic and pulmonary) open to pump blood into the major arteries.
Assertion (A): A thick cuticle reduces transpiration by acting as a barrier.
Reason (R): Desert plants have large, thin leaves for transpiration.
| Option | Choice |
|---|---|
| (a) | (A) is true and (R) is false. ✅ |
| (b) | (A) is false and (R) is true. |
| (c) | Both (A) and (R) are true and (R) is the correct explanation. |
| (d) | Both (A) and (R) are true but (R) is not the correct explanation. |
Answer: (a) (A) is true and (R) is false.
Reason: The assertion is correct — a waxy cuticle prevents water loss. The reason is false: desert plants (xerophytes) have small, needle-like or succulent leaves (not large thin ones) to minimize transpiration.
A DNA sequence has 300 nitrogenous base pairs, of which 75 are Guanine. What is the number of Thymine?
| Option | Choice |
|---|---|
| (a) | 150 |
| (b) | 100 |
| (c) | 50 |
| (d) | 75 ✅ |
Answer: (d) 75
Calculation (Chargaff's Rule — G = C and A = T):
- G = 75, therefore C = 75
- Total G + C = 150
- Remaining bases = 300 − 150 = 150
- Since A = T → Thymine = 150 / 2 = 75
Assertion (A): Abscisic acid promotes stomatal closure during a drought.
Reason (R): Abscisic acid helps the plant to conserve water during stress.
| Option | Choice |
|---|---|
| (a) | (A) is true and (R) is false. |
| (b) | (A) is false and (R) is true. |
| (c) | Both (A) and (R) are true and (R) is the correct explanation. ✅ |
| (d) | Both (A) and (R) are true but (R) is not the correct explanation. |
Answer: (c) Both true; (R) correctly explains (A).
Reason: ABA (Abscisic Acid) is the plant "stress hormone." It triggers stomatal closure during water deficit to minimize water loss via transpiration — conserving water is precisely the mechanism by which it closes the stomata.
Assertion (A): Leukoderma is the biological term for blood cancer.
Reason (R): An abnormal increase in WBCs causes blood cancer.
| Option | Choice |
|---|---|
| (a) | (A) is true and (R) is false. |
| (b) | (A) is false and (R) is true. ✅ |
| (c) | Both (A) and (R) are true and (R) is the correct explanation. |
| (d) | Both (A) and (R) are true but (R) is not the correct explanation. |
Answer: (b) (A) is false and (R) is true.
Reason: Leukoderma (vitiligo) is a skin pigmentation disorder. The correct term for blood cancer is Leukemia. The reason is correct — Leukemia involves uncontrolled production of abnormal WBCs.
A health organisation wants to educate rural audiences about population control using visually engaging methods. Which are effective?
P. Posters | Q. Loudspeakers | R. Film shows | S. Street plays
| Option | Choice |
|---|---|
| (a) | P, R and S ✅ |
| (b) | Q, R and S |
| (c) | P, Q and R |
| (d) | P, Q and S |
Answer: (a) P, R and S
Reason: Posters, film shows, and street plays are visual/performative media. Loudspeakers (Q) are purely auditory — they do not qualify as "visually engaging."
Mother is a carrier (X^c X) and father has normal vision (XY). What is the probability of their sons being colour blind?
| Option | Choice |
|---|---|
| (a) | 25% |
| (b) | 50% ✅ |
| (c) | 75% |
| (d) | 0% |
Answer: (b) 50%
Punnett Square:
X Y X^c X^c X (Carrier female) X^c Y (Colour blind son) X XX (Normal female) XY (Normal son) 1 out of 2 possible son genotypes is colour blind → 50% probability among sons.
Bharat missed his school bus. The sympathetic nervous system was activated. This resulted in:
| Option | Choice |
|---|---|
| (a) | Constriction of coronary arteries |
| (b) | Muscle relaxation |
| (c) | Decrease in respiration rate |
| (d) | Bronchodilation ✅ |
Answer: (d) Bronchodilation
Reason: The sympathetic system triggers the "fight-or-flight" response. The body needs more oxygen during stress, so bronchodilation widens the airways to increase oxygen intake and enhance respiration.
Which is the correct sequence of blood flow in Pulmonary and Systemic Circulation?
| Option | Choice |
|---|---|
| (a) | Right Atrium → Right Ventricle → Lungs → Left Atrium → Left Ventricle → Body tissues ✅ |
| (b) | Left Ventricle → Left Atrium → Body tissues → Right Atrium → Right Ventricle → Lungs |
| (c) | Left Ventricle → Left Atrium → Lungs → Right Ventricle → Right Atrium → Body tissues |
| (d) | Right Atrium → Right Ventricle → Body tissues → Left Atrium → Left Ventricle → Lungs |
Answer: (a) Right Atrium → Right Ventricle → Lungs → Left Atrium → Left Ventricle → Body tissues
Reason: Deoxygenated blood enters the Right Atrium → Right Ventricle → Lungs (oxygenation) → Left Atrium → Left Ventricle → Body tissues. This correctly traces both pulmonary and systemic circuits.
Karan fell and sustained a head injury. His pupils lost the ability to constrict in bright light. Which structure is damaged?
| Option | Choice |
|---|---|
| (a) | Suspensory ligaments |
| (b) | Medulla oblongata ✅ |
| (c) | Eye lens |
| (d) | Eye lid |
Answer: (b) Medulla oblongata
Reason: Pupillary constriction in response to light is a reflex action controlled by the brainstem. Damage to the medulla oblongata disrupts these involuntary reflex responses.
A person with kidney failure has proteins in the urine. What is this condition called?
| Option | Choice |
|---|---|
| (a) | Haematuria |
| (b) | Glycosuria |
| (c) | Albuminuria ✅ |
| (d) | Anaemia |
Answer: (c) Albuminuria
Reason: Albumin is the main blood protein. When the glomerular filtration membrane is damaged, albumin leaks into urine → Albuminuria. Haematuria = blood in urine; Glycosuria = glucose in urine.
What does the Swachh Bharat Abhiyan aim to achieve in India?
| Option | Choice |
|---|---|
| (a) | Increase in deforestation to dump waste. |
| (b) | Expansion of landfill areas to accommodate more waste. |
| (c) | Improved sanitation and solid waste management. ✅ |
| (d) | Greater industrial waste production. |
Answer: (c) Improved sanitation and solid waste management.
Reason: The Swachh Bharat Abhiyan (Clean India Mission) is a national campaign aimed at eliminating open defecation and improving solid waste management across India.
Varun's mother added plenty of salt to mango pickle. The reasons are:
| Option | Choice |
|---|---|
| (a) | A and C |
| (b) | B and C |
| (c) | C and D |
| (d) | B and D ✅ |
Answer: (d) B and D
Reason: Salt creates a hypertonic solution outside microbial cells, causing water to exit by osmosis (plasmolysis), thereby inhibiting microbial growth and preventing spoilage.
During which phase of the menstrual cycle does the endometrium shed?
| Option | Choice |
|---|---|
| (a) | Follicular phase |
| (b) | Ovulatory phase |
| (c) | Menstrual phase ✅ |
| (d) | Luteal phase |
Answer: (c) Menstrual phase
Reason: The menstrual phase (menses) is the first phase of the cycle. The thickened uterine lining (endometrium) breaks down and is discharged when fertilization has not occurred.
| Part | Description | Answer |
|---|---|---|
| (a) | Tropic movement where tendrils of a pea plant twine around a support | Thigmotropism (Haptotropism) |
| (b) | Eye defect where some parts of an object are in focus while others are blurred | Astigmatism |
| (c) | Type of waste generated in hospitals and pathological laboratories | Biomedical Waste (Clinical Waste) |
| (d) | Surgical technique for females to prevent pregnancy | Tubectomy (Tubal Ligation) |
| (e) | Evolutionary process by which new species arise from existing ones | Speciation |
| Blank | Answer |
|---|---|
| (a) Cap-like organelle on the sperm head | Acrosome |
| (b) Enzyme produced by the acrosome | Hyaluronidase |
| (c) Number of chromosomes in the sperm nucleus | 23 chromosomes |
| (d) Organelle in the middle piece providing energy | Mitochondria |
| (e) Mixture of sperms and fluids from male accessory glands | Semen |
| Set | Odd One Out | Category of Others |
|---|---|---|
| (a) Auxin, Oxytocin, Gibberellin, Cytokinin | Oxytocin | Plant Hormones (Phytohormones) |
| (b) Growth Hormone, Vasopressin, TSH, Gonadotropic Hormone | Vasopressin | Anterior Pituitary Hormones |
| (c) Urochrome, Urea, Uric acid, Nucleic acid | Nucleic acid | Nitrogenous Waste Products |
| (d) Cervix, Chordae Tendinea, Papillary Muscles, Sinoatrial node | Cervix | Parts of the Mammalian Heart |
| (e) Morula, Blastocyst, Oviduct, Foetus | Oviduct | Stages of Embryonic Development |
Note (b): Vasopressin (ADH) is synthesised in the hypothalamus and released by the posterior pituitary, while the others are produced by the anterior pituitary.
Note (d): The Cervix is part of the female reproductive system, whereas the others are structural or functional components of the heart.
Mohit, 30, is a software professional with a sedentary lifestyle. He showed high blood sugar during a routine check-up despite having a normal body weight.
| Part | Question | Answer |
|---|---|---|
| (a) | Hormonal disorder he is suffering from | Diabetes Mellitus |
| (b) | Hormone responsible for this disorder | Insulin (deficiency / insufficient secretion) |
| (c) | Organ that secretes this hormone | Pancreas (Islets of Langerhans) |
| (d) | One symptom experienced by Mohit | Polyuria / Polydipsia / Glycosuria |
| (e) | One lifestyle change to lower blood sugar | Regular physical exercise / Reduce sugar and refined carbohydrate intake |
| Structure | Function |
|---|---|
| Pelvis | Receives urine which flows into the ureter |
| Renal Cortex | Contains Malpighian capsules (Bowman's capsule + glomerulus) |
| Renal Medulla | Contains Henle's loops |
| Renal Artery | Carries oxygenated blood to the kidney |
| Renal Vein | Carries deoxygenated blood away from the kidney |
| Ureter | Transports urine from kidney to urinary bladder |
Answer: Interphase
The cell grows, replicates DNA, and prepares for division. It is metabolically very active despite appearing "resting."
Answer: Binocular vision provides depth perception (stereoscopic vision), allowing eagles to accurately judge distances and the speed of prey — essential for precise hunting.
| Type | Number | Description |
|---|---|---|
| Autosomes | 44 (22 pairs) | Non-sex chromosomes carrying general genetic information |
| Allosomes (Sex chromosomes) | 2 (1 pair) | XX in females, XY in males |
Two identical, well-watered plants were placed in bright light — one at 15°C and one at 38°C. The plant at 38°C wilted by end of day.
| Part | Question | Answer |
|---|---|---|
| (a) | Which plant phenomenon caused wilting? | Excessive Transpiration — rate of water loss exceeded the rate of water absorption |
| (b) | Factor being tested in this experiment | Temperature |
Draw a neat labelled diagram of an animal cell in Prophase with four chromosomes.
Your diagram must show:
Answer: Homo sapiens
(Underline or italicise each word separately when handwriting)
| Structure | Cytons (Cell Bodies) | Axons |
|---|---|---|
| Cerebrum | Outer portion — Cerebral Cortex (Grey matter) | Inner portion (White matter) |
| Spinal Cord | Inner portion — H-shaped Grey matter | Outer portion (White matter) |
| Part | Question | Answer |
|---|---|---|
| (a) | Who proposed the Theory of Natural Selection? | Charles Darwin |
| (b) | Organism used to explain Industrial Melanism | Peppered Moth (Biston betularia) |
| Feature | Plasmolysis | Deplasmolysis |
|---|---|---|
| Definition | Shrinkage of protoplasm from cell wall when placed in a hypertonic solution | Return of a plasmolysed cell to its original state when placed in a hypotonic solution |
| Water Movement | Exosmosis — water moves OUT of the cell | Endosmosis — water moves INTO the cell |
| Cell Condition | Cell becomes flaccid | Cell becomes turgid |
| Part | Question | Answer |
|---|---|---|
| (a) | Location of the prostate gland | Just below the urinary bladder, surrounding the upper part of the urethra |
| (b) | Why does the prostate produce alkaline secretion? | To neutralize vaginal acidity, protecting sperm and increasing their motility and survival |
| (c) | Structure regulating urine flow from bladder to urethra | Urethral sphincter (internal and external sphincters) |
Without a nucleus, RBCs:
| Chain | Correct Sequence |
|---|---|
| (a) Small fish, Algae, Mosquito larvae, Kingfisher | Algae → Mosquito larvae → Small fish → Kingfisher |
| (b) Frog, Snail, Crow, Green leaves | Green leaves → Snail → Frog → Crow |
| Part | Question | Answer |
|---|---|---|
| (a) | One function of the placenta | Supplies oxygen and nutrients from mother to foetus; removes CO2 and urea from the foetus |
| (b) | What connects the placenta to the foetus? | Umbilical cord |
Any two of the following:
| Part | Question | Answer |
|---|---|---|
| (a) | Name the eye disorder | Presbyopia (age-related loss of lens elasticity) |
| (b) | How can it be corrected? | Convex lenses (reading glasses or bifocals) |
| (c) | Where is the image formed? | Behind the retina |
Population density is the number of individuals living per unit area (per km²) at a given time. It measures how densely a region is inhabited.
| Part | Question | Answer |
|---|---|---|
| (a) | Hypersecretion of which hormone causes Adrenal Virilism? | Adrenal Androgens (male sex hormones secreted by the adrenal cortex) |
| (b) | One symptom of this disorder | Development of male secondary sexual characteristics — e.g., facial hair (hirsutism) or deepening of voice |
| Feature | Animal Cell | Plant Cell |
|---|---|---|
| Method | Cleavage furrow formation | Cell plate formation |
| Direction | Centripetal (outside → inside) | Centrifugal (centre → periphery) |
| Part | Question | Answer |
|---|---|---|
| (a) | Why was the plant kept in the dark for 48 hours? | To destarch the leaves — all stored starch is consumed or translocated, ensuring any new starch formed is solely due to the experiment |
| (b) | Significance of boiling the leaf in alcohol | To remove chlorophyll (decolourise the leaf) so that the blue-black colour change with iodine solution is clearly visible |
Structure: Cross-section (T.S.) of the Spinal Cord
| Structure | Location | Description |
|---|---|---|
| Grey matter | Inner H-shaped (butterfly-shaped) region | Contains cytons (cell bodies) of neurons |
| White matter | Outer region surrounding grey matter | Contains axons (nerve fibres) forming tracts |
6CO2 + 6H2O ──(Sunlight + Chlorophyll)──► C6H12O6 + 6O2(Carbon dioxide + Water → Glucose + Oxygen)
| Abbreviation | Full Form |
|---|---|
| NADP | Nicotinamide Adenine Dinucleotide Phosphate |
| ADP | Adenosine Diphosphate |
(a) Define Synapse:
A synapse is a minute gap/junction between the axon terminal of one neuron and the dendrites of the next neuron, through which nerve impulses are transmitted.
(b) Neurotransmitter at the synapse:
Acetylcholine (also: Dopamine, Noradrenaline)
| Structure | Role |
|---|---|
| Leydig cells | Secrete testosterone (male sex hormone) — regulates sperm production and secondary sexual characteristics |
| Seminiferous tubules | Site of spermatogenesis — where sperms are produced within the testes |
(a) One significant problem caused by the reduction in urban greenery:
The reduction in urban greenery leads to an increase in atmospheric CO2 levels, which intensifies the greenhouse effect and contributes to global warming. It also causes the Urban Heat Island effect, where city temperatures rise significantly due to the lack of shade and the loss of transpiration-led cooling by plants.
(b) How green plants contribute to improving air quality:
Green plants improve air quality through photosynthesis, absorbing carbon dioxide and releasing oxygen. They also act as natural filters by trapping suspended particulate matter (dust) on their leaf surfaces and absorbing certain harmful gases such as sulfur dioxide.
(c) Role of a citizen in protecting urban greenery:
As a citizen, one can participate in Vanamahotsava or local afforestation drives to plant more trees. One can also advocate for the preservation of local parks, prevent the illegal felling of trees, and practise kitchen gardening or rooftop gardening to increase green cover in residential areas.
Answer: Turgor Pressure
The pressure exerted by the cell contents (vacuole) against the cell wall due to water absorbed by osmosis.
| Part | Question | Answer |
|---|---|---|
| (a) | Name the fluid between the meninges in the spinal cord | Cerebrospinal Fluid (CSF) |
| (b) | Function of CSF | Acts as a shock absorber protecting the spinal cord from mechanical injury; provides nutrients and removes waste from nervous tissue |
Copy the diagram and label the following structures:
| Structure to Label | Location in the Diagram |
|---|---|
| Vacuole | Large, clear central space occupying most of the cell |
| Plasma membrane | Thin lining immediately inside the thick, outer cell wall |
List given: Styrofoam, Metallic cans, Decaying fruits, Plastic bottles, Newspapers
Answer: Decaying fruits and Newspapers
Reason: These are organic/plant-based materials that can be broken down by microorganisms into simpler substances. Styrofoam, metallic cans, and plastic bottles are non-biodegradable.
| Part | Question | Answer |
|---|---|---|
| (a) | Collective term for structures in the internal ear | Membranous Labyrinth |
| (b) | Sensory organ in the Cochlea that was damaged | Organ of Corti |
| (c) | Types of pollution faced by quarry workers | Noise Pollution (high decibel sounds) and Air Pollution (silica dust from drilling/blasting) |
End of Solved Paper — ICSE 2026 Biology | All Questions Covered: Section A (Q1-Q2) and Section B (Q3-Q8)
/Previous-Year-Questions/ICSE/Exam-Questions/biology_paper_2026.mdx2020 Biology Science Paper - 3
Complete biology examination paper with Section I (40 marks) covering basic concepts and Section II (40 marks) with detailed questions on photosynthesis, circulation, human eye, nephron, transpiration, genetics, and human reproduction.
ICSE Biology Exam Analysis
Prediction of ICSE Biology Question Papers Based on the Trends