ICSE 2026 — Biology (Science Paper 3)

Fully Solved Question Paper with Explanations

SECTION A (40 Marks)

Question 1 — Multiple Choice & Assertion-Reason

(i) Genetic Disorders — Correct Examples

Four friends P, Q, R and S discussed genetic disorders. Their examples:

• P: Colour blindness and Malaria
• Q: Albinism and Cholera
• R: Haemophilia and Colour blindness
• S: Haemophilia and Albinism

Who gave the correct examples?

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.

(ii) Ventricular Systole — Valve Action

During ventricular systole, the atrioventricular valves (P) _______ and the semilunar valves (Q) _______.

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.

(iii) Assertion–Reason: Cuticle and Transpiration

Assertion (A): A thick cuticle reduces transpiration by acting as a barrier.

Reason (R): Desert plants have large, thin leaves for transpiration.

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.

(iv) DNA Nitrogenous Base Count

A DNA sequence has 300 nitrogenous base pairs, of which 75 are Guanine. What is the number of Thymine?

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

(v) Assertion–Reason: Abscisic Acid

Assertion (A): Abscisic acid promotes stomatal closure during a drought.

Reason (R): Abscisic acid helps the plant to conserve water during stress.

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.

(vi) Assertion–Reason: Leukoderma vs Leukemia

Assertion (A): Leukoderma is the biological term for blood cancer.

Reason (R): An abnormal increase in WBCs causes blood cancer.

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.

(vii) Population Control — Visual Methods

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

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."

(viii) Colour Blindness Inheritance — Probability

Mother is a carrier (X^c X) and father has normal vision (XY). What is the probability of their sons being colour blind?

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.

(ix) Sympathetic Nervous System — Fight or Flight

Bharat missed his school bus. The sympathetic nervous system was activated. This resulted in:

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.

(x) Correct Sequence of Blood Flow

Which is the correct sequence of blood flow in Pulmonary and Systemic Circulation?

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.

(xi) Pupillary Reflex — Structure Damaged

Karan fell and sustained a head injury. His pupils lost the ability to constrict in bright light. Which structure is damaged?

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.

(xii) Proteins in Urine — Medical Term

A person with kidney failure has proteins in the urine. What is this condition called?

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.

(xiii) Swachh Bharat Abhiyan — Objective

What does the Swachh Bharat Abhiyan aim to achieve in India?

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.

(xiv) Salt in Pickle — Purpose

Varun's mother added plenty of salt to mango pickle. The reasons are:

• A. Enhance the colour
• B. Inhibit growth of microorganisms
• C. Increase nutritional value
• D. Create a hypertonic solution

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.

(xv) Menstrual Cycle — Endometrium Shedding

During which phase of the menstrual cycle does the endometrium shed?

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.

Question 2 — Terminology, Diagrams & Identification

(i) Biological / Technical Terms

(ii) Human Sperm — Fill in the Blanks

(iii) Odd One Out

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.

(iv) Case Study: Diabetes Mellitus — Mohit

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.

(v) Kidney Structure — Match the Function

SECTION B (40 Marks)

Question 3 — Short Answer

(i) Resting but Metabolically Active Stage of Cell Cycle

Answer: Interphase

The cell grows, replicates DNA, and prepares for division. It is metabolically very active despite appearing "resting."

(ii) Advantage of Binocular Vision in Eagles

Answer: Binocular vision provides depth perception (stereoscopic vision), allowing eagles to accurately judge distances and the speed of prey — essential for precise hunting.

(iii) Autosomes and Allosomes in Human Body Cell

(iv) Plant Wilting — Temperature Experiment

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.

(v) Prophase Stage of Mitosis — Diagram Guidelines

Draw a neat labelled diagram of an animal cell in Prophase with four chromosomes.

Your diagram must show:

1. Cell membrane (no cell wall — animal cell)
2. Centrioles at opposite poles with aster rays
3. Four distinct chromosomes, each with two sister chromatids joined at the centromere
4. Nuclear membrane beginning to disintegrate
5. Early spindle fibres forming between the poles

Question 4 — Short Answer

(i) Scientific Name of Modern Man

Answer: Homo sapiens

(Underline or italicise each word separately when handwriting)

(ii) Arrangement of Cytons and Axons

(iii) Natural Selection and Industrial Melanism

(iv) Plasmolysis vs Deplasmolysis

(v) Case Study: Prostate Gland — Akshay's Father

Question 5 — Short Answer

(i) Advantage of Absence of Nucleus in RBCs

Without a nucleus, RBCs:

1. Carry more haemoglobin → transport more oxygen
2. Have a biconcave shape → increased surface area for gas exchange
3. Are more flexible → can squeeze through narrow capillaries

(ii) Food Chain Arrangement

(iii) Case Study: Pregnant Lady — Placenta

(iv) Secondary Sexual Characteristics in a 15-year-old Boy

Any two of the following:

1. Growth of facial and body hair (beard, moustache, pubic hair)
2. Deepening of the voice due to enlargement of the larynx
3. Broadening of the shoulders and increased muscular development

(v) Case Study: Tara's Grandmother — Eye Disorder

Question 6 — Short Answer

(i) Population Density — Definition

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.

(ii) Case Study: Adrenal Virilism — 17-year-old Girl

(iii) Cytokinesis: Plant Cell vs Animal Cell

(iv) Case Study: Sara's Starch Test Experiment

(v) Spinal Cord Cross-Section — Diagram

Structure: Cross-section (T.S.) of the Spinal Cord

Question 7 — Short Answer

(i) Overall Chemical Equation for Photosynthesis

6CO2  +  6H2O  ──(Sunlight + Chlorophyll)──►  C6H12O6  +  6O2

(Carbon dioxide + Water → Glucose + Oxygen)

(ii) Abbreviations

(iii) Synapse — Explanation and Neurotransmitter

(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)

(iv) Role of Testicular Structures

(v) Vanishing Greenery — Urban Crisis

(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.

Question 8 — Short Answer

(i) Pressure Exerted by Cell Contents on Cell Wall

Answer: Turgor Pressure

The pressure exerted by the cell contents (vacuole) against the cell wall due to water absorbed by osmosis.

(ii) Fluid Between the Meninges

(iii) Turgid Plant Cell — Diagram Labelling Guide

Copy the diagram and label the following structures:

(iv) Biodegradable Wastes — Selection

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.

(v) Case Study: Rajat Singh — Stone Quarry Ear Damage

End of Solved Paper — ICSE 2026 Biology | All Questions Covered: Section A (Q1–Q2) and Section B (Q3–Q8)