ICSE Biology 2026 Prediction Paper V2 — High Probability Questions with Solutions
Tushar Parik
Author
Table of Contents
ICSE Biology 2026 Prediction Paper V2
V2 — Harder Questions, Higher Probability
Complete prediction paper with application-based questions, dihybrid & sex-linked crosses, assertion-reason MCQs, and detailed solutions with Punnett squares — prepared by expert Biology teachers at Bright Tutorials.
What's New in V2?
V2 is designed for students who have already practised V1. Every question is entirely different, with elevated difficulty and enhanced question formats:
- More Assertion-Reason MCQs — Two A-R questions testing analytical reasoning on left ventricle thickness and ADH function
- Application-Based Questions — Real-world scenarios like farmer observing seedling bending, pain perception delay in reflex arc, Delhi smog case study
- ASCII Diagrams — Six detailed diagrams including brain L.S., Moll's half-leaf experiment, reflex arc, double circulation, female reproductive system, and cell/neuron MCQs
- Dihybrid Crosses — Complete 4x4 Punnett square for RrYy x RrYy with phenotypic ratio analysis
- Sex-Linked Inheritance — Haemophilia cross (carrier mother x normal father) with probability analysis and justification
- Comprehensive Tables — Menstrual cycle 4-phase table, endocrine gland completion, tropism table, transport comparison
- "Identify the INCORRECT statement" MCQ — Testing critical evaluation of photosynthesis statements
- Diagram-Based MCQs — Visual identification questions with ASCII art representations
Download the complete V2 paper as a printable PDF
Download Biology 2026 V2 Prediction Paper (PDF)Free • No sign-up required • Printable A4 format
ICSE CLASS X — BIOLOGY (SCIENCE PAPER 3)
HIGH-PROBABILITY PREDICTION PAPER V2 — 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 [ ].
V2 NOTE: This paper contains entirely different questions from V1 with increased emphasis on application-based reasoning, assertion-reason format, and higher-order thinking. Difficulty level is slightly elevated.
SECTION A (40 Marks)
Attempt all questions from this section.
Question 1
Choose the correct answers to the questions from the given options. [15]
(i) During meiosis, the event that introduces maximum genetic variation by producing new allele combinations on the same chromosome is:
- (a) Synapsis
- (b) Crossing over
- (c) Independent assortment
- (d) Cytokinesis
(ii) A patient has been diagnosed with exophthalmic goitre. Which of the following hormonal conditions is responsible?
- (a) Hyposecretion of thyroxine
- (b) Hypersecretion of thyroxine
- (c) Hyposecretion of growth hormone
- (d) Hypersecretion of insulin
(iii) Assertion-Reason Type:
Assertion (A): The left ventricle has the thickest muscular wall among all four chambers of the heart.
Reason (R): The left ventricle pumps oxygenated blood to all parts of the body through the aorta.
- (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
(iv) In a dihybrid cross between two heterozygous parents (RrYy × RrYy), the ratio of offspring that are homozygous recessive for both traits is:
- (a) 1/16
- (b) 3/16
- (c) 9/16
- (d) 1/4
(v) Study the diagram below and identify the structure marked 'X':
┌──────────────────────┐
│ Cell Membrane │
│ ┌────────────────┐ │
│ │ Cytoplasm │ │
│ │ ┌────────┐ │ │
│ │ │Nucleus │ │ │
│ │ │ ┌────┐ │ │ │
│ │ │ │ X │ │ │ │
│ │ │ └────┘ │ │ │
│ │ └────────┘ │ │
│ └────────────────┘ │
└──────────────────────┘
X = ? (darkly staining body inside nucleus)
- (a) Ribosome
- (b) Nucleolus
- (c) Centriole
- (d) Lysosome
(vi) A plant cell is placed in a hypertonic solution. After 30 minutes, when observed under a microscope, the cell shows:
- (a) The cell membrane pulled away from the cell wall with the space filled by the external solution
- (b) The cell wall pulled away from the cell membrane
- (c) No change in the cell
- (d) The cell bursting open
(vii) Which of the following correctly represents the path of urine formation in the nephron?
- (a) Glomerular filtrate → Selective reabsorption → Tubular secretion → Urine
- (b) Tubular secretion → Glomerular filtrate → Selective reabsorption → Urine
- (c) Selective reabsorption → Glomerular filtrate → Tubular secretion → Urine
- (d) Glomerular filtrate → Tubular secretion → Selective reabsorption → Urine
(viii) Assertion-Reason Type:
Assertion (A): Vasopressin (ADH) deficiency leads to production of large volumes of dilute urine.
Reason (R): ADH promotes reabsorption of water from the collecting ducts of nephrons.
- (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
(ix) During the secretory phase of the menstrual cycle, which hormone is predominantly responsible for maintaining the thickened endometrium?
- (a) Follicle Stimulating Hormone (FSH)
- (b) Luteinizing Hormone (LH)
- (c) Estrogen
- (d) Progesterone
(x) Identify the INCORRECT statement from the following:
- (a) Photolysis of water occurs during the light reaction in the grana of chloroplasts
- (b) Carbon dioxide fixation occurs during the dark reaction in the stroma of chloroplasts
- (c) Oxygen released during photosynthesis comes from the splitting of carbon dioxide
- (d) NADPH₂ produced during the light reaction is used in the dark reaction to reduce CO₂
(xi) Study the diagram of a neuron below and identify the part labeled 'P':
Dendrites
/ | \
/ | \
/ | \
┌───────────────────┐
│ Cell Body │
│ (Cyton) │
│ ┌─────────┐ │
│ │ Nucleus │ │
│ └─────────┘ │
└────────┬──────────┘
│
┌────────────┼────────────┐
│ P ════════╪════════ │ ← Myelin sheath
│ ══════════╪══════════ │
└────────────┼────────────┘
│
┌──────┴──────┐
│ Synaptic │
│ Knob │
└─────────────┘
- (a) Dendron
- (b) Axon
- (c) Synapse
- (d) Node of Ranvier
(xii) A farmer notices that his crop seedlings are bending towards a window on one side of the greenhouse. This response is due to:
- (a) Geotropism caused by unequal distribution of gibberellins
- (b) Phototropism caused by unequal distribution of auxins
- (c) Hydrotropism caused by unequal distribution of cytokinins
- (d) Thigmotropism caused by contact stimulus
(xiii) Which of the following blood vessels carries deoxygenated blood from the lower body back to the right atrium?
- (a) Pulmonary vein
- (b) Superior vena cava
- (c) Inferior vena cava
- (d) Hepatic artery
(xiv) In a family, both parents are carriers of sickle cell anaemia (Ss × Ss). What is the probability of their child being a carrier but not showing the disease?
- (a) 25%
- (b) 50%
- (c) 75%
- (d) 100%
(xv) The greenhouse effect is primarily intensified by which of the following human activities?
- (a) Excessive use of pesticides in agriculture
- (b) Burning of fossil fuels releasing CO₂ and methane
- (c) Discharge of industrial effluents into rivers
- (d) Excessive use of chemical fertilizers in soil
Question 2
(i) The diagram below represents a longitudinal section of the human brain. Study it and answer the questions that follow: [5]
LONGITUDINAL SECTION OF HUMAN BRAIN
=====================================
┌─────────────────────────┐
/ ┌───────────────────┐ \
/ │ A (Cerebrum) │ \
│ │ ┌─────────────┐ │ │
│ │ │ Convolutions │ │ │
│ │ │ (Gyri & │ │ │
│ │ │ Sulci) │ │ │
│ └──┴─────────────┴──┘ │
│ │ │
│ ┌────┴────┐ │
│ │ B │ ← (Rounded │
│ │(mid- │ structure) │
│ │ brain) │ │
│ └────┬────┘ │
│ ┌────┴─────────────┐ │
│ │ C (Cerebellum) │ │
│ │ ┌───────────┐ │ │
│ │ │Tree-like │ │ │
│ │ │pattern │ │ │
│ │ │(Arbor │ │ │
│ │ │ Vitae) │ │ │
│ │ └───────────┘ │ │
│ └────┬─────────────┘ │
│ ┌────┴────┐ │
\ │ D │ ← (Continues │
\ │(Medulla │ to spinal │
\ │Oblongata│ cord) │
\└─────────┘ /
└───────────────────────┘
│
Spinal Cord
- (a) Identify the parts labeled A, B, C, and D.
- (b) State one specific function of part C that distinguishes it from part A.
- (c) Name the part of the brain that acts as a relay station for sensory impulses. Where is it located in relation to part B?
- (d) What is the "arbor vitae" visible in part C? Why does it appear tree-like?
- (e) A person suffers an injury to part D. Name two vital involuntary functions that would be affected.
(ii) Give reasons for the following: [5]
- (a) Root hair cells have a higher concentration of cell sap than the surrounding soil solution.
- (b) The rate of transpiration increases on a windy day even if other conditions remain constant.
- (c) A person with blood group O is called a "universal donor" but can only receive blood from group O.
- (d) Identical twins are always of the same sex, whereas fraternal twins may be of different sexes.
- (e) The tubular reabsorption of glucose in the nephron is described as an active process.
(iii) Fill in the blanks by choosing the correct option from the brackets: [5]
- (a) The phase of mitosis in which chromosomes align along the equatorial plate of the cell is called ______. (Anaphase / Metaphase / Prophase)
- (b) The hormone responsible for the "fight or flight" response is __ secreted by the adrenal ____. (Adrenaline...medulla / Cortisol...cortex / Insulin...pancreas)
- (c) In the light reaction of photosynthesis, the splitting of water molecules is known as ______. (Hydrolysis / Photolysis / Glycolysis)
- (d) The muscular wall that separates the right and left sides of the heart is called the ______. (Pericardium / Septum / Endocardium)
- (e) The contraceptive device that prevents ovulation by releasing synthetic hormones is the ______. (Copper-T / Oral pill / Condom)
(iv) Identify the substance or structure from the descriptions given below. Choose your answers from the list provided: [5]
List: Corpus luteum, Eustachian tube, Thrombin, Aqueous humour, Oxytocin, Loop of Henle, Acetylcholine, Lymph, Auxin, Semicircular canals
- (a) A U-shaped portion of the nephron situated in the medulla of the kidney that plays a key role in concentrating urine.
- (b) A neurotransmitter released at the synapse that transmits nerve impulses from one neuron to the next.
- (c) A yellowish body formed from the remnants of the Graafian follicle after ovulation, which secretes progesterone.
- (d) A straw-coloured fluid similar to blood plasma but lacking red blood cells and platelets, found in lymphatic vessels.
- (e) A plant hormone produced at the shoot tip that causes cell elongation and is responsible for phototropic responses.
(v) Name the following: [5]
- (a) The specific stage of meiosis during which homologous chromosomes exchange segments of chromatids.
- (b) The type of white blood cell that produces antibodies as part of the immune response.
- (c) The outermost protective membrane that encloses the human brain and spinal cord.
- (d) The process by which glucose is reabsorbed from the nephric filtrate back into the blood capillaries surrounding the tubule.
- (e) The phenomenon in which the tendrils of a pea plant coil around a support upon physical contact.
SECTION B (40 Marks)
Attempt any four questions from this section.
Question 3 — Cell Division & Genetics [10]
(i) Explain the process of meiosis by describing the key events of each stage of Meiosis I (Prophase I, Metaphase I, Anaphase I, Telophase I). State any three ways in which meiosis is biologically significant. [4]
(ii) In garden peas, round seed shape (R) is dominant over wrinkled (r) and yellow colour (Y) is dominant over green (y). A cross is made between two plants that are heterozygous for both traits (RrYy × RrYy). [3]
- (a) Draw the Punnett square for this dihybrid cross.
- (b) State the phenotypic ratio obtained in the F₂ generation.
- (c) How many of the 16 offspring would you expect to be wrinkled and green?
(iii) Haemophilia is a sex-linked recessive disorder carried on the X chromosome. A carrier woman (X^H X^h) marries a normal man (X^H Y). [3]
- (a) Draw the genetic cross showing all possible genotypes of the offspring.
- (b) What is the probability of a son being haemophilic?
- (c) Can any daughter from this cross be haemophilic? Justify your answer.
Question 4 — Plant Physiology [10]
(i) Differentiate between the following in a tabular format (any three points each): [3]
- (a) Active transport and Passive transport
- (b) Plasmolysis and Deplasmolysis
(ii) Describe Moll's half-leaf experiment to demonstrate that CO₂ is necessary for photosynthesis. Include the following in your answer: [4]
MOLL'S HALF-LEAF EXPERIMENT SETUP
===================================
┌─────────────────────────────────────┐
│ Split Cork │
│ ┌─────────┬─────────┐ │
│ │ │ │ │
│ │ LEAF │ LEAF │ │
│ │ (Half │ (Half │ │
│ │ inside │ outside│ │
│ │ flask) │ flask) │ │
│ │ │ │ │
│ └─────────┴─────────┘ │
│ │ │
│ ┌────┴────────┐ │
│ │ Flask │ │
│ │ containing │ ← KOH solution │
│ │ KOH │ absorbs CO₂ │
│ │ solution │ │
│ └─────────────┘ │
│ │
│ Vaseline seal on cork │
│ to make it airtight │
└─────────────────────────────────────┘
- (a) What is the purpose of KOH in the flask?
- (b) Why is the leaf destarched before the experiment?
- (c) What result do you observe when the leaf is tested with iodine solution after being kept in sunlight for several hours?
- (d) State the conclusion drawn from this experiment.
(iii) Describe the Ganong's potometer experiment. With reference to the experiment, answer: [3]
- (a) What does the potometer actually measure — transpiration or water uptake? Explain.
- (b) How would you use this apparatus to demonstrate that wind increases the rate of transpiration?
- (c) Why must all joints in the apparatus be made airtight and no air bubble should enter the system other than the measured one?
Question 5 — Nervous System & Endocrine System [10]
(i) Describe the structure of a myelinated motor neuron. In your answer, explain the role of the following: [3]
- (a) Nissl granules
- (b) Myelin sheath and Nodes of Ranvier
- (c) Synaptic vesicles at the axon terminal
(ii) Draw a neat labeled diagram of a reflex arc showing the path of a spinal reflex when a person accidentally touches a hot object. Label the following parts and describe the sequence of events: [3]
REFLEX ARC (Withdrawal Reflex)
================================
Hot object
│
▼
┌─────────┐ Sensory ┌────────────┐
│Receptor │────(afferent)─────▶│ Dorsal │
│(Pain │ neuron │ Root │
│receptor │ │ Ganglion │
│in skin) │ └─────┬──────┘
└─────────┘ │
▼
┌──────────────┐
│ Grey │
│ Matter │
│ (Relay / │
│ Interneuron)│
└──────┬───────┘
│
┌─────────┐ Motor ┌─────┴──────┐
│Effector │◀───(efferent)─────│ Ventral │
│(Muscle │ neuron │ Root │
│of hand) │ └────────────┘
└─────────┘
Hand pulls away
- (a) Why is this response called "involuntary"?
- (b) Name the centre of this reflex action.
- (c) Why does the person feel pain only after withdrawing the hand?
(iii) Study the table below and complete it by filling in the missing information (indicated by blanks): [4]
| Endocrine Gland | Hormone | Function | Disorder (Hypo/Hyper) |
|---|---|---|---|
| Thyroid | Thyroxine | Regulates _ rate | Hypo: _ in adults |
| Pancreas (Islets of Langerhans) | _ | Lowers blood glucose level | Hypo: Diabetes _ |
| Adrenal Cortex | _ | Regulates salt and water balance | Hypo: Addison's disease |
| Pituitary (Anterior) | Growth Hormone | Promotes growth of _ | Hyper: _ in adults |
| Ovary | _ | Development of female secondary sexual characteristics | — |
Question 6 — Circulatory & Excretory System [10]
(i) Explain the concept of "double circulation" in humans. Trace the flow of blood through the pulmonary and systemic circuits starting from the right atrium, using the flow chart format below: [4]
DOUBLE CIRCULATION IN HUMANS
==============================
PULMONARY CIRCUIT:
Right Atrium
│ (through tricuspid valve)
▼
Right Ventricle
│ (through pulmonary semilunar valve)
▼
Pulmonary Artery ──────▶ LUNGS
(deoxygenated) (Gas exchange:
CO₂ released,
O₂ absorbed)
Pulmonary Veins ◀────── LUNGS
(oxygenated)
│
▼
Left Atrium
SYSTEMIC CIRCUIT:
Left Atrium
│ (through bicuspid/mitral valve)
▼
Left Ventricle
│ (through aortic semilunar valve)
▼
Aorta ──────────────▶ BODY ORGANS & TISSUES
(oxygenated) (O₂ delivered,
CO₂ picked up)
Vena Cava ◀────────── BODY ORGANS & TISSUES
(Superior & Inferior)
(deoxygenated)
│
▼
Right Atrium ← (Cycle repeats)
- (a) Why is human circulation called "double" circulation?
- (b) Name the only artery that carries deoxygenated blood and the only vein that carries oxygenated blood.
- (c) What is the role of valves in the heart? Name the valve between the left atrium and left ventricle.
(ii) With reference to blood groups and the Rh factor, answer the following: [3]
- (a) A mother has blood group A (heterozygous, I^A i) and the father has blood group B (heterozygous, I^B i). Show, using a genetic cross, all possible blood groups of their children.
- (b) What is erythroblastosis foetalis? Under what conditions does it occur?
- (c) Why is blood cross-matching essential before a blood transfusion even when the ABO blood group is known?
(iii) Compare haemodialysis with the normal functioning of a healthy kidney by answering the following: [3]
- (a) What principle does the dialysis machine work on? Name the fluid used and state one key property of this fluid.
- (b) Name two substances that pass through the dialysis membrane and two substances that do not.
- (c) State two limitations of haemodialysis compared to the normal kidney function.
Question 7 — Reproductive System & Development [10]
(i) Study the diagram of the female reproductive system given below and answer the questions: [3]
FEMALE REPRODUCTIVE SYSTEM
============================
Fallopian Tube (Oviduct)
┌──────────────────────────┐
/ Fimbriae \
/ ┌───┐ \
│ │ A │ ← (Site of │
│ └───┘ fertilization) │
│ \ │
│ ┌─────┴──────┐ │
│ │ │ │
│ │ B (Ovary) │ │
│ │ ┌────────┐ │ │
│ │ │Graafian│ │ │
│ │ │Follicle│ │ │
│ │ └────────┘ │ │
│ └────────────┘ │
│ \ │
│ ┌─────┴───────────┐ │
│ │ │ │
│ │ C (Uterus) │ │
│ │ │ │
│ │ Endometrium │ │
│ │ (lining) │ │
│ └────────┬────────┘ │
│ │ │
│ ┌─────┴─────┐ │
│ │ D │ │
│ │ (Cervix) │ │
│ └─────┬─────┘ │
│ │ │
│ ┌─────┴─────┐ │
│ │ Vagina │ │
│ └───────────┘ │
- (a) Identify the parts labeled A, B, C, and D.
- (b) Name the process that releases the ovum from the structure labeled B. Which hormone triggers this process?
- (c) What happens to the lining of part C if fertilization does not occur?
(ii) Describe the four phases of the menstrual cycle. For each phase, state the approximate duration, the hormones involved, and the changes occurring in the ovary and uterus: [4]
| Phase | Duration (approx.) | Key Hormone(s) | Ovarian Changes | Uterine Changes |
|---|---|---|---|---|
| Menstrual Phase | _ | _ | _ | _ |
| Follicular Phase | _ | _ | _ | _ |
| Ovulatory Phase | _ | _ | _ | _ |
| Luteal / Secretory Phase | _ | _ | _ | _ |
(iii) Describe the events that occur from fertilization to implantation. In your answer, include: [3]
- (a) Where does fertilization normally take place? What is the resulting cell called and how many chromosomes does it have?
- (b) Describe the changes the fertilized egg undergoes as it travels towards the uterus (cleavage, morula, blastocyst).
- (c) State three functions of the placenta during pregnancy.
Question 8 — Pollution, Population & Chemical Coordination in Plants [10]
(i) With reference to air pollution, answer the following: [3]
- (a) Explain the mechanism by which acid rain is formed. Name two gases primarily responsible and state two harmful effects of acid rain on the environment.
- (b) Distinguish between the greenhouse effect and global warming. Why is a moderate greenhouse effect essential for life on Earth?
- (c) What is smog? Name one city in India that frequently suffers from severe smog episodes and state one health hazard caused by prolonged smog exposure.
(ii) With reference to population growth and its impact: [3]
- (a) India's population crossed 1.4 billion in recent years. State three major reasons for this rapid population growth.
- (b) Explain how overpopulation leads to depletion of natural resources. Give two specific examples.
- (c) Name two government programmes or initiatives aimed at population control in India and state their primary objective.
(iii) With reference to tropic movements in plants, answer the following: [4]
- (a) Define the term "tropism." How does a positive tropism differ from a negative tropism?
- (b) Complete the following table:
| Type of Tropism | Stimulus | Example | Positive or Negative |
|---|---|---|---|
| Phototropism | _ | Shoot tip bends towards light | _ |
| Geotropism | _ | _ | Positive (for roots) |
| Hydrotropism | _ | _ | Positive (for roots) |
| Thigmotropism | _ | _ | Positive |
| Chemotropism | _ | Pollen tube grows towards ovule | _ |
- (c) Explain the role of auxin in phototropism. Why does the shoot bend towards the light source even though auxin causes cell elongation?
- (d) A potted plant is placed horizontally. After a few days, the stem curves upward and the root curves downward. Explain this observation in terms of auxin distribution and sensitivity.
---
ANSWER KEY
Question 1 — MCQ Answers [15]
| Q. No. | Answer | Explanation |
|---|---|---|
| (i) | (b) Crossing over | Crossing over during Prophase I of meiosis exchanges chromatid segments between homologous chromosomes, creating new combinations of alleles on the same chromosome (recombinant types). Independent assortment shuffles whole chromosomes, not alleles within a chromosome. |
| (ii) | (b) Hypersecretion of thyroxine | Exophthalmic goitre (Graves' disease) is caused by overproduction of thyroxine, leading to bulging eyes (exophthalmia), increased metabolic rate, weight loss, and an enlarged thyroid gland. |
| (iii) | (a) Both A and R are true and R is the correct explanation of A | The left ventricle must generate the highest pressure to pump oxygenated blood through the aorta to all body parts (systemic circulation). This requires the thickest muscular wall of all four chambers. |
| (iv) | (a) 1/16 | In a dihybrid cross RrYy × RrYy, the probability of homozygous recessive for both traits (rryy) = 1/4 (rr) × 1/4 (yy) = 1/16. |
| (v) | (b) Nucleolus | The nucleolus is a darkly staining, dense body found inside the nucleus. It is the site of ribosomal RNA synthesis. |
| (vi) | (a) The cell membrane pulled away from the cell wall with the space filled by the external solution | In a hypertonic solution, the cell loses water by exosmosis. The cell membrane shrinks and pulls away from the rigid cell wall (plasmolysis). The space between them fills with the external hypertonic solution. |
| (vii) | (a) Glomerular filtrate → Selective reabsorption → Tubular secretion → Urine | Urine formation proceeds in order: ultrafiltration at Bowman's capsule produces glomerular filtrate, useful substances are selectively reabsorbed in the tubule, unwanted substances are secreted into the tubule, and the final product is urine. |
| (viii) | (a) Both A and R are true and R is the correct explanation of A | ADH (vasopressin) acts on collecting ducts to promote water reabsorption. Its deficiency (diabetes insipidus) prevents this reabsorption, resulting in large volumes of very dilute urine. R correctly explains A. |
| (ix) | (d) Progesterone | During the secretory (luteal) phase, the corpus luteum secretes progesterone which maintains the thickened, vascularised endometrium in preparation for possible implantation. |
| (x) | (c) Oxygen released during photosynthesis comes from the splitting of carbon dioxide | This is INCORRECT. Oxygen released during photosynthesis comes from the photolysis (splitting) of water molecules (H₂O), not carbon dioxide. This was demonstrated by the isotope tracer experiments using O¹⁸. |
| (xi) | (b) Axon | The long fibre extending from the cell body (cyton) covered by the myelin sheath is the axon. It transmits nerve impulses away from the cell body towards the synaptic knob. |
| (xii) | (b) Phototropism caused by unequal distribution of auxins | Seedlings bending towards light is positive phototropism. Auxin migrates to the shaded side, causing greater cell elongation there, which bends the shoot towards the light. |
| (xiii) | (c) Inferior vena cava | The inferior vena cava (IVC) is the large vein that collects deoxygenated blood from the lower body (legs, abdomen, kidneys) and returns it to the right atrium of the heart. |
| (xiv) | (b) 50% | Cross: Ss × Ss → SS (25%, normal), Ss (50%, carrier), ss (25%, affected). The probability of being a carrier (Ss) without showing the disease is 50%. |
| (xv) | (b) Burning of fossil fuels releasing CO₂ and methane | The greenhouse effect is intensified by increased concentrations of greenhouse gases — primarily CO₂ and methane released from burning fossil fuels (coal, oil, natural gas) in vehicles, factories, and power plants. |
Question 2 — Answers
(i) Brain Diagram — Answers [5]
(a) Parts identified:
- A = Cerebrum (largest part of the brain, the seat of intelligence, memory, thinking, and voluntary actions)
- B = Midbrain (connects the cerebrum to the hindbrain; contains centres for visual and auditory reflexes)
- C = Cerebellum (second largest part of the brain, located behind the medulla oblongata)
- D = Medulla Oblongata (lowermost part of the brain, continuous with the spinal cord)
(b) The cerebellum (C) coordinates voluntary muscular movements and maintains balance and posture of the body. Unlike the cerebrum (A), which initiates voluntary actions and is the centre for thought and reasoning, the cerebellum specifically coordinates the precision and timing of muscle movements.
(c) The thalamus (diencephalon / part of the forebrain) acts as a relay station for sensory impulses. It is located below the cerebrum and above the midbrain (B), forming part of the walls of the third ventricle.
(d) The arbor vitae is the tree-like pattern of white matter (myelinated nerve fibres) seen in a section of the cerebellum. It appears tree-like because the white matter branches extensively into the folia (folds) of the cerebellum's grey matter, resembling the branches of a tree.
(e) If part D (Medulla Oblongata) is injured, the following involuntary functions would be affected:
1. Breathing / Respiratory rhythm — the respiratory centre in the medulla controls the rate and depth of breathing.
2. Heartbeat regulation — the cardiac centre in the medulla controls heart rate.
(Other acceptable answers: swallowing, vomiting reflex, blood pressure regulation, coughing, sneezing.)
(ii) Give Reasons — Answers [5]
(a) Root hair cells have a higher concentration of cell sap (lower water potential) than the surrounding soil solution because they contain dissolved salts, sugars, and organic acids in their vacuolar sap. This creates a concentration gradient that allows water to enter the root hair cell by osmosis — from the region of higher water potential (dilute soil solution) to the region of lower water potential (concentrated cell sap). Without this difference, absorption of water would not occur.
(b) On a windy day, the moving air currents continuously sweep away the water vapour that has accumulated around the stomata on the leaf surface. This reduces the humidity of the air immediately surrounding the leaf, thereby increasing the diffusion gradient for water vapour between the leaf interior (saturated) and the external air. A steeper concentration gradient causes water vapour to diffuse out of the stomata faster, increasing the rate of transpiration.
(c) A person with blood group O has neither antigen A nor antigen B on their red blood cells, so their blood will not be agglutinated (clumped) by anti-A or anti-B antibodies present in any recipient's blood — hence "universal donor." However, their plasma contains both anti-A and anti-B antibodies. If they receive blood of any group other than O (which has antigens A, B, or both), the antibodies in the recipient's plasma will cause agglutination of the donated red blood cells, leading to a fatal transfusion reaction.
(d) Identical (monozygotic) twins develop from a single fertilized egg (zygote) that splits into two embryos. Since they originate from the same sperm and egg, they share the same sex chromosomes (either XX or XY), so they are always the same sex. Fraternal (dizygotic) twins develop from two separate eggs fertilized by two different sperm cells. Each fertilization is independent, so the sex chromosome combination (XX or XY) may differ between the two zygotes, and they may be of different sexes.
(e) The reabsorption of glucose in the nephron (primarily in the proximal convoluted tubule) is an active process because glucose is transported from the nephric filtrate (lower concentration in the tubular lumen after considerable reabsorption) back into the blood (higher concentration in the peritubular capillaries) against its concentration gradient. This transport requires energy in the form of ATP and involves specific carrier proteins in the tubular cell membranes. Passive processes cannot move substances against a concentration gradient.
(iii) Fill in the Blanks — Answers [5]
- (a) Metaphase — During metaphase, chromosomes align at the equatorial plate (metaphase plate) of the cell, attached to spindle fibres at their centromeres.
- (b) Adrenaline...medulla — Adrenaline (epinephrine), secreted by the adrenal medulla, triggers the fight or flight response: increased heart rate, dilated pupils, rapid breathing, and release of glucose into the blood.
- (c) Photolysis — Photolysis of water (photolysis = light-induced splitting) occurs in the grana of chloroplasts during the light reaction: 2H₂O → 4H⁺ + 4e⁻ + O₂
- (d) Septum — The septum (interventricular and interatrial) is the muscular wall dividing the right and left sides of the heart, preventing mixing of oxygenated and deoxygenated blood.
- (e) Oral pill — Oral contraceptive pills contain synthetic estrogen and progesterone that suppress ovulation by inhibiting the release of FSH and LH from the pituitary gland.
(iv) Identify the Substance/Structure — Answers [5]
- (a) Loop of Henle — The U-shaped loop in the nephron located in the medulla, consisting of a descending limb (permeable to water) and an ascending limb (impermeable to water but actively transports salts), essential for creating a concentration gradient to concentrate urine.
- (b) Acetylcholine — A neurotransmitter that is released from synaptic vesicles into the synaptic cleft when a nerve impulse reaches the synaptic knob. It binds to receptors on the postsynaptic membrane, initiating a new impulse in the next neuron.
- (c) Corpus luteum — After ovulation, the empty Graafian follicle transforms into the corpus luteum (yellow body), which secretes progesterone to maintain the uterine lining. If fertilization does not occur, it degenerates.
- (d) Lymph — A straw-coloured fluid derived from blood plasma that leaks out of capillaries into tissue spaces. It lacks RBCs and platelets, contains fewer proteins than blood plasma, and flows through lymphatic vessels. It plays a role in immunity and fat absorption.
- (e) Auxin — A growth hormone (indole-3-acetic acid / IAA) synthesized at shoot tips. It promotes cell elongation and is responsible for tropic movements in plants. In phototropism, auxin migrates to the shaded side, causing differential growth.
(v) Name the Following — Answers [5]
- (a) Pachytene (of Prophase I of Meiosis I) — During the pachytene sub-stage, crossing over occurs where non-sister chromatids of homologous chromosomes exchange segments at points called chiasmata.
- (b) Lymphocytes (B-lymphocytes / B-cells) — B-lymphocytes differentiate into plasma cells that produce and secrete antibodies (immunoglobulins) to neutralize specific antigens.
- (c) Dura mater — The dura mater is the outermost, toughest, and most fibrous of the three meninges (protective membranes: dura mater, arachnoid membrane, pia mater) surrounding the brain and spinal cord.
- (d) Selective reabsorption (or Tubular reabsorption) — The process by which useful substances like glucose, amino acids, water, and salts are reabsorbed from the nephric filtrate in the renal tubule back into the peritubular blood capillaries.
- (e) Thigmotropism — The directional growth movement of a plant part in response to the stimulus of touch or physical contact. Tendrils of pea plants show positive thigmotropism by coiling around a support.
Question 3 — Cell Division & Genetics — Answers [10]
(i) Meiosis I Stages and Significance [4]
Prophase I:
- Longest and most complex stage of meiosis.
- Chromosomes condense and become visible. Homologous chromosomes pair up (synapsis) to form bivalents.
- Crossing over occurs — non-sister chromatids of homologous chromosomes exchange genetic segments at chiasmata.
- Nuclear membrane and nucleolus begin to disappear. Centrioles move to opposite poles and spindle fibres begin forming.
Metaphase I:
- Bivalents (tetrads) align at the equatorial plate of the cell.
- Spindle fibres from opposite poles attach to the centromeres of homologous chromosomes (not sister chromatids as in mitosis).
- The orientation of each bivalent is random (independent assortment).
Anaphase I:
- Homologous chromosomes separate and move to opposite poles of the cell (disjunction).
- Unlike mitosis, the centromeres do NOT split — each chromosome still consists of two sister chromatids joined at the centromere.
- This is the reduction step — each pole now receives the haploid number of chromosomes.
Telophase I:
- Chromosomes reach the respective poles and may partially uncoil.
- Nuclear membrane may or may not re-form (varies by species).
- Cytokinesis occurs, dividing the cell into two daughter cells, each with the haploid number of chromosomes.
Biological Significance of Meiosis (any three):
1. Reduction in chromosome number: Produces haploid gametes (n) from diploid cells (2n), ensuring the chromosome number is restored to diploid upon fertilization, maintaining the constancy of chromosome number across generations.
2. Genetic variation: Crossing over (Prophase I) and independent assortment (Metaphase I) generate new combinations of alleles, producing offspring that are genetically different from each other and from the parents.
3. Essential for sexual reproduction: Without meiosis, gamete formation would be impossible, and each generation would double in chromosome number. Meiosis ensures the formation of functional gametes (sperm and ova).
(ii) Dihybrid Cross [3]
(a) Punnett Square:
Cross: RrYy × RrYy
Gametes of Parent 1: RY, Ry, rY, ry
Gametes of Parent 2: RY, Ry, rY, ry
RY Ry rY ry
┌─────────┬─────────┬─────────┬─────────┐
RY │ RRYY │ RRYy │ RrYY │ RrYy │
│ Round │ Round │ Round │ Round │
│ Yellow │ Yellow │ Yellow │ Yellow │
├─────────┼─────────┼─────────┼─────────┤
Ry │ RRYy │ RRyy │ RrYy │ Rryy │
│ Round │ Round │ Round │ Round │
│ Yellow │ Green │ Yellow │ Green │
├─────────┼─────────┼─────────┼─────────┤
rY │ RrYY │ RrYy │ rrYY │ rrYy │
│ Round │ Round │Wrinkled │Wrinkled │
│ Yellow │ Yellow │ Yellow │ Yellow │
├─────────┼─────────┼─────────┼─────────┤
ry │ RrYy │ Rryy │ rrYy │ rryy │
│ Round │ Round │Wrinkled │Wrinkled │
│ Yellow │ Green │ Yellow │ Green │
└─────────┴─────────┴─────────┴─────────┘
(b) Phenotypic Ratio (F₂):
- Round Yellow : Round Green : Wrinkled Yellow : Wrinkled Green
- 9 : 3 : 3 : 1
(c) Out of 16 offspring, the number expected to be wrinkled and green (rryy) = 1 out of 16.
(iii) Sex-linked Inheritance — Haemophilia [3]
(a) Genetic Cross:
Mother (Carrier): X^H X^h × Father (Normal): X^H Y
X^H Y
┌──────────────┬──────────────┐
X^H │ X^H X^H │ X^H Y │
│ Normal │ Normal │
│ Daughter │ Son │
├──────────────┼──────────────┤
X^h │ X^H X^h │ X^h Y │
│ Carrier │ Haemophilic │
│ Daughter │ Son │
└──────────────┴──────────────┘
Offspring Genotypes:
- X^H X^H — Normal daughter (25%)
- X^H X^h — Carrier daughter (25%)
- X^H Y — Normal son (25%)
- X^h Y — Haemophilic son (25%)
(b) The probability of a son being haemophilic = 50% (1 out of 2 sons, or 25% of all children). Out of the two possible male genotypes (X^H Y and X^h Y), one is haemophilic.
(c) No, no daughter from this cross can be haemophilic. For a daughter to be haemophilic, she must be homozygous recessive (X^h X^h), receiving the X^h allele from both parents. In this cross, the father is normal (X^H Y) and can only contribute X^H to his daughters. Since no daughter receives X^h from the father, none can be haemophilic. At most, a daughter can be a carrier (X^H X^h).
Question 4 — Plant Physiology — Answers [10]
(i) Differences [3]
(a) Active Transport vs. Passive Transport:
| Feature | Active Transport | Passive Transport |
|---|---|---|
| Energy requirement | Requires metabolic energy (ATP) | Does not require energy |
| Direction of movement | Against the concentration gradient (low to high concentration) | Along the concentration gradient (high to low concentration) |
| Carrier proteins | Requires specific carrier proteins | May or may not require carrier proteins |
| Example | Absorption of minerals by root cells | Diffusion of CO₂ through stomata |
(b) Plasmolysis vs. Deplasmolysis:
| Feature | Plasmolysis | Deplasmolysis |
|---|---|---|
| Definition | Shrinkage of the protoplasm away from the cell wall when a cell is placed in a hypertonic solution | Recovery of the protoplasm to its original position when a plasmolysed cell is placed in a hypotonic solution |
| Water movement | Water moves out of the cell by exosmosis | Water moves into the cell by endosmosis |
| Solution type | Occurs in hypertonic solution (higher external solute concentration) | Occurs in hypotonic solution (lower external solute concentration) |
| Cell condition | Cell becomes flaccid; protoplasm shrinks | Cell regains turgidity; protoplasm expands back |
(ii) Moll's Half-Leaf Experiment [4]
Procedure:
A potted plant is destarched by keeping it in the dark for 48 hours. A healthy leaf is selected, and one half is inserted into a wide-mouthed flask containing KOH (potassium hydroxide) solution through a split cork. The cork and all openings are sealed with vaseline to make the setup airtight. The other half of the leaf remains outside, exposed to normal air. The plant is placed in sunlight for several hours. After sufficient exposure, the leaf is plucked, boiled in water, then in alcohol to remove chlorophyll, washed, and tested with iodine solution.
(a) The KOH (potassium hydroxide) in the flask absorbs all the carbon dioxide from the air inside the flask. This ensures that the half of the leaf inside the flask is deprived of CO₂, the raw material for photosynthesis.
(b) The leaf is destarched (by keeping the plant in darkness for 48 hours) to ensure that any starch detected at the end of the experiment was produced during the experiment and not pre-existing. It removes all previously stored starch, providing a clear baseline for testing.
(c) When tested with iodine solution:
- The half of the leaf outside the flask (exposed to normal air with CO₂) turns blue-black, indicating the presence of starch (photosynthesis occurred).
- The half of the leaf inside the flask (deprived of CO₂ by KOH) remains brown/yellowish, indicating the absence of starch (photosynthesis did not occur).
(d) Conclusion: Carbon dioxide is essential for photosynthesis. In the absence of CO₂, even in the presence of light, water, and chlorophyll, the leaf cannot manufacture starch. This proves that CO₂ is a necessary raw material for the process of photosynthesis.
(iii) Ganong's Potometer Experiment [3]
Description: Ganong's potometer consists of a graduated horizontal capillary tube connected to a reservoir at one end and a leafy shoot at the other, with all joints sealed airtight with vaseline. The apparatus is filled with water, and a small air bubble is introduced at the open end of the capillary tube. As the shoot transpires, it absorbs water, and the air bubble moves along the graduated scale towards the shoot, allowing measurement of the rate of water uptake.
(a) The potometer actually measures the rate of water uptake by the shoot, not transpiration directly. This is because the movement of the air bubble indicates how much water is being absorbed by the cut end of the shoot. However, since about 95-97% of the water absorbed is lost through transpiration, the rate of water uptake is approximately equal to the rate of transpiration under normal conditions. It gives an indirect measure of transpiration.
(b) To demonstrate that wind increases the rate of transpiration:
- First, record the rate of movement of the air bubble under calm (still air) conditions over a fixed time interval.
- Then, place a fan near the leafy shoot to simulate wind and record the rate of movement of the air bubble over the same time interval.
- Compare the two readings. The air bubble will move faster (covering more distance per unit time) in the windy condition, proving that wind increases the rate of transpiration.
(c) All joints must be airtight and no unwanted air bubbles should enter because:
- Any air leak would allow air to enter the apparatus from points other than the designated entry point, causing the measured air bubble to move erratically or not at all.
- The movement of the single air bubble is the basis of measurement. Additional air bubbles would give false readings, making the experiment unreliable.
- Airtight sealing ensures that the only cause of water movement (and air bubble displacement) is transpirational pull from the leafy shoot.
Question 5 — Nervous System & Endocrine System — Answers [10]
(i) Structure of a Myelinated Motor Neuron [3]
A myelinated motor neuron (efferent neuron) consists of:
- Cell body (cyton) containing the nucleus, cytoplasm, and Nissl granules
- Dendrites — short, branched fibres that receive impulses
- Axon — a long fibre that transmits impulses away from the cell body, covered by a myelin sheath
- Axon terminal (synaptic knob) — the end of the axon containing synaptic vesicles
(a) Nissl granules: These are granular bodies found in the cytoplasm of the cell body and dendrites (but absent from the axon). They are composed of rough endoplasmic reticulum and ribosomes, and their primary function is the synthesis of proteins necessary for the maintenance and repair of the neuron and for the production of neurotransmitters. They are the site of intense protein synthesis activity.
(b) Myelin sheath and Nodes of Ranvier:
- The myelin sheath is a white, fatty insulating layer formed by Schwann cells wrapped around the axon. It serves as an electrical insulator, preventing the leakage of nerve impulses and greatly increasing the speed of impulse conduction.
- The Nodes of Ranvier are gaps or constrictions in the myelin sheath at regular intervals where the axon membrane is exposed. Nerve impulses "jump" from one node to the next (saltatory conduction), which makes transmission much faster than continuous conduction along an unmyelinated fibre.
(c) Synaptic vesicles at the axon terminal:
- Synaptic vesicles are small membrane-bound sacs at the synaptic knob (axon terminal) that contain chemical neurotransmitters (e.g., acetylcholine).
- When a nerve impulse arrives at the synaptic knob, the vesicles fuse with the presynaptic membrane and release the neurotransmitter into the synaptic cleft (the gap between two neurons).
- The neurotransmitter diffuses across the cleft, binds to receptors on the postsynaptic membrane of the next neuron, and initiates a new electrical impulse. After transmission, the neurotransmitter is quickly broken down by enzymes (e.g., cholinesterase) to prevent continuous stimulation.
(ii) Reflex Arc [3]
Sequence of events in the withdrawal reflex (touching a hot object):
- Receptor (pain receptor in skin): Detects the heat stimulus and generates a nerve impulse.
- Sensory (afferent) neuron: Carries the impulse from the receptor to the spinal cord via the dorsal root. The cell body of the sensory neuron is located in the dorsal root ganglion.
- Relay (inter) neuron in grey matter: Receives the impulse from the sensory neuron within the grey matter of the spinal cord and transmits it to the motor neuron. This is the integration centre.
- Motor (efferent) neuron: Carries the impulse from the spinal cord via the ventral root to the effector organ.
- Effector (muscle of hand): The muscle contracts, and the hand is rapidly withdrawn from the hot object.
(a) This response is called "involuntary" because it occurs automatically without conscious thought or involvement of the brain. The response is controlled by the spinal cord, which acts as the reflex centre. The impulse travels through the reflex arc directly to the effector organ without first being processed by the brain. This makes it much faster than a voluntary response, which is critical for protection from harm.
(b) The centre of this reflex action is the spinal cord (specifically, the grey matter of the spinal cord where the relay/interneuron is located).
(c) The person feels pain only after withdrawing the hand because the reflex arc and the sensory pathway to the brain operate simultaneously but at different speeds. The reflex action (spinal cord pathway) is shorter and faster, so the hand is withdrawn almost instantly. Meanwhile, a branch of the sensory impulse also travels up the spinal cord to the brain (cerebrum). The brain takes slightly longer to process and interpret the impulse as "pain." Therefore, the conscious sensation of pain is perceived a fraction of a second after the reflex withdrawal has already occurred.
(iii) Endocrine Glands Table [4]
| Endocrine Gland | Hormone | Function | Disorder (Hypo/Hyper) |
|---|---|---|---|
| Thyroid | Thyroxine | Regulates basal metabolic rate | Hypo: Myxoedema in adults (puffy face, sluggishness, weight gain, low body temperature) |
| Pancreas (Islets of Langerhans) | Insulin (from beta cells) | Lowers blood glucose level by promoting glucose uptake by cells and its conversion to glycogen | Hypo: Diabetes mellitus (high blood sugar, glucose in urine, excessive thirst and urination) |
| Adrenal Cortex | Aldosterone (mineralocorticoid) | Regulates salt (sodium) and water balance by promoting reabsorption of sodium in kidney tubules | Hypo: Addison's disease (low blood pressure, weakness, darkening of skin, salt craving) |
| Pituitary (Anterior) | Growth Hormone (Somatotropin) | Promotes growth of bones and body tissues | Hyper: Acromegaly in adults (abnormal enlargement of hands, feet, jaw, and facial features after growth plates have fused) |
| Ovary | Estrogen (from Graafian follicle) | Development of female secondary sexual characteristics (breast development, widening of hips, growth of pubic hair, onset of menstruation) | — |
Question 6 — Circulatory & Excretory System — Answers [10]
(i) Double Circulation [4]
(a) Human circulation is called "double" circulation because the blood passes through the heart twice in one complete cycle through the body. In one complete circuit, blood flows through two distinct loops:
1. Pulmonary circuit (right side of heart → lungs → left side of heart): Deoxygenated blood is sent from the right ventricle to the lungs for oxygenation and returns as oxygenated blood to the left atrium.
2. Systemic circuit (left side of heart → body organs → right side of heart): Oxygenated blood is pumped from the left ventricle to all body organs and tissues, where oxygen is delivered and CO₂ is picked up, and returns as deoxygenated blood to the right atrium.
Thus, the blood passes through the heart twice — once through the right side (pulmonary) and once through the left side (systemic) — in each complete circulation, hence "double circulation."
(b)
- The only artery that carries deoxygenated blood is the Pulmonary artery (from right ventricle to lungs).
- The only vein that carries oxygenated blood is the Pulmonary vein (from lungs to left atrium).
(c) The valves in the heart prevent the backflow of blood, ensuring that blood flows in only one direction — from atria to ventricles and from ventricles to arteries. They open to allow forward flow and close to prevent backward flow, maintaining efficient circulation. The valve between the left atrium and left ventricle is the bicuspid valve (mitral valve), which has two flaps.
(ii) Blood Groups and Rh Factor [3]
(a) Genetic Cross for Blood Groups:
Mother: I^A i (Blood Group A) × Father: I^B i (Blood Group B)
I^B i
┌──────────────┬──────────────┐
I^A │ I^A I^B │ I^A i │
│ Blood │ Blood │
│ Group AB │ Group A │
├──────────────┼──────────────┤
i │ I^B i │ ii │
│ Blood │ Blood │
│ Group B │ Group O │
└──────────────┴──────────────┘
Possible blood groups of children: Group AB (25%), Group A (25%), Group B (25%), Group O (25%).
(b) Erythroblastosis Foetalis:
Erythroblastosis foetalis (Haemolytic Disease of the Newborn) is a condition in which the red blood cells of the foetus are destroyed by the mother's antibodies. It occurs when:
- The mother is Rh-negative (Rh⁻) and the father is Rh-positive (Rh⁺).
- The foetus inherits Rh-positive blood from the father.
- During the first pregnancy (or after exposure to Rh⁺ blood), some foetal Rh⁺ red blood cells enter the mother's bloodstream during delivery. The mother's immune system recognizes the Rh antigen as foreign and produces anti-Rh antibodies (sensitization).
- In subsequent pregnancies with an Rh⁺ foetus, the mother's anti-Rh antibodies (which are small enough to cross the placenta) attack and destroy the foetal red blood cells, causing severe anaemia, jaundice, and potentially death of the foetus.
(c) Blood cross-matching is essential even when the ABO blood group is known because:
- There are many minor blood group antigens (beyond ABO and Rh) that can cause transfusion reactions.
- Cross-matching involves mixing the donor's red blood cells with the recipient's serum (and vice versa) and checking for agglutination (clumping). This detects any incompatibility due to these minor antigens.
- It serves as a final safety check to confirm compatibility and prevent potentially fatal transfusion reactions.
(iii) Haemodialysis vs. Normal Kidney Function [3]
(a) The dialysis machine works on the principle of diffusion (and osmosis) across a semi-permeable membrane. The fluid used is called dialysate (dialyzing fluid). One key property: the dialysate has a composition similar to normal blood plasma — it contains the same concentration of glucose, salts, and other essential substances as blood but lacks urea and other waste products. This ensures that only waste products diffuse out of the blood into the dialysate along the concentration gradient, while useful substances are retained.
(b)
- Substances that pass through the dialysis membrane (small molecules): Urea and excess salts (e.g., potassium, sodium chloride).
- Substances that do not pass through the dialysis membrane (large molecules): Blood cells (RBCs, WBCs) and plasma proteins (albumin, globulins).
(c) Two limitations of haemodialysis compared to normal kidney function:
1. Haemodialysis cannot perform the endocrine functions of the kidney — a healthy kidney produces hormones such as erythropoietin (stimulates red blood cell production) and renin (regulates blood pressure), which the dialysis machine cannot replicate.
2. Dialysis must be performed repeatedly (typically 3 times a week for 4-5 hours each session), is time-consuming, expensive, and significantly reduces the patient's quality of life. A healthy kidney works continuously 24 hours a day, maintaining homeostasis in real-time.
Question 7 — Reproductive System & Development — Answers [10]
(i) Female Reproductive System Diagram [3]
(a) Parts identified:
- A = Ampulla (widened region of the Fallopian tube / oviduct) — the usual site of fertilization
- B = Ovary — the female gonad that produces ova (eggs) and female sex hormones (estrogen, progesterone)
- C = Uterus (womb) — the muscular, hollow organ where the fertilized egg implants and the embryo/foetus develops during pregnancy
- D = Cervix — the narrow lower part of the uterus that opens into the vagina
(b) The process is called ovulation. It is triggered by a surge in Luteinizing Hormone (LH) from the anterior pituitary gland. The mature Graafian follicle in the ovary ruptures, releasing the secondary oocyte (ovum) into the Fallopian tube, usually around day 14 of the menstrual cycle.
(c) If fertilization does not occur, the corpus luteum degenerates, causing a sharp drop in progesterone and estrogen levels. Without hormonal support, the thickened, vascularised endometrium (lining of the uterus — part C) breaks down and is shed along with blood, mucus, and the unfertilized ovum through the vagina. This is called menstruation, and it marks the beginning of a new menstrual cycle.
(ii) Menstrual Cycle Phases [4]
| Phase | Duration (approx.) | Key Hormone(s) | Ovarian Changes | Uterine Changes |
|---|---|---|---|---|
| Menstrual Phase | Day 1–4 (about 4–5 days) | Drop in progesterone and estrogen triggers menstruation | Follicles are in a resting / early development stage; corpus luteum from previous cycle has fully degenerated | Endometrium breaks down and is shed along with blood vessels, mucus, and unfertilized egg — menstrual bleeding occurs |
| Follicular Phase | Day 5–13 (about 9–10 days) | FSH (Follicle Stimulating Hormone) from anterior pituitary; rising estrogen from developing follicle | A primary follicle in the ovary begins to mature into a Graafian follicle under the influence of FSH; the follicle grows and the ovum develops inside it | Estrogen stimulates the uterine endometrium to regenerate, thicken, and become richly supplied with blood vessels (proliferation) |
| Ovulatory Phase | Day 14 (about 1 day) | Surge in LH (Luteinizing Hormone); peak estrogen | The mature Graafian follicle ruptures and releases the secondary oocyte (ovum) into the Fallopian tube — this is ovulation | Endometrium is fully thickened and well-prepared; continues to remain thickened |
| Luteal / Secretory Phase | Day 15–28 (about 14 days) | Progesterone (from corpus luteum); some estrogen | The ruptured Graafian follicle transforms into the corpus luteum, which secretes progesterone; if no fertilization occurs, the corpus luteum degenerates by Day 28 | Progesterone further maintains and enriches the endometrium; uterine glands secrete mucus and nutrients to prepare for possible implantation; if no implantation occurs, the cycle restarts with menstruation |
(iii) Fertilization to Implantation [3]
(a) Fertilization normally takes place in the ampulla (or ampullary-isthmic junction) of the Fallopian tube (oviduct). When a sperm penetrates the secondary oocyte, their nuclei fuse (syngamy), forming a zygote. The zygote contains 46 chromosomes (23 from the sperm + 23 from the ovum), restoring the diploid (2n) number.
(b) After fertilization, the zygote undergoes a series of rapid mitotic cell divisions called cleavage as it travels down the Fallopian tube towards the uterus:
- The first cleavage produces a 2-celled stage, then 4-celled, 8-celled, 16-celled, and so on.
- By about 3–4 days, it forms a solid ball of 16–32 cells called the morula (resembling a mulberry).
- The morula continues dividing and develops a fluid-filled cavity, becoming a hollow sphere called the blastocyst (blastula). The blastocyst has an outer layer of cells called the trophoblast (which later forms the placenta) and an inner cell mass (which develops into the embryo).
- By about Day 6–7 after fertilization, the blastocyst reaches the uterus and embeds itself into the thickened endometrium. This process is called implantation.
(c) Three functions of the placenta during pregnancy:
1. Nutrition: The placenta transports nutrients (glucose, amino acids, fatty acids, vitamins, minerals) from the mother's blood to the foetal blood, providing nourishment for the growing foetus.
2. Gas exchange: Oxygen diffuses from the mother's blood to the foetal blood, and carbon dioxide diffuses from the foetal blood to the mother's blood across the placental membrane, functioning like the foetal lungs.
3. Hormone production: The placenta produces hormones such as human chorionic gonadotropin (hCG), progesterone, and estrogen, which maintain pregnancy, prevent menstruation, and support the development of the foetus and preparation for lactation.
(Other acceptable functions: Excretion — removal of nitrogenous wastes like urea from foetal blood; Protection — acts as a barrier against many pathogens and harmful substances.)
Question 8 — Pollution, Population & Chemical Coordination in Plants — Answers [10]
(i) Air Pollution [3]
(a) Mechanism of acid rain formation:
When fossil fuels (coal, petroleum, natural gas) are burned in factories, power plants, and vehicles, they release sulphur dioxide (SO₂) and nitrogen oxides (NOₓ) into the atmosphere. These gases rise into the atmosphere and react with water vapour and oxygen through chemical reactions:
- SO₂ + H₂O → H₂SO₃ (sulphurous acid); further oxidation → H₂SO₄ (sulphuric acid)
- 2NO₂ + H₂O → HNO₃ (nitric acid) + HNO₂ (nitrous acid)
These acids dissolve in rainwater and fall as acid rain (precipitation with pH below 5.6).
Two harmful effects of acid rain:
1. Acid rain damages crops and vegetation — it leaches essential nutrients from the soil, damages leaf surfaces, and inhibits plant growth, reducing agricultural productivity.
2. Acid rain corrodes buildings and monuments — it reacts with marble (CaCO₃) and limestone, causing deterioration of historical monuments (e.g., the Taj Mahal in Agra is affected by acid rain from nearby industries).
(b) Greenhouse effect vs. Global warming:
- The greenhouse effect is a natural process in which certain gases in the atmosphere (CO₂, methane, water vapour, nitrous oxide) trap heat radiated from the Earth's surface, keeping the planet warm enough to support life. Without it, the average global temperature would be about -18°C, far too cold for life.
- Global warming refers to the unnatural and excessive increase in the Earth's average temperature caused by the enhanced greenhouse effect due to human activities — primarily the burning of fossil fuels, deforestation, and industrial emissions that increase the concentration of greenhouse gases far beyond natural levels.
- A moderate greenhouse effect is essential because it maintains the Earth's average temperature at approximately 15°C, which is necessary for liquid water, weather patterns, and the survival of all living organisms.
(c) Smog is a type of severe air pollution that is a combination of smoke and fog. It is formed when pollutants from vehicle exhaust, industrial emissions, and the burning of fossil fuels react with sunlight to form ground-level ozone and particulate matter, which combine with fog to create a thick, hazy layer of polluted air.
- One Indian city that frequently suffers from severe smog: Delhi (New Delhi) — especially during the winter months (October–January) due to crop stubble burning in neighboring states, vehicular emissions, construction dust, and industrial pollution.
- One health hazard: Prolonged exposure to smog causes respiratory diseases such as asthma, bronchitis, and chronic obstructive pulmonary disease (COPD), and can aggravate existing heart and lung conditions. Fine particulate matter (PM2.5) penetrates deep into the lungs and even enters the bloodstream.
(ii) Population Growth and Impact [3]
(a) Three major reasons for rapid population growth in India:
1. Decline in death rate: Improved medical facilities, widespread vaccination, better sanitation, and control of epidemic diseases have significantly reduced mortality rates, especially infant mortality, leading to a larger surviving population.
2. High birth rate: Despite family planning programmes, the birth rate remains high due to social and cultural factors — preference for male children, early marriages, lack of education (especially female literacy), and religious beliefs that oppose contraception.
3. Illiteracy and lack of awareness: In rural and economically weaker sections, poor access to education and family planning services means many people are unaware of or unable to practice birth control methods effectively.
(b) Overpopulation leads to depletion of natural resources because the demand for food, water, energy, land, and raw materials increases with every additional person:
1. Deforestation: Forests are cleared at alarming rates to create agricultural land for food production and to provide wood for fuel and construction to support the growing population. This leads to loss of biodiversity, soil erosion, and disruption of the water cycle.
2. Water scarcity: Increasing population leads to over-extraction of groundwater for drinking, agriculture, and industry. Rivers and lakes are polluted by sewage and industrial waste, reducing the availability of clean freshwater. Many Indian cities face severe water shortages.
(c) Two government programmes for population control in India:
1. National Family Planning Programme (now National Family Welfare Programme): Its primary objective is to promote the adoption of small family norms through awareness campaigns, free distribution of contraceptives, and providing incentives for sterilization and the use of birth control methods.
2. Beti Bachao Beti Padhao (Save the Girl Child, Educate the Girl Child): While primarily aimed at addressing the declining child sex ratio and promoting girls' education, it indirectly controls population by empowering women through education, which is one of the most effective factors in reducing birth rates. Educated women tend to marry later and have fewer children.
(iii) Tropic Movements in Plants [4]
(a) Tropism is the directional growth movement of a plant or plant part in response to an external stimulus. The direction of the stimulus determines the direction of growth.
- Positive tropism: The plant grows towards the stimulus. Example: Shoot growing towards light (positive phototropism).
- Negative tropism: The plant grows away from the stimulus. Example: Shoot growing away from gravity (negative geotropism).
(b) Completed Table:
| Type of Tropism | Stimulus | Example | Positive or Negative |
|---|---|---|---|
| Phototropism | Light | Shoot tip bends towards light | Positive (for shoot) |
| Geotropism | Gravity | Root grows downward into the soil | Positive (for roots) |
| Hydrotropism | Water / Moisture | Roots grow towards a source of water in the soil | Positive (for roots) |
| Thigmotropism | Touch / Contact | Tendrils of a pea plant coil around a support | Positive |
| Chemotropism | Chemical substance | Pollen tube grows towards ovule (attracted by chemicals from the ovule) | Positive |
(c) Role of auxin in phototropism:
When a plant shoot is illuminated from one side, auxin (produced at the shoot tip) migrates laterally from the illuminated side to the shaded side of the stem. As a result:
- The shaded side has a higher concentration of auxin, which promotes greater cell elongation on that side.
- The illuminated side has a lower concentration of auxin, resulting in less cell elongation.
- Because cells on the shaded side elongate more than those on the illuminated side, the shoot bends towards the light (positive phototropism).
The shoot bends towards light precisely because auxin causes cell elongation — more elongation on the shaded side creates differential growth, curving the shoot towards the light source.
(d) When a potted plant is placed horizontally, gravity causes auxin to accumulate on the lower side of both the stem and the root due to gravitational pull:
In the stem (negative geotropism):
- Higher auxin concentration on the lower side stimulates cell elongation (stems are stimulated by moderate to high auxin concentrations).
- Lower auxin concentration on the upper side causes less cell elongation.
- The lower side grows faster, causing the stem to curve upward (away from gravity).
In the root (positive geotropism):
- Higher auxin concentration on the lower side inhibits cell elongation (roots are sensitive to auxin and are inhibited by the same concentration that stimulates stems).
- Lower auxin concentration on the upper side allows normal cell elongation.
- The upper side grows faster than the inhibited lower side, causing the root to curve downward (towards gravity).
This demonstrates that roots and stems have different sensitivities to auxin — the same concentration that promotes growth in stems inhibits growth in roots.
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TOPIC-WISE PROBABILITY ANALYSIS
| Topic | Probability of Appearing | Marks Expected | V2 Changes from V1 |
|---|---|---|---|
| Cell Cycle & Cell Division | Very High (95%) | 6–8 marks | Emphasis on meiosis stages with detailed sub-stages; crossing over mechanism |
| Genetics (Mendel's Laws) | Very High (98%) | 8–10 marks | Dihybrid cross with full Punnett square; sex-linked inheritance (haemophilia); genetic cross for blood groups |
| Absorption by Roots | High (85%) | 4–5 marks | Active vs. passive transport comparison; plasmolysis/deplasmolysis differences; osmosis reasoning |
| Transpiration | High (85%) | 4–5 marks | Ganong's potometer experiment in detail; application-based question on wind effect |
| Photosynthesis | Very High (95%) | 6–8 marks | Moll's half-leaf experiment with diagram; photolysis of water; light/dark reaction concepts |
| Chemical Coordination in Plants | High (80%) | 4–6 marks | Comprehensive tropism table; auxin role in phototropism and geotropism; differential sensitivity |
| Circulatory System | Very High (95%) | 8–10 marks | Double circulation flow chart; blood group genetics (ABO and Rh); erythroblastosis foetalis |
| Excretory System | High (90%) | 5–6 marks | Haemodialysis comparison; nephron pathway; selective reabsorption reasoning |
| Nervous System | Very High (95%) | 6–8 marks | Brain diagram with arbor vitae; motor neuron structure; reflex arc with pain perception reasoning |
| Endocrine System | High (90%) | 5–6 marks | Gland-hormone-disorder table completion; assertion-reason on ADH; exophthalmic goitre |
| Reproductive System | Very High (95%) | 8–10 marks | Menstrual cycle detailed table; fertilization to implantation events; female reproductive system diagram |
| Population | High (80%) | 3–4 marks | Government programmes; resource depletion examples; application to Indian context |
| Pollution | High (85%) | 4–5 marks | Acid rain mechanism; greenhouse effect vs. global warming distinction; smog and Delhi case study |
KEY IMPROVEMENTS IN V2 OVER V1
- Two Assertion-Reason MCQs added (Q1 iii and viii) — testing analytical reasoning on left ventricle thickness and ADH function, requiring students to evaluate both statement and explanation.
- Two Diagram-based MCQs (Q1 v and xi) — with ASCII diagrams of a cell and neuron structure, testing identification skills from visual representations.
- One "Identify the INCORRECT statement" MCQ (Q1 x) — on photosynthesis, requiring students to critically evaluate multiple statements and spot the error.
- Enhanced application-based questions throughout — real-world scenarios like the farmer observing seedlings bending (Q1 xii), explaining pain perception delay in reflex arc (Q5 ii c), Delhi smog case study (Q8 i c).
- More detailed genetics problems — dihybrid cross with complete 4×4 Punnett square, sex-linked inheritance (haemophilia cross), and ABO blood group genetics with Rh factor complications.
- Deeper physiological reasoning — Questions ask "why" and "how" rather than "what" (e.g., why potometer measures water uptake not transpiration, why roots and stems respond differently to the same auxin concentration).
- Comprehensive tabular questions — Menstrual cycle four-phase table, endocrine gland table completion, tropism table completion, and transport comparison tables.
- Higher-order thinking in Section B — Questions require synthesis of concepts (e.g., double circulation flow with valve names, dialysis vs. normal kidney comparison, fertilization-to-implantation sequence).
- All questions are completely different from V1 — no repeated stems, different diagram focus (brain instead of heart, motor neuron instead of kidney, female reproductive system instead of male), different experiments (Moll's half-leaf instead of light necessity, Ganong's potometer instead of general transpiration).
- More ASCII diagrams — six detailed ASCII diagrams provided (brain section, Moll's experiment setup, reflex arc pathway, double circulation flow chart, female reproductive system, and cell/neuron in MCQs), enhancing visual learning.
PREPARATION TIPS FOR V2
- Practice drawing and labeling diagrams from memory — brain (L.S.), reflex arc, nephron, heart, female reproductive system, neuron.
- Master genetic crosses — monohybrid, dihybrid (with complete Punnett squares), sex-linked inheritance, and blood group inheritance.
- Understand experiments thoroughly — not just the procedure, but the scientific reasoning behind each step (why destarching, why KOH, why airtight joints).
- Focus on "Give Reasons" type questions — ICSE frequently asks reasoning-based questions. Practice explaining the "why" behind biological processes.
- Know hormone-disorder connections — create your own table linking each gland to its hormone(s), function(s), and hypo/hyper disorders.
- Compare and contrast — active vs. passive transport, arteries vs. veins, mitosis vs. meiosis, photosynthesis vs. respiration.
- Revise the menstrual cycle — know all four phases with hormones, ovarian and uterine changes, and approximate timings.
★ BRIGHT TUTORIALS ★
Prepared by Bright Tutorials | brighttutorials.in
For ICSE 2026 Board Examination Preparation
DISCLAIMER: This is a prediction paper based on analysis of previous years' question papers, weightage patterns, and current syllabus emphasis. It is intended for practice purposes only. The actual board examination paper may differ in format, content, and difficulty. Students are advised to study the entire syllabus comprehensively and not rely solely on prediction papers.
All questions in V2 are entirely different from V1. V2 has been designed with slightly higher difficulty, more application-based reasoning, and enhanced question formats (assertion-reason, diagram-based MCQs, identify-the-incorrect-statement) to challenge students who have already practised V1.
© 2026 Bright Tutorials. All rights reserved.
Topic-Wise Probability Analysis (V2)
Based on 10+ years of ICSE board paper analysis, syllabus weightage, and V2 emphasis on application-based reasoning:
| Topic | Probability | Level | V2 Focus |
|---|---|---|---|
| Genetics (Mendel's Laws, Sex-Linked) | ⬛⬛⬛⬛⬛⬛⬛⬛⬛⬛ | Very High (98%) | Dihybrid + Haemophilia |
| Nervous System (Brain, Reflex Arc, Neuron) | ⬛⬛⬛⬛⬛⬛⬛⬛⬛⬛ | Very High (95%) | Brain L.S. + Arbor Vitae |
| Reproductive System (Menstrual Cycle, Organs) | ⬛⬛⬛⬛⬛⬛⬛⬛⬛⬛ | Very High (95%) | 4-Phase Table + Implantation |
| Circulatory System (Double Circulation, Blood Groups) | ⬛⬛⬛⬛⬛⬛⬛⬛⬛⬛ | Very High (95%) | Blood Group Genetics + Rh |
| Photosynthesis (Moll's Experiment, Reactions) | ⬛⬛⬛⬛⬛⬛⬛⬛⬛⬛ | Very High (95%) | Half-Leaf Experiment |
| Cell Division (Meiosis Stages, Significance) | ⬛⬛⬛⬛⬛⬛⬛⬛⬛⬛ | Very High (95%) | Detailed Sub-Stages |
| Endocrine System (Hormones, Glands, Disorders) | ⬛⬛⬛⬛⬛⬛⬛⬛⬛ | High (90%) | Table Completion + ADH |
| Excretory System (Nephron, Dialysis) | ⬛⬛⬛⬛⬛⬛⬛⬛⬛ | High (90%) | Haemodialysis Comparison |
| Transpiration (Potometer, Factors) | ⬛⬛⬛⬛⬛⬛⬛⬛ | High (85%) | Ganong's Potometer |
| Absorption by Roots (Osmosis, Transport) | ⬛⬛⬛⬛⬛⬛⬛⬛ | High (85%) | Active vs Passive Transport |
| Pollution (Acid Rain, Smog, Greenhouse) | ⬛⬛⬛⬛⬛⬛⬛⬛ | High (85%) | Delhi Smog Case Study |
| Chemical Coordination in Plants (Tropisms) | ⬛⬛⬛⬛⬛⬛⬛⬛ | High (80%) | Auxin Differential Sensitivity |
| Population (Growth, Control Measures) | ⬛⬛⬛⬛⬛⬛⬛⬛ | High (80%) | Govt Programmes + Indian Context |
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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.