ICSE Class 10 Biology Board Exam Question Paper 2010 with Solutions

SECTION-I (40 Marks)

(Attempt all questions from this Section.)

Question 1.

(a) Name the following: [5 Marks]
(i) The type of cell division which occurs in the cells of the reproductive organs.
(ii) A plant with sunken stomata.
(iii) A foreign body that induces the formation of antibodies in the body.
(iv) The place where fertilization occurs in the female reproductive system.
(v) An organization that looks after maternal and child welfare centres.

Answer:
(i) Meiosis
(ii) Nerium
(iii) Antigen
(iv) Fallopian tube / Oviduct
(v) Red Cross

Teacher's Note:
a) Meiosis is crucial for sexual reproduction, producing gametes with half the chromosome number.
b) Sunken stomata are an adaptation in xerophytes to reduce water loss through transpiration.
c) Antigens are specific molecules that trigger an immune response, leading to antibody production.
d) Fertilization typically occurs in the fallopian tube, where the sperm meets the egg.
e) The Red Cross is a well-known international organization involved in humanitarian aid, including maternal and child welfare.

(b) State whether the following statements are true or false. If false, rewrite the correct form of the statement by changing the first or last word only. [5 Marks]
(i) Tubectomy is the surgical method of sterilisation in males.
(ii) Mitosis is the type of cell division occurring in the cells of injured parts of the body.
(iii) Photolysis is the process of splitting of water molecules in the presence of grana and temperature.
(iv) Dilation of the pupil is brought about by the sympathetic nervous system.
(v) Chromosomes other than the pair of sex chromosome are called alleles.

Answer:
(i) False; Vasectomy is the surgical method of sterilisation in males.
(ii) True.
(iii) False; Photolysis is the process of splitting of water molecules in the presence of grana and light.
(iv) True.
(v) False; Chromosomes other than the pair of sex chromosome are called autosomes.

Teacher's Note:
a) Tubectomy is female sterilization, while vasectomy is male sterilization.
b) Mitosis is essential for growth and repair, including healing injured tissues.
c) Photolysis requires light energy, not temperature, to split water molecules during photosynthesis.
d) The sympathetic nervous system prepares the body for "fight or flight," which includes pupil dilation.
e) Autosomes are non-sex chromosomes, while alleles are different forms of a gene.

(c) Given below are five sets of five terms each. In each case, rewrite the terms in logical sequences as directed at the end of each statement. [5 Marks]
One has been done for you as an example.
Example : Anaphase, Telophase, Prophase, Metaphase, Interphase. (sequential order of Karyokinesis)
Answer : Interphase, Prophase, Metaphase, Anaphase, Telophase.
(i) Vagina, Ovary, Uterus, Oviduct, Cervix (pathway of egg after ovulation)
(ii) Motor Neuron, Receptor, Sensory Neuron, Effector, Association Neuron. (pathway of a nerve impulse)
(iii) Pupil, Yellow Spot, Cornea, Lens, Aqueous humour (path of entry of light into the eye from an object)
(iv) Stoma, Mesophyll cells, Xylem, Substomatal space, Intercellular space. (loss of water due to transpiration)
(v) Cortical cells, root hair, soil, water, endodermis, xylem. (entry of water into the plant from the soil)

Answer:
(i) Ovary, Oviduct, Uterus, Cervix, Vagina.
(ii) Receptor, Sensory Neuron, Association Neuron, Motor Neuron, Effector.
(iii) Cornea, Aqueous humour, Pupil, Lens, Yellow spot.
(iv) Xylem, Mesophyll cells, Intercellular space, Substomatal space, Stoma.
(v) Soil, Water, Root hair, Cortical cells, Endodermis, Xylem.

Teacher's Note:
a) Understanding the sequence of events in biological processes is key to answering such questions.
b) For pathway questions, trace the path from the origin to the destination.
c) For the eye, remember the order light passes through structures to reach the retina.
d) For water movement in plants, recall the path from soil to the vascular tissue.

(d) There are five sets consisting of five terms given below. In each set there is a word which is an odd one. For each of these sets write down the category of the group having identified the odd one out, as shown in the example : [5 Marks]
Example: (0) cell wall, vacuole, centrosome, plastids, mitochondria.

Answer:

Teacher's Note:
a) Identify the common category shared by four terms and then pinpoint the one that doesn't fit.
b) For (i), "Knitting without looking" is a conditioned reflex, not a simple reflex.
c) For (ii), Cretinism is a hormonal disorder, not an eye defect.
d) For (iii), Lachrymal gland produces tears, not part of the male reproductive system. Vasopressin is secreted by the posterior pituitary, not anterior.

(e) Choose the correct answer to the following statements out of the three choices given after each statement. [5 Marks]
(i) A point of contact between two neurons is termed :
(1) Synapsis
(2) Neuro motor junction
(3) Synapse
(ii) Loss of water as droplets from hydathodes is called :
(1) Transpiration
(2) Bleeding
(3) Guttation
(iii) The technical term for the fertilized egg is:
(1) Placenta
(2) Zygote
(3) Morula
(iv) The photo receptor cells of the retina sensitive to colour are:
(1) Cones
(2) Rods
(3) Organ of Corti
(v) Salk's vaccine is used to build immunity against :
(1) Tuberculosis
(2) Poliomyelitis
(3) Malaria

Answer: (i) (3) Synapse
Answer: (ii) (3) Guttation
Answer: (iii) (2) Zygote
Answer: (iv) (1) Cones
Answer: (v) (2) Poliomyelitis

Teacher's Note:
a) Synapse is the correct term for the junction between two neurons, facilitating nerve impulse transmission.
b) Guttation is the exudation of xylem sap from hydathodes, distinct from transpiration.
c) A zygote is the single cell formed by the fusion of male and female gametes.
d) Cones are responsible for colour vision and function best in bright light.
e) Salk's vaccine is a well-known inactivated polio vaccine (IPV) used for immunization against poliomyelitis.

(f) The figure below represents an experiment set up to study a physiological process in plants: [5 Marks]

[Figure: An experiment setup showing a plant in a bell jar, placed under sunlight. A test tube is inverted over the plant, collecting a gas. The plant is submerged in water in a beaker. Labels: Sunlight, Oxygen Gas, Water.]

(i) Name the physiological process being studied.
(ii) Explain the process.
(iii) What is the aim of the experiment?
(iv) Give a wall balanced equation to represent the process.

Answer:
(i) Photosynthesis.
(ii) Photosynthesis is the process by which green plants manufacture glucose from carbon dioxide and water in the presence of sunlight and chlorophyll, releasing oxygen as a byproduct.
(iii) The aim of the experiment is to demonstrate that oxygen is given out during photosynthesis.
(iv) \( 6\text{CO}_2 + 12\text{H}_2\text{O} \xrightarrow{\text{light energy, chlorophyll}} \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{H}_2\text{O} + 6\text{O}_2 \uparrow \)

Teacher's Note:
a) The presence of sunlight, a green plant, and the collection of gas (oxygen) are key indicators of photosynthesis.
b) A complete explanation of photosynthesis should include reactants, conditions, products, and its significance.
c) The balanced chemical equation for photosynthesis is crucial and must be memorized.
d) The question has a typo "wall balanced equation"; it should be "well balanced equation".

(g) Given below is an example of a certain structure and its special functional activity: [5 Marks]
Example: (0) Ribosomes and Protein synthesis. On a similar pattern complete the following:
(i) Hypothalamus and . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 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(h) Explain the following terms : [5 Marks]
(i) Antibiotics
(ii) Antiseptics
(iii) Hormones
(iv) Diffusion
(v) Destarched plant.

Answer:
(i) Antibiotics: These are chemical substances produced by microorganisms (like bacteria or fungi) that can inhibit the growth of or kill other harmful microorganisms (bacteria). For example, Penicillin.
(ii) Antiseptics: These are chemical substances applied to living tissues (skin, mucous membranes) to destroy or inhibit the growth of microorganisms, thereby preventing infection. They are generally milder than disinfectants. Examples include Dettol, Savlon, Hydrogen peroxide.
(iii) Hormones: Hormones are chemical messengers secreted by endocrine glands directly into the bloodstream. They travel to target organs or tissues and regulate specific physiological processes, growth, and metabolism. For example, Insulin, Thyroxine.
(iv) Diffusion: It is the net movement of particles (atoms, ions, or molecules) from a region of higher concentration to a region of lower concentration, down a concentration gradient. This movement occurs due to the random motion of particles and does not require energy.
(v) Destarched plant: A plant whose leaves have been freed of all stored starch. This is achieved by keeping the plant in complete darkness for 24-48 hours, allowing the existing starch to be used up or translocated. Such a plant is used in experiments to demonstrate that starch is produced during photosynthesis.

Teacher's Note:
a) Distinguish clearly between antibiotics (internal use, target specific microbes) and antiseptics (external use, broad-spectrum).
b) For hormones, emphasize their role as chemical messengers and their endocrine origin.
c) Diffusion is a passive process driven by a concentration gradient.
d) Destarching a plant is a critical preliminary step in many photosynthesis experiments to ensure any starch detected is newly formed.

SECTION-II (40 Marks)

(Attempt any Four questions from this Section.)

Question 2.

(a) Given below is the outline of the male reproductive system : [5 Marks]

[Figure: Outline diagram of the human male reproductive system. Labels point to: 1 - Seminal vesicle, 2 - Prostate gland, 3 - Urethra, 4 - Vas deferens (sperm duct), 5 - Testis.]

(i) Name the parts labelled 1 to 5.
(ii) State the functions of the parts labelled 1 and 4.
(iii) Name the cells of part 5 that produce testosterone.
(iv) Why is the structure 5 present outside the body in the scrotal sacs ?
(v) What is semen?

Answer:
(i) 1 - Seminal vesicle
2 - Prostate gland
3 - Urethra
4 - Sperm duct / Vas deferens
5 - Testis
(ii) Function of Part 1 (Seminal vesicle): It secretes a fluid rich in fructose, prostaglandins, and other substances that provide nourishment to sperm and aid in their motility.
Function of Part 4 (Sperm duct / Vas deferens): It transports mature sperm from the epididymis to the ejaculatory duct.
(iii) Leydig cells or interstitial cells of part 5 (Testis) produce testosterone.
(iv) The structure 5 (Testis) is present outside the body in the scrotal sacs because spermatogenesis (sperm production) requires a temperature 2-3°C lower than the normal body temperature. The scrotum helps regulate this temperature by contracting when cold (bringing testes closer to the body) and relaxing when warm (moving testes away from the body).
(v) Semen is the milky fluid ejaculated by males, consisting of sperm suspended in seminal fluid (secretions from the seminal vesicles, prostate gland, and bulbourethral glands).

Teacher's Note:
a) Accurately identifying the parts of the male reproductive system is fundamental.
b) Remember the specific contributions of each gland to the seminal fluid.
c) The temperature regulation function of the scrotum is a common exam question.
d) Semen is a mixture of sperm and glandular secretions, not just sperm.

(b) Given one point of difference between the following on the basis of what is given in the brackets: [5 Marks]
(i) Myopia and Hypermetropia (cause of the defect)
(ii) Cerebrum and Spinal cord. (arrangement of cytons and axons of neuron)
(iii) Genotype and Phenotype. (definition)
(iv) Karyokinesis and Cytokinesis. (explain the term)
(v) Light reaction and Dark reaction. (site of occurrence).

Answer:

Teacher's Note:
a) For eye defects, remember the relationship between eyeball length/lens curvature and the focal point.
b) The arrangement of grey and white matter differs significantly between the brain (cerebrum) and spinal cord.
c) Genotype is the genetic code, while phenotype is its expression.
d) Karyokinesis and cytokinesis are sequential steps in cell division, nuclear division first, then cytoplasmic.
e) Knowing the specific sites of light and dark reactions within the chloroplast is essential for understanding photosynthesis.

Question 3.

(a) (i) State Mendel's Law of Dominance. [5 Marks]
(ii) A pure tall plant (TT) is crossed with a pure dwarf plant (tt). Draw Punnett squares to show (1) F₁ generation (2) F2 generation.
(iii) Give the Phenotype of the F2 generation.
(iv) Give the Phenotypic and Genotypic ratio of the F₁ and F2 generation.
(v) Name any one X-linked disease found in humans.

Answer:
(i) Mendel's Law of Dominance: Out of a pair of contrasting characters present together, only one is able to express itself (dominant trait) while the other remains suppressed (recessive trait).
(ii) Punnett Squares:
F₁ generation:

All F₁ plants are Tt (Tall).

F₂ generation:

(iii) Phenotype of the F₂ generation: Tall : Dwarf

(iv) F₁ generation:
Phenotypic ratio: All Tall (Hybrid)
Genotypic ratio: Tt
F₂ generation:
Phenotypic ratio: 3 (Tall) : 1 (Dwarf)
Genotypic ratio: 1 (TT) : 2 (Tt) : 1 (tt)

(v) Haemophilia / Colour blindness

Teacher's Note:
a) Clearly state the Law of Dominance, identifying dominant and recessive traits.
b) Punnett squares must be drawn correctly, showing parental gametes and offspring genotypes.
c) Distinguish between phenotypic (observable) and genotypic (genetic makeup) ratios.
d) Remember common examples of X-linked diseases in humans.

(b) Answer the following briefly: [5 Marks]
(i) Three functions of WHO.
(ii) Three advantages of a small family.
(iii) Explain the terms:
(1) Population density
(2) Natality.

Answer:
(i) Three functions of WHO (World Health Organization):
1. To direct and coordinate international health projects.
2. To encourage and conduct scientific research related to health.
3. To organize international campaigns to control and eliminate diseases like AIDS, Polio, etc.
(ii) Three advantages of a small family:
1. Children receive proper education and better opportunities.
2. Children get proper medical facilities and healthcare.
3. Children receive proper diet and nutrition, leading to better health.
(iii) Explanation of terms:
(1) Population density: It is the number of individuals of a species per unit area or volume at a given time. It is typically expressed as individuals per square kilometre or square mile.
(2) Natality: It refers to the birth rate, specifically the number of live births per 1000 individuals in a population per year.

Teacher's Note:
a) For WHO functions, focus on its global role in health coordination, research, and disease control.
b) Advantages of a small family often relate to improved quality of life for family members.
c) Population density is a measure of how crowded an area is with a specific population.
d) Natality is a key demographic factor influencing population growth.

Question 4.

(a) Given below is a diagram of a double helical structure of DNA : [5 Marks]

[Figure: Diagram of a double helical DNA molecule. The two strands are shown spiraling, with horizontal bars representing base pairs. The structure is labeled "Double Strand".]

(i) Name the four nitrogenous bases that form a DNA molecule.
(ii) Give the full form of DNA.
(iii) Name the unit of heredity.
(iv) Mention two points of difference between Mitosis and Meiosis.

Answer:
(i) The four nitrogenous bases that form a DNA molecule are Adenine (A), Guanine (G), Cytosine (C), and Thymine (T).
(ii) The full form of DNA is Deoxyribonucleic Acid.
(iii) The unit of heredity is a Gene.
(iv)

Teacher's Note:
a) Remember the four nitrogenous bases and their pairing rules (A-T, G-C).
b) The full form of DNA is a basic concept.
c) Genes are segments of DNA that carry hereditary information.
d) Key differences between mitosis and meiosis include the type of cells involved, number of divisions, and ploidy of daughter cells.

(b) (i) Draw a well labelled diagram of a Neuron showing the following parts: Perikaryon, Dendrites, Axon, Node of Ranvier and Myelin sheath. [5 Marks]
(ii) State the function of sensory neuron and a motor neuron.
(iii) What is a nerve made up of?

Answer:
(i) [Figure: diagram to be added]
A well-labelled diagram of a neuron should include:
- Perikaryon (Cell body): Contains the nucleus and cytoplasm.
- Dendrites: Short, branched extensions that receive signals from other neurons.
- Axon: A long, slender projection that transmits nerve impulses away from the cell body.
- Myelin sheath: A fatty layer insulating the axon, speeding up impulse transmission.
- Node of Ranvier: Gaps in the myelin sheath where the action potential jumps.
(ii) Function of Sensory Neuron: It transmits nerve impulses from sensory receptors (e.g., in skin, eyes, ears) towards the central nervous system (brain and spinal cord).
Function of Motor Neuron: It transmits nerve impulses from the central nervous system to effector organs (muscles or glands), causing a response.
(iii) A nerve is made up of a bundle of nerve fibres (axons) enclosed within connective tissue sheaths.

Teacher's Note:
a) Practice drawing and labelling a neuron accurately, as it's a frequently tested diagram.
b) Clearly differentiate the roles of sensory (afferent) and motor (efferent) neurons.
c) Understand that a nerve is a collection of axons, not a single neuron.
d) The myelin sheath and Nodes of Ranvier are important for efficient nerve impulse conduction.

Question 5.

(a) Given below is the diagram of an apparatus set up to study a very important physiological process: [5 Marks]

[Figure: An experiment setup showing a thistle funnel inverted into a beaker of water. The mouth of the thistle funnel is covered with a semipermeable membrane and contains a sugar solution. The beaker contains plain water. Labels: Thistle Funnel, Water, Beaker.]

(i) Name the process being studied.
(ii) Explain the process.
(iii) What change would you observe in the thistle funnel containing sugar solution after about 10 minutes?
(iv) Is sugar solution hypertonic or hypotonic ?
(v) Name the part of the plant cell which is represented by the sugar solution.
(vi) Explain why much salt is added to pickles.

Answer:
(i) Osmosis.
(ii) Osmosis is the diffusion of water molecules from a region of higher water concentration (dilute solution) to a region of lower water concentration (concentrated solution) through a selectively permeable membrane.
(iii) After about 10 minutes, the sugar solution in the thistle funnel will rise up.
(iv) The sugar solution is hypertonic relative to the plain water in the beaker.
(v) The sugar solution represents the cell sap of the root hair cell.
(vi) Much salt is added to pickles to preserve them. The high salt concentration creates a hypertonic environment outside the microbial cells (bacteria, fungi) that cause spoilage. This causes water to move out of the microbial cells by osmosis, leading to their plasmolysis and death, thus preventing spoilage.

Teacher's Note:
a) The thistle funnel experiment is a classic demonstration of osmosis.
b) Remember that water moves from hypotonic to hypertonic solutions across a semipermeable membrane.
c) The rise in the thistle funnel indicates the net movement of water into the funnel.
d) The principle of osmosis is applied in food preservation methods like pickling and salting.

(b) Explain the following terms: [5 Marks]
(i) Reflex action
(ii) Vaccination
(iii) Turgidity
(iv) Bleeding in plants
(v) Cataract.

Answer:
(i) Reflex action: An automatic, rapid, and involuntary response to a stimulus that does not involve conscious thought. It is mediated by a reflex arc. Examples include knee-jerk reflex or withdrawal of hand from a hot object.
(ii) Vaccination: The process of introducing a weakened, killed, or inactivated form of a pathogen (or its toxins/antigens) into the body to stimulate the immune system to produce antibodies and develop immunity against the disease without causing the disease itself.
(iii) Turgidity: The state of a plant cell when its cell membrane is pressed firmly against the cell wall due to the uptake of water by osmosis. This makes the cell firm and rigid, providing structural support to plants.
(iv) Bleeding in plants: The exudation of sap (xylem sap) from a cut or injured surface of a plant. This occurs due to root pressure, which forces water and dissolved minerals upwards in the xylem.
(v) Cataract: An eye condition characterized by the clouding of the natural lens inside the eye, which leads to blurred vision, reduced light perception, and eventually, if untreated, blindness. It is often associated with aging.

Teacher's Note:
a) Reflex actions are protective mechanisms, bypassing the brain for speed.
b) Vaccination relies on the body's adaptive immune response to create memory cells.
c) Turgidity is vital for plant support and maintaining cell shape.
d) Bleeding in plants is a visible manifestation of root pressure.
e) Cataract affects the lens, impairing vision due to opacification.

Question 6.

(a) Given below is an outline of the human body showing the important glands. [5 Marks]

[Figure: Outline diagram of the human body with five glands labelled. 1 - Pituitary gland (in head), 2 - Thyroid gland (in neck), 3 - Pancreas (in abdomen), 4 - Adrenal gland (above kidneys), 5 - Ovary (in pelvic region, labelled "Testis in males" which is incorrect for ovary, but the question asks for glands 1-5 and 5 is clearly ovary in a female outline, so I will assume it's ovary for this context).]

(i) Name the glands marked 1 to 5.
(ii) Name the hormone secreted by 2. Give one important function of this hormone.
(iii) Name the endocrine cells present in part 3.
(iv) Name the hormone secreted by part 4. Give one important function of this hormone.

Answer:
(i) 1 - Pituitary gland
2 - Thyroid gland
3 - Pancreas
4 - Adrenal gland
5 - Ovary
(ii) The hormone secreted by part 2 (Thyroid gland) is Thyroxine.
Function: It regulates the basal metabolic rate (BMR) of the body, influencing growth, development, and energy production.
(iii) The endocrine cells present in part 3 (Pancreas) are the Islets of Langerhans.
(iv) The hormone secreted by part 4 (Adrenal gland) is Adrenaline (also known as Epinephrine).
Function: It prepares the body for "fight or flight" responses during stress or emergency situations by increasing heart rate, blood pressure, and glucose levels.

Teacher's Note:
a) Correctly identify the major endocrine glands and their locations.
b) Associate each gland with its primary hormone(s) and their key functions.
c) Remember that the pancreas has both exocrine and endocrine functions, with the Islets of Langerhans being the endocrine part.
d) Adrenaline's role in emergency responses is a classic example of hormonal action.

(b) Give the biological/technical term for the following : [5 Marks]
(i) Cessation of menstruation in females.
(ii) An eye defect in which the cornea becomes uneven.
(iii) The period of complete intrauterine development of the embryo.
(iv) Inflammation of meninges.
(v) Non identical twins produced by the fertilization of two eggs.
(vi) Membrane that protects the foetus and secretes a protective fluid.
(vii) Process of conversion of several molecules of glucose to one molecule of starch.
(viii) The photosensitive pigment present in the cone cells of the retina.
(ix) The fluid present in the anterior part in front of the eye lens.
(x) Extracts of toxins secreted by bacteria.

Answer:
(i) Menopause
(ii) Astigmatism
(iii) Gestation
(iv) Meningitis
(v) Fraternal twins / Dizygotic twins
(vi) Amnion
(vii) Polymerisation
(viii) Iodopsin
(ix) Aqueous humour
(x) Toxoids

Teacher's Note:
a) Be precise with biological terms; slight variations can change the meaning.
b) For eye defects, distinguish between conditions affecting the lens, cornea, or eyeball shape.
c) Understand the difference between identical and fraternal twins.
d) Toxoids are detoxified bacterial toxins used in vaccines to stimulate immunity.

Question 7.

(a) Given below is a diagram representing a stage during mitotic cell division in an animal cell : [5 Marks]

[Figure: Diagram of an animal cell undergoing mitosis. Chromosomes are condensed and scattered within the cell, with no clear nuclear membrane. Centrosomes with asters are visible at opposite poles, and spindle fibers are forming. Labels: 1 - Aster, 2 - Duplicated chromosomes, 3 - Centromere (point of attachment on chromosome), 4 - Spindle fibres.]

(i) Identify the above stage. Give a reason to support your answer.
(ii) Name the parts labelled 1, 2, 3 and 4.
(iii) What is the function of part 3 ?
(iv) Name the stage that comes just after the stage shown in the diagram. Draw a well labelled diagram of this stage.

Answer:
(i) The given stage is Prophase of mitosis cell division.
Reason: In this stage, the nuclear membrane and nucleolus disappear, chromosomes condense and become visible, and sister chromatids are attached at the centromere. The chromosomes start moving towards the equator, and the spindle apparatus begins to form.
(ii) 1 - Aster
2 - Duplicated chromosomes / Chromatids
3 - Centromere
4 - Spindle fibres
(iii) Function of Part 3 (Centromere): It is the constricted region on a chromosome where sister chromatids are joined. It serves as the attachment point for spindle fibers during cell division, ensuring proper segregation of chromosomes to daughter cells.
(iv) The stage that comes just after Prophase is Metaphase.
[Figure: diagram to be added]
A well-labelled diagram of Metaphase should show:
- Chromosomes aligned at the metaphase plate (equatorial plate).
- Each chromosome consisting of two sister chromatids.
- Spindle fibers attached to the centromeres of each chromosome, extending from opposite poles.
- Asters at the poles (in animal cells).

Teacher's Note:
a) Recognize the key events of each mitotic stage, especially chromosome condensation and spindle formation in prophase.
b) Accurately label all parts of the mitotic apparatus.
c) The centromere's role in chromosome segregation is critical for genetic stability.
d) For metaphase, the defining characteristic is the alignment of chromosomes at the equatorial plate.

(b) Account for the following : [5 Marks]
(i) Wilted lettuce leaves become crisp/firm when placed in cold water for a while.
(ii) One feels blinded for a short time while coming out of a dark room.
(iii) The leaves of certain plants roll up on a bright sunny day.
(iv) An alcoholic person walks unsteadily when drunk.
(v) Sleeping under a tree at night is not advisable.

Answer:
(i) Wilted lettuce leaves become crisp/firm when placed in cold water due to endosmosis. The cells of the lettuce leaves are hypotonic compared to the cold water. Water enters the cells by osmosis, causing them to swell and become turgid, which makes the leaves crisp and firm.
(ii) When one comes out of a dark room into bright light, the eyes experience a temporary blinding effect. This is called light adaptation. In the dark, the pupils are dilated to let in more light, and the rods (light-sensitive photoreceptors) are highly active. Upon sudden exposure to bright light, the pupils constrict, and the rods become overstimulated, while the cones (color-sensitive photoreceptors) take time to adjust and become fully functional, leading to temporary blindness.
(iii) The leaves of certain plants roll up on a bright sunny day to reduce the surface area exposed to sunlight and minimize water loss through transpiration. This is a mechanism to conserve water and prevent excessive wilting under high temperatures and intense sunlight.
(iv) An alcoholic person walks unsteadily when drunk because alcohol affects the cerebellum, which is the part of the brain responsible for coordinating muscular movements, maintaining balance, and regulating posture. Alcohol impairs the cerebellum's ability to process sensory information and coordinate motor commands effectively.
(v) Sleeping under a tree at night is not advisable because plants primarily respire at night, taking in oxygen and releasing carbon dioxide. If a person sleeps under a tree, especially a large one, the concentration of carbon dioxide in the immediate vicinity can increase significantly, potentially leading to discomfort, suffocation, or other health issues due to reduced oxygen availability.

Teacher's Note:
a) Relate the crispness of lettuce to turgor pressure and osmosis.
b) Explain light adaptation by discussing pupil reflex and the roles of rods and cones.
c) Plant leaf rolling is an adaptive response to reduce transpiration.
d) Connect unsteady gait in alcoholics to the cerebellum's function in coordination and balance.
e) Emphasize the respiratory activity of plants at night and its impact on ambient air composition.