ICSE Class 10 Biology Sample Paper 2023 with Solutions

SECTION A

(Attempt all questions from this Section.)

Question 1

Select the correct answers to the questions from the given options. (Do not copy the question. Write the correct answer only) : [15 Marks]

(i) A muscular wall is absent in: [1 Mark]
(a) Capillary
(b) Arteriole
(c) Venule
(d) Vein

Answer: (a) Capillary

Capillaries are extremely narrow blood vessels made up of a single layer of endothelial cells and lack a muscular wall.

Teacher's Note:
a) Capillaries consist only of an endothelium layer to facilitate rapid diffusion of materials.
b) Students often confuse capillaries with venules and arterioles, both of which possess thin muscular walls.

(ii) On which day of the menstrual cycle does ovulation take place? [1 Mark]
(a) 1st day
(b) 5th day
(c) 14th day
(d) 28th day

Answer: (c) 14th day

Ovulation typically occurs around the 14th day in a standard 28-day menstrual cycle due to the luteinizing hormone surge.

Teacher's Note:
a) The 14th day is the midpoint of a normal 28-day cycle.
b) Remember that the duration can vary among women, but 14 days before the next expected period is the standard textbook reference.

(iii) Ganong's Potometer is used to study: [1 Mark]
(a) Photosynthesis
(b) Rate of uptake of water
(c) Exosmosis
(d) Guttation

Answer: (b) Rate of uptake of water

Ganong's potometer measures the rate of water intake by a cut shoot, which corresponds closely to the rate of transpiration.

Teacher's Note:
a) Potometers measure water absorption, not direct water loss, assuming most absorbed water is transpired.
b) Do not confuse potometer with other experimental setups like cobalt chloride paper tests.

(iv) The number of chromosomes in a human skin cell are: [1 Mark]
(a) 22
(b) 23
(c) 44
(d) 46

Answer: (d) 46

Skin cells are somatic cells and therefore contain the diploid number of chromosomes, which is 46 in humans.

Teacher's Note:
a) Somatic cells are always diploid (2n), whereas gametes are haploid (n).
b) Ensure students read carefully whether the question asks for chromosomes or pairs of chromosomes.

(v) Cretinism and Myxedema are due to: [1 Mark]
(a) Hypersecretion of thyroxine
(b) Hypersecretion of growth hormone
(c) Hyposecretion of thyroxine
(d) Hypersecretion of growth hormone

Answer: (c) Hyposecretion of thyroxine

Both conditions are caused by an under-secretion of the thyroid hormone thyroxine (cretinism in infants, myxedema in adults).

Teacher's Note:
a) Hyposecretion means reduced hormone output.
b) Hypersecretion of thyroxine leads to Exophthalmic Goitre.

(vi) Light dependent phase of photosynthesis in green leaves takes place in: [1 Mark]
(a) Grana of chloroplast
(b) Stroma of chloroplast
(c) Nucleus of palisade cells
(d) Cytoplasm of palisade cells

Answer: (a) Grana of chloroplast

The light-dependent reaction (Hill reaction) occurs in the grana part of the chloroplasts where chlorophyll pigments are embedded.

Teacher's Note:
a) Grana contain photosystems necessary for photolysis of water.
b) The light-independent (dark) phase takes place in the stroma.

(vii) An example of a biodegradable substance is: [1 Mark]
(a) Aluminium
(b) Paper
(c) Plastic
(d) Steel

Answer: (b) Paper

Paper is made from plant cellulose and can be broken down naturally by microorganisms.

Teacher's Note:
a) Biodegradable materials decompose naturally through biological action.
b) Aluminium, plastic, and steel are non-biodegradable waste items.

(viii) The part that is cut in Vasectomy is: [1 Mark]
(a) Urethra
(b) Oviduct
(c) Fallopian tube
(d) Vas deferens

Answer: (d) Vas deferens

Vasectomy is a surgical sterilization procedure for males where the sperm ducts (vas deferens) are cut and tied.

Teacher's Note:
a) Fallopian tube ligation is the corresponding sterilization method in females (tubectomy).
b) Always distinguish clearly between male and female surgical methods.

(ix) Gestation period of human foetus is: [1 Mark]
(a) 40 days
(b) 280 days
(c) 280 weeks
(d) 40 months

Answer: (b) 280 days

The average human gestation period is approximately 280 days, which equals 40 weeks or 9 calendar months.

Teacher's Note:
a) Watch out for distractor options like 280 weeks or 40 months which are factually incorrect.
b) 280 days is counted from the first day of the last menstrual period.

(x) The part of the human eye where the rods and cones are located is: [1 Mark]
(a) Iris
(b) Retina
(c) Sclera
(d) Choroid

Answer: (b) Retina

The retina is the innermost, light-sensitive layer of the eyeball containing photoreceptor cells called rods and cones.

Teacher's Note:
a) Rods are sensitive to dim light, while cones are sensitive to bright light and color.
b) The point of no vision where the optic nerve leaves is the blind spot.

(xi) Organ of Corti is present in: [1 Mark]
(a) Utriculus
(b) Sacculus
(c) Cochlea
(d) Incus

Answer: (c) Cochlea

The Organ of Corti is the sensitive hearing organ located within the cochlea of the inner ear.

Teacher's Note:
a) The cochlea is responsible for hearing, while the semicircular canals and vestibule deal with balance.
b) Incus is an ear ossicle in the middle ear.

(xii) The outermost covering of the brain is: [1 Mark]
(a) Arachnoid
(b) Piamater
(c) Pericardium
(d) Duramater

Answer: (d) Duramater

The duramater is the tough, fibrous outermost meningeal layer protecting the brain and spinal cord.

Teacher's Note:
a) The three meninges from outside inwards are Duramater, Arachnoid mater, and Piamater.
b) Pericardium is the covering of the heart.

(xiii) Cytokinins are predominantly present in: [1 Mark]
(a) Meristematic tissues
(b) Permanent tissues
(c) Endodermis
(d) Epidermis

Answer: (a) Meristematic tissues

Cytokinins are plant hormones that promote cell division (cytokinesis) and are found in high concentrations in actively dividing meristematic tissues.

Teacher's Note:
a) Cytokinins work synergistically with auxins to regulate plant growth and organ formation.
b) They are abundant in areas like root apices and developing seeds.

(xiv) Marine fish when placed in tap water bursts because of: [1 Mark]
(a) Diffusion
(b) Plasmolysis
(c) Endosmosis
(d) Exosmosis

Answer: (c) Endosmosis

When a marine fish is placed in hypotonic tap water, water enters its body cells rapidly by endosmosis, causing them to swell and burst.

Teacher's Note:
a) Endosmosis is the inward movement of water through a semipermeable membrane.
b) Marine fish are adapted to hypertonic marine environments and cannot osmoregulate in fresh water.

(xv) Urine is carried from kidney to urinary bladder by: [1 Mark]
(a) Uterus
(b) Urethra
(c) Umbilical cord
(d) Ureter

Answer: (d) Ureter

Each kidney is connected to the urinary bladder by a muscular tube called the ureter.

Teacher's Note:
a) Urethra carries urine from the urinary bladder to the outside of the body.
b) Uterus is part of the female reproductive system; avoid spelling confusion between ureter and uterus.

Question 2

(i) Name the following: [5 Marks]

(a) The suppressed allele of a gene. [1 Mark]

Answer: Recessive allele.

Teacher's Note:
a) A recessive allele's expression is masked in the presence of a dominant allele.
b) It only expresses itself in homozygous condition.

(b) The knot like mass of blood capillaries in Bowman's capsule. [1 Mark]

Answer: Glomerulus.

Teacher's Note:
a) The glomerulus is formed by the branching of the afferent arteriole.
b) It is the primary site for ultrafiltration in the nephron.

(c) The mineral element required for the synthesis of thyroxine. [1 Mark]

Answer: Iodine.

Teacher's Note:
a) Iodine is an essential trace element required by the thyroid gland.
b) Its deficiency causes simple goitre.

(d) One gaseous compound that depletes the ozone layer. [1 Mark]

Answer: Chlorofluorocarbon (CFC) (or Methane / Nitrous oxide).

Teacher's Note:
a) CFCs release chlorine radicals in the stratosphere which break down ozone molecules.
b) Mentioning any recognized ozone-depleting substance is acceptable.

(e) The statistical study of human population. [1 Mark]

Answer: Demography.

Teacher's Note:
a) Demography involves analyzing birth rates, death rates, and population growth trends.
b) Spelling must be accurate.

(ii) Arrange and rewrite the terms in each group in the correct order as to be in a logical sequence beginning with the term that is underlined. [5 Marks]

(a) Soil water, Xylem, Root hair, Cortex [1 Mark]

Answer: Soil water -> Root hair -> Cortex -> Xylem

Teacher's Note:
a) This sequence represents the pathway of water absorption from soil into the plant transport tissue.
b) Ensure the underlined starting term is placed first as instructed.

(b) Tympanum, Incus, Malleus, Stapes [1 Mark]

Answer: Tympanum -> Malleus -> Incus -> Stapes

Teacher's Note:
a) Sound waves hit the tympanum (eardrum), which transmits vibrations across ear ossicles: malleus (hammer), incus (anvil), and stapes (stirrup).
b) Malleus is attached to the inner side of the tympanum.

(c) Pulmonary Vein, Left Ventricle, Aorta, Left auricle [1 Mark]

Answer: Aorta -> Left ventricle -> Left auricle -> Pulmonary vein (tracing backwards or forwards logically from Aorta: Aorta is supplied by Left ventricle, which receives blood from Left auricle, which receives blood from Pulmonary vein. Therefore, logical flow starting with Aorta or following pathway: Pulmonary vein -> Left auricle -> Left ventricle -> Aorta. Wait, the underlined term is Aorta. The sequence should begin with Aorta: Aorta -> Body tissues -> Vena cava -> Right auricle... Let us check standard ordering. Usually, questions ask to arrange in the direction of blood flow. If Aorta is underlined as the starting term: Aorta -> Systemic circulation -> Right side -> Lungs -> Left auricle -> Left ventricle. Alternatively, if it follows physiological sequence leading to Aorta: Pulmonary vein -> Left auricle -> Left ventricle -> Aorta. Since the instruction says "beginning with the term that is underlined", starting with Aorta: Aorta -> Body organs -> Vena Cava -> Right atrium -> Right ventricle -> Pulmonary artery -> Lungs -> Pulmonary vein -> Left atrium -> Left ventricle. Let us give the complete circulatory loop starting with Aorta or the direct upstream chain. Standard answer key treats the underlined term as the starting point of the sequence: Aorta, Tissues, Vena Cava, Right atrium, Right ventricle, Pulmonary artery, Lungs, Pulmonary vein, Left atrium, Left ventricle. Or if it is a simple linear pathway: Pulmonary vein -> Left auricle -> Left ventricle -> Aorta (here Aorta is at the end). Let us write the sequence starting with Aorta as the root: Aorta -> Tissues -> Vena Cava -> Right Atrium -> Right Ventricle -> Pulmonary Artery -> Lungs -> Pulmonary Vein -> Left Atrium -> Left Ventricle.)

Answer: Aorta -> Body organs -> Vena cava -> Right auricle -> Right ventricle -> Pulmonary artery -> Lungs -> Pulmonary vein -> Left auricle -> Left ventricle.

Teacher's Note:
a) When a specific term is underlined, the sequence must begin with that term, completing the full circulatory circuit if necessary.
b) Pay close attention to the direction of blood flow specified by the underlined word.

(d) Sperm, Urethra, Sperm duct, Epididymis [1 Mark]

Answer: Urethra -> (or starting from site of formation: Epididymis -> Sperm duct -> Urethra -> Sperm? Wait, if Urethra is underlined as the starting term: Urethra is the exit point. The pathway of sperm from production to exit is: Testis -> Epididymis -> Sperm duct -> Urethra -> Exterior. If starting with Urethra: Urethra, Exterior. But the terms given are Sperm, Urethra, Sperm duct, Epididymis. The pathway of sperm is Epididymis -> Sperm duct -> Urethra, carrying Sperm. Let us start with Urethra if it is underlined, or follow the natural pathway where Urethra comes last. If the question underlined Urethra as the starting point: Urethra -> external opening. Let us provide the standard pathway starting from Epididymis: Epididymis -> Sperm duct -> Urethra, with Sperm passing through.)

Answer: Epididymis -> Sperm duct -> Urethra -> Sperm (or Sperm -> Epididymis -> Sperm duct -> Urethra).

Teacher's Note:
a) Spermatozoa are formed in the testes, stored temporarily in the epididymis, transported via the sperm duct, and expelled through the urethra.
b) Follow the exact order of the transit route of sperms.

(e) Aqueous humour, Optic nerve, Retina, Lens [1 Mark]

Answer: Lens -> Aqueous humour -> Retina -> Optic nerve (Wait, light path: Cornea -> Aqueous humour -> Pupil -> Lens -> Vitreous humour -> Retina -> Optic nerve. Here the given terms are Aqueous humour, Optic nerve, Retina, Lens. Starting with Lens: Lens -> Vitreous humour -> Retina -> Optic nerve, or including aqueous humour before lens. Let us list: Aqueous humour -> Lens -> Retina -> Optic nerve. But Lens is underlined! So starting with Lens: Lens -> Retina -> Optic nerve, but aqueous humour comes before lens. Let us write: Aqueous humour -> Lens -> Retina -> Optic nerve, or if starting strictly with Lens: Lens, Retina, Optic nerve.)

Answer: Aqueous humour -> Lens -> Retina -> Optic nerve (Note: If starting strictly with the underlined term Lens, the pathway through remaining given terms is: Lens -> Retina -> Optic nerve, preceded by Aqueous humour).

Teacher's Note:
a) Light rays pass through the cornea, aqueous humour, pupil, lens, and vitreous humour before reaching the retina.
b) Impulses from the retina are transmitted to the brain via the optic nerve.

(iii) Match the items given in Column I with the most appropriate ones in Column II and rewrite the correct matching pairs. [5 Marks]

Answer:
(a) Natality - 6. Birth rate
(b) Soil pollutant - 1. DDT
(c) Starch test - 4. Iodine solution
(d) Mortality - 2. Death rate
(e) Air pollutant - 3. Carbon monoxide

Teacher's Note:
a) Natality refers to the birth rate in a population, whereas mortality refers to the death rate.
b) Iodine solution turns blue-black in the presence of starch.

(iv) Choose the odd one out from the following terms and name the category to which the others belong: [5 Marks]

(a) Thyroid gland, Lacrimal gland, Pituitary gland, Adrenal gland. [1 Mark]

Answer: Odd one out: Lacrimal gland.
Category: Endocrine glands (ductless glands).

Teacher'sNote:
a) Lacrimal glands are exocrine glands that secrete tears.
b) Thyroid, pituitary, and adrenal glands are endocrine glands that secrete hormones directly into the blood.

(b) Detergents, Sewage, X-rays, Oil spills [1 Mark]

Answer: Odd one out: X-rays.
Category: Water pollutants.

Teacher's Note:
a) X-rays are a form of radiation and a source of radiation pollution.
b) Detergents, sewage, and oil spills are major causes of water pollution.

(c) Spinal cord, Cerebrum, Pons, Cerebellum [1 Mark]

Answer: Odd one out: Spinal cord.
Category: Parts of the brain.

Teacher's Note:
a) The spinal cord is a part of the central nervous system, but it is an extension of the brain, not a part of the brain itself.
b) Cerebrum, pons, and cerebellum are distinct regions of the human brain.

(d) Chloroplast, Cell wall, Large Vacuoles, Centrosome. [1 Mark]

Answer: Odd one out: Centrosome.
Category: Plant cell organelles / structures not found in animal cells (or typical plant cell features).

Teacher's Note:
a) Centrosomes are typically found in animal cells and lower plant cells.
b) Chloroplasts, cell walls, and large central vacuoles are characteristic features of plant cells.

(e) Auxin, Oxytocin, Gibberellin, Cytokinin [1 Mark]

Answer: Odd one out: Oxytocin.
Category: Plant hormones (Phytohormones).

Teacher's Note:
a) Oxytocin is a mammalian hormone secreted by the posterior pituitary.
b) Auxin, gibberellin, and cytokinin are plant growth hormones.

(v) State the exact location of the following structures: [5 Marks]

(a) Thylakoids [1 Mark]

Answer: Inside the stroma of the chloroplast.

Teacher's Note:
a) Thylakoids are stacked to form grana inside chloroplasts.
b) They contain chlorophyll pigments essential for light absorption.

(b) Corpus callosum [1 Mark]

Answer: A thick band of nerve fibers connecting the left and right cerebral hemispheres of the brain.

Teacher's Note:
a) It facilitates communication between both cerebral hemispheres.
b) Mentioning connection between left and right cerebral hemispheres is key.

(c) Chordae tendinae [1 Mark]

Answer: Attached to the edges of the tricuspid and bicuspid (mitral) valves and papillary muscles inside the ventricles of the heart.

Teacher's Note:
a) They prevent the valves from inverting into the atria during ventricular systole.
b) Commonly known as heart strings.

(d) Prostate gland [1 Mark]

Answer: Surrounding the urethra just below the urinary bladder in human males.

Teacher's Note:
a) It secretes an alkaline fluid that forms part of semen and helps activate sperm.
b) Exact location relative to the urinary bladder and urethra must be stated.

(e) Adrenal glands [1 Mark]

Answer: Like caps, one on top of each kidney.

Teacher's Note:
a) Also known as suprarenal glands.
b) Divided into an outer cortex and inner medulla.

SECTION B

(Attempt any four questions from this Section.)

Question 3

(i) Define Guttation. [1 Mark]

Answer: Guttation is the exudation of sap (water containing dissolved salts) in the form of liquid droplets from the edges or tips of leaves of certain plants through hydathodes.

Teacher's Note:
a) It occurs when root pressure is high and transpiration is very low (e.g., at night or early morning).
b) Do not confuse guttation with dew, which is atmospheric moisture condensing on plant surfaces.

(ii) Give one difference between Lenticels and Stomata. [2 Marks]

Answer:

Teacher's Note:
a) Both structures facilitate gaseous exchange and transpiration.
b) Lenticels lack guard cells, whereas stomata possess specialized guard cells.

(iii) What is Parthenocarpy? Give one example. [2 Marks]

Answer: Parthenocarpy is the condition in which fruit develops without fertilization, resulting in seedless fruits. Example: Banana or seedless grapes / watermelon.

Teacher's Note:
a) Parthenocarpic fruits are commercially valuable because they lack seeds.
b) Plant growth regulators like auxins and gibberellins can induce artificial parthenocarpy.

(iv) State Mendel's Law of Segregation. [2 Marks]

Answer: Mendel's Law of Segregation states that the two alleles of a gene pair separate (segregate) from each other during gamete formation, so that each gamete receives only one allele from each pair.

Teacher's Note:
a) This is also known as Mendel's First Law of inheritance.
b) It is based on monohybrid crosses.

(v) Study the diagram given below and answer the questions that follow: [3 Marks]

[Figure: A potted plant shoot enclosed with a test tube containing water and a layer of oil floating on top of the water, demonstrating transpiration measurement via water level drop]

(a) Name process being studied in the above experiment. [1 Mark]

Answer: Transpiration.

Teacher's Note:
a) Transpiration is the loss of water in the form of water vapour from the aerial parts of the plant.
b) The setup measures water uptake by the shoot.

(b) What will you observe with regard to the level of water when this setup is placed in bright sunlight. [1 Mark]

Answer: The level of water in the test tube will decrease rapidly.

Teacher's Note:
a) Bright sunlight increases temperature and light intensity, which accelerates the rate of transpiration.
b) Consequently, water absorption and uptake by the shoot increase.

(c) Mention one adaptation found in plants to overcome the process mentioned in (i). [1 Mark]

Answer: Presence of a thick cuticle, sunken stomata, or reduction of leaves into spines (e.g., in xerophytes).

Teacher's Note:
a) Plants adapt to reduce excessive water loss in arid environments.
b) Any one valid xerophytic adaptation is awarded full credit.

Question 4

(i) Expand the abbreviation - A T P. [1 Mark]

Answer: Adenosine triphosphate.

Teacher's Note:
a) ATP is known as the energy currency of the cell.
b) Spelling of Adenosine must be accurate.

(ii) Name any two nitrogenous bases. [2 Marks]

Answer: Adenine and Thymine (or Cytosine and Guanine / Uracil).

Teacher's Note:
a) Nitrogenous bases form the fundamental building blocks of nucleic acids (DNA and RNA).
b) Adenine pairs with Thymine (or Uracil in RNA), and Cytosine pairs with Guanine.

(iii) Addition of salt to pickles prevents the growth of bacteria. Explain by giving two suitable reasons. [2 Marks]

Answer:
1. High salt concentration creates a hypertonic external medium, causing bacterial cells to lose water through exosmosis.
2. This plasmolysis and dehydration kills or inhibits the metabolic activity and reproduction of bacteria.

Teacher's Note:
a) High osmotic pressure prevents microbial spoilage.
b) Exosmosis is the core concept required by examiners.

(iv) Mention two adaptations in leaves to perform Photosynthesis. [2 Marks]

Answer:
1. Broad and flat leaf lamina to provide a large surface area for maximum absorption of sunlight and carbon dioxide.
2. Presence of numerous stomata in the epidermis for rapid gaseous exchange.

Teacher's Note:
a) Other valid points include being thin to allow light to penetrate and presence of abundant chloroplasts in mesophyll cells.
b) Any two clear adaptations are sufficient for full marks.

(v) Given below is a diagram representing a stage during the mitotic cell division. Answer the following questions: [3 Marks]

[Figure: A plant cell undergoing mitosis showing chromosomes condensed at the equatorial plate with spindle fibres attached to centromeres]

(a) Identify the stage. [1 Mark]

Answer: Metaphase.

Teacher's Note:
a) Chromosomes align at the equator (metaphase plate) during this phase.
b) Spindle fibers are clearly attached to the centromeres.

(b) Give a suitable reason for your answer in (a). [1 Mark]

Answer: The chromosomes are arranged at the equatorial plane of the cell.

Teacher's Note:
a) Alignment at the equator is the defining characteristic of metaphase.
b) Centromeres are attached to spindle fibers.

(c) Name the stage that follows the one shown in the diagram. [1 Mark]

Answer: Anaphase.

Teacher's Note:
a) During anaphase, sister chromatids separate and move towards opposite poles.
b) The order of mitotic stages is Prophase -> Metaphase -> Anaphase -> Telophase.

Question 5

(i) Define - Excretion. [1 Mark]

Answer: Excretion is the biological process of removal of harmful metabolic nitrogenous waste products from the body.

Teacher's Note:
a) Emphasize that excretion deals with metabolic wastes (like urea, uric acid), distinct from egestion (removal of undigested food).
b) Mentioning nitrogenous wastes secures full marks.

(ii) What is the significance of Hepatic Portal Vein? [2 Marks]

Answer:
1. It transports nutrient-rich blood directly from the digestive tract (stomach and intestines) to the liver before it enters general systemic circulation.
2. This allows the liver to regulate blood sugar levels, store excess glucose as glycogen, and detoxify harmful substances.

Teacher's Note:
a) A portal system starts in capillaries and ends in capillaries.
b) The hepatic portal system is vital for metabolic processing of absorbed nutrients.

(iii) State two functions of vitreous humour. [2 Marks]

Answer:
1. It helps maintain the spherical shape of the eyeball.
2. It protects the internal structures of the eye and refracts light onto the retina.

Teacher's Note:
a) Vitreous humour is the jelly-like substance situated behind the lens.
b) Aqueous humour is found in the anterior chamber in front of the lens.

(iv) Which gland secretes Glucagon? What is its effect on blood sugar level? [2 Marks]

Answer: Glucagon is secreted by the alpha cells of the Islets of Langerhans in the pancreas. It increases blood sugar levels by promoting the conversion of glycogen to glucose in the liver.

Teacher's Note:
a) Glucagon works antagonistically to insulin to maintain blood glucose homeostasis.
b) Mentioning alpha cells of the pancreas is important.

(v) Draw a neat labelled diagram to show the internal structure of a human kidney. [3 Marks]

Answer:

[Figure: Diagram of longitudinal section of human kidney showing renal cortex, renal medulla, renal pelvis, pyramids, calyx, ureter, renal artery, and renal vein]

Teacher's Note:
a) Diagrams should be drawn neatly with sharp pencils and clearly labelled.
b) Essential labels include cortex, medulla, pelvis, ureter, renal artery, and renal vein.

Question 6

(i) Define - Gene. [1 Mark]

Answer: A gene is a specific segment of DNA located on a chromosome that codes for a specific polypeptide or protein, determining a hereditary trait.

Teacher's Note:
a) Genes are recognized as the functional units of heredity.
b) They are composed of nucleotide sequences.

(ii) Differentiate between Cell wall and Cell membrane with reference to permeability. [2 Marks]

Answer:

Teacher's Note:
a) The cell wall is non-living and composed mainly of cellulose in plants.
b) The cell membrane is living and composed of lipoproteins.

(iii) State the function of Medulla Oblongata with a suitable example. [2 Marks]

Answer: The medulla oblongata controls involuntary vital functions of the body such as breathing, heartbeat, and peristalsis. Example: Regulation of the rate of respiration or heartbeat.

Teacher's Note:
a) It forms the lower part of the brainstem connecting the brain to the spinal cord.
b) Damage to the medulla oblongata is usually fatal.

(iv) Colour blindness is generally seen in males. Explain. [2 Marks]

Answer:
1. Colour blindness is an X-linked recessive genetic disorder.
2. Since males have only one X chromosome (XY), a single recessive mutant allele on their X chromosome is sufficient to express the condition, whereas females (XX) require two defective alleles to be color blind.

Teacher's Note:
a) Females can be carriers without showing symptoms if they have one normal and one mutant allele.
b) Mentioning X-linked inheritance explains why males are more frequently affected.

(v) Study the diagram given below and answer the questions that follow: [3 Marks]

[Figure: Diagram of the inner ear showing semicircular canals, vestibule, cochlea, with label A pointing to the cochlea or auditory nerve/organ of Corti]

(a) Identify the structure. [1 Mark]

Answer: Inner ear (membranous labyrinth / cochlea apparatus).

Teacher's Note:
a) The inner ear consists of the cochlea (for hearing) and vestibular apparatus (for balance).
b) Identify carefully based on the pointer arrow.

(b) In which part of the ear is it located? [1 Mark]

Answer: Inner ear (within the temporal bone / fluid-filled bony labyrinth).

Teacher's Note:
a) The ear is divided into outer, middle, and inner parts.
b) The inner ear is filled with endolymph and perilymph.

(c) What is the function of the part marked A? [1 Mark]

Answer: Hearing (transduction of sound vibrations into nerve impulses via the Organ of Corti).

Teacher's Note:
a) Assuming pointer A points to the cochlea, its function is auditory perception.
b) If pointing to semicircular canals, the function is dynamic balance.

Question 7

(i) Explain - Accommodation of eye. [1 Mark]

Answer: Accommodation is the ability of the eye lens to alter its curvature and focal length in order to focus clearly on objects at varying distances.

Teacher's Note:
a) This is achieved through the contraction and relaxation of ciliary muscles.
b) Essential for clear vision of both near and distant objects.

(ii) Give two reasons for a sharp rise in world human population. [2 Marks]

Answer:
1. Advancement in medical science and healthcare, leading to a significant drop in mortality rates and increased life expectancy.
2. Better food production, sanitation, and control of epidemic diseases.

Teacher's Note:
a) Population explosion is primarily driven by declining death rates while birth rates remain relatively high.
b) Any two valid socioeconomic or medical reasons are accepted.

(iii) Mention two functions of Amniotic fluid. [2 Marks]

Answer:
1. It acts as a shock absorber, protecting the developing foetus from mechanical shocks and physical injury.
2. It prevents desiccation and maintains a constant temperature around the foetus.

Teacher's Note:
a) Amniotic fluid surrounds the embryo inside the amnion.
b) It also allows free movement of the foetus.

(iv) What is the difference between Phenotype and Genotype? [2 Marks]

Answer:

Teacher's Note:
a) Phenotype is determined by genotype interacting with the environment.
b) Genotype cannot always be determined by observing the phenotype alone.

(v) Draw neat labelled diagrams showing the cross sections of an Artery and a Vein. [3 Marks]

Answer:

[Figure: Cross-sectional diagrams of an artery and a vein showing lumen size, thickness of tunica media, endothelium, and presence of valves in the vein]

Teacher's Note:
a) Arteries have thick muscular walls and narrow lumina, while veins have thin walls, wide lumina, and internal valves.
b) Correct labeling of endothelium, muscular coat, and lumen is required.

Question 8

(i) Define - Pollution. [1 Mark]

Answer: Pollution is the introduction of harmful substances or contaminants into the environment that cause adverse changes, making it impure or harmful to living organisms.

Teacher's Note:
a) Pollutants can be physical, chemical, or biological.
b) It affects air, water, and soil.

(ii) Plants droop on a hot day even though the soil is well watered. Explain. [2 Marks]

Answer:
1. On a hot day, the rate of transpiration exceeds the rate of water absorption by the roots.
2. This temporary water deficit causes cells to lose turgidity (flaccidity), leading to the drooping or wilting of leaves.

Teacher's Note:
a) Loss of turgor pressure in plant cells causes wilting.
b) Plants usually recover in the evening when temperatures drop and transpiration slows down.

(iii) Differentiate between Menarche and Menopause. [2 Marks]

Answer:

Teacher's Note:
a) Menarche marks the beginning of the reproductive phase in females.
b) Menopause marks the end of the reproductive phase.

(iv) State two harmful effects of acid rain. [2 Marks]

Answer:
1. It lowers the pH of soil and water bodies, making lakes acidic and killing aquatic life.
2. It corrodes buildings, historical monuments (like the Taj Mahal), and metal structures.

Teacher's Note:
a) Acid rain is caused by sulfur dioxide and nitrogen oxides reacting with atmospheric moisture.
b) Any two clear environmental or structural damage points score full marks.