ICSE Class 10 Biology Board Exam Question Paper 2023 with Solutions

ICSE Class 10 Biology Board Exam Question Paper with Solutions

SECTION A (40 Marks)

(Attempt all questions from this section)

Question 1. Select the correct answers to the questions from the given options. [15 Marks]
(Do not copy the questions, write the correct answer only).

(i) The sex chromosome in a human ovum is: [1 Mark]
(a) X chromosome
(b) Y chromosome
(c) Both X and Y chromosomes
(d) Either X or Y chromosome

Answer: (a) X chromosome

Ovum contains one single X chromosome while sperm can have either X or Y chromosome.

Teacher's Note:
a) Human females are homogametic and produce ova containing only the X chromosome.
b) Remember that the sex of the child is determined by the type of sperm (X or Y) that fertilizes the ovum.

(ii) Which one of the following is a biodegradable waste? [1 Mark]
(a) Metal cans
(b) E-waste
(c) Plastic
(d) Flowers

Answer: (d) Flowers

Flowers are biodegradable as they can be degraded by the microbes present in the soil.

Teacher's Note:
a) Biodegradable wastes are broken down by biological processes into harmless simpler substances.
b) Plastics, metal cans, and e-waste are non-biodegradable and persist in the environment for a long time.

(iii) The heart sound 'Dup' is produced when [1 Mark]
(a) Semilunar valves open
(b) Atrioventricular valves close
(c) Semilunar valves close
(d) Atrioventricular valves open

Answer: (c) Semilunar valves close

The first heart sound is produced by the closure of the AV valves while the second heart sound is produced by the closure of the semilunar valves.

Teacher's Note:
a) The first heart sound 'Lubb' is longer and is due to the closure of tricuspid and bicuspid (AV) valves.
b) The second heart sound 'Dup' is short and sharp, caused by the closure of the aortic and pulmonary semilunar valves.

(iv) Deplasmolysis occurs when a plasmolysed cell is placed in [1 Mark]
(a) Concentrated salt solution
(b) Tap water
(c) Crated agar solution
(d) Hypertonic salt solution

Answer: (b) Tap water

When a deplasmolysed cell is placed in tap water which is a hypotonic solution the water will move inside the cell. This is also known as endosmosis.

Teacher's Note:
a) Deplasmolysis is the recovery or swelling of a plasmolysed cell back to its normal turgid state when placed in water.
b) Ensure you distinguish clearly between hypertonic, hypotonic, and isotonic solutions and their effects on plant cells.

(v) Alpha cells of Pancreas secrete [1 Mark]
(a) Glycogen
(b) Glucose
(c) Glucagon
(d) Insulin

Answer: (c) Glucagon

Alpha cells secrete glucagon hormone which converts glycogen back to glucose.

Teacher's Note:
a) The Islets of Langerhans contain alpha cells (secreting glucagon) and beta cells (secreting insulin).
b) Glucagon is hyperglycemic in action, whereas insulin is hypoglycemic.

(vi) Haploid number of chromosomes are found in [1 Mark]
(a) Nephrons
(b) Neurons
(c) Skin cells
(d) Sperms

Answer: (d) Sperms

Sperms have half of the chromosome hence called haploid (22+X or 22+Y).

Teacher's Note:
a) Gametes (sperms and ova) are always haploid (n), containing half the somatic number of chromosomes.
b) Nephrons, neurons, and skin cells are somatic cells and possess the diploid (2n) number of chromosomes.

(vii) The lifespan of an RBC is [1 Mark]
(a) 120 days
(b) 220 days
(c) 20 days
(d) 2 weeks

Answer: (a) 120 days

The RBC gets destroyed after 120 days.

Teacher's Note:
a) Mature mammalian red blood cells lack a nucleus, which maximizes their space for hemoglobin transport.
b) Worn out RBCs are destroyed primarily in the spleen and liver.

(viii) The statistical study of human population is called [1 Mark]
(a) Mortality
(b) Demography
(c) Natality
(d) Equality

Answer: (b) Demography

The study of the human population is called demography.

Teacher's Note:
a) Demography involves analyzing birth rates, death rates, density, and distribution of populations.
b) Mortality refers to the death rate, while natality refers to the birth rate.

(ix) The pale yellow colour of normal human urine is due to the pigment: [1 Mark]
(a) Melanin
(b) Anthocyanin
(c) Urochrome
(d) Hemoglobin

Answer: (c) Urochrome

Urine has a yellow tint due to the presence of urochrome. It is formed through the breakdown of bile pigments in the liver, preceded by the breakdown of hemoglobin.

Teacher's Note:
a) Urochrome is a pigment excreted continuously in urine, giving it its characteristic yellow coloration.
b) Melanin is responsible for skin pigmentation, while anthocyanin is a plant pigment.

(x) Stimulation of the nerves of the sympathetic nervous system [1 Mark]
(a) Accelerates heartbeat
(b) Constricts pupil of eyes
(c) Increases peristalsis
(d) Retards heartbeat

Answer: (a) Accelerates heartbeat

Sympathetic nervous system is a component of the autonomic nervous system which accelerates heartbeat.

Teacher's Note:
a) The sympathetic nervous system prepares the body for flight or fight responses.
b) Parasympathetic nervous system acts antagonistically, promoting resting and digestive functions (such as slowing heartbeat).

(xi) The site of light reaction in the cells of a green leaf is [1 Mark]
(a) Nucleus
(b) Grana of chloroplast
(c) Cytoplasm
(d) Stroma of chloroplast

Answer: (b) Grana of chloroplast

Stacks of lamellae in plastids is known as grana. These are the sites of conversion of light energy into chemical energy.

[Figure: Diagram showing light reaction occurring in the thylakoid/grana producing ATP and NADPH, and dark reaction (Calvin cycle) occurring in the stroma producing sugar from carbon dioxide, with labels: 1) Thylakoid, 2) Stroma, 3) Chloroplast]

Teacher's Note:
a) Light-dependent reactions take place in the thylakoids (grana) producing ATP and NADPH.
b) Light-independent reactions (dark reactions) take place in the stroma of the chloroplast.

(xii) The paper used to demonstrate unequal transpiration in a dicot leaf is [1 Mark]
(a) Filter paper
(b) Litmus paper
(c) Starch paper
(d) Cobalt chloride paper

Answer: (d) Cobalt chloride paper

[Figure: Diagram showing a potted plant with cobalt chloride paper strips attached to the upper and lower surfaces of leaves using clips and glass slides]

Teacher's Note:
a) Dry cobalt chloride paper is blue and turns pink in the presence of water vapor.
b) Dicot leaves are dorsiventral, showing greater transpiration from the lower surface due to a higher stomatal density.

(xiii) Vitreous humour is present between: [1 Mark]
(a) Cornea and Iris
(b) Lens and Retina
(c) Iris and Lens
(d) Cornea and Lens

Answer: (b) Lens and Retina

[Figure: Diagram of the human eye showing internal structures with numbered labels including: 1) Optic nerve, 2) Optic disc, 3) Fovea centralis, 4) Retina, 5) Sclera, 6) Choroid, 7) Ciliary body, 8) Lens, 9) Cornea, 10) Pupil, 11) Aqueous humour, 12) Iris, 13) Suspensory ligament, 14) Vitreous body]

Teacher's Note:
a) Vitreous humour is a jelly-like substance that maintains the shape of the eyeball and supports the retina.
b) Aqueous humour is present in the anterior chamber between the cornea and the lens.

(xiv) Oxygenated blood to liver is supplied by [1 Mark]
(a) Hepatic artery
(b) Hepatic vein
(c) Inferior vena cava
(d) Hepatic portal vein

Answer: (a) Hepatic artery

Hepatic artery is the major blood vessel that carries blood to the liver.

Teacher's Note:
a) The hepatic artery supplies oxygen-rich blood to the liver tissues.
b) The hepatic portal vein brings nutrient-rich blood from the alimentary canal to the liver for processing.

(xv) During the synthesis phase of the cell cycle, more of [1 Mark]
(a) RNA is synthesised
(b) RNA and proteins are synthesised
(c) DNA is synthesised
(d) Glucose is synthesized

Answer: (c) DNA is synthesised

S phase (Synthesis) - DNA replication takes place during this phase. If the initial quantity of DNA in the cell is denoted as 2N, then after replication it becomes 4N. However the number of chromosomes does not vary, viz., if the number of chromosomes during G1 phase was 2n, it will remain 2n at the end of S phase. The centriole also divides into two centriole pairs in the cells which contain centriole.

[Figure: Diagram of the cell cycle showing interphase (G1, S, G2) and M phase (Mitotic phase), along with G0 resting phase]

Teacher's Note:
a) The S phase of interphase is dedicated to DNA replication and histone synthesis.
b) RNA and protein synthesis mainly occur vigorously during the G1 and G2 phases.

Question 2 [20 Marks]

(i) Name the following: [5 Marks]
(a) The organelle that forms the aster during cell division.
(b) A genetic disorder in which the blood does not clot.
(c) The permanent stoppage of menstruation in human females around the age of 45.
(d) The openings on the barks of trees through which transpiration occurs.
(e) A gaseous plant hormone which promotes ripening of fruits.

Answer:
(a) Centrosome
(b) Hemophilia
(c) Menopause
(d) Lenticels
(e) Ethylene Hormone

Teacher's Note:
a) Centrosomes contain centrioles which radiate astral rays during animal cell division.
b) Lenticels permit gaseous exchange and transpiration through woody barks where stomata are absent.

(ii) Arrange and rewrite the terms in each group in correct order to be in a logical sequence beginning with the term that is underlined [5 Marks]
(a) Snake, Rabbit, Cabbage, Hawk
(b) Xylem, Soil water, Cortical cells, Root hair
(c) Receptor, Response, Effector, Spinal Cord
(d) Fovea, Lens, Cornea, Conjunctiva
(e) Testis, Urethra, Sperm duct, Epididymis

Answer:
(a) Cabbage, Rabbit, Snake, Hawk
(b) Soil water, Root hair, Cortical cells, Xylem
(c) Receptor, Spinal cord, Effector, Response (Note: following standard reflex pathway starting with receptor or as per underlined term sequence: Receptor, Spinal cord, Effector, Response)
(d) Conjunctiva, Cornea, Lens, Fovea
(e) Testis, Epididymis, Sperm duct, Urethra

Teacher's Note:
a) Logical sequence questions require tracking pathways or food chains from the specified starting term.
b) Always double-check the exact starting underlined term given in the sub-part.

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

Answer:

Teacher's Note:
a) Match hormone disorders carefully based on whether they involve hypo-secretion or hyper-secretion.
b) Hyposecretion of thyroxine in infants leads to cretinism, whereas in adults it causes myxedema.

(iv) Choose the odd one out from the following terms and name the category to which the others belong. [5 Marks]
(a) Used bandages, Pesticides, Face masks, Syringes
(b) Dust, Smoke, Carbon monoxide, Effluents
(c) Uterus, Urethra, Urinary bladder, Ureter
(d) Menstrual phase, Telophase, Follicular phase, Luteal phase
(e) Malleus, Incus, Cochlea, Stapes

Answer:
(a) Odd one out: Pesticides. Category: Biomedical waste.
(b) Odd one out: Effluents. Category: Air pollutants.
(c) Odd one out: Uterus. Category: Parts of the urinary system.
(d) Odd one out: Telophase. Category: Phases of the menstrual cycle.
(e) Odd one out: Cochlea. Category: Ear ossicles (bones of the middle ear).

Teacher's Note:
a) To answer this type of question correctly, first identify the common category for three of the terms.
b) Clearly state both the odd term and the collective category name to secure full marks.

(v) State the exact location of the following structures [5 Marks]
(a) Thyroid gland
(b) Dura mater
(c) Amniotic fluid
(d) Papillary muscles
(e) Islets of Langerhans

Answer:
(a) Thyroid gland: Situated in the anterior portion of the neck, ventral to the larynx.
(b) Dura mater: The outermost tough fibrous protective membrane covering the brain and spinal cord.
(c) Amniotic fluid: Located in the amniotic cavity between the amnion and the developing embryo.
(d) Papillary muscles: Located within the ventricles of the heart, attached to the ventricular walls and connected to chordae tendineae.
(e) Islets of Langerhans: Scattered in the pancreas (endocrine portion).

Teacher's Note:
a) Location questions require precise anatomical descriptions specifying surrounding structures.
b) Practice precise terminology for membranes, glands, and internal chambers.

SECTION B (40 Marks)
(Attempt any four questions from this Section)

Question 3 [10 Marks]

(i) Write the overall chemical equation for photosynthesis. [2 Marks]

Answer:
\( 6CO_{2} + 12H_{2}O \xrightarrow{\text{Light/Chlorophyll}} C_{6}H_{12}O_{6} + 6O_{2} + 6H_{2}O \)
- For each molecule of glucose (\( C_{6}H_{12}O_{6} \)) produced during photosynthesis, six molecules of carbon dioxide (\( CO_{2} \)) and twelve molecules of water (\( H_{2}O \)) are required.
- The molecules of water get oxidized and the electrons so released are then utilised for the reduction of carbon dioxide to form glucose.

Teacher's Note:
a) Always balance photosynthesis and respiration equations correctly with proper molecular stoichiometry.
b) Mentioning the essential external conditions (sunlight and chlorophyll) is mandatory.

(ii) Mention any two functions of blood. [2 Marks]

Answer:
1. Transportation of oxygen from the lungs to the tissues.
2. Transportation of digested food from the small intestine to the tissues and cells around the body.

Teacher's Note:
a) Blood also plays a key role in defense against pathogens and regulation of body temperature.
b) Keep functional points concise and distinct.

(iii) Differentiate between Karyokinesis and Cytokinesis [2 Marks]

Answer:

Teacher's Note:
a) Karyokinesis always precedes cytokinesis during standard cell division.
b) Present differences in a tabular format with corresponding comparison parameters.

(iv) Excessive use of fertilizers in agricultural fields reduces the yield of crops. Justify the statement. [2 Marks]

Answer:
The excessive use of fertilizers in agricultural fields can actually have a negative impact on crop yields in the long run. This is because excessive fertilizer use can lead to a number of problems, including:
- Soil acidification: Overuse of nitrogen-based fertilizers can cause the soil to become more acidic, which can ultimately reduce the soil's ability to support healthy plant growth.
- Nutrient imbalances: Overuse of a particular type of fertilizer can lead to imbalances in soil nutrients, which can cause some nutrients to become unavailable to the plant, while others are present in excess. This can lead to stunted growth and reduced yields.

Teacher's Note:
a) Explain concepts like osmotic stress (fertilizer burn) and soil degradation clearly.
b) Link high chemical concentration in soil water to exosmosis in plant root hairs.

(v) Study the diagram given below and answer the questions that follow [2 Marks]
(a) Name the phenomenon depicted by the shoot in the above diagram
(b) Which plant hormone plays an important role in the above movement?
(c) Complete and rewrite the given statement by filling in the correct terms: Shoots show positive_________________ whereas, roots show positive________________.

[Figure: Diagram of a potted plant near a window showing shoot bending towards the unidirectional sunlight coming from the window]

Answer:
(a) The phenomenon depicted by the shoot in the above diagram is phototropism.
(b) Auxin plays an important role in phototropism.
(c) Shoots show positive phototropism whereas, roots show positive geotropism.

Teacher's Note:
a) Tropisms are directional growth movements in response to environmental stimuli.
b) Ensure proper fill-in terminology matches standard physiological definitions.

Question 4 [10 Marks]

(i) Expand the abbreviation - DNA [1 Mark]

Answer:
Deoxyribonucleic acid.

Teacher's Note:
a) Spelling of chemical names must be accurate.
b) DNA is the primary genetic material in most living organisms.

(ii) What is Active transport? [1 Mark]

Answer:
Active Transport is defined as a process that involves the movement of molecules from a region of lower concentration to a region of higher concentration against a concentration gradient with the use of metabolic energy (ATP).

Teacher's Note:
a) Active transport requires cellular energy unlike passive transport (diffusion and osmosis).
b) Mentioning movement against the concentration gradient is essential.

(iii) Mention the two pairs of nitrogenous bases which pair with each other with hydrogen bonds. [2 Marks]

Answer:
Adenine pairs with Thymine, and Cytosine pairs with Guanine.

Teacher's Note:
a) Adenine and Thymine are linked by two hydrogen bonds, while Cytosine and Guanine are linked by three hydrogen bonds.
b) This complementary base pairing is known as Chargaff's rule.

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

Answer:
Mendel's law of segregation states that: During the formation of gametes, the two alleles of a gene separate (segregate) from each other so that each gamete carries only one allele for each gene.

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

(v) Draw a neat, labelled diagram of a human sperm [4 Marks]

[Figure: Diagram of a human sperm showing Head (containing Acrosome and Nucleus with 23 chromosomes), Mid piece (containing Centriole and Mitochondria in collar), and Tail/Flagellum]

Answer:
[Diagram of human sperm with correct labels: Head, Acrosome, Nucleus, Mid-piece, Mitochondria, Centriole, Tail/Flagellum]

Teacher's Note:
a) Diagrams must be neat, clean, and properly proportioned with sharp pencil lines.
b) Essential labels include acrosome, nucleus, mitochondria, and flagellum.

Question 5 [10 Marks]

(i) Explain the term "Population density". [2 Marks]

Answer:
Population density means the number of people living per unit area. It is normally expressed as per square kilometer.

Teacher's Note:
a) High population density places severe pressure on local natural resources.
b) Formula is total population divided by total land area.

(ii) Name the two surgical methods of population control. [2 Marks]

Answer:
1. Vasectomy (in males)
2. Tubectomy (in females)

Teacher's Note:
a) Vasectomy involves ligation of the sperm ducts (vas deferens).
b) Tubectomy involves ligation of the fallopian tubes.

(iii) Mention two factors responsible for population explosion in India. [2 Marks]

Answer:
1. Illiteracy
2. Desire for male children / traditional preference for sons

Teacher's Note:
a) Other factors include early marriage and decline in death rate due to better medical facilities.
b) Keep points precise as requested by the question.

(iv) Name any two resources which come under pressure due to rising population. [2 Marks]

Answer:
1. Food
2. Land

Teacher's Note:
a) Water and forest resources also face severe depletion due to overpopulation.
b) Direct and standard examples secure full credit.

(v) The diagram given below depicts the climate change on planet Earth. Answer the following questions: [2 Marks]
(a) Name the climatic phenomenon for the increase in Earth's temperature.
(b) Mention one reason for this warming
(c) What measures can be taken to prevent this climate change?

[Figure: Poster depicting Earth with the text "The climate is changing, why aren't we?"]

Answer:
(a) Global warming
(b) Due to the increase in concentration of greenhouse gases such as Carbon dioxide, Methane, Ozone, Nitrous oxide, and Water vapour.
(c) Measures to prevent this climate change are:
1. Stop deforestation and promote afforestation.
2. Reduce air pollution caused due to vehicles and various industries.

Teacher's Note:
a) Global warming is primarily driven by the enhanced greenhouse effect.
b) Sustainable practices and transition to renewable energy help mitigate climate change.

Question 6 [10 Marks]

(i) Define the term Transpiration. [1 Mark]

Answer:
Transpiration is the process in which water is lost as water vapour from the aerial parts of the plants through stomata. Transpiration is essentially evaporation of water from the leaves of the plant.

Teacher's Note:
a) Mentioning loss of water in the form of water vapour is crucial.
b) It creates a suction force (transpirational pull) aiding ascent of sap.

(ii) State any two adaptations in plants to reduce transpiration. [2 Marks]

Answer:
1. Spines instead of leaves: The leaves in desert plants are modified into spines to decrease the surface area for transpiration.
2. Thick cuticle on leaves: A waxy layer called cuticle on the surface of the leaves lowers the transpiration rate.

Teacher's Note:
a) Xerophytic adaptations are essential for survival in water-scarce regions.
b) Sunken stomata are another key structural adaptation.

(iii) Mention any two functions of the human foetal placenta. [2 Marks]

Answer:
1. The placenta provides nutrients and oxygen to the embryo while also eliminating carbon dioxide and waste materials produced by the embryo.
2. The placenta produces hormones such as estrogens, human chorionic gonadotropin (hCG), and progesterone.

Teacher's Note:
a) Placenta acts as an endocrine, nutritive, and excretory organ for the foetus.
b) Maternal and foetal blood do not mix directly; exchange occurs across the placental membrane via diffusion.

(iv) What is the significance of the human testes being located in scrotal sacs outside the abdomen? [1 Mark]

Answer:
The presence of testes outside the abdominal cavity in the scrotum keeps the temperature of testes 2 to 3 degrees Celsius below the internal body temperature, which is essential for the production of healthy sperm (spermatogenesis).

Teacher's Note:
a) Spermatogenesis cannot occur efficiently at normal core body temperature.
b) This is a vital homeostatic adaptation in mammals.

(v) Draw a neat, labelled diagram of a Malpighian Capsule. [4 Marks]

[Figure: Diagram of Malpighian capsule showing Afferent arteriole, Efferent arteriole, Glomerulus, Bowman's capsule, Basement membrane, Proximal convoluted tubule (PCT), and Microvilli]

Answer:
[Diagram of Malpighian Capsule with correct labels: Afferent arteriole, Efferent arteriole, Glomerulus, Bowman's capsule, Proximal Convoluted Tubule (PCT)]

Teacher's Note:
a) Malpighian corpuscle consists of the glomerulus enclosed within Bowman's capsule.
b) Ensure clear distinction between afferent arteriole (wider) and efferent arteriole (narrower).

Question 7 [10 Marks]

(i) What is a Reflex action? [1 Mark]

Answer:
Reflex action is an involuntary, automatic, and sudden response to a stimulus, controlled primarily by the spinal cord.

Teacher's Note:
a) It bypasses conscious brain control for a rapid protective response.
b) The pathway followed is called a reflex arc.

(ii) Renal cortex has a dotted appearance and Renal medulla has a striped appearance. Explain. [2 Marks]

Answer:
The nephron has two parts - a cup-shaped body called Malpighian corpuscle or renal corpuscle and a tubular part called renal tubule. The cortex has a dotted appearance because of the presence of these Malpighian corpuscles. The striated appearance of the medulla is due to the parallel arrangement of Henle's loops and collecting ducts (renal tubules).

Teacher's Note:
a) Malpighian corpuscles are situated exclusively in the renal cortex.
b) The straight tubules and collecting ducts running through the medulla give it a striated or striped look.

(iii) What are the two functions of cerebellum? [2 Marks]

Answer:
1. It maintains the balance and posture of the body.
2. It coordinates voluntary muscular activities.

Teacher's Note:
a) Damage to the cerebellum leads to jerky and uncoordinated muscular movements.
b) It is the second largest part of the human brain.

(iv) Distinguish between Semicircular canals and Utriculus based on their function. [2 Marks]

Answer:
- Semicircular canals respond to rotational movements (dynamic equilibrium / angular acceleration).
- Utriculus (along with saccule) responds to changes in the position of the head with respect to gravity (static equilibrium / linear acceleration).

Teacher's Note:
a) Both structures are part of the inner ear (vestibular apparatus).
b) Clearly mention dynamic versus static equilibrium parameters.

(v) A potted plant with variegated leaves was kept in dark for 24 hours and then placed in bright sunlight. Answer the following questions: [3 Marks]
(a) Which aspect of photosynthesis is being tested in the above diagram?
(b) Why was the plant kept in the dark for 24 hours?
(c) After the starch test what will be the colour of the yellow and green parts of the leaf? Give reasons to support your answer.

[Figure: Diagram of a potted plant with variegated leaves showing pale yellow non-green areas and green areas, with arrows pointing to them]

Answer:
(a) Necessity of chlorophyll for photosynthesis.
(b) The plant was kept in the dark to destarch the leaves (eliminate existing starch).
(c) After the starch test, the green parts of the leaf will turn blue-black while the yellow parts lacking chlorophyll will show a negative starch test (remain brown/yellow color of iodine).
Reason: The green part contains chlorophyll and synthesizes starch, whereas the yellow part lacks chlorophyll and cannot synthesize starch.

Teacher's Note:
a) Variegated leaf experiments are standard test designs for proving requirements of photosynthesis.
b) Iodine solution turns blue-black in the presence of starch.

Question 8 [10 Marks]

(i) Define the term Mutation. [1 Mark]

Answer:
Mutation is a sudden, heritable change in the DNA base pair sequence due to environmental factors such as UV radiation, or mistakes during DNA replication.

Teacher's Note:
a) Mutations are a primary source of genetic variation.
b) They can be gene mutations or chromosomal mutations.

(ii) A pure breeding red flower variety of pea plant (RR) is crossed with a pure breeding white flower variety of pea plant (rr). Draw a Punnett square to find out the Phenotypic and Genotypic ratios of the progeny belonging to the F2 generation. [3 Marks]

Answer:
Cross: RR (Red) × rr (White)
F1 generation: Rr (All red flowers)
F2 generation Punnett Square:

Phenotypic ratio is 3:1 (3 Red : 1 White)
Genotypic ratio is 1:2:1 (1 RR : 2 Rr : 1 rr)

Teacher's Note:
a) Always show both phenotypic and genotypic ratios clearly in genetic cross problems.
b) Verify that the Punnett square axes correspond to male and female gametes.

(iii) Leaves of certain plants roll up on a hot sunny day. Explain by giving suitable reasons. [2 Marks]

Answer:
Leaves of some plants roll up on a bright sunny day to reduce the effective surface area for transpiration. The reduced surface area ultimately reduces the rate of excessive water loss.

Teacher's Note:
a) This is a protective mechanism in grasses and certain other plants against wilting.
b) It minimizes exposure of stomata to direct sunlight and wind.

(iv) What is a semi permeable membrane? Name the semi permeable membrane present in a plant cell. [2 Marks]

Answer:
- Semi-permeable membrane: A membrane through which only smaller molecules like water can pass freely while preventing the passage of bigger molecules like solute particles.
- Plant cell membrane: Cell membrane or Plasma membrane.

Teacher's Note:
a) Cell membrane is selectively permeable, allowing specific molecules to pass.
b) Cell wall is freely permeable and does not restrict solute or solvent movement.

(v) The diagram below depicts the human heart in one of its phases. Answer the questions that follow: [2 Marks]
(a) Which part of the heart is in the contraction phase?
(b) Give a suitable reason to justify your answer in (a)
(c) Distinguish between Systole and Diastole

[Figure: Diagram of the human heart showing ventricles contracting and blood being forced out into the pulmonary artery and aorta]

Answer:
(a) Ventricles are in the contraction phase.
(b) Blood is moving into the respective arteries (pulmonary artery and aorta) because the ventricles are contracting.
(c) Distinguish between Systole and Diastole:

Teacher's Note:
a) Ventricular systole forces blood into systemic and pulmonary aortae.
b) Diastole is the relaxation phase allowing chambers to refill with venous and oxygenated blood.