ICSE Class 10 Biology Board Exam Question Paper 2008 with Solutions

ICSE Paper 2008 BIOLOGY

SECTION-I (40 Marks)

(Attempt all questions from this Section)

Question 1:

(a) Name the following:

(i) A membrane that disappears during late prophase. [1 Mark]

Answer: Nuclear Membrane.

Teacher's Note:
a) The nuclear membrane disintegrates during late prophase, allowing chromosomes to spread in the cytoplasm.
b) This is a crucial step for the spindle fibres to attach to the centromeres of the chromosomes.
c) Its disappearance marks the transition from prophase to metaphase.
d) In telophase, the nuclear membrane reforms around the separated sets of chromosomes.

(ii) A fluid that occupies the larger cavity of the eyeball behind the lens. [1 Mark]

Answer: Vitreous humour.

Teacher's Note:
a) Vitreous humour is a transparent, jelly-like substance that fills the space between the lens and the retina.
b) It helps maintain the spherical shape of the eyeball.
c) It also supports the retina and keeps it pressed against the choroid.
d) Unlike aqueous humour, vitreous humour is not continuously replaced.

(iii) The ground substance present in a chloroplast. [1 Mark]

Answer: Stroma.

Teacher's Note:
a) The stroma is the fluid-filled space within the chloroplast, surrounding the thylakoids.
b) It is the site where the dark reactions (Calvin cycle) of photosynthesis occur.
c) The stroma contains enzymes necessary for carbon fixation and sugar synthesis.
d) It also contains chloroplast DNA, ribosomes, and starch granules.

(iv) A specific part of a chromosome that determines hereditary characteristics. [1 Mark]

Answer: Genes.

Teacher's Note:
a) Genes are segments of DNA located on chromosomes.
b) They carry the genetic information that determines specific traits or characteristics.
c) Each gene codes for a particular protein or functional RNA molecule.
d) The study of genes and heredity is known as genetics.

(v) A neurotransmitter stored at the terminal end of the axon. [1 Mark]

Answer: Acetylcholine.

Teacher's Note:
a) Acetylcholine is a common neurotransmitter found in both the central and peripheral nervous systems.
b) It plays a crucial role in muscle contraction, learning, and memory.
c) It is released from the axon terminal into the synaptic cleft to transmit signals to the next neuron or effector cell.
d) Other neurotransmitters include dopamine, serotonin, and norepinephrine.

(b) The following paragraph is related to absorption of water from the soil.
Copy and complete the following paragraph by selecting the correct word from those given in the box. You may use the term only once.
Exosmosis, Hypertonic, Osmosis, Isotonic, Hypotonic, Cortical, Endosmosis
Water enters the root hair from the soil by the process of .......... .This is because the solution in the soil is .......... whereas the cell sap in the root hair cell is .......... . The water then passes through the cells by cell to cell .......... and reaches the xylem of the root. [5 Marks]

Answer:
Water enters the root hair from the soil by the process of Endosmosis. This is because the solution in the soil is Hypotonic whereas the cell sap in the root hair cell is Hypertonic. The water then passes through the cells by cell to cell Cortical and reaches the xylem of the root.

Teacher's Note:
a) Endosmosis is the movement of water into a cell when the external solution is hypotonic.
b) A hypotonic solution has a lower solute concentration than the cell sap, causing water to move in.
c) The cortical cells form the cortex of the root, through which water moves from the root hair to the xylem.
d) This process is essential for water absorption by plants from the soil.

(c) Given below are sets of 5 terms each. Without changing the first term, rearrange the remaining four so as to be in logical sequence as per the directions given in brackets for each. One has been done for you as an example.
Example: Pathogen, active immunity, produces antibodies, lymphocytes, antigen, (defence mechanism of the body)
Answer : Pathogen -> antigen -> lymphocytes -> produces antibodies -> active immunity.

(i) Destarched plant, iodine added, washed in water, a leaf boiled in alcohol, placed in sunlight.
(testing for presence of starch) [1 Mark]

Answer: Destarched plant -> placed in sunlight -> a leaf boiled in alcohol -> washed in water -> iodine added.

Teacher's Note:
a) The correct sequence for testing starch in a leaf begins with destarching the plant.
b) Placing the plant in sunlight allows photosynthesis and starch formation.
c) Boiling in alcohol removes chlorophyll, making the starch test visible.
d) Washing in water removes the alcohol before adding iodine, which tests for starch.

(ii) Interphase, Anaphase, Prophase, Telophase, Metaphase (sequential stages in Karyokinesis). [1 Mark]

Answer: Interphase -> Prophase -> Metaphase -> Anaphase -> Telophase.

Teacher's Note:
a) Interphase is the preparatory phase before cell division, where the cell grows and DNA replicates.
b) Prophase is the first stage of mitosis where chromosomes condense and the nuclear envelope breaks down.
c) Metaphase involves chromosomes aligning at the equatorial plate.
d) Anaphase sees sister chromatids separating, and Telophase involves the formation of two new nuclei.

(iii) Seminiferous tubule, penis, urethra, epididymis, vas deferens. (course of passage of sperms in man). [1 Mark]

Answer: Seminiferous tubule -> Epididymis -> Vas deferens -> Urethra -> Penis.

Teacher's Note:
a) Sperms are produced in the seminiferous tubules within the testes.
b) They mature and are stored in the epididymis.
c) From the epididymis, sperms travel through the vas deferens.
d) The urethra carries sperms (and urine) out of the body through the penis.

(iv) Pinna, cochlea, tympanum, ear ossicles, auditory canal (route through which vibrations of sound enter the ear). [1 Mark]

Answer: Pinna -> auditory canal -> tympanum -> ear ossicles -> cochlea.

Teacher's Note:
a) The pinna collects sound waves, which then travel through the auditory canal.
b) These waves cause the tympanum (eardrum) to vibrate.
c) The vibrations are amplified by the ear ossicles (malleus, incus, stapes).
d) Finally, the vibrations are transmitted to the fluid in the cochlea, where they are converted into nerve impulses.

(v) Soil water, xylem, cortex, enaodermis, root hair (coduction of water) [1 Mark]

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

Teacher's Note:
a) Water is absorbed from the soil by the root hairs.
b) It then moves through the cortical cells of the root cortex.
c) The endodermis regulates the movement of water into the vascular cylinder.
d) Finally, water enters the xylem vessels for transport to other parts of the plant.

(d) State whether the following statements are True or False. If False rewrite the correct form of the statement by only changing the last word of the statement.

(i) The alpha cells dfthe pancreas secrete insulin. [1 Mark]

Answer: False.
The alpha cells of the pancreas secrete glucagon.

Teacher's Note:
a) Alpha cells of the pancreas produce glucagon, which increases blood glucose levels.
b) Beta cells of the pancreas produce insulin, which lowers blood glucose levels.
c) This hormonal regulation is crucial for maintaining blood sugar homeostasis.
d) Incorrect identification of cell types and their secretions is a common mistake.

(ii) Duplicated chromosomes remain attached at a point termed centrosome. [1 Mark]

Answer: False.
Duplicated chromosomes remain attached at a point termed centromere.

Teacher's Note:
a) The centromere is the constricted region of a chromosome where sister chromatids are joined.
b) It is the attachment site for spindle fibers during cell division.
c) A centrosome is an organelle in animal cells that organizes microtubules and acts as a spindle pole.
d) Distinguishing between centromere and centrosome is important for understanding cell division.

(iii) The number of pairs ofautosomes in man is 22. [1 Mark]

Answer: True.

Teacher's Note:
a) Humans have 23 pairs of chromosomes in total.
b) Of these, 22 pairs are autosomes, which determine non-sexual traits.
c) The remaining one pair consists of sex chromosomes (XX for female, XY for male).
d) This count applies to diploid somatic cells.

(iv) Penicillin obtained from si fungus is an example of an antibody. [1 Mark]

Answer: False.
Penicillin obtained from a fungus is an example of an antibiotic.

Teacher's Note:
a) Penicillin is an antibiotic, a substance produced by microorganisms (like the fungus Penicillium) that inhibits the growth of or kills other microorganisms.
b) Antibodies are proteins produced by the immune system in response to antigens.
c) Antibiotics are used to treat bacterial infections, while antibodies are part of the body's natural defense.
d) It's important not to confuse these two terms, which have distinct biological roles.

(v) Plants that manufacture their own food are termed heterotrophs. [1 Mark]

Answer: False.
Plants that manufacture their own food are termed autotrophs.

Teacher's Note:
a) Autotrophs are organisms that produce their own food, typically through photosynthesis.
b) Heterotrophs are organisms that obtain food by consuming other organisms or organic matter.
c) Plants are primary producers in most ecosystems, forming the base of food chains.
d) This fundamental distinction is key to understanding ecological roles.

(e) Given below is an example of a particular structure and its special functional activity, e.g., Glomerulous and ultra filtration.
On a similar pattern complete the following:

(i) Corpus luteum and .......... [1 Mark]

Answer: Corpus luteum and secretion of progesterone.

Teacher's Note:
a) The corpus luteum forms in the ovary after ovulation from the ruptured follicle.
b) Its primary function is to secrete progesterone, which prepares the uterus for pregnancy.
c) It also produces some estrogen.
d) If pregnancy does not occur, the corpus luteum degenerates.

(ii) Iris of the eye and .......... [1 Mark]

Answer: Iris of the eye and regulates the amount of light entering the eye.

Teacher's Note:
a) The iris is the colored part of the eye.
b) It contains muscles that control the size of the pupil.
c) By adjusting pupil size, the iris regulates how much light enters the eye, protecting the retina.
d) This mechanism is an example of a reflex action.

(iii) Seminal vesicle and .......... [1 Mark]

Answer: Seminal vesicle and semen.

Teacher's Note:
a) The seminal vesicles are glands that contribute a significant portion of the fluid to semen.
b) This fluid is rich in fructose, which provides energy for sperm motility.
c) It also contains prostaglandins and clotting factors.
d) Semen is the fluid containing sperm and secretions from accessory glands.

(iv) Phloem and .......... [1 Mark]

Answer: Phloem and translocation of food.

Teacher's Note:
a) Phloem is a vascular tissue in plants responsible for transporting sugars (food) from leaves to other parts.
b) This process is called translocation.
c) Xylem, in contrast, transports water and minerals.
d) The official key states "Phloem and photosynthesis," which is incorrect as photosynthesis occurs in chloroplasts, not phloem.

(v) Eustachian tube and .......... [1 Mark]

Answer: Eustachian tube and balancing the air pressure on either side of the eardrum.

Teacher's Note:
a) The Eustachian tube connects the middle ear to the nasopharynx.
b) Its primary function is to equalize air pressure between the middle ear and the outside atmosphere.
c) This equalization is crucial for proper hearing and preventing discomfort during changes in altitude.
d) It also helps drain fluid from the middle ear.

(f) Given alongside is an experimental set up to study a particular process:

[Figure: An experimental setup showing a potted plant covered by a bell jar. Water drops are visible on the inner surface of the bell jar. The pot is covered with a plastic sheet. Labels include "Water drops", "Bell jar", "Twig", "Covered potted plant".]

(i) Name the process being studied. [1 Mark]

Answer: Transpiration.

Teacher's Note:
a) Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers.
b) The water drops observed inside the bell jar are condensed water vapor released by the plant.
c) This experiment demonstrates the release of water vapor by plants.
d) The bell jar creates a closed environment where water vapor can accumulate and condense.

(ii) Explain the process named in (i) above. [1 Mark]

Answer: Transpiration is the loss of water as water vapour from the aerial parts of the plant, primarily through stomata on leaves.

Teacher's Note:
a) Water vapor is released into the atmosphere from the plant's surface.
b) Most transpiration occurs through small pores called stomata on the leaves.
c) This process creates a transpiration pull, which helps in the ascent of sap.
d) It also helps in cooling the plant.

(iii) Why is the pot covered with a plastic sheet ? [1 Mark]

Answer: The pot is covered with a plastic sheet to prevent the evaporation of water from the soil surface, ensuring that any water drops observed come only from the plant's transpiration.

Teacher's Note:
a) Covering the pot eliminates the possibility of water evaporating directly from the soil.
b) This makes the experiment a fair test for transpiration from the plant itself.
c) Without the plastic sheet, it would be difficult to distinguish between water lost by the plant and water lost by the soil.
d) This is a crucial step in experimental design to isolate the variable being studied.

(iv) Mention one way in which this process is beneficial to the plant. [1 Mark]

Answer: Transpiration helps in the ascent of sap by producing a suction force (transpiration pull) that draws water and dissolved minerals from the roots up to the leaves.

Teacher's Note:
a) The transpiration pull is the main force responsible for water transport in tall plants.
b) It also helps in the distribution of mineral salts throughout the plant.
c) Transpiration also has a cooling effect on the plant, preventing overheating.
d) Maintaining turgor pressure in cells is another indirect benefit.

(v) Suggest a suitable control for this experiment. [1 Mark]

Answer: A suitable control would be an identical experimental setup with an empty pot (or a pot with soil but no plant) covered by a plastic sheet, placed under the same conditions as the experimental setup.

Teacher's Note:
a) A control experiment helps to confirm that the observed effect is due to the variable being tested (the plant).
b) In this case, the control would show no water drops, proving that the plant is indeed transpiring.
c) It rules out the possibility of condensation from the surrounding air or evaporation from the pot itself.
d) The official key's answer is a bit verbose; a simpler control is sufficient.

(g) Given below are incomplete explanations of certain biological processes I terms where a key word has been left out. Rewrite the completed explanation by inserting the key word in the space indicated by '^'.

(i) Birth rate is the number of '^' birth per thousand of the population per year. [1 Mark]

Answer: Birth rate is the number of 'live' birth per thousand of the population per year.

Teacher's Note:
a) Birth rate specifically refers to live births, excluding stillbirths or miscarriages.
b) It is a key demographic indicator used to study population growth.
c) The rate is typically expressed per 1,000 individuals in a population.
d) This term is important in population studies and public health.

(ii) Photolysis is the splitting of water molecules into hydrogen ions and hydroxyl ions in the presence of '^' and light. [1 Mark]

Answer: Photolysis is the splitting of water molecules into hydrogen ions and hydroxyl ions in the presence of 'chlorophyll' and light.

Teacher's Note:
a) Photolysis is a crucial step in the light-dependent reactions of photosynthesis.
b) Chlorophyll absorbs light energy, which is then used to split water molecules.
c) This process releases electrons, protons (hydrogen ions), and oxygen.
d) The electrons replace those lost by chlorophyll, and oxygen is released as a byproduct.

(iii) Vaccine is a preparation consisting of '^' microbes which help to build immunity in the human body. [1 Mark]

Answer: Vaccine is a preparation consisting of 'killed or weakened' microbes which help to build immunity in the human body.

Teacher's Note:
a) Vaccines contain attenuated (weakened) or inactivated (killed) forms of pathogens, or their toxins/parts.
b) These components stimulate the immune system to produce antibodies and memory cells.
c) This provides active immunity without causing the actual disease.
d) Vaccination is a highly effective method of preventing infectious diseases.

(iv) Osmosis is the movement of water molecules from its region of high concentration to its region of low concentration through a '^' membrane. [1 Mark]

Answer: Osmosis is the movement of water molecules from its region of high concentration to its region of low concentration through a 'semipermeable' membrane.

Teacher's Note:
a) A semipermeable membrane allows the passage of solvent molecules (water) but restricts solute molecules.
b) Water moves down its concentration gradient, from an area of higher water potential to lower water potential.
c) This process is vital for water absorption by roots and maintaining cell turgor.
d) It is a type of passive transport, requiring no energy input from the cell.

(v) Antiseptics are chemical substances applied to the '^' to destroy or prevent the growth and multiplication of harmful microbes. [1 Mark]

Answer: Antiseptics are chemical substances applied to the 'body' to destroy or prevent the growth and multiplication of harmful microbes.

Teacher's Note:
a) Antiseptics are used on living tissues (like skin) to reduce the risk of infection.
b) Disinfectants, in contrast, are used on inanimate objects.
c) Examples of antiseptics include iodine, alcohol, and hydrogen peroxide.
d) They are crucial for hygiene and preventing the spread of pathogens.

(h) Briefly explain the following terms :

(i) Destarched plant [1 Mark]

Answer: A destarched plant is one from which all stored starch has been removed from its leaves by keeping it in complete darkness for 24 to 48 hours.

Teacher's Note:
a) This process ensures that any starch detected later in an experiment was newly formed.
b) Plants convert starch to sugar for transport and respiration in the dark.
c) Destarching is a prerequisite for experiments demonstrating the necessity of light or chlorophyll for photosynthesis.
d) It provides a baseline for measuring starch production.

(ii) Phenotype [1 Mark]

Answer: Phenotype refers to the observable physical or biochemical characteristics of an organism, which are the expression of its genotype and environmental influences.

Teacher's Note:
a) Examples include height, eye color, blood type, or presence of a disease.
b) It is what is seen or measured, as opposed to the genetic makeup (genotype).
c) The phenotype can be influenced by both genetic factors and environmental conditions.
d) Understanding phenotype is crucial in genetics and heredity studies.

(iii) Death rate [1 Mark]

Answer: Death rate (or mortality rate) is the number of deaths per 1,000 individuals in a population per year.

Teacher's Note:
a) It is a key demographic indicator used to assess the health and well-being of a population.
b) Factors like disease, healthcare access, nutrition, and age structure influence death rates.
c) Along with birth rate and migration, it determines population change.
d) It is often expressed as crude death rate or age-specific death rates.

(iv) Power of accommodation of the eye. [1 Mark]

Answer: The power of accommodation of the eye is the ability of the eye lens to change its focal length to focus objects at different distances onto the retina.

Teacher's Note:
a) This is achieved by the ciliary muscles changing the curvature and thickness of the eye lens.
b) For distant objects, the ciliary muscles relax, and the lens becomes thinner, increasing its focal length.
c) For near objects, the ciliary muscles contract, and the lens becomes thicker, decreasing its focal length.
d) This ability diminishes with age, leading to presbyopia.

(v) Natural immunity [1 Mark]

Answer: Natural immunity (or innate immunity) is the non-specific defense system that an individual is born with, providing immediate protection against pathogens without prior exposure.

Teacher's Note:
a) It includes physical barriers like skin and mucous membranes, and cellular components like phagocytes.
b) This immunity does not involve memory cells and does not improve with repeated exposure.
c) It is the first line of defense against infections.
d) In contrast, acquired (adaptive) immunity is specific and develops after exposure to pathogens.

SECTION—II (40 Marks)

(Attempt any four questions from this Section)

Question 2:

(a) Given below is a diagrammatic representation of the internal structure of an organelle found in a plant cell Study the same and then answer the questions that follow:

[Figure: A diagram showing the internal structure of a chloroplast. It is an oval-shaped organelle with an outer membrane and an inner membrane. Inside, there are stacks of disc-like structures called grana (labelled 1), which are interconnected. The fluid-filled space surrounding the grana is labelled as Matrix (labelled 2). Other labels include "Membrane" and "Fret".]

(i) Identify the organelle. [1 Mark]

Answer: Chloroplast.

Teacher's Note:
a) Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis.
b) They are characterized by their double membrane and internal stacks of thylakoids (grana) within the stroma.
c) The presence of chlorophyll gives them their green color.
d) They are the primary sites of food production in plants.

(ii) Name the physiological process occurring in this organelle. [1 Mark]

Answer: Photosynthesis.

Teacher's Note:
a) Photosynthesis is the process by which green plants and some other organisms use sunlight to synthesize foods from carbon dioxide and water.
b) It involves two main stages: light-dependent reactions and light-independent (dark) reactions.
c) This process converts light energy into chemical energy stored in glucose.
d) Oxygen is released as a byproduct, which is essential for most life forms.

(iii) Mention one way in which, this process is beneficial to man. [1 Mark]

Answer: Photosynthesis produces oxygen, which is essential for human respiration, and it forms the basis of all food chains, providing food for humans directly or indirectly.

Teacher's Note:
a) Oxygen released during photosynthesis is vital for aerobic respiration in humans and other animals.
b) Plants, as producers, form the foundation of nearly all ecosystems, providing food for herbivores, which in turn are food for carnivores.
c) Photosynthesis also helps regulate the Earth's climate by absorbing carbon dioxide.
d) Many medicines and raw materials also originate from plants.

(iv) Name the phases of the process occurring in the part labelled 1 and 2. [1 Mark]

Answer:
Part 1 (Grana): Light Reaction (or Photochemical reaction or Hill reaction).
Part 2 (Matrix/Stroma): Dark Reaction (or Biosynthetic reaction or Calvin cycle).

Teacher's Note:
a) The light-dependent reactions occur in the thylakoid membranes (grana) where light energy is captured.
b) The dark reactions (Calvin cycle) occur in the stroma, where carbon dioxide is converted into glucose.
c) These two phases are interconnected, with the products of the light reaction (ATP and NADPH) fueling the dark reaction.
d) Understanding the location of these reactions within the chloroplast is key to understanding photosynthesis.

(v) A chemical substance `NADP' play s an active part in one of the phases. Give the expanded form of NADP and state its role in the above process. [1 Mark]

Answer:
Expanded form of NADP: Nicotinamide Adenine Dinucleotide Phosphate.
Role: NADP acts as an electron acceptor in the light reaction, getting reduced to NADPH. NADPH then carries hydrogen and electrons to the dark reaction, where it provides the reducing power for the synthesis of glucose from carbon dioxide.

Teacher's Note:
a) NADP⁺ is a coenzyme that functions as an electron carrier in photosynthesis.
b) It accepts electrons and protons during the light-dependent reactions, forming NADPH.
c) NADPH is a vital energy-carrying molecule that provides the necessary reducing power for the Calvin cycle.
d) Without NADP⁺, the energy from light reactions could not be efficiently transferred to synthesize sugars.

(vi) Represent the physiological process mentioned in (ii) above in the form of a chemical question. [1 Mark]

Answer:
6CO₂ + 12H₂O → C₆H₁₂O₆ + 6H₂O + 6O₂
(Above the arrow: light energy; Below the arrow: chlorophyll)

Teacher's Note:
a) This balanced chemical equation summarizes the overall process of photosynthesis.
b) Carbon dioxide and water are the reactants, and glucose, water, and oxygen are the products.
c) Light energy and chlorophyll are essential conditions for the reaction to occur.
d) The equation shows that water is both consumed and produced, but 12 molecules are used and 6 are produced, indicating a net consumption of 6 water molecules.

(b) Give the technical / biological term for the following:

(i) Onset of menstruation in a young girl around the age of 13 years. [1 Mark]

Answer: Menarche.

Teacher's Note:
a) Menarche marks the first menstrual period in a female.
b) It signifies the beginning of reproductive maturity.
c) The age of menarche can vary due to genetic, nutritional, and environmental factors.
d) It is a key event during puberty.

(ii) Eye defect occurring in old people whereby they are unable to see near objects. [1 Mark]

Answer: Presbyopia.

Teacher's Note:
a) Presbyopia is a common age-related vision condition.
b) It results from the hardening of the eye's lens, making it less flexible.
c) This reduces the eye's ability to accommodate and focus on close-up objects.
d) It is typically corrected with reading glasses or bifocals.

(iii) The mucous membrane lining the uterus [1 Mark]

Answer: Endometrium.

Teacher's Note:
a) The endometrium is the inner lining of the uterus.
b) It undergoes cyclical changes in response to hormones, preparing for embryo implantation.
c) If implantation does not occur, the superficial layer of the endometrium is shed during menstruation.
d) It is crucial for successful pregnancy.

(iv) The process of conversion of ADP to ATP during the first phase of photosynthesis. [1 Mark]

Answer: Photophosphorylation.

Teacher's Note:
a) Photophosphorylation is the process of synthesizing ATP from ADP and inorganic phosphate using light energy.
b) It occurs during the light-dependent reactions of photosynthesis.
c) The energy stored in ATP is then used in the dark reactions to synthesize glucose.
d) This is a key mechanism for energy conversion in photosynthetic organisms.

(v) The point of contact between two neurons. [1 Mark]

Answer: Synapse.

Teacher's Note:
a) A synapse is a specialized junction where one neuron communicates with another neuron or an effector cell.
b) Neurotransmitters are released from the presynaptic neuron and bind to receptors on the postsynaptic neuron.
c) This allows for the transmission of nerve impulses.
d) Synapses are crucial for information processing and communication in the nervous system.

(vi) Protective membranes covering the human brain and spinal cord. [1 Mark]

Answer: Meninges.

Teacher's Note:
a) The meninges consist of three layers: dura mater, arachnoid mater, and pia mater.
b) They provide physical protection to the brain and spinal cord.
c) They also contain cerebrospinal fluid, which cushions the central nervous system.
d) Inflammation of the meninges is known as meningitis.

(vii) Respiratory openings found OP the stem of woody plants. [1 Mark]

Answer: Lenticels.

Teacher's Note:
a) Lenticels are porous tissues consisting of cells with large intercellular spaces.
b) They facilitate gas exchange (oxygen, carbon dioxide, water vapor) between the atmosphere and the internal tissues of woody stems and roots.
c) Unlike stomata, lenticels are not regulated by guard cells.
d) They appear as small, raised pores on the bark surface.

(viii) The process by which white blood cells engulf harmful microbes. [1 Mark]

Answer: Phagocytosis.

Teacher's Note:
a) Phagocytosis is a type of endocytosis where a cell engulfs large particles, such as bacteria or cellular debris.
b) Phagocytes, like neutrophils and macrophages, are specialized white blood cells that perform this function.
c) It is a crucial part of the innate immune response, protecting the body from infection.
d) The engulfed particles are then broken down by enzymes within the phagocyte.

(ix) The process of mixing of two different substances molecules. [1 Mark]

Answer: Diffusion.

Teacher's Note:
a) Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.
b) This process occurs due to the random motion of molecules.
c) It is a passive process, meaning it does not require cellular energy.
d) Diffusion is important for gas exchange in the lungs and nutrient absorption in the intestines.

(x) Exudation of sap firm injured parts of a plant. [1 Mark]

Answer: Bleeding.

Teacher's Note:
a) Bleeding in plants refers to the exudation of sap from cut or injured parts.
b) This phenomenon is often attributed to root pressure, which pushes sap upwards.
c) The sap contains water, sugars, and other dissolved substances.
d) It can be observed in certain plants when their stems are cut.

Question 3:

(a) Draw a diagram of the human eye as seen in a vertical sect ion a nd label the part which suits the following functions/descriptions :

(i) The layer which prevents reflection of light. [1 Mark]

Answer: Choroid.

Teacher's Note:
a) The choroid is a vascular layer of the eye, located between the retina and the sclera.
b) It contains dark pigments that absorb stray light, preventing internal reflection.
c) This absorption ensures clear vision by preventing light from scattering within the eye.
d) It also supplies nutrients to the retina.

(ii) The structure that alters the focal length of the lens. [1 Mark]

Answer: Ciliary body with ciliary muscles.

Teacher's Note:
a) The ciliary body contains ciliary muscles that contract or relax.
b) These muscles are connected to the suspensory ligaments, which hold the lens.
c) Their action changes the curvature and thickness of the lens, thereby altering its focal length.
d) This process is known as accommodation, allowing the eye to focus on objects at varying distances.

(iii) The region of distinct vision. [1 Mark]

Answer: Fovea Centralis (Yellow Spot).

Teacher's Note:
a) The fovea centralis is a small pit in the macula lutea of the retina.
b) It contains a high concentration of cone cells and is responsible for sharp, detailed color vision.
c) When we look directly at an object, its image is focused on the fovea.
d) The yellow spot is the broader area around the fovea, also rich in cones.

(iv) The part which transmits the impulse to the brain. [1 Mark]

Answer: Optic Nerve.

Teacher's Note:
a) The optic nerve is a bundle of nerve fibers that transmits visual information from the retina to the brain.
b) It exits the back of the eye at the optic disc, which is a blind spot as it lacks photoreceptors.
c) The impulses are generated by photoreceptor cells (rods and cones) in the retina.
d) Damage to the optic nerve can lead to vision loss.

(v) The outermost transparent layer in front of the eye lens. [1 Mark]

Answer: Cornea.

Teacher's Note:
a) The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber.
b) It is responsible for most of the eye's focusing power.
c) It protects the eye from dust, germs, and other foreign particles.
d) The cornea is avascular, meaning it has no blood vessels.

(vi) The fluid present in the aiitermf part of the eye in front of the eye lens. [1 Mark]

Answer: Aqueous Humor.

Teacher's Note:
a) Aqueous humor is a clear, watery fluid that fills the space between the cornea and the lens (anterior chamber).
b) It provides nutrients to the avascular cornea and lens.
c) It helps maintain the intraocular pressure of the eye.
d) This fluid is continuously produced and drained, maintaining a healthy eye environment.

(b) Complete the following table by filling in the blanks 1 to 10 which the appropriate terms: [5 Marks]

Answer:

Teacher's Note:
a) This table tests knowledge of endocrine glands, their hormones, and their physiological effects.
b) Testosterone is the primary male sex hormone, crucial for male reproductive development.
c) Adrenal glands produce both adrenaline (for fight-or-flight response) and corticoids (for metabolic regulation).
d) Thyroxin from the thyroid gland regulates metabolic rate, while growth hormone from the pituitary controls overall body growth.

Question 4:

(a) Given below are diagrams shqwing different stages in the process of fertilization of an egg in the female reproductive tract:

[Figure: Four diagrams (A, B, C, D) illustrating stages of fertilization.
Diagram A: A zygote, showing fusion of male and female pronuclei.
Diagram B: A sperm entering the egg, with the sperm head inside and tail outside.
Diagram C: The sperm nucleus and egg nucleus (pronuclei) are visible inside the egg, moving towards each other but not yet fused.
Diagram D: An unfertilized egg with a single nucleus and polar bodies.]

(i) Use the alphabets given below each diagram to show the correct order in the process of fertilization. [1 Mark]

Answer: D -> B -> C -> A.

Teacher's Note:
a) D represents the unfertilized egg, the starting point.
b) B shows the sperm penetrating the egg, initiating fertilization.
c) C depicts the male and female pronuclei approaching each other within the egg.
d) A illustrates the fusion of the pronuclei, forming a zygote, which completes fertilization.

(ii) Where in the female reproductive system does this process normally take place ? [1 Mark]

Answer: Fallopian tube (or oviduct).

Teacher's Note:
a) Fertilization typically occurs in the ampulla, the widest section of the fallopian tube.
b) The egg is released from the ovary and travels into the fallopian tube.
c) Sperm travel from the vagina, through the uterus, and into the fallopian tubes to meet the egg.
d) If fertilization occurs, the resulting zygote then travels to the uterus for implantation.

(iii) What is the biological term for the product of fusion ? [1 Mark]

Answer: Zygote.

Teacher's Note:
a) A zygote is the diploid cell formed when two haploid gametes (sperm and egg) fuse during fertilization.
b) It is the first cell of a new organism.
c) The zygote undergoes rapid cell division (cleavage) to form an embryo.
d) This fusion restores the diploid chromosome number characteristic of the species.

(iv) What is the chromosome number of (1) the egg (2) the fused product ? [1 Mark]

Answer:
(1) The egg: n (haploid)
(2) The fused product (zygote): 2n (diploid)

Teacher's Note:
a) Gametes (egg and sperm) are haploid, meaning they contain half the number of chromosomes (n).
b) Upon fertilization, the haploid nuclei of the egg and sperm fuse.
c) This fusion restores the diploid chromosome number (2n) in the zygote.
d) Maintaining the correct chromosome number across generations is essential for species continuity.

(v) Draw a neat labelled diagram of a mature human sperm. [1 Mark]

Answer:
[Figure: A diagram of a mature human sperm, showing three main parts:
1. Head: Oval-shaped, containing the Acrosome (at the tip) and Nucleus (below the acrosome).
2. Middle Piece: Cylindrical, located below the head, containing Mitochondria.
3. Tail: Long, whip-like structure extending from the middle piece, containing an Axial filament.]

Teacher's Note:
a) The head contains the genetic material (nucleus) and the acrosome, which helps in egg penetration.
b) The middle piece is packed with mitochondria, providing energy for sperm motility.
c) The tail (flagellum) provides the propulsive force for the sperm to swim.
d) Students should practice drawing and labeling the key structures accurately.

(b) Differentiate between the following on the basis of what is given in brackets :

(i) Myopia and Hypermetropia (Condition of eyeball) [1 Mark]

Answer:

Teacher's Note:
a) Myopia (nearsightedness) causes distant objects to appear blurry because light focuses in front of the retina.
b) Hypermetropia (farsightedness) causes near objects to appear blurry because light focuses behind the retina.
c) Myopia is corrected with concave lenses, while hypermetropia is corrected with convex lenses.
d) Understanding the anatomical cause helps in distinguishing these common refractive errors.

(ii) Rods and Cones (Pigment Present) [1 Mark]

Answer:

Teacher's Note:
a) Rods are photoreceptor cells responsible for vision in dim light (scotopic vision) and detecting motion.
b) Cones are photoreceptor cells responsible for color vision and high-acuity vision in bright light (photopic vision).
c) Rhodopsin is highly sensitive to light, while iodopsin (photopsin) is less sensitive and comes in three types for different colors.
d) The differential distribution and function of rods and cones allow for both night and day vision.

(iii) Tonoplast and Plasma membrane (Location) [1 Mark]

Answer:

Teacher's Note:
a) The tonoplast is a single membrane that encloses the central vacuole in plant cells.
b) It regulates the movement of ions and other substances into and out of the vacuole.
c) The plasma membrane (cell membrane) is the outer boundary of the cytoplasm in all cells.
d) Both are selectively permeable membranes, but they enclose different cellular compartments.

(iv) Wall pressure and Turgor pressure (Explain briefly) [1 Mark]

Answer:

Teacher's Note:
a) Turgor pressure develops when water enters a plant cell by osmosis, causing the protoplast to swell and push against the cell wall.
b) Wall pressure is the equal and opposite pressure exerted by the rigid cell wall in response to turgor pressure.
c) These two pressures are always equal and opposite in a turgid plant cell.
d) Turgor pressure is essential for maintaining cell rigidity, plant support, and various physiological processes.

(v) DPT and BCG (Expanded form of the vaccine). [1 Mark]

Answer:

Teacher's Note:
a) DPT is a combination vaccine that protects against three bacterial diseases: diphtheria, pertussis (whooping cough), and tetanus.
b) BCG is a vaccine primarily used against tuberculosis (TB).
c) Both are crucial vaccines included in routine immunization programs worldwide.
d) Knowing the full forms helps in understanding the diseases they protect against.

Question 5:

(a) The diagram given below depicts the cross section of the spinal cord Study the same and then answer the Questions that follow:

[Figure: A cross-section of the spinal cord showing grey matter (H-shaped, inner) and white matter (outer). A central canal (labelled 5) is in the center of the grey matter. A dorsal root ganglion (labelled 2) is shown outside the spinal cord, connected to the dorsal root. A sensory neuron (labelled 1) enters the dorsal horn of the grey matter. An afferent neuron (labelled 3) carries impulses towards the grey matter. A synapse (labelled 4) is shown within the grey matter. An efferent neuron (labelled 7) exits the ventral horn of the grey matter. A motor neuron (labelled 6) is shown in the ventral horn.]

(i) Name the process that is being depicted. [1 Mark]

Answer: Reflex Action.

Teacher's Note:
a) A reflex action is an involuntary, rapid response to a stimulus.
b) It involves a reflex arc, which is the neural pathway that mediates the reflex action.
c) The spinal cord plays a central role in many reflex actions, allowing for quick responses without brain involvement.
d) This mechanism provides immediate protection against harm.

(ii) Name the parts labelled 2, 5, and 6. [1 Mark]

Answer:
Part 2: Dorsal Root Ganglion
Part 5: Central Canal
Part 6: Gray Matter

Teacher's Note:
a) The dorsal root ganglion contains the cell bodies of sensory neurons.
b) The central canal runs through the center of the spinal cord and contains cerebrospinal fluid.
c) Gray matter, located centrally in the spinal cord, is composed mainly of neuron cell bodies, dendrites, and unmyelinated axons.
d) White matter, surrounding the gray matter, consists of myelinated axons that transmit signals up and down the spinal cord.

(iii) Name the cells in contact with the part labelled `1′. [1 Mark]

Answer: Receptor cells.

Teacher's Note:
a) Part 1 represents a sensory neuron, which receives impulses from receptor cells.
b) Receptor cells are specialized cells that detect specific stimuli (e.g., touch, pain, temperature).
c) They convert the stimulus into an electrical signal (nerve impulse).
d) This impulse is then transmitted to the sensory neuron.

(iv) What is the function of the parts labelled 3, 4 and 7 ? What is the technical term given to the pathway represented by 3, 4, and 7 ? [1 Mark]

Answer:
Functions:
Part 3 (Afferent/Sensory nerve fibre): Carries sensory impulses from the receptor organ to the spinal cord.
Part 4 (Synapse): A junction where the sensory neuron transmits the impulse to an interneuron or motor neuron.
Part 7 (Efferent/Motor neuron): Carries motor impulses from the spinal cord to the effector organ (muscle or gland).
Technical term for the pathway: Reflex Arc.

Teacher's Note:
a) The reflex arc is the neural pathway that mediates a reflex action, typically involving a sensory neuron, an interneuron (sometimes), and a motor neuron.
b) The afferent pathway (Part 3) brings information to the central nervous system.
c) The synapse (Part 4) is where the signal is transferred between neurons.
d) The efferent pathway (Part 7) carries the command from the CNS to the effector for a response.

(v) How does the arrangement of cells in the spinal cord differ from that in the brain ? [1 Mark]

Answer: In the spinal cord, the gray matter is located on the inner side (H-shaped core) and is surrounded by white matter on the outer side. In the brain, this arrangement is reversed: the gray matter forms the outer layer (cortex), and the white matter is located on the inner side.

Teacher's Note:
a) Gray matter consists primarily of neuron cell bodies, dendrites, and unmyelinated axons, involved in processing information.
b) White matter consists mainly of myelinated axons, responsible for transmitting signals.
c) The arrangement reflects the different functions: spinal cord primarily for relay and reflexes, brain for complex processing.
d) This structural difference is a key distinction between the two major components of the central nervous system.

(b) (i) Mention any three functions of the Red Cross. [1 Mark]

Answer:
1. To extend relief and help to the victims of any calamity such as flood, fire, famine, and earthquake.
2. To produce and supply blood for the needy victims of war or other calamities.
3. To extend all possible first aid in any accident.

Teacher's Note:
a) The Red Cross is an international humanitarian movement providing aid during emergencies.
b) Its core principles include humanity, impartiality, neutrality, independence, voluntary service, unity, and universality.
c) Beyond disaster relief, it also promotes health services and community welfare.
d) Students should be aware of the broad scope of its humanitarian activities.

(ii) Name any two microbes that cause diseases in man. In each case give an example of a disease caused by them. [2 Marks]

Answer:
1. Microbe: Plasmodium (Protozoan)
Disease: Malaria
2. Microbe: HIV Virus (Virus)
Disease: AIDS

Teacher's Note:
a) Plasmodium is a protozoan parasite transmitted by Anopheles mosquitoes, causing malaria.
b) HIV (Human Immunodeficiency Virus) is a retrovirus that causes AIDS (Acquired Immunodeficiency Syndrome).
c) Other examples include bacteria (e.g., Mycobacterium tuberculosis causing TB) and fungi (e.g., Candida albicans causing candidiasis).
d) Understanding the causative agents of diseases is fundamental to public health and prevention.

(iii) Mention three reasons why the growth of population has not been appreciably checked in India. [2 Marks]

Answer:
1. Illiteracy: Lack of education, especially among women, often leads to a lack of awareness about family planning methods and the benefits of smaller families.
2. Traditional beliefs and desire for a male child: Cultural preferences for male offspring often lead couples to continue having children until a son is born.
3. High infant mortality rate: Historically, high infant mortality rates encouraged parents to have more children to ensure some survive to adulthood.

Teacher's Note:
a) Other factors include early marriage, religious beliefs opposing family planning, and limited access to healthcare and contraception.
b) Socio-economic factors play a significant role in population dynamics.
c) Government initiatives and education campaigns are crucial for addressing these challenges.
d) Understanding these reasons is important for formulating effective population control policies.

Question 6:

(a) Given alongside are diagrams of plant cells as seen under the microscope after having been placed in two different solutions:

[Figure: Two diagrams of plant cells, A and B.
Cell A: Shows a turgid plant cell. The plasma membrane is pressed against the cell wall, and the vacuole is large. Labels include "Cell wall" and "Plasma Membrane".
Cell B: Shows a plasmolysed plant cell. The plasma membrane has shrunk away from the cell wall, and the vacuole is smaller. Labels include "Cell wall" and "Plasma Membrane".]

(i) What is the technical term for the condition of:
1. Cell A
2. Cell B? [1 Mark]

Answer:
1. Cell A: Turgid cell
2. Cell B: Plasmolysed cell (or Flaccid cell)

Teacher's Note:
a) A turgid cell has absorbed water, causing its protoplast to swell and press against the cell wall.
b) A plasmolysed cell has lost water, causing its protoplast to shrink away from the cell wall.
c) Flaccid refers to a cell that has lost turgor but not necessarily undergone full plasmolysis.
d) These conditions demonstrate the effects of osmosis on plant cells.

(ii) From the solutions given in brackets (water, strong sugar solution, 1% salt solution) name the solution into which :
1. Cell A
2. Cell B was placed before being viewed under the microscope. [1 Mark]

Answer:
1. Cell A was placed in: Water (Hypotonic solution)
2. Cell B was placed in: Strong sugar solution (Hypertonic solution)

Teacher's Note:
a) Placing a plant cell in pure water (hypotonic) causes water to enter the cell by endosmosis, making it turgid.
b) Placing a plant cell in a strong sugar solution (hypertonic) causes water to leave the cell by exosmosis, leading to plasmolysis.
c) A 1% salt solution would also be hypertonic to most plant cells, causing plasmolysis.
d) The concentration gradient between the cell sap and the external solution determines water movement.

(iii) Under what conditions in the soil will the root hair cell resemble :
1. Cell A
2. CellB ? [1 Mark]

Answer:
1. Root hair cell will resemble Cell A (turgid) when the soil is over-flooded with water (hypotonic soil solution).
2. Root hair cell will resemble Cell B (plasmolysed) in the case of excessive application of fertilizers in the fields (hypertonic soil solution).

Teacher's Note:
a) Over-flooding creates a very dilute (hypotonic) soil solution, causing root hair cells to absorb water and become turgid.
b) Excessive fertilizers increase the solute concentration in the soil water, making it hypertonic to the root hair cells.
c) This hypertonic condition causes root hair cells to lose water by exosmosis, leading to plasmolysis and wilting.
d) Understanding these conditions is crucial for proper irrigation and fertilization practices in agriculture.

(iv) Name the pressure responsible for the movement of water from the root hair cell to the xylem of the root. How is it set up ? [1 Mark]

Answer:
The pressure responsible is Root Pressure.
It is set up due to the continuous absorption of water by root hair cells, which creates a positive pressure in the root xylem. This pressure is generated by the active transport of mineral ions into the xylem, followed by osmotic movement of water, and cell-to-cell osmosis in the root tissues, where one turgid cell presses the next, forcing water inward.

Teacher's Note:
a) Root pressure is a relatively weak upward push of water in the xylem, primarily observed at night or when transpiration is low.
b) It is an active process involving the expenditure of energy by root cells to accumulate ions.
c) The osmotic gradient created by ion accumulation draws water into the xylem.
d) While important, root pressure is not the primary force for water transport in tall plants; transpiration pull is more significant.

(v) Name the pressure that helps in the movement of water up the xylem of the root. [1 Mark]

Answer: Transpiration pull.

Teacher's Note:
a) Transpiration pull is the main driving force for the ascent of sap in plants.
b) It is created by the evaporation of water from the leaves (transpiration), which generates a negative pressure (tension) in the xylem.
c) This tension pulls the continuous column of water upwards from the roots to the leaves due to cohesion and adhesion properties of water.
d) The official key's answer describes root pressure, which contributes but is not the primary force for upward movement in most plants.

(b) (i) Explain the following terms :
1. Mutation [1 Mark]

Answer: Mutation is a sudden, heritable change in the genetic material (DNA or chromosomes) of an organism, which may result in new traits or characteristics not present in the parents or ancestors. Example: Albinism.

Teacher's Note:
a) Mutations can occur spontaneously due to errors during DNA replication or repair.
b) They can also be induced by mutagens like radiation or certain chemicals.
c) Mutations are the ultimate source of genetic variation, driving evolution.
d) While some mutations are harmful, others can be neutral or even beneficial.

2. Homologous chromosomes [1 Mark]

Answer: Homologous chromosomes are a pair of chromosomes (one inherited from each parent) that are similar in size, shape, and gene sequence, and they pair up during meiosis.

Teacher's Note:
a) Each homologous chromosome carries genes for the same traits at the same loci (positions).
b) Although they carry genes for the same traits, the alleles (alternative forms of genes) on homologous chromosomes may be different.
c) They are crucial for sexual reproduction and genetic diversity.
d) Humans have 23 pairs of homologous chromosomes (22 autosomes and 1 pair of sex chromosomes).

3. Alleles [1 Mark]

Answer: Alleles are alternative forms of a gene that occupy the same locus (position) on homologous chromosomes and determine contrasting expressions of a particular trait. Example: The alleles for free and attached earlobes.

Teacher's Note:
a) For any given gene, an individual inherits two alleles, one from each parent.
b) These alleles can be dominant or recessive, determining how the trait is expressed.
c) If both alleles are identical, the individual is homozygous for that trait; if different, heterozygous.
d) Understanding alleles is fundamental to Mendelian genetics.

(ii) Give the dihybrid ratio. Narhe and state the law which explains the same. [1 Mark]

Answer:
Dihybrid Ratio: 9:3:3:1.
Law: Mendel's Law of Independent Assortment.
Statement: This law states that when two pairs of contrasting characters are involved in a cross, the distribution of the members of one pair into the gametes is independent of the distribution of the other pair.

Teacher's Note:
a) The dihybrid ratio of 9:3:3:1 is observed in the F2 generation of a dihybrid cross when both parents are heterozygous for two traits.
b) This ratio reflects the independent segregation of alleles for different genes during gamete formation.
c) The law applies to genes located on different chromosomes or far apart on the same chromosome.
d) It is a cornerstone of classical genetics, explaining how traits are inherited in combination.

(iii) Mention three main reasons for the sharp rise in 'Human population' in the world. [1 Mark]

Answer:
1. Better health care: Advances in medicine, sanitation, and public health have significantly reduced death rates, especially infant mortality.
2. Minimized food shortages: Improvements in agricultural practices (Green Revolution) have led to increased food production, reducing starvation and malnutrition.
3. Large scale immunization: Widespread vaccination programs have eradicated or controlled many infectious diseases, leading to increased life expectancy.

Teacher's Note:
a) Other contributing factors include increased fertility rates in some regions and lack of awareness/access to family planning.
b) The demographic transition model explains how societies move from high birth/death rates to low birth/death rates.
c) Rapid population growth can strain resources and infrastructure.
d) Understanding these factors is crucial for addressing global population challenges.

Question 7:

(a) (i) Draw a diagram of the nucleds of a cell, having chromosome number 6, as it would appear in the Metaphase stage of Mitosis and label the following parts in the diagram:
1. Aster
2. Achromatic spindle
3. Chromatid
4. Centromere. [3 Marks]

Answer:
[Figure: A diagram of a cell nucleus in the Metaphase stage of Mitosis, showing 6 chromosomes (3 pairs) aligned at the equatorial plate. Each chromosome consists of two sister chromatids joined at the centromere. Spindle fibers (achromatic spindle) extend from the poles to the centromeres. Asters are visible at the poles.
Labels:
- Centromere: The constricted region joining sister chromatids.
- Aster: Star-shaped array of microtubules radiating from the centrosomes at the poles.
- Achromatic spindle: Spindle fibers (microtubules) extending between the poles and attaching to centromeres.
- Chromatid: One of the two identical halves of a duplicated chromosome.]

Teacher's Note:
a) In metaphase, chromosomes are maximally condensed and align precisely at the metaphase plate.
b) Each chromosome consists of two sister chromatids, which will separate in anaphase.
c) The spindle fibers (achromatic spindle) are crucial for chromosome movement.
d) Asters are characteristic of animal cell mitosis, forming around the centrosomes.

(ii) Mention the difference between Mitosis and Meiosis with reference to :
1. No. of daughter cells formed at the end of the division.
2. The chromosome number of the daughter cells formed. [2 Marks]

Answer:

Teacher's Note:
a) Mitosis is a type of cell division that produces two genetically identical daughter cells, essential for growth and repair.
b) Meiosis is a specialized cell division that produces four genetically distinct haploid daughter cells (gametes), essential for sexual reproduction.
c) The reduction in chromosome number in meiosis ensures that the diploid number is restored upon fertilization.
d) Crossing over and independent assortment in meiosis contribute to genetic variation.

(b) Account for the following briefly:

(i) The pituitary gland is known as the `Master gland'. [1 Mark]

Answer: The pituitary gland is known as the 'Master gland' because it secretes several hormones that control the functions of other endocrine glands, such as the thyroid gland, adrenal glands, and gonads.

Teacher's Note:
a) Hormones like TSH, ACTH, FSH, and LH from the pituitary regulate the activity of other glands.
b) It acts as a central coordinator, integrating nervous and endocrine systems.
c) Despite its small size, its influence on the body's overall hormonal balance is immense.
d) It is itself regulated by the hypothalamus.

(ii) Animals owe their existence to Chlorophyll. [1 Mark]

Answer: Animals owe their existence to chlorophyll because chlorophyll is essential for photosynthesis in plants, which are the primary producers of food and oxygen on Earth. Animals are heterotrophs and depend directly or indirectly on plants for their food and the oxygen they breathe.

Teacher's Note:
a) Chlorophyll captures light energy, initiating the process of photosynthesis.
b) Photosynthesis produces glucose (food) and releases oxygen, both vital for animal life.
c) Without chlorophyll, plants could not produce food, and the entire food web would collapse.
d) This highlights the fundamental interdependence between plants and animals in ecosystems.

(iii) Twins may or may not be identical. [1 Mark]

Answer: Twins may or may not be identical because there are two types: identical (monozygotic) twins, which develop from a single fertilized egg that splits, resulting in genetically identical individuals; and fraternal (dizygotic) twins, which develop from two separate eggs fertilized by two different sperm, resulting in genetically distinct individuals.

Teacher's Note:
a) Monozygotic twins share 100% of their genes and are always of the same sex.
b) Dizygotic twins are like any other siblings, sharing about 50% of their genes, and can be of the same or different sexes.
c) The official key only mentions fraternal twins; adding identical twins provides a complete explanation.
d) The timing of the splitting of the zygote determines whether identical twins share the same placenta and amniotic sac.

(iv) Herbaceous plants growing in well watered soils are found to wilt on a hot day. [1 Mark]

Answer: Herbaceous plants growing in well-watered soils may wilt on a hot day because the rate of transpiration (water loss from leaves) exceeds the rate of water absorption by the roots. This leads to a net loss of water from the plant, causing cells to lose turgidity and the plant to wilt.

Teacher's Note:
a) High temperatures and low humidity on a hot day increase the rate of transpiration.
b) Even with sufficient soil water, the plant's vascular system might not be able to transport water fast enough to compensate for the rapid loss.
c) Wilting is a temporary loss of turgor pressure, which can be reversed if water absorption catches up.
d) This mechanism helps plants conserve water by reducing the surface area exposed to the sun.

(v) Throat infections can lead to ear infections. [1 Mark]

Answer: Throat infections can lead to ear infections because the throat and the middle ear are connected by the Eustachian tube. Pathogens from a throat infection can travel up this tube to the middle ear, causing an infection there.

Teacher's Note:
a) The Eustachian tube helps equalize pressure and drain fluid from the middle ear.
b) In children, the Eustachian tube is shorter, narrower, and more horizontal, making them more susceptible to ear infections from throat infections.
c) Inflammation and swelling from a throat infection can block the Eustachian tube, trapping fluid and creating a breeding ground for bacteria.
d) This connection explains why common colds and sore throats often precede earaches.