ICSE Class 10 Biology Board Exam Question Paper 2019 with Solutions

ICSE Board Class 10 Biology Board Exam Question Paper with Solutions

SECTION I (40 Marks)

Question 1

(a) Name the following: [5]
(i) The layer of the eyeball that provides nourishment to the eye.

Answer: Choroid

Teacher's Note:
a) The choroid is a vascular layer containing blood vessels that supply oxygen and nourishment to the outer layers of the retina.
b) Students often confuse the choroid with the sclera or retina; remember that choroid is vascular and pigmented.

(ii) One gaseous compound which depletes the ozone layer. [1 Mark]

Answer: Chlorofluorocarbons (CFCs)

Teacher's Note:
a) CFCs release chlorine atoms in the stratosphere which catalytically break down ozone molecules into oxygen.
b) Always spell chemical groups or acronyms clearly; writing just CFCs or Chlorofluorocarbons is acceptable.

(iii) The structure which connects the placenta and the foetus. [1 Mark]

Answer: Umbilical cord

Teacher's Note:
a) The umbilical cord contains blood vessels (two umbilical arteries and one umbilical vein) that transport nutrients and wastes between the foetus and placenta.
b) Avoid spelling errors such as writing chord instead of cord.

(iv) A pair of corresponding chromosomes of the same shape and size and derived one from each parent. [1 Mark]

Answer: Homologous chromosomes

Teacher's Note:
a) Homologous chromosomes carry genes controlling the same inherited characteristics at the same loci.
b) Do not confuse with sister chromatids, which are identical copies formed by DNA replication of a single chromosome.

(v) The compound formed when hemoglobin combines with carbon dioxide in blood. [1 Mark]

Answer: Carbaminohemoglobin

Teacher's Note:
a) Carbon dioxide binds reversibly to the amino groups of hemoglobin to form carbaminohemoglobin for transport.
b) Do not confuse this with carboxyhemoglobin, which is formed when carbon monoxide binds to hemoglobin.

(b) Correct and rewrite the statements by changing the biological term that is underlined for each statement: [5]
(i) The theory of inheritance of acquired characters was proposed by Watson and Crick.

Answer: The theory of inheritance of acquired characters was proposed by Jean-Baptiste Lamarck.

Teacher's Note:
a) Lamarckism states that physical changes acquired during an organism's lifetime can be passed on to offspring.
b) Watson and Crick are famous for proposing the double helix model of DNA structure, not evolutionary inheritance theories.

(ii) The protective sac which develops around the developing embryo is called the pericardium. [1 Mark]

Answer: The protective sac which develops around the developing embryo is called the amniotic sac.

Teacher's Note:
a) The amniotic sac encloses the embryo and contains amniotic fluid which cushions against mechanical shock.
b) Pericardium is the double-walled sac that encloses the heart, not the embryo.

(iii) Maintaining balance of the body and coordinating muscular activities is carried out by the cerebrum. [1 Mark]

Answer: Maintaining balance of the body and coordinating muscular activities is carried out by the cerebellum.

Teacher's Note:
a) The cerebellum acts as the center for equilibrium and muscle coordination.
b) Cerebrum is primarily responsible for higher mental functions, intelligence, memory, and voluntary actions.

(iv) The kidney is composed of a number of neurons. [1 Mark]

Answer: The kidney is composed of a number of nephrons.

Teacher's Note:
a) Nephrons are the structural and functional units of the kidney responsible for filtering blood and forming urine.
b) Neurons are the structural and functional units of the nervous system.

(v) The part of the eye which can be donated from a clinically dead person is the retina. [1 Mark]

Answer: The part of the eye which can be donated from a clinically dead person is the cornea.

Teacher's Note:
a) The cornea is avascular and receives nutrients from aqueous humor, allowing successful transplantation without blood type matching.
b) The retina cannot be easily transplanted because it is nervous tissue connected directly to the optic nerve.

(c) Give suitable biological reasons for the following statements: [5]
(i) The birth rate in India is very high.

Answer: High birth rate in India is attributed to factors such as early marriage, illiteracy, preference for male children, traditional beliefs, and lack of awareness and accessibility regarding family planning and birth control methods, especially in rural areas.

Teacher's Note:
a) Socio-economic factors heavily influence population growth rates in developing regions.
b) Answers should include at least two distinct socio-cultural reasons to secure full credit.

(ii) Carbon monoxide is dangerous when inhaled. [1 Mark]

Answer: Carbon monoxide has a much higher affinity for hemoglobin than oxygen. When inhaled, it combines irreversibly with hemoglobin to form carboxyhemoglobin, which prevents the transport of oxygen to body tissues, leading to suffocation and death.

Teacher's Note:
a) Emphasize the formation of carboxyhemoglobin and the blocking of oxygen transport.
b) Mentioning the relative affinity compared to oxygen highlights strong scientific understanding.

(iii) Root hairs become flaccid and droop when excess fertilizers are added to the moist soil around them. [1 Mark]

Answer: Adding excess fertilizers creates a hypertonic solution in the soil water compared to the cell sap of root hairs. Water flows out of the root hair cells into the soil via exosmosis, causing the cells to lose turgidity and become flaccid.

Teacher's Note:
a) Use key terms such as hypertonic medium and exosmosis in your explanation.
b) This condition is commonly known as fertilizer burn or physiological drought.

(iv) Acid rain is harmful to the environment. [1 Mark]

Answer: Acid rain lowers the pH of soil and water bodies making them acidic, which harms aquatic life and damages vegetation. It also corrodes buildings, historical monuments made of marble or limestone, and metal structures.

Teacher's Note:
a) Acid rain is primarily caused by emissions of sulfur dioxide and nitrogen oxides from industries and vehicles.
b) Providing impacts on both living systems and non-living structures ensures complete evaluation.

(v) All life on Earth is supported by photosynthesis. [1 Mark]

Answer: Photosynthesis produces organic food (glucose) and releases oxygen into the atmosphere. Green plants act as primary producers supporting all herbivores and carnivores in food chains, while oxygen is essential for aerobic respiration in living organisms.

Teacher's Note:
a) Photosynthesis converts solar energy into chemical energy stored in food.
b) Both food production and oxygen release must be mentioned as key pillars supporting life.

(d) Match the items given in Column A with the most appropriate ones in Column B and rewrite the correct matching pairs: [5]

Teacher's Note:
a) Matching questions require exact pairing without altering terms.
b) Students should write out the matched pairs explicitly as requested in the instruction.

(e) Choose the correct answer from the four options given below:
(i) While recording the pulse rate, where exactly does a doctor press on our wrist?
A. Nerve
B. Vein
C. Artery
D. Capillary

Answer: (C) Artery

Blood flows under high pressure through arteries near the surface, producing a palpable pulse.

Teacher's Note:
a) The radial artery at the wrist is typically used to measure pulse rate.
b) Veins lie closer to the surface with valves and do not pulsate perceptibly under normal conditions.

(ii) In a human male, a sperm will contain [1 Mark]
A. Both X and Y chromosomes
B. Only Y chromosome
C. Only X chromosome
D. Either X or Y chromosome

Answer: (D) Either X or Y chromosome

Human males produce two types of sperms in equal proportions - 22 + X and 22 + Y.

Teacher's Note:
a) A single sperm contains only one sex chromosome, which is either X or Y.
b) Do not confuse the genetic constitution of human males (XY) with the contents of an individual sperm cell.

(iii) A muscular wall is absent in [1 Mark]
A. Capillary
B. Venule
C. Arteriole
D. Vein

Answer: (A) Capillary

Capillaries are extremely narrow blood vessels whose walls consist of a single layer of squamous epithelium (endothelium) without any muscular coat.

Teacher's Note:
a) The absence of a muscular wall facilitates rapid diffusion of gases, nutrients, and wastes across capillary walls.
b) Arteries, arterioles, veins, and venules all possess muscular and fibrous tissue layers in their walls.

(iv) On which day of the menstrual cycle does ovulation take place? [1 Mark]
A. 5th day
B. 28th day
C. 14th day
D. 1st day

Answer: (C) 14th day

In a standard 28-day menstrual cycle, ovulation typically occurs on the 14th day due to a surge in luteinizing hormone (LH).

Teacher's Note:
a) Ovulation is the release of a secondary oocyte from the mature Graafian follicle.
b) The exact day can vary depending on individual cycle lengths.

(v) Which one of the following does not affect the rate of transpiration? [1 Mark]
A. Light
B. Humidity
C. Wind
D. Age of the plant

Answer: (D) Age of the plant

While light, humidity, and wind directly influence the vapor pressure gradient and stomatal opening, the age of the plant is not a direct environmental factor controlling transpiration rates.

Teacher's Note:
a) External factors affecting transpiration include light, temperature, humidity, and wind speed.
b) Internal factors include leaf surface area, cuticle thickness, and stomatal frequency.

(f) Identify the ODD term in each set and name the CATEGORY in which the remaining of these belong: [5]
(i) Addison's disease, Cushing's Syndrome, Acromegaly, Leukemia

Answer:
Odd term: Leukemia
Category: The remaining three are endocrinal disorders / hormonal disorders.

Teacher's Note:
a) Leukemia is a malignant cancer of blood-forming tissues, whereas the others are caused by hormonal imbalances.
b) Clearly state both the odd term and the common biological category of the remaining items.

(ii) Insulin, Adrenaline, Pepsin, Thyroxine [1 Mark]

Answer:
Odd term: Pepsin
Category: The remaining three are hormones secreted by endocrine glands.

Teacher's Note:
a) Pepsin is a digestive enzyme produced by gastric glands, not a hormone.
b) Insulin, adrenaline, and thyroxine are all chemical messengers (hormones) poured directly into the blood.

(iii) Axon, Dendron, Photon, Cyton [1 Mark]

Answer:
Odd term: Photon
Category: The remaining three are parts of a neuron / nerve cell.

Teacher's Note:
a) A photon is a fundamental particle of light, whereas axon, dendron, and cyton constitute a neuron.
b) Ensure all structural parts are correctly linked to nervous tissue.

(iv) Chicken pox, Colour blindness, Haemophilia, Albinism [1 Mark]

Answer:
Odd term: Chicken pox
Category: The remaining three are genetic disorders / hereditary disorders.

Teacher's Note:
a) Chicken pox is an infectious viral disease, unlike genetic disorders which are inherited through genes.
b) Haemophilia, colour blindness, and albinism are transmitted from parents to offspring.

(v) Polythene bag, Crop residue, Animal waste, Decaying vegetable [1 Mark]

Answer:
Odd term: Polythene bag
Category: The remaining three are biodegradable wastes.

Teacher's Note:
a) Polythene bags are non-biodegradable synthetic polymers that persist in the environment for centuries.
b) Biodegradable wastes can be broken down naturally by microorganisms.

(g) Expand the following biological abbreviations: [5]
(i) ABA - Abscisic acid

Answer: Abscisic acid

Teacher's Note:
a) Abscisic acid is a plant hormone that generally acts as an inhibitor of plant growth and promotes dormancy.
b) Check spelling carefully; 'Abscisic' has a 'c'.

(ii) IAA - Indole acetic acid [1 Mark]

Answer: Indole acetic acid

Teacher's Note:
a) IAA is the principal naturally occurring auxin found in plants.
b) It promotes cell elongation and tropisms.

(iii) ATP - Adenosine triphosphate [1 Mark]

Answer: Adenosine triphosphate

Teacher's Note:
a) ATP is the energy currency of the cell, storing and transporting chemical energy.
b) Spelling 'triphosphate' correctly is crucial.

(iv) DNA - Deoxyribonucleic Acid [1 Mark]

Answer: Deoxyribonucleic Acid

Teacher's Note:
a) DNA carries genetic instructions used in growth, development, functioning, and reproduction of all living organisms.
b) Ensure capitalization and spelling match scientific standards.

(v) TSH - Thyroid Stimulating Hormone [1 Mark]

Answer: Thyroid Stimulating Hormone

Teacher's Note:
a) TSH is secreted by the anterior pituitary gland and stimulates the thyroid gland to produce thyroxine.
b) Also known as thyrotropin.

Study the picture given below and answer the following questions: [5]

[Figure: An illustration showing water pollution with factory effluents discharged into a water body containing dead fish and polluted water]

(i) Identify the type of pollution.

Answer: Water pollution

Teacher's Note:
a) Water pollution is the contamination of water bodies by harmful pollutants.
b) Direct observation of factory pipes releasing waste into water indicates water pollution.

(ii) Name one pollutant that causes the above pollution. [1 Mark]

Answer: Industrial effluent (or heavy metals / nitrates / oil spills)

Teacher's Note:
a) Industrial effluents contain toxic chemicals that degrade water quality.
b) Any valid water pollutant is accepted.

(iii) Mention the impact of this pollution on human health. [1 Mark]

Answer: Consumption of contaminated water containing heavy metals or pathogenic microorganisms causes water-borne diseases such as cholera, typhoid, dysentery, and serious neurological or gastrointestinal disorders.

Teacher's Note:
a) Focus on direct health hazards linked to polluted water consumption.
b) Mentioning specific water-borne diseases adds clarity.

(iv) State one measure to control this pollution. [1 Mark]

Answer: Industrial effluents and sewage must be treated in effluent treatment plants (ETPs) to remove toxic substances before being discharged into water bodies.

Teacher's Note:
a) Proper waste treatment prevents toxic chemicals from entering aquatic ecosystems.
b) Strict legal enforcement against untreated dumping is vital.

(v) What is a pollutant? Explain the term. [1 Mark]

Answer: A pollutant is any substance, chemical, or waste material introduced into the environment that alters its normal properties and causes adverse effects on living organisms and natural resources.

Teacher's Note:
a) Pollutants can be solid, liquid, or gaseous agents.
b) The key aspect is the harmful alteration of environmental quality.

SECTION II (40 Marks)

Attempt any four questions from this section.

Question 2

(a) Given below is an experimental setup to demonstrate a particular tropical movement in germinating seeds. Study the diagram and answer the questions that follows:

[Figure: Experimental setup showing germinating seeds placed on a perforated horizontal trough with moist sawdust, with roots growing downwards through the perforations due to gravity/water]

(i) Label the parts 1 and 2.

Answer:
1: Radicle
2: Plumule

Teacher's Note:
a) The radicle develops into the root system, while the plumule develops into the shoot system.
b) Ensure correct identification corresponding to the pointer numbers in the diagram.

(ii) Name the tropical movement shown in part 1. [1 Mark]

Answer: Geotropism (Positive geotropism) / Hydrotropism

Teacher's Note:
a) The radicle grows downwards in response to gravity and moisture.
b) Both geotropism and hydrotropism are demonstrated in this experiment.

(iii) Part 1 is affected by two stimuli. Which one of the two is stronger? [1 Mark]

Answer: Hydrotropism (Stimulus of water is stronger than gravity).

Teacher's Note:
a) Roots tend to grow towards water even if it opposes gravitational pull under specific experimental conditions.
b) Water stimulus overrides gravity in such directional growth responses.

(iv) What is thigmotropism? Give one example. [1 Mark]

Answer: Thigmotropism is the directional growth movement of a plant part in response to touch or contact with a solid object. Example: Tendrils of climbing plants (like peas or grapes) coil around a support.

Teacher's Note:
a) Thigmotropism is commonly observed in climbers and twiners.
b) Provide both the definition and a clear biological example for full marks.

(v) What is meant by 'positive' and 'negative' tropic movement in plants? [1 Mark]

Answer: Positive tropic movement is the growth of a plant part towards a stimulus (e.g., stem growing towards light). Negative tropic movement is the growth of a plant part away from a stimulus (e.g., roots growing away from light).

Teacher's Note:
a) Tropisms are directional growth responses determined by the direction of the external stimulus.
b) Including examples for both positive and negative movements adds clarity.

(b) Mention the exact location of each of the following: [5]
(i) Testis

Answer: Testis are contained in a sac of skin called the scrotum, located outside the abdominal cavity.

Teacher's Note:
a) Extra-abdominal location maintains a lower temperature necessary for spermatogenesis.
b) Always specify exact anatomical location.

(ii) Incus [1 Mark]

Answer: Located in the middle ear cavity, between the malleus and the stapes.

Teacher's Note:
a) Incus is the anvil-shaped middle ear ossicle.
b) It transmits sound vibrations from the malleus to the stapes.

(iii) Thylakoids [1 Mark]

Answer: Located inside the chloroplasts, stacked to form grana within the stroma.

Teacher's Note:
a) Thylakoid membranes contain chlorophyll pigments essential for the light-dependent reaction of photosynthesis.
b) Specify their presence inside chloroplasts.

(iv) Amniotic fluid [1 Mark]

Answer: Contained within the amniotic sac surrounding the developing embryo inside the uterus.

Teacher's Note:
a) Amniotic fluid protects the embryo from physical shocks and prevents desiccation.
b) Mention the enclosing amniotic sac and uterus.

(v) Corpus callosum [1 Mark]

Answer: Located at the base of the longitudinal fissure of the brain, connecting the left and right cerebral hemispheres.

Teacher's Note:
a) It is a thick band of nerve fibers facilitating communication between both cerebral hemispheres.
b) Essential anatomical landmark in human brain structure questions.

Question 3

(a) The diagram given below represents an experiment to prove the importance of a factor in photosynthesis. Answer the questions that follow: [5]

[Figure: Potted plant with a leaf partially covered with a strip of black paper held by paper clips, tested for starch]

(i) Name the factor studied in the experiment.

Answer: Light is necessary for photosynthesis.

Teacher's Note:
a) Black paper blocks light from reaching the covered portion of the leaf.
b) This is a classic starch test experiment.

(ii) What will you observe in experimental leaf after the starch test? [1 Mark]

Answer: The uncovered part of the leaf turns blue-black (indicating starch presence), while the covered part turns brown (indicating absence of starch).

Teacher's Note:
a) Iodine solution turns blue-black in the presence of starch.
b) The covered area received no light, so no photosynthesis occurred.

(iii) Explain the process of photosynthesis. [1 Mark]

Answer: Photosynthesis is a biochemical process by which green plants synthesize organic food (glucose) from carbon dioxide and water using solar energy trapped by chlorophyll, releasing oxygen as a byproduct.

Teacher's Note:
a) Mention raw materials, energy source, and products.
b) Define it as an anabolic, endergonic process.

(iv) Give a balanced chemical reaction to represent the process of photosynthesis. [1 Mark]

Answer: 6CO₂ + 12H₂O → (Chlorophyll and Sunlight) → C₆H₁₂O₆ + 6O₂ + 6H₂O

Teacher's Note:
a) Ensure the chemical equation is balanced with 12 molecules of water on the reactant side and 6 molecules of water on the product side.
b) Writing conditions (sunlight and chlorophyll) over the arrow is mandatory.

(v) Draw a neat labeled diagram of experimental set-up to show that oxygen is released during photosynthesis. [1 Mark]

Answer: [Figure: Diagram showing Hydrilla plant in a beaker filled with water, covered with a funnel, inverted test tube over the stem of the funnel collecting gas bubbles, exposed to sunlight]

Teacher's Note:
a) Label essential parts: beaker, water, Hydrilla plant, inverted glass funnel, test tube, and gas bubbles.
b) Mention that glowing splinter test confirms the collected gas is oxygen.

(b) State the main function of the following: [5]
(i) Medulla Oblongata

Answer: Controls involuntary vital functions such as heartbeat, breathing, blood pressure, and peristalsis.

Teacher's Note:
a) The medulla oblongata is part of the hindbrain.
b) Damage to this region is fatal as it regulates autonomic reflex centers.

(ii) Cytokinins [1 Mark]

Answer: Promote cell division, cell enlargement, and organ formation in plants, and counteract apical dominance.

Teacher's Note:
a) Cytokinins stimulate cytokinesis (cell division).
b) They delay leaf senescence and promote lateral bud growth.

(iii) Tears [1 Mark]

Answer: Lubricate the cornea, keep the eyeball moist, wash away dust particles, and contain lysozyme to destroy bacteria.

Teacher's Note:
a) Tears are secreted by the lacrimal glands.
b) Mentioning antimicrobial action via lysozyme earns full credit.

(iv) Coronary Artery [1 Mark]

Answer: Supplies oxygenated blood and nutrients directly to the heart muscle (myocardium).

Teacher's Note:
a) Blockage of coronary arteries leads to myocardial infarction (heart attack).
b) Distinguish coronary vessels from general systemic circulation.

(v) Seminal vesicles [1 Mark]

Answer: Secrete an alkaline seminal fluid containing fructose, proteins, and prostaglandins that nourishes sperms and aids their motility.

Teacher's Note:
a) Seminal fluid forms a major part of the ejaculate (semen).
b) Fructose provides energy to the moving spermatozoa.

Question 4

(a) The diagram given below represents an organ system in the human body. Study the same and answer the questions that follow: [5]

[Figure: Diagram of the human excretory system showing kidneys (1), ureters (2), urinary bladder (3), sphincter (4), and urethra (5)]

(i) Identify the system.

Answer: Human excretory system (Urinary system)

Teacher's Note:
a) The primary organs include kidneys, ureters, urinary bladder, and urethra.
b) Responsible for nitrogenous waste elimination and osmoregulation.

(ii) Label the parts marked 2 - 4. Mention the function of part 5. [1 Mark]

Answer:
2: Ureter
3: Urinary bladder
4: Sphincter muscle
Function of part 5 (Urethra): Transports urine from the urinary bladder to the exterior of the body during urination.

Teacher's Note:
a) Ensure all three labels are correctly matched with parts 2, 3, and 4.
b) State the distinct function of the urethra clearly.

(iii) Name the structural and functional units of the part marked 1. [1 Mark]

Answer: Nephrons

Teacher's Note:
a) Part 1 refers to the kidney.
b) Each human kidney contains over a million nephrons.

(iv) What is the fluid that accumulates in part 3? Which is the main nitrogenous waste present in it? [1 Mark]

Answer: Urine accumulates in the urinary bladder (part 3). The main nitrogenous waste present in it is urea.

Teacher's Note:
a) Urea is synthesized in the liver from excess amino acids via the urea cycle.
b) Other minor components include uric acid, creatinine, and mineral salts.

(v) Draw a neat labeled diagram showing longitudinal section of part - 1. [1 Mark]

Answer: [Figure: Longitudinal section of kidney showing cortex, medulla, renal pyramids, renal pelvis, calyx, renal artery, renal vein, and ureter]

Teacher's Note:
a) Important labels: cortex, medulla, renal pelvis, ureter, renal artery, and renal vein.
b) Diagrams must be neatly drawn and clearly labeled.

(b) The diagram given below represents an endocrine gland in the human body. Study the diagram and answer the following questions: [5]

[Figure: Diagram of the pituitary gland showing anterior lobe, posterior lobe, infundibulum, and surrounding hypothalamic region]

(i) Identify the endocrine gland. Where is it located?

Answer: Pituitary gland. It is located at the base of the brain just below the hypothalamus in a bony depression called the sella turcica.

Teacher's Note:
a) The pituitary gland is a pea-sized gland connected to the hypothalamus.
b) Precise anatomical location scores full marks.

(ii) Why is the above gland referred to as the 'master gland'? [1 Mark]

Answer: It is called the master gland because it secretes tropic hormones that regulate and control the secretory activity of most other endocrine glands in the body.

Teacher's Note:
a) It controls thyroid, adrenal cortex, gonads, etc., via tropic hormones.
b) Note that the hypothalamus ultimately regulates the pituitary gland.

(iii) Name the hormone which in deficiency causes diabetes insipidus. How does this disorder differ from diabetes mellitus? [1 Mark]

Answer: Antidiuretic hormone (ADH) or vasopressin deficiency causes diabetes insipidus. Difference: Diabetes insipidus involves excessive dilution of urine and frequent urination due to water reabsorption failure without high blood sugar, whereas diabetes mellitus is caused by insulin deficiency leading to high blood glucose levels and sugar in the urine.

Teacher's Note:
a) Specify ADH (vasopressin) as the deficient hormone for diabetes insipidus.
b) Contrast the presence of sugar in diabetes mellitus with the excessive water loss in diabetes insipidus.

(iv) Explain the term 'hormone'. What is the role of tropic hormones in the human body? [1 Mark]

Answer: A hormone is a non-nutrient chemical messenger secreted in trace amounts by endocrine glands directly into the bloodstream, acting on target organs to regulate physiological processes. Role of tropic hormones: They stimulate other endocrine glands to secrete their specific hormones.

Teacher's Note:
a) Hormones act as chemical coordinators in the body.
b) Define both the general term hormone and the specific function of tropic hormones.

(v) Which lobe of the above gland secretes Oxytocin, ACTH, Growth Hormone? [1 Mark]

Answer:
Oxytocin: Posterior pituitary lobe
ACTH: Anterior pituitary lobe
Growth Hormone: Anterior pituitary lobe

Teacher's Note:
a) Posterior pituitary stores and releases oxytocin and vasopressin (synthesized by hypothalamus).
b) Anterior pituitary synthesizes and secretes tropic hormones including ACTH and growth hormone.

Question 5

(a) Given below is an apparatus which was set up to investigate a physiological process in plants. The set-up was placed in bright sunlight. Answer the questions that follow: [5]

[Figure: Ganong's bell jar experiment showing a potted plant with soil covered in a rubber sheet/plastic bag, placed under a sealed glass bell jar with water droplets formed on the inner walls]

(i) Name the process being studied. Define the process.

Answer: Transpiration. It is the loss of water in the form of water vapour from the aerial parts of a plant, primarily through the stomata.

Teacher's Note:
a) Transpiration creates a suction force that pulls water up the xylem.
b) Emphasize the loss of water vapor from aerial parts.

(ii) Why was the pot enclosed in a rubber sheet? [1 Mark]

Answer: To prevent the evaporation of water directly from the soil surface, ensuring that the water vapour collected inside the bell jar comes solely from plant transpiration.

Teacher's Note:
a) This acts as a control measure in the experiment.
b) Soil evaporation would interfere with accurate results.

(iii) Mention two external factors which can accelerate the above process. [1 Mark]

Answer: High temperature and wind speed (or intense light and low humidity).

Teacher's Note:
a) Increased temperature increases the rate of evaporation.
b) Wind removes water vapor accumulating around stomata, maintaining a steep concentration gradient.

(iv) List two adaptations in plants to reduce the above process. [1 Mark]

Answer: 1. Thick cuticle on leaves. 2. Reduction of leaf surface area into spines or needles (or sunken stomata).

Teacher's Note:
a) Xerophytic adaptations help plants conserve water in arid conditions.
b) Mention any two structural modifications correctly.

(v) Draw a neat labelled diagram of a stomatal apparatus. [1 Mark]

Answer: [Figure: Diagram of stomatal apparatus showing guard cells with chloroplasts, stoma/stomatal pore, subsidiary cells, and epidermal cells]

Teacher's Note:
a) Important labels: guard cells, stomatal pore, chloroplasts, and epidermal cells.
b) Show kidney-shaped guard cells with thicker inner walls.

(b) Given below are two stages in the evolution of man. Study them and answer the questions that follow: [5]

[Figure: Illustrations of early human ancestors - A: Neanderthal man, B: Australopithecus]

(i) Identify Australopithecus and Neanderthal man from the above pictures.

Answer: A represents Neanderthal man and B represents Australopithecus.

Teacher's Note:
a) Australopithecus represents an earlier ape-man stage.
b) Neanderthal man represents an advanced prehistoric human species.

(ii) Mention two characteristic features each for the two stages. [1 Mark]

Answer:
Australopithecus features: 1. Combination of ape-like and human-like traits. 2. Distinct lumbar curve present in the vertebral column.
Neanderthal man features: 1. Walked upright with bipedal movement. 2. Thick skull bones, heavy brow ridges, and deep jaws without a distinct chin.

Teacher's Note:
a) Provide clear anatomical features for both ancestral stages.
b) Focus on posture, cranial features, and skeletal differences.

(iii) Who proposed the theory of 'natural selection'? [1 Mark]

Answer: Charles Darwin (along with Alfred Russel Wallace)

Teacher's Note:
a) Natural selection is the cornerstone of modern evolutionary theory.
b) Emphasize survival of the fittest driven by environmental pressures.

(iv) Name the organism used as an example to explain 'industrial melanism'. [1 Mark]

Answer: Peppered moth (Biston betularia)

Teacher's Note:
a) Classic evolutionary example demonstrating natural selection due to environmental pollution.
b) Mention both common and scientific names for completeness.

(v) Give two examples of vestigial organs in humans. [1 Mark]

Answer: Vermiform appendix and wisdom teeth (or nictitating membrane, ear muscles).

Teacher's Note:
a) Vestigial organs are non-functional remnants of organs that were functional in ancestral species.
b) Give any two standard human examples.

Question 6

In Mendel's experiments, tall pea plants (T) are dominant over dwarf pea plants (t). [5]
(i) What is the phenotype and genotype of the F1 generation if a homozygous tall plant is crossed with a homozygous dwarf plant?

Answer:
Phenotype: All tall plants
Genotype: Heterozygous tall (Tt)

Teacher's Note:
a) Crossing TT with tt yields 100 percent Tt offspring in the F1 generation.
b) Distinguish clearly between phenotype (observable trait) and genotype (genetic makeup).

(ii) Draw a Punnett square board to show the gametes and offspring when both parents are heterozygous for tallness. [1 Mark]

Answer:

Teacher's Note:
a) Parents are heterozygous (Tt × Tt), producing gametes T and t in equal ratios.
b) Label gametes along the top and side grids correctly.

(iii) What is the phenotypic and genotypic ratio of above cross in (ii)? [1 Mark]

Answer:
Phenotypic ratio: 3:1 (3 Tall : 1 Dwarf)
Genotypic ratio: 1:2:1 (1 TT : 2 Tt : 1 tt)

Teacher's Note:
a) Monohybrid cross of heterozygous parents always yields these standard Mendelian ratios.
b) Clearly distinguish phenotypic ratios from genotypic ratios.

(iv) State Mendel's Law of Dominance. [1 Mark]

Answer: Out of a pair of contrasting factors (alleles) representing a trait, only one is able to express itself in the F1 generation (dominant factor), while the other remains hidden or masked (recessive factor).

Teacher's Note:
a) This law explains why F1 hybrids display only the dominant trait.
b) Use terms like alleles/factors, dominant, and recessive.

(v) What is a dihybrid cross? [1 Mark]

Answer: A breeding experiment between two parent organisms that differ in two pairs of contrasting traits is called a dihybrid cross.

Teacher's Note:
a) Dihybrid crosses demonstrate Mendel's Law of Independent Assortment.
b) Example: Crossing pea plants differing in seed shape and seed color.

(b) Given below is a diagram representing a stage during mitotic cell division. Study the diagram and answer the questions. [5]

[Figure: Diagram of an animal cell undergoing mitosis showing sister chromatids pulled apart toward opposite poles by spindle fibers attached to centrioles]

(i) Identify the stage by giving a suitable reason.

Answer: Anaphase. Reason: Sister chromatids of each chromosome have separated and are moving towards opposite poles.

Teacher's Note:
a) Movement of daughter chromosomes to opposite poles is the hallmark of anaphase.
b) State both the phase name and the visible justification.

(ii) Is it a plant or an animal cell? Give a reason to support your answer. [1 Mark]

Answer: It is an animal cell. Reason: Centrioles are present at the opposite poles and aster rays are visible.

Teacher's Note:
a) Plant cells lack centrioles and undergo cytokinesis via cell plate formation.
b) Centrioles are characteristic of animal cell division.

(iii) Draw a neat, labelled diagram of the stage which follows the one shown in the diagram. [1 Mark]

Answer: [Figure: Diagram of Telophase showing two nuclear membranes reforming around daughter chromosomes at opposite poles, cleavage furrow deepening in the animal cell]

Teacher's Note:
a) The stage following anaphase is telophase.
b) Important labels: cleavage furrow, nuclear membrane, daughter chromosomes, and nucleolus.

(iv) How many chromosomes will each daughter cell have after the completion of the above division? [1 Mark]

Answer: Each daughter cell will have the same number of chromosomes as the parent cell (diploid number / 2n).

Teacher's Note:
a) Mitosis is an equational division.
b) Chromosome number remains constant in daughter cells.

(v) Name the four nitrogenous bases. [1 Mark]

Answer: Adenine, Thymine, Cytosine, and Guanine

Teacher's Note:
a) These nitrogenous bases form the nucleotide building blocks of DNA.
b) Adenine pairs with thymine, and cytosine pairs with guanine.

Question 7

(a) Answer the following questions briefly:
(i) How are cytons and axons placed in the brain and spinal cord?

Answer: In the brain, grey matter containing cytons is located in the outer cortex and white matter containing axons is located in the inner medulla. In the spinal cord, this arrangement is reversed: grey matter is on the inside and white matter is on the outside.

Teacher's Note:
a) Contrast the anatomical arrangement of grey and white matter between the brain and spinal cord.
b) Cytons form grey matter while myelinated axons form white matter.

(ii) Which part of the Human ear gives 'dynamic balance' and 'static balance' to the body? [1 Mark]

Answer: Semicircular canals provide dynamic balance (equilibrium during rotational movements), while the utriculus and sacculus (containing maculae) provide static balance (equilibrium related to head position relative to gravity).

Teacher's Note:
a) Both structures are located in the inner ear vestibule and semicircular canals.
b) Distinguish clearly between dynamic and static equilibrium receptors.

(iii) Explain how the human eye adapts itself to bright light and dim light. [1 Mark]

Answer: In bright light, circular muscles of the iris contract while radial muscles relax, causing the pupil to constrict (reduce size) to limit light entry. In dim light, radial muscles of the iris contract while circular muscles relax, causing the pupil to dilate (enlarge) to allow more light to enter.

Teacher's Note:
a) This involuntary reflex is known as pupillary light reflex.
b) Explain the antagonistic action of circular and radial muscles for both lighting conditions.

(iv) What is parthenocarpy? Give one example. [1 Mark]

Answer: Parthenocarpy is the development of fruit without fertilization, resulting in seedless fruits. Example: Banana or seedless grapes.

Teacher's Note:
a) Parthenocarpic fruits are naturally occurring or induced using plant growth regulators like auxins.
b) Emphasize the absence of seeds in parthenocarpic fruits.

(v) Mention any two objectives of 'Swachh Bharat Abhiyaan'. [1 Mark]

Answer: 1. To construct individual household toilets and community toilets to eliminate open defecation. 2. To promote proper solid and liquid waste management and maintain overall sanitation across rural and urban areas.

Teacher's Note:
a) Swachh Bharat Abhiyaan is a national cleanliness and sanitation campaign.
b) List two clear and relevant objectives.

(b) The diagram given below represents a system in the human body. Study the diagram and answer the following questions: [5]

[Figure: Diagram of the female reproductive system showing ovary (1), fallopian tube/oviduct (5), uterus (3), cervix (6), vagina (4), and infundibulum (2)]

(i) Identify the system.

Answer: Female reproductive system

Teacher's Note:
a) Major organs include ovaries, fallopian tubes, uterus, and vagina.
b) Responsible for producing ova, hormone secretion, and supporting embryonic development.

(ii) Label the parts marked 5 and 6. [1 Mark]

Answer:
5: Fallopian tube (Oviduct)
6: Cervix (External os)

Teacher's Note:
a) Ensure accurate anatomical terminology for both parts.
b) Part 5 connects the ovary to the uterus.

(iii) Name the two hormones secreted by 1. [1 Mark]

Answer: Oestrogen and Progesterone

Teacher's Note:
a) Part 1 refers to the ovary.
b) Ovaries also secrete relaxin and inhibin.

(iv) Mention the number and the name of the part involved in fertilization and implantation from the above diagram. [1 Mark]

Teacher's Note:
a) Fertilization normally takes place in the ampulla of the fallopian tube.
b) Implantation occurs in the endometrium of the uterus.

(v) Mention the surgical methods of contraception in 1. [1 Mark]

Answer: Surgical method of contraception in females is called tubectomy (ligating or cutting fallopian tubes). In males, it is called vasectomy (ligating or cutting vas deferens).

Teacher's Note:
a) Mention both tubectomy (female) and vasectomy (male) for completeness.
b) These are permanent sterilization methods preventing gamete transport.