ICSE Class 10 Biology Board Exam Question Paper 2016 with Solutions

ICSE Class 10 Biology Board Exam Question Paper with Solutions

SECTION-I (40 Marks)

(Attempt all questions from this Section.)

Question 1:

(a) Name the following: [5]
(i) The exchange of chromatid parts between the maternal and the paternal chromatids of a pair of homologous chromosomes during meiosis.
(ii) The number of individuals inhabiting per unit area.
(iii) The immunity acquired by providing readymade antibodies from outside for treating certain infectious diseases.
(iv) The pollutants that cannot be broken down to simple and harmless products.
(v) The part of the brain that carries impulses from one hemisphere of the cerebellum to the other.

Answer:
(i) Crossing over
(ii) Population density
(iii) Passive immunity
(iv) Non-biodegradable pollutants
(v) Pons varolii

Teacher's Note:
a) This question tests fundamental biological terminology across various topics like genetics, ecology, immunology, environmental science, and human anatomy.
b) Students should focus on precise definitions and specific terms as required, avoiding general descriptions. For instance, "non-biodegradable" is more specific than just "pollutants."

(b) Choose the correct answer from the four options given below : [5]
(i) A plant cell may burst when :
(A) Turgor pressure equalises wall pressure.
(B) Turgor pressure exceeds wall pressure.
(C) Wall pressure exceeds turgor pressure.
(D) None of the above

Answer: (B) Turgor pressure exceeds wall pressure.

Teacher's Note:
a) A plant cell bursts when the inward pressure exerted by the cell membrane (turgor pressure) becomes greater than the outward pressure exerted by the cell wall (wall pressure), leading to lysis.
b) The cell wall normally prevents bursting by exerting an equal and opposite pressure, but if water influx is excessive, the turgor pressure can overcome the wall's elasticity.

(ii) The individual flattened stacks of membranous structures inside the chloroplasts are known as :
(A) Grana
(B) Stroma
(C) Thylakoids
(D) Cristae

Answer: (C) Thylakoids

Teacher's Note:
a) Thylakoids are individual disc-shaped sacs within the chloroplasts where the light-dependent reactions of photosynthesis occur.
b) A stack of thylakoids is called a granum (plural: grana), and the fluid-filled space surrounding the grana is the stroma. Cristae are folds in the inner mitochondrial membrane.

(iii) The nephrons discharge their urine at the :
(A) Urinary bladder
(B) Urethra
(C) Renal pelvis
(D) Renal pyramid

Answer: (C) Renal pelvis

Teacher's Note:
a) Nephrons filter blood and produce urine, which then drains into collecting ducts, then into the renal papillae, and finally into the renal pelvis, which is the funnel-shaped structure in the kidney that collects urine before it passes to the ureter.
b) The urinary bladder stores urine, and the urethra expels it from the body. Renal pyramids contain parts of nephrons and collecting ducts, but the urine is discharged into the pelvis from the papillae at the tip of the pyramids.

(iv) Gigantism and Acromegaly are due to :
(A) Hyposecretion of Thyroxine
(B) Hyposecretion of Growth hormone
(C) Hypersecretion of Thyroxine
(D) Hypersecretion of Growth hormone

Answer: (D) Hypersecretion of Growth hormone

Teacher's Note:
a) Gigantism results from hypersecretion of growth hormone during childhood, leading to excessive growth, while acromegaly results from hypersecretion of growth hormone in adulthood, causing enlargement of bones in the face, hands, and feet.
b) Hyposecretion of growth hormone leads to dwarfism. Thyroxine is involved in metabolism, and its hypersecretion causes conditions like Graves' disease.

(v) The mineral ion needed for the formation of blood clot is :
(A) Potassium
(B) Sodium
(C) Calcium
(D) Iron

Answer: (C) Calcium

Teacher's Note:
a) Calcium ions (Ca²⁺) are essential cofactors in several steps of the blood clotting cascade, particularly in the activation of prothrombin to thrombin and fibrinogen to fibrin.
b) While other ions like potassium and sodium are important for various bodily functions, calcium plays a direct and crucial role in coagulation.

(c) In each set of terms given below, there is an odd one and cannot be grouped in the same category to which the other three belong. Identify the odd term in each set and name the category to which the remaining three belong. [5]
Example: Ovary, Fallopian tube, Ureter, Uterus
Odd term: Ureter
Category: Parts of female reproductive system
(i) Sewage, Newspaper, Styrofoam, Hay.
(ii) Thymine, Cytosine, Adenine, Pepsin.
(iii) Malleus, Iris, Stapes, Incus.
(iv) Cortisone, Somatotropin, Adrenocorticotropic hormone. Vasopressin.
(v) Typhoid, Haemophilia, Albinism, Colour blindness.

Answer:
(i) Odd term: Styrofoam
Category: Biodegradable wastes

Teacher's Note:
a) Sewage, Newspaper, and Hay are all biodegradable materials, meaning they can be broken down by natural processes. Styrofoam is a non-biodegradable plastic.
b) Understanding the classification of materials based on their degradability is important for environmental studies.

(ii) Odd term: Pepsin
Category: Nitrogen bases of DNA molecule

Teacher's Note:
a) Thymine, Cytosine, and Adenine are three of the four nitrogenous bases found in DNA (the fourth being Guanine). Pepsin is a digestive enzyme.
b) Students should clearly distinguish between the components of nucleic acids and proteins/enzymes.

(iii) Odd term: Iris
Category: Ear ossicles/Tiny bones present in the middle ear

Teacher's Note:
a) Malleus, Stapes, and Incus are the three tiny bones (ossicles) found in the middle ear, responsible for transmitting sound vibrations. The Iris is a part of the eye.
b) Knowledge of the anatomy of sensory organs (ear and eye) is crucial for such questions.

(iv) Odd term: Cortisone
Category: Hormones secreted by Pituitary gland

Teacher's Note:
a) Somatotropin (Growth Hormone), Adrenocorticotropic hormone (ACTH), and Vasopressin (ADH) are all hormones secreted by the pituitary gland. Cortisone is a corticosteroid hormone secreted by the adrenal cortex.
b) Students need to know the specific hormones produced by different endocrine glands, especially the pituitary as the "master gland." The official key states "Hormones secreted by Pituitary gland" as the category, which is correct for Somatotropin, ACTH, and Vasopressin. Cortisone is the odd one out.

(v) Odd term: Typhoid
Category: Sex linked inheritance

Teacher's Note:
a) Haemophilia, Albinism, and Colour blindness are all genetic disorders that can be inherited, with haemophilia and colour blindness being sex-linked. Typhoid is an infectious disease caused by bacteria, not an inherited genetic condition.
b) Differentiating between infectious diseases and genetic disorders is a key concept in biology.

(d) Complete the following paragraph by filling in the blanks (i) to (ii) with appropriate words: [5]
The amount of urine output is under the regulation of a hormone called (i) __________ secreted by the (ii) _________ lobe of the pituitary gland. If this hormone secretion is reduced, there is an increased production of urine. This disorder is called (iii) __________. Sometimes excess glucose is passed with urine due to hyposecretion of another hormone called (iv) __________ leading to the cause of a disease called (v) __________.

Answer:
(i) Antidiuretic hormone
(ii) Posterior
(iii) Diabetes insipidus
(iv) Insulin
(v) Diabetes mellitus

Teacher's Note:
a) This paragraph tests knowledge of hormonal regulation of urine formation and blood glucose levels, specifically involving ADH and insulin.
b) Students should be careful to distinguish between Diabetes insipidus (related to ADH) and Diabetes mellitus (related to insulin), as these are common points of confusion.

(e) State the exact location of the following structures : [5]
(i) Centromere
(ii) Chordae tendinae
(iii) Thyroid gland
(iv) Ciliary body
(v) Proximal convoluted tubule.

Answer:
(i) Centromere: Between two chromatids of a chromosome.

Teacher's Note:
a) The centromere is the constricted region of a chromosome that holds sister chromatids together and serves as the attachment point for spindle fibers during cell division.
b) Its position can vary (metacentric, submetacentric, acrocentric, telocentric), but its fundamental role is in chromatid attachment.

(ii) Chordae tendinae: At the flaps of the bicuspid and tricuspid valves.

Teacher's Note:
a) Chordae tendinae are fibrous cords that connect the papillary muscles to the tricuspid and bicuspid (mitral) valves in the heart, preventing the valve flaps from inverting during ventricular contraction.
b) They are crucial for the proper functioning of the atrioventricular valves, ensuring unidirectional blood flow.

(iii) Thyroid gland: In front of the neck/lower part of the neck below the larynx.

Teacher's Note:
a) The thyroid gland is an endocrine gland located in the neck, anterior to the trachea and inferior to the larynx.
b) Its position is important for understanding symptoms related to thyroid disorders, such as goiter.

(iv) Ciliary body: Extension of choroid layer as a muscular ring around the lens.

Teacher's Note:
a) The ciliary body is a part of the eye, located behind the iris, that produces aqueous humor and contains the ciliary muscle, which controls the shape of the lens for accommodation.
b) It is an anterior extension of the choroid, forming a ring around the lens.

(v) Proximal Convoluted Tubule: In the cortex of the kidney.

Teacher's Note:
a) The proximal convoluted tubule (PCT) is the first segment of the renal tubule, located in the renal cortex, responsible for reabsorbing most of the filtered water, ions, and organic nutrients.
b) Its location in the cortex is distinct from the loop of Henle, which extends into the medulla.

(f) Given below is a diagram depicting a defect of the human eye, study the same and then answer the questions that follow : [5]

[Figure: Diagram showing light rays converging in front of the retina, indicating myopia. The eyeball appears elongated.]

(i) Name the defect shown in the diagram.

Answer:
(i) Myopia (Nearsightedness).

Teacher's Note:
a) Myopia is a vision defect where light rays from distant objects converge in front of the retina, causing distant objects to appear blurry.
b) The diagram clearly shows the focal point before the retina, which is characteristic of myopia.

(ii) What are the two possible reasons that cause this defect ?

Answer:
(ii) 1. The eyeball is too long from front to back.
2. The lens is too curved (or has too much converging power).

Teacher's Note:
a) The two primary causes of myopia are an elongated eyeball (axial myopia) or an excessively curved cornea/lens (refractive myopia), both leading to light focusing too early.
b) Students should remember these structural abnormalities as the root causes of the refractive error.

(iii) Name the type of lens used to correct this defect.

Answer:
(iii) Concave lens.

Teacher's Note:
a) A concave lens is a diverging lens that spreads out light rays before they enter the eye, effectively shifting the focal point backward onto the retina.
b) This correction compensates for the excessive converging power of the myopic eye or its elongated shape.

(iv) With the help of a diagram show how the defect shown above is rectified using a suitable lens.

Answer:

[Figure: Diagram showing a concave lens placed in front of an eye with myopia. Parallel light rays from a distant object first pass through the concave lens, diverge slightly, and then enter the eye. The eye's lens then converges these rays, causing them to focus precisely on the retina, correcting the vision defect. The concave lens is clearly labelled.]

Teacher's Note:
a) The diagram should clearly show parallel rays from a distant object diverging after passing through the concave lens and then converging exactly on the retina within the eye.
b) Proper labelling of the concave lens, eye, and retina is essential for full marks.

(g) Given in the box below are a set of 14 biological terms. Of these, 12 can be paired into 6 matching pairs. Out of the six pairs, one has been done for you as an example.
Example: endosmosis – Turgid cell.
Identify the remaining five matching pairs:
Cushing's syndrome, Turgid cell, Iris, Free of rod and cone cells, Colour of eyes, Hypoglycemia, Active transport, Aerosome, Addison's disease, Blind spot, Hyperglycemia, Spermatozoa, Endosmosis, Clotting of blood.

Answer:
(i) Hyperglycemia – Cushing's syndrome

Teacher's Note:
a) Cushing's syndrome is caused by prolonged exposure to high levels of cortisol, which can lead to hyperglycemia (high blood sugar).
b) This pair links a specific medical condition with one of its key physiological symptoms.

(ii) Hypoglycemia – Addison's disease

Teacher's Note:
a) Addison's disease is characterized by adrenal insufficiency, leading to low cortisol levels, which can result in hypoglycemia (low blood sugar).
b) This pair connects another endocrine disorder with its associated blood glucose imbalance.

(iii) Blind Spot – Free of rod and cone cells

Teacher's Note:
a) The blind spot (optic disc) is the area on the retina where the optic nerve leaves the eye; it lacks photoreceptor cells (rods and cones), hence it is insensitive to light.
b) This pair relates a specific anatomical feature of the eye to its functional characteristic.

(iv) Iris – Colour of eyes

Teacher's Note:
a) The iris is the pigmented, muscular diaphragm in the eye that controls the size of the pupil and gives the eye its characteristic colour.
b) The colour of the eyes is determined by the amount and type of melanin pigment in the iris.

(v) Acrosome – Spermatozoa

Teacher's Note:
a) The acrosome is a cap-like organelle located at the head of a spermatozoon (sperm cell), containing enzymes essential for penetrating the egg during fertilization.
b) This pair links a specific structure to the cell type it belongs to and its function in reproduction.

(h) State the main function of the following: [5]
(i) Lymphocytes of blood

Answer:
(i) Lymphocytes of blood: Produce antibodies (B lymphocytes) and kill infected cells (T lymphocytes).

Teacher's Note:
a) Lymphocytes are key components of the adaptive immune system, responsible for specific immunity against pathogens.
b) B lymphocytes produce antibodies, while T lymphocytes directly attack infected cells or regulate immune responses.

(ii) Leydig cells

Answer:
(ii) Leydig cells: Secrete male sex hormone testosterone.

Teacher's Note:
a) Leydig cells (interstitial cells) are found in the connective tissue between the seminiferous tubules in the testes.
b) Testosterone is crucial for the development of male secondary sexual characteristics and spermatogenesis.

(iii) Guard cells

Answer:
(iii) Guard cells: Regulate the opening and closing of stomata in leaf to facilitate transpiration and exchange of gases.

Teacher's Note:
a) Guard cells surround stomata and control their aperture, thereby regulating the rate of gas exchange (CO₂ uptake for photosynthesis, O₂ release) and water loss through transpiration.
b) Their turgor changes, influenced by water potential and ion movement, dictate stomatal opening and closing.

(iv) Eustachian tube

Answer:
(iv) Eustachian tube: Balance air pressure on either sides of the ear drum. So that ear drum can vibrate freely.

Teacher's Note:
a) The Eustachian tube connects the middle ear to the nasopharynx, allowing air pressure to equalize on both sides of the tympanic membrane (eardrum).
b) This equalization is vital for the eardrum to vibrate efficiently and for clear hearing, especially during changes in altitude.

(v) Corpus luteum

Answer:
(v) Corpus luteum: Secretes hormones oestrogen, progesterone and relaxin.

Teacher's Note:
a) The corpus luteum forms in the ovary after ovulation from the ruptured follicle and primarily secretes progesterone, which is essential for maintaining the uterine lining during pregnancy.
b) It also produces some estrogen and relaxin, the latter helping to relax pelvic ligaments during childbirth.

SECTION-II (40 Marks)

(Attempt any Four questions from this Section.)

Question 2:

(a) The figure given below is a diagrammatic representation of a part of the cross section of the root in the root hair zone. Study the same and then answer the questions that follow: [5]

[Figure: Diagram showing a root hair cell (labelled 1) extending into the soil. Soil particles and soil water (labelled 2) are shown outside the root hair. Inside the root, there are cortical cells (labelled 4) and xylem vessels (labelled 3) in the center. Arrows indicate the movement of water from soil to root hair, then through cortical cells to xylem.]

(i) Name the parts indicated by the guidelines 1 to 4.

Answer:
(i) 1. Root hair
2. Soil water
3. Xylem Vessels
4. Cortical cells

Teacher's Note:
a) Accurate identification of the labelled parts is crucial for understanding the process of water absorption by roots.
b) Students should be familiar with the basic anatomy of a root in the root hair zone.

(ii) Which is the process that enables the passage of water from the soil into the root hair ?

Answer:
(ii) Osmosis Process

Teacher's Note:
a) Water moves from the soil (higher water potential) into the root hair cells (lower water potential) across the semi-permeable cell membrane by the process of osmosis.
b) This passive movement is driven by the water potential gradient.

(iii) Name the pressure that is responsible for the movement of water in the direction indicated by the arrows. Define it.

Answer:
(iii) Osmotic pressure: The pressure exerted by a solution to prevent the entry of water molecules, through the semi-permeable membrane is called Osmotic pressure.

Teacher's Note:
a) Osmotic pressure is a measure of the tendency of water to move into a solution by osmosis. In the context of water movement in plants, the difference in osmotic pressure (or water potential) between the soil and root cells drives water uptake.
b) A clear and concise definition of osmotic pressure is important, emphasizing the role of the semi-permeable membrane.

(iv) Due to an excess of this pressure sometimes drops of water are found along the leaf margins of some plants especially in the early mornings. What is the phenomenon called ?

Answer:
(iv) Guttation.

Teacher's Note:
a) Guttation is the exudation of xylem sap from the tips or edges of leaves, typically in the early morning, due to high root pressure and low transpiration rates.
b) It is distinct from dew, which is condensed atmospheric moisture.

(v) Draw a well labelled diagram of the root hair cell as it would appear if an excess of fertiliser is added to the soil close to it.

Answer:

[Figure: Diagram of a root hair cell in soil with excess fertilizers. The cell membrane is shown to have pulled away from the cell wall, indicating plasmolysis. The cytoplasm is shrunken, and the cell appears flaccid. The soil surrounding the root hair is labelled "Fertilizers in soil" and the shrunken cell membrane is labelled "Shrunken Cell Membrane of root hair".]

Teacher's Note:
a) Adding excess fertilizer to the soil increases the solute concentration in the soil water, making it hypertonic to the root hair cell sap. This causes water to move out of the root hair cell by osmosis, leading to plasmolysis.
b) The diagram should clearly show the protoplast shrinking and pulling away from the cell wall, which is the characteristic appearance of a plasmolyzed cell.

(b) Differentiate between the following pairs on the basis of what is mentioned within brackets: [5]
(i) Human skin cell and. Human ovum (number of chromosomes)

Answer:
(i) Human skin cell: 46 Chromosomes
Human ovum: 23 Chromosomes

Teacher's Note:
a) Human skin cells are somatic cells and are diploid (2n), containing 46 chromosomes. A human ovum is a gamete and is haploid (n), containing 23 chromosomes.
b) This distinction highlights the difference between somatic cells and germ cells in terms of chromosome number.

(ii) Sperm duct and fallopian tube (function)

Answer:
(ii) Sperm Duct: Transfer mature sperm from testis for release.
Fallopian Tube: Site of fertilisation in human female.

Teacher's Note:
a) The sperm duct (vas deferens) transports sperm from the epididymis to the ejaculatory duct. The fallopian tube (oviduct) transports the ovum from the ovary to the uterus and is the usual site of fertilization.
b) Students should clearly state the primary function of each reproductive structure.

(iii) Red Cross and WHO (one activity)

Answer:
(iii) Red Cross: Supply blood to victims of war (or disaster relief, humanitarian aid).
WHO: Set pharmaceutical standards (or promote global health, combat diseases).

Teacher's Note:
a) The Red Cross is a humanitarian organization providing emergency assistance, disaster relief, and blood donation services. The World Health Organization (WHO) is a specialized agency of the United Nations concerned with international public health.
b) Students should be able to differentiate between the roles and activities of these two important international organizations.

(iv) Rod cells and cone cells (pigment)

Answer:
(iv) Rod cells: Rhodopsin
Cone cells: Iodopsin

Teacher's Note:
a) Rod cells contain the pigment rhodopsin and are responsible for vision in dim light (scotopic vision) and detecting motion. Cone cells contain iodopsin (photopsins) and are responsible for colour vision and high acuity vision in bright light (photopic vision).
b) Knowing the specific photoreceptor pigments and their associated functions is key to understanding vision.

(v) LUBB and DUP (names of the valves whose closure produce the sound)

Answer:
(v) LUBB: Atrioventricular valves (Tricuspid and Bicuspid/Mitral valves)
DUP: Semilunar valves (Aortic and Pulmonary valves)

Teacher's Note:
a) The "LUBB" sound (first heart sound, S1) is produced by the closure of the atrioventricular valves at the beginning of ventricular systole. The "DUP" sound (second heart sound, S2) is produced by the closure of the semilunar valves at the beginning of ventricular diastole.
b) Understanding the origin of heart sounds is fundamental to cardiac physiology.

Question 3:

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

[Figure: Outline of human body with four glands labelled: 1 (Pituitary gland in the brain), 2 (Thyroid gland in the neck), 3 (Pancreas in the abdomen), 4 (Adrenal gland above the kidney).]

(i) Name the glands marked 1 to 4.

Answer:
(i) 1. Pituitary gland
2. Thyroid gland
3. Pancreas
4. Adrenal gland

Teacher's Note:
a) This question tests the student's knowledge of the location of major endocrine glands in the human body.
b) Accurate identification of these glands is fundamental to understanding the endocrine system.

(ii) Name the hormone secreted by part 2. Give one important function of this hormone.

Answer:
(ii) Hormone secreted by part 2 (Thyroid gland): Thyroxine.
Function: It regulates basal metabolism of the body (or promotes growth and development, controls body temperature).

Teacher's Note:
a) Thyroxine is the primary hormone produced by the thyroid gland and plays a crucial role in regulating metabolic rate, growth, and development.
b) Students should be able to associate specific hormones with their respective glands and primary functions.

(iii) Name the endocrine part of the part numbered 3.

Answer:
(iii) Endocrine part of part 3 (Pancreas): Islets of Langerhans.

Teacher's Note:
a) The pancreas has both exocrine (digestive enzymes) and endocrine (hormones) functions. The endocrine function is carried out by specialized clusters of cells called the Islets of Langerhans.
b) These islets contain alpha cells (secreting glucagon) and beta cells (secreting insulin), which regulate blood glucose levels.

(iv) Why is the part labelled 1 called, the master gland ? Which part of the forebrain controls the gland labelled 1 ?

Answer:
(iv) Part 1 (Pituitary gland) is called the master gland because it controls the secretions of all the other endocrine glands.
The part of the forebrain that controls gland 1 is the Hypothalamus.

Teacher's Note:
a) The pituitary gland is called the "master gland" because its hormones regulate the function of many other endocrine glands (e.g., thyroid, adrenal cortex, gonads).
b) However, the pituitary itself is controlled by the hypothalamus, which acts as the link between the nervous and endocrine systems.

(v) Name the gland, that secretes the 'emergency hormone'.

Answer:
(v) The gland that secretes the 'emergency hormone' is the Adrenal medulla (part of Adrenal gland).

Teacher's Note:
a) The adrenal medulla secretes adrenaline (epinephrine) and noradrenaline (norepinephrine), which are often called 'emergency hormones' due to their role in the "fight or flight" response.
b) These hormones prepare the body for stressful situations by increasing heart rate, blood pressure, and glucose levels.

(b) The diagram of an apparatus given below demonstrates a physiological process in plants. Study the same and answer the Questions that follow. [5]

[Figure: Diagram of a Ganong's Potometer. It consists of a leafy shoot inserted into a tube filled with water, connected to a graduated capillary tube. An air bubble is visible in the capillary tube, which is immersed in a beaker of coloured water. A reservoir is also attached to the main tube.]

(i) Name the apparatus.

Answer:
(i) Ganong's potometer.

Teacher's Note:
a) A potometer is a device used to measure the rate of water uptake by a plant, which is an indirect measure of the rate of transpiration.
b) Students should be able to identify common laboratory apparatus used in plant physiology experiments.

(ii) Which phenomenon is demonstrated, by this apparatus

Answer:
(ii) Transpiration.

Teacher's Note:
a) The potometer measures the rate at which water is absorbed by the plant, which is largely equivalent to the rate of water lost through transpiration, assuming the plant is not wilting.
b) The movement of the air bubble indicates the volume of water absorbed to compensate for transpirational loss.

(iii) Explain the phenomenon mentioned in (ii) above.

Answer:
(iii) Transpiration is the process in which water is given out in the form of vapour through the aerial parts of the plant.

Teacher's Note:
a) Transpiration is primarily the evaporation of water from the stomata on leaves, but also occurs to a lesser extent from the cuticle and lenticels.
b) It creates a transpiration pull that helps in the ascent of sap in plants.

(iv) State two limitations of using this apparatus.

Answer:
(iv) 1. The small twig cannot remain alive for a long time.
2. Introducing a single air bubble is practically very difficult.

Teacher's Note:
a) Limitations include the artificial conditions (cut shoot), the difficulty in ensuring a perfect airtight seal, and the fact that water uptake is not always exactly equal to transpiration (some water is used in photosynthesis).
b) The twig's limited lifespan means experiments cannot be prolonged, and air bubbles can be tricky to manipulate accurately.

(v) What is the importance of the air bubble in, the experiment ?

Answer:
(v) The movement of the air bubble shows the amount of water transpired by the twig in a given time.

Teacher's Note:
a) The air bubble acts as an indicator. As the plant transpires, it absorbs water, causing the air bubble to move along the graduated capillary tube.
b) The distance the bubble moves over a specific time interval allows for the calculation of the rate of water uptake/transpiration.

(vi) Name the structures in a plant through which the above process takes place.

Answer:
(vi) 1. Cuticle
2. Stomata
3. Lenticel

Teacher's Note:
a) Transpiration primarily occurs through stomata (stomatal transpiration), but also to a lesser extent through the cuticle (cuticular transpiration) and lenticels on stems (lenticular transpiration).
b) Stomata are the most significant sites for transpiration due to their ability to open and close.

Question 4:

(a) (i) Draw a well labelled diagram of the membranous labyrinth found in the inner ear.

Answer:

[Figure: Diagram of the membranous labyrinth of the inner ear. It shows three semicircular canals (anterior, posterior, lateral) connected to the utriculus and sacculus. The cochlea, a spiral-shaped structure, is also shown, connected to the sacculus. The ampulla, a swelling at the base of each semicircular canal, is labelled. Key labels include: Semicircular Canal, Ampulla, Utriculus, Sacculus, Cochlea.]

Teacher's Note:
a) The membranous labyrinth is a system of fluid-filled sacs and ducts within the bony labyrinth of the inner ear, containing the sensory organs for hearing and balance.
b) Key structures to label include the cochlea (hearing), semicircular canals (dynamic equilibrium), and utricle and saccule (static equilibrium).

(ii) Based on the diagram drawn above in (i) give a suitable term for each of the following descriptions :
1. The sensory cells that helps in hearing.
2. The part that is Responsible for static balance of the body.
3. The membrane covered opening that connects the middle ear to the inner ear.
4. The fluid present in the middle chamber of cochlea.
5. The structure that maintains dynamic equilibrium of the body. [5]

Answer:
(ii) 1. Organ of Corti
2. Utriculus and Sacculus
3. Oval window
4. Endolymph
5. Semicircular canals

Teacher's Note:
a) This part tests specific knowledge of the structures and functions within the inner ear related to hearing and balance.
b) Students should differentiate between structures responsible for static (utricle, saccule) and dynamic (semicircular canals) equilibrium, and the specific sensory organ for hearing (Organ of Corti).

(b) Give the Biological / technical term for the following: [5]
(i) Complete stoppage of menstrual cycle in females.

Answer:
(i) Menopause

Teacher's Note:
a) Menopause is the natural cessation of menstruation and fertility, typically occurring in women between 45 and 55 years of age.
b) It marks the end of a woman's reproductive years.

(ii) Pigment providing colour to urine.

Answer:
(ii) Urochrome

Teacher's Note:
a) Urochrome (also known as urobilin) is a yellow pigment that is a breakdown product of hemoglobin and is responsible for the characteristic yellow colour of urine.
b) The intensity of the yellow colour depends on the concentration of urochrome, which is influenced by hydration levels.

(iii) The vein which drains the blood from the intestine to the liver.

Answer:
(iii) Hepatic portal vein

Teacher's Note:
a) The hepatic portal vein carries nutrient-rich, deoxygenated blood from the gastrointestinal tract (including the intestines) and spleen to the liver.
b) This allows the liver to process absorbed nutrients and detoxify harmful substances before the blood enters the general circulation.

(iv) The canal through which the testes descend into the scrotum just before the birth of a male baby.

Answer:
(iv) Inguinal canal

Teacher's Note:
a) The inguinal canal is a passage in the anterior abdominal wall through which the testes descend from the abdominal cavity into the scrotum during fetal development.
b) Failure of descent can lead to cryptorchidism, and the canal is also a common site for hernias.

(v) The process causing an undesirable change in the environment.

Answer:
(v) Pollution

Teacher's Note:
a) Pollution is the introduction of contaminants into the natural environment that cause adverse change.
b) It can affect air, water, and land, impacting ecosystems and human health.

(vi) The removal of nitrogenous wastes from the body.

Answer:
(vi) Excretion

Teacher's Note:
a) Excretion is the process by which metabolic waste products, particularly nitrogenous wastes like urea, uric acid, and creatinine, are eliminated from the body.
b) The kidneys are the primary organs of excretion in mammals.

(vii) The repeating components of each DNA strand lengthwise.

Answer:
(vii) Nucleotide

Teacher's Note:
a) DNA is a polymer made up of repeating monomer units called nucleotides. Each nucleotide consists of a deoxyribose sugar, a phosphate group, and a nitrogenous base.
b) The sequence of these nucleotides forms the genetic code.

(viii) An alteration in the genetic material that can be inherited.

Answer:
(viii) Mutation

Teacher's Note:
a) A mutation is a permanent change in the DNA sequence of an organism. If it occurs in germ cells, it can be inherited by offspring.
b) Mutations are the ultimate source of genetic variation and can be beneficial, harmful, or neutral.

(ix) The process of uptake of mineral ions against the concentration gradient using energy from the cell.

Answer:
(ix) Active absorption

Teacher's Note:
a) Active absorption (or active transport) is the movement of substances across a cell membrane against their concentration gradient, requiring energy (ATP) and specific carrier proteins.
b) This process allows cells to accumulate essential mineral ions even when their concentration is lower in the external environment.

(x) Blood vessels carrying blood to the left atrium.

Answer:
(x) Pulmonary veins

Teacher's Note:
a) Pulmonary veins carry oxygenated blood from the lungs to the left atrium of the heart.
b) They are unique among veins as they carry oxygenated blood, unlike most other veins that carry deoxygenated blood.

Question 5:

(a) The given diagram shows a stage during mitotic division in an animal cell: [5]

[Figure: Diagram showing an animal cell in Prophase of mitosis. Chromosomes are condensed and visible as paired chromatids. The nuclear membrane is disappearing, and centrosomes with centrioles are moving towards opposite poles, with spindle fibers beginning to form.]

(i) Identify the stage. Give a reason to support your answer.

Answer:
(i) Stage: Prophase
Reason: Chromosomes are clearly visible as paired chromatids connected by centromere. Centrosomes have split into centrioles and are moving to opposite poles. The nuclear membrane and nucleolus are disappearing. Chromosomes are not arranged in any specific pattern (like at the metaphase plate).

Teacher's Note:
a) Key features of prophase include chromosome condensation, disappearance of the nuclear envelope and nucleolus, and the formation of the spindle apparatus.
b) The absence of chromosomes aligned at the equatorial plate distinguishes it from metaphase.

(ii) Draw a neat labelled diagram of the cell as it would appear in the next stage. Name the stage.

Answer:

[Figure: Diagram of an animal cell in Metaphase of mitosis. The chromosomes are clearly visible, condensed, and aligned along the equatorial plate (metaphase plate) of the cell. Spindle fibers are attached to the centromeres of each chromosome, extending from the centrosomes at opposite poles.]

Stage: Metaphase

Teacher's Note:
a) The defining characteristic of metaphase is the alignment of all chromosomes at the metaphase plate, equidistant from the two spindle poles.
b) The diagram should clearly show the chromosomes lined up in the middle and spindle fibers attached to their centromeres.

(iii) In what two ways is mitotic division in an animal cell different from the mitotic division in a plant cell ?

Answer:

Teacher's Note:
a) The primary differences lie in the presence of centrioles (animal cells only) and the method of cytokinesis (cell plate formation in plants vs. furrowing in animals).
b) Students should clearly articulate these two distinct features for full marks.

(iv) Name the type of cell division that occurs during : A. Growth of a shoot B. Formation of pollen grains

Answer:
(iv) A – Mitosis.
B – Meiosis.

Teacher's Note:
a) Mitosis is responsible for growth, repair, and asexual reproduction, leading to genetically identical daughter cells. Meiosis is involved in sexual reproduction, producing haploid gametes.
b) Growth of a shoot involves an increase in cell number through mitosis, while pollen grain formation (microsporogenesis) involves meiosis to produce haploid microspores.

(b) Give scientific reasons for the following statements : [5]
(i) Colour blindness is more common in men than in women.

Answer:
(i) Colour blindness is an X-linked inheritance. Women have two X-chromosomes, so even when one X-chromosome carries colour blindness, the other X-chromosome overcomes the abnormal trait. Whereas men have only one X-chromosome. So when it is affected the man becomes colour blind.

Teacher's Note:
a) Colour blindness is a recessive trait carried on the X chromosome. Females have two X chromosomes, so they need two copies of the recessive allele to be colour blind, making them often carriers.
b) Males have only one X chromosome, so if they inherit the recessive allele on that X chromosome, they will express the trait, making it more prevalent in males.

(ii) Injury to medulla oblongata leads to death.

Answer:
(ii) Medulla oblongata controls the involuntary activities like respiration, heart beats etc. So any injury to this part of brain arrests these movements and cause death.

Teacher's Note:
a) The medulla oblongata is a vital part of the brainstem that regulates essential involuntary functions such as breathing, heart rate, blood pressure, and reflexes like swallowing and vomiting.
b) Damage to this region can therefore lead to immediate cessation of these life-sustaining functions, resulting in death.

(iii) When an ovum gets fertilized, menstrual cycle stops temporarily in a woman.

Answer:
(iii) Menstrual cycle occurs due to rupture and shedding of the endometrium lining of the uterus. When an ovum gets fertilised the endometrium gets thickened, and vascularized to house the embryo. So during the whole term when the embryo/foetus is in the uterus, menstrual cycle stops temporarily.

Teacher's Note:
a) Fertilization and subsequent implantation of the embryo trigger the production of hormones (initially hCG, then progesterone from the corpus luteum and placenta) that maintain the uterine lining (endometrium).
b) This hormonal support prevents the breakdown of the endometrium, thus inhibiting menstruation throughout pregnancy.

(iv) Mature erythrocytes in humans lack nucleus and mitochondria.

Answer:
(iv) Presence of nucleus would occupy space and reduce the oxygen carrying capacity. Nucleus is also not required as a mature RBC does not divide. Mitochondria is absent so that oxygen is not consumed by the RBC and all the oxygen is transported to target areas.

Teacher's Note:
a) The absence of a nucleus allows mature red blood cells (erythrocytes) to have a biconcave shape and more space for hemoglobin, maximizing oxygen-carrying capacity. Since they don't divide, a nucleus is not needed.
b) Lacking mitochondria ensures that RBCs do not consume the oxygen they transport, allowing all oxygen to be delivered to body tissues.

(v) Blood flows in arteries in spurts and is under pressure.

Answer:
(v) Arteries carry blood from heart. With every pump of heart blood flows with a jerk and pressure through it.

Teacher's Note:
a) Arteries receive blood directly from the ventricles of the heart during systole, which is a powerful contraction. This forceful ejection creates high pressure and causes blood to flow in pulsatile spurts.
b) The elastic walls of arteries help to maintain this pressure and smooth out the blood flow somewhat, but the pulsatile nature is still evident.

Question 6:

(a) The diagram given below is that of a developing human foetus. Study the diagram and then answer the questions that follow : [5]

[Figure: Diagram of a human foetus within the uterus. Part 1 points to the umbilical cord, part 2 points to the placenta, and part 3 points to the amniotic cavity/fluid surrounding the foetus.]

(i) Label the parts numbered 1 to 3 in the diagram.

Answer:
(i) 1. Umbilical cord
2. Placenta
3. Amniotic cavity/Amniotic fluid

Teacher's Note:
a) This question assesses knowledge of the structures involved in fetal development and their correct anatomical labels.
b) Accurate identification of the umbilical cord, placenta, and amniotic cavity is essential for understanding fetal support systems.

(ii) Mention any two functions of the part labelled 2 in the diagram.

Answer:
(ii) Functions of Placenta:
1. Transfer nutrients and oxygen from mother's blood to foetus.
2. Releases hormones called oestrogens, progesterone (to maintain pregnancy).

Teacher's Note:
a) The placenta is a vital organ that facilitates the exchange of nutrients, oxygen, and waste products between the mother and the foetus, while also acting as an endocrine gland.
b) Other functions include providing immunity (transfer of antibodies) and acting as a barrier against some harmful substances.

(iii) Explain the significance of the part numbered 3 in the diagram.

Answer:
(iii) Significance of Amniotic Fluid:
1. Protects the foetus against jerks, mechanical shocks, and injury.
2. Allows foetus movements.
3. Keeps the pressure even, around the foetus.
4. Prevents sticking of foetus to the amnion.

Teacher's Note:
a) The amniotic fluid acts as a protective cushion, absorbing shocks and preventing physical trauma to the developing foetus.
b) It also provides a stable temperature, allows for fetal movement, and prevents adhesion of the foetus to the amniotic membrane.

(iv) Define the term 'Gestation'. What is the normal gestational period of the developing human embryo ?

Answer:
(iv) Gestation: The full term of development of the embryo in the uterus.
In a developing human embryo, the gestational period is of 280 days (approximately 9 months or 40 weeks).

Teacher's Note:
a) Gestation refers to the period from conception to birth, during which the embryo and foetus develop inside the mother's uterus.
b) Knowing the approximate duration of human gestation is a standard biological fact.

(v) Mention the sex chromosomes in a male and female embryo

Answer:
(v) Male embryo = XY
Female embryo = XX.

Teacher's Note:
a) In humans, sex is determined by the sex chromosomes: females have two X chromosomes (XX), and males have one X and one Y chromosome (XY).
b) The presence of the Y chromosome determines maleness, specifically the SRY gene on the Y chromosome.

(b) The following diagram demonstrates a physiological process taking place in green plants. The whole set up was placed in bright sunlight for several hours. Study the diagram and answer the questions that follow :

[Figure: Diagram of an experiment demonstrating photosynthesis. An inverted funnel is placed over an aquatic plant (Hydrilla) in a beaker of water. A test tube is inverted over the stem of the funnel, collecting gas bubbles released by the plant. The setup is exposed to light.]

(i) What aspect of the physiological process is being examined ?

Answer:
(i) Photosynthesis (specifically, the release of oxygen during photosynthesis).

Teacher's Note:
a) This experiment is a classic demonstration of photosynthesis, showing that green plants produce oxygen in the presence of light.
b) The gas bubbles collected in the test tube can be tested to confirm they are oxygen.

(ii) Explain the physiological process mentioned in (i) above.

Answer:
(ii) Photosynthesis is the process in which plant cells having chlorophyll take raw materials like carbon dioxide from air & water from soil and manufacture glucose in presence of light. Oxygen is a waste product during this process.

Teacher's Note:
a) A complete explanation of photosynthesis should include the raw materials (CO₂, H₂O), conditions (light, chlorophyll), products (glucose, oxygen), and its location (chloroplasts).
b) Emphasize that oxygen is a byproduct, while glucose is the primary energy product.

(iii) Label the parts numbered 1 and 2 in the diagram.

Answer:
(iii) Part 1 - Oxygen gas.
Part 2 - Hydrilla plant.

Teacher's Note:
a) Part 1 represents the gas collected, which is oxygen, a product of photosynthesis. Part 2 is the aquatic plant, Hydrilla, commonly used in such experiments.
b) Correctly identifying these parts is crucial for understanding the experimental setup.

(iv) Write a well balanced chemical equation for the physiological process explained in (ii) above.

Answer:
(iv)
6CO₂ + 12H₂O \(\xrightarrow{\text{Light}}\) C₆H₁₂O₆ + 6O₂ + 6H₂O
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          The following is a list of the top 10 most expensive cities for expats in 2024, according to Mercer's Cost of Living Survey: 1. **Hong Kong** 2. **Singapore** 3. **Zurich** 4. **Geneva** 5. **Basel** 6. **Bern** 7. **New York City** 8. **London** 9. **Nassau** 10. **Los Angeles** This list highlights a continued trend of Asian and Swiss cities dominating the top spots due to high housing costs and strong currencies. New York City and London remain prominent due to their status as global financial hubs and high demand for living. Nassau's inclusion reflects its growing appeal as a financial center and luxury destination.