ICSE Class 10 Biology Board Exam Question Paper 2018 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 :
(i) The organization which procures and supplies blood during an emergency.

Answer: Red Cross.

Teacher's Note:
a) The Red Cross is an international humanitarian movement that provides emergency aid, disaster relief, and blood services.
b) Students should remember the specific role of the Red Cross in blood procurement and supply during emergencies.

(ii) The blood vessel which supplies blood to the liver.

Answer: Hepatic artery.

Teacher's Note:
a) The hepatic artery carries oxygenated blood to the liver, while the hepatic portal vein carries nutrient-rich, deoxygenated blood from the digestive organs to the liver.
b) It's crucial to distinguish between the hepatic artery (supplying oxygenated blood) and the hepatic portal vein (carrying absorbed nutrients) to the liver.

(iii) The number of chromosomes present in a nerve cell of a human being.

Answer: 46 (23 pairs).

Teacher's Note:
a) A nerve cell (neuron) is a somatic cell, meaning it is diploid and contains the full set of chromosomes for a human, which is 46 chromosomes or 23 pairs.
b) Students should remember that all somatic cells in humans have 46 chromosomes, while gametes (sperm and egg) have 23 chromosomes.

(iv) The layer of the eyeball that forms the transparent Cornea.

Answer: Sclerotic layer (Sclera).

Teacher's Note:
a) The sclera is the tough, white outer layer of the eyeball, and its anterior transparent part is modified to form the cornea.
b) Students often confuse the cornea as a separate layer; it is actually a specialized, transparent part of the sclera.

(v) The wax-like layer on the epidermis of leaves which reduces transpiration.

Answer: Cuticle.

Teacher's Note:
a) The cuticle is a protective, waxy layer covering the epidermis of leaves and stems, primarily to prevent water loss through transpiration.
b) Understanding the function of the cuticle in reducing water loss is key to understanding plant adaptations to terrestrial environments.

(b) Choose the correct answer from each of the four options given below:
(i) The number of Spinal nerves in a human being are :
(A) 31 pairs
(B) 10 pairs
(C) 21 pairs
(D) 30 pairs

Answer: (A) 31 pairs

Teacher's Note:
a) Humans have 31 pairs of spinal nerves, which emerge from the spinal cord and are part of the peripheral nervous system.
b) Students should remember the specific number of spinal nerve pairs (31) and cranial nerve pairs (12) in humans.

(ii) Which one of the following is non-biodegradable?
(A) DDT
(B) Vegetable peel (C) Cardboard
(D) Bark of trees

Answer: (A) DDT

Teacher's Note:
a) Non-biodegradable substances cannot be broken down by natural biological processes, leading to their accumulation in the environment. DDT (Dichlorodiphenyltrichloroethane) is a persistent organic pollutant.
b) Students should understand the difference between biodegradable (e.g., vegetable peel, cardboard, bark of trees) and non-biodegradable substances and their environmental impact.

(iii) Aqueous humour is present between the :
(A) Lens and Retina
(C) Cornea and Iris
(B) Iris and Lens
(D) Cornea and Lens

Answer: (D) Cornea and Lens

Teacher's Note:
a) The aqueous humour is a clear fluid that fills the anterior chamber of the eye, located between the cornea and the lens.
b) Students should correctly identify the location of aqueous humour (anterior chamber) and vitreous humour (posterior chamber) within the eye.

(iv) A strong chemical substance which is used on objects and surfaces in our surroundings to kill germs:
(A) Cresol
(B) Carbolic acid (C) Iodine
(D) Mercurochrome

Answer: (A) Cresol

Teacher's Note:
a) Cresol is a strong disinfectant used to kill germs on inanimate objects and surfaces. Carbolic acid (phenol) is also a disinfectant, but cresol is a common component in household disinfectants.
b) Students should differentiate between antiseptics (used on living tissues, e.g., iodine, mercurochrome) and disinfectants (used on non-living surfaces, e.g., cresol, carbolic acid).

(v) Which one of the following is a Greenhouse gas?
(A) Oxygen
(B) Methane
(C) Sulphur dioxide (D) Nitrogen

Answer: (B) Methane

Teacher's Note:
a) Greenhouse gases trap heat in the Earth's atmosphere, contributing to global warming. Methane (\(CH_4\)) is a potent greenhouse gas.
b) Students should be able to identify major greenhouse gases like carbon dioxide, methane, nitrous oxide, and water vapor, and distinguish them from atmospheric gases like oxygen and nitrogen.

(c) Complete the following paragraph by filling in the blank (i) to (v) with appropriate words:
To test a leaf for starch, the leaf is boiled in water to (i) _______. It is then boiled in Methylated spirit to (ii) _______. The leaf is dipped in warm water to soften it. It is placed in a petri dish, and (iii) _______ solution is added. The region of the leaf which contains starch, turns (iv) _______ and the region while does not contain starch, turns (v) _______.

Answer:
(i) to kill the cells.
(ii) remove the chlorophyll
(iii) Iodine solution
(iv) blue-black in colour
(v) brown

Teacher's Note:
a) This paragraph describes the standard procedure for the starch test in a leaf, which involves killing cells, removing chlorophyll, and then testing with iodine solution.
b) Students must remember the purpose of each step: boiling in water kills cells, boiling in methylated spirit removes chlorophyll, and iodine solution tests for starch (blue-black indicates presence, brown indicates absence).

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

Column A
(i) Cretinism
(ii) Diabetes insipidus
(iii) Exophthalmic Goitre
(iv) Adrenal virilism
(v) Dwarfism

Column B
(a) Hypersecretion of adrenal cortex
(b) Hyposecretion of Thyroxine
(c) Hyposecretion of growth hormone
(d) Hyposecretion of Vasopressin
(e) Hyposecretion of adrenal cortex
(f) Hypersecretion of Growth hormone
(g) Hypersecretion of Thyroxine

Answer:
(i) Cretinism : Hyposecretion of Thyroxine
(ii) Diabetes insipidus : Hyposecretion of Vasopressin
(iii) Exophthalmic Goitre : Hypersecretion of Thyroxine
(iv) Adrenal virilism : Hypersecretion of adrenal cortex
(v) Dwarfism : Hyposecretion of growth hormone

Teacher's Note:
a) This question tests knowledge of endocrine disorders and their causes (hypo- or hypersecretion of specific hormones).
b) Students should carefully associate each condition with the correct hormone and its secretion level (e.g., cretinism with hyposecretion of thyroxine, exophthalmic goitre with hypersecretion of thyroxine).

(e) Correct the following statements by changing the underlined words:
(i) Normal pale yellow colour of the urine is due to the presence of the pigment Melanin.

Answer: Urochrome

Teacher's Note:
a) Urochrome is the pigment responsible for the yellow color of urine, a byproduct of hemoglobin breakdown.
b) Students should know that melanin is a pigment found in skin and hair, not urine, and correctly identify urochrome as the urinary pigment.

(ii) The outermost layer of Meninges is Pia mater.

Answer: Dura mater

Teacher's Note:
a) The meninges consist of three layers protecting the brain and spinal cord: dura mater (outermost), arachnoid mater (middle), and pia mater (innermost).
b) Remembering the order of meningeal layers from outermost to innermost (DAP - Dura, Arachnoid, Pia) is a helpful mnemonic.

(iii) The cell sap of root hair is Hypotonic.

Answer: Hypertonic

Teacher's Note:
a) The cell sap of root hair cells is hypertonic (has a higher solute concentration) compared to the soil water, which creates a water potential gradient for water absorption by osmosis.
b) Understanding the concept of tonicity is crucial for explaining water movement in plants; root hair cells must be hypertonic to absorb water from the hypotonic soil solution.

(iv) Xylem transports starch from the leaves to all parts of the plant body.

Answer: Phloem

Teacher's Note:
a) Phloem is the vascular tissue responsible for translocating sugars (produced during photosynthesis, often stored as starch) from leaves to other parts of the plant.
b) Students must differentiate the functions of xylem (water and mineral transport) and phloem (food transport) correctly.

(v) Nitrogen bonds are present between the complementary nitrogenous bases of DNA.

Answer: Hydrogen bonds

Teacher's Note:
a) Hydrogen bonds are weak intermolecular forces that hold together the complementary nitrogenous bases (A-T and G-C) in the DNA double helix.
b) It's important to specify "hydrogen bonds" as the type of bond between bases, not just "nitrogen bonds," which is chemically incorrect in this context.

(f) Choose between the two options to answer the question specified in the brackets for the following:
An example is illustrated below.
Example: Corolla or Calyx (Which is the miter whorl?) Answer : Calyx
(i) Blood in the renal artery or renal vein (Which one has more urea ?)

Answer: Renal artery

Teacher's Note:
a) The renal artery carries blood to the kidneys for filtration, so it contains a higher concentration of urea before filtration. The renal vein carries filtered blood away from the kidneys, thus having less urea.
b) Students should understand the direction of blood flow and the function of the kidneys in removing urea to correctly identify the vessel with more urea.

(ii) Perilymph or endolymph (Which one surrounds the organ of Corti?)

Answer: Endolymph

Teacher's Note:
a) The organ of Corti, located within the cochlea, is bathed in endolymph, which is found in the scala media. Perilymph fills the scala vestibuli and scala tympani.
b) Knowing the specific fluid environment of the organ of Corti is essential for understanding its role in hearing.

(iii) Lenticels or stomata (Which one remains open always ?)

Answer: Lenticels

Teacher's Note:
a) Lenticels are pores on the bark of woody stems that allow for gas exchange and are permanently open. Stomata, found on leaves, regulate their opening and closing.
b) Students should distinguish between stomata (regulated pores) and lenticels (permanently open pores) in terms of their structure and function in gas exchange.

(iv) Sclerotic layer or choroid layer. (Which one forms the Iris ?)

Answer: Choroid layer

Teacher's Note:
a) The choroid layer is the middle vascular layer of the eye, and its anterior part differentiates to form the ciliary body and the iris.
b) Students should recall the three main layers of the eyeball (sclera, choroid, retina) and the structures derived from each, particularly the iris from the choroid.

(v) Blood in the pulmonary artery or pulmonary vein (Which one contains less oxyhaemoglobin?)

Answer: Pulmonary artery

Teacher's Note:
a) The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs, hence it contains less oxyhaemoglobin. The pulmonary vein carries oxygenated blood from the lungs to the left atrium, thus having more oxyhaemoglobin.
b) This question tests the understanding of the pulmonary circulation, where arteries carry deoxygenated blood and veins carry oxygenated blood, which is an exception to the general rule for systemic circulation.

(g) Given below is a representation of a type pollution.
Study the picture and answer the questions :

[Figure: A cartoon depicting a city scene with factories emitting smoke, cars emitting exhaust, and a person covering their nose, indicating air pollution.]

(i) Name the type of pollution shown in the picture.

Answer: Air pollution

Teacher's Note:
a) The image clearly shows smoke from factories and vehicles, which are characteristic sources of air pollution.
b) Students should be able to identify different types of pollution based on visual cues and common sources.

(ii) Name one source of this pollution.

Answer: Smoke from vehicles

Teacher's Note:
a) The picture explicitly shows vehicles emitting smoke, which is a primary source of air pollution.
b) Other valid sources from the picture include industrial emissions (factories) or burning of fossil fuels.

(iii) How does this pollution affect human health?

Answer: Air pollution results in respiratory problems, lung disorders etc.

Teacher's Note:
a) Air pollutants like particulate matter, sulfur dioxide, and nitrogen oxides can irritate the respiratory tract, leading to conditions like asthma, bronchitis, and other lung diseases.
b) Students should be aware of the direct health impacts of air pollution, particularly on the respiratory system.

(iv) Write one measure to reduce this pollution.

Answer:
(A) Use of unleaded petrol and of CNG.
(B) Switching off automobile engines at red lights and when not in use.

Teacher's Note:
a) Measures to reduce air pollution from vehicles include using cleaner fuels (unleaded petrol, CNG) and adopting practices that minimize fuel consumption and emissions.
b) Other valid measures could include promoting public transport, cycling, carpooling, or using electric vehicles.

(v) State one gaseous compound that leads to the depletion of the ozone layer and creates ‘Ozone holes'.

Answer: CFC's (chlorofluorocarbons) released from refrigerators, aerosol-sprayers etc.

Teacher's Note:
a) Chlorofluorocarbons (CFCs) are synthetic organic compounds that, when released into the atmosphere, rise to the stratosphere and break down ozone molecules, leading to ozone layer depletion.
b) Students should know CFCs as the primary culprits for ozone depletion and be able to name common sources like refrigerants and aerosol propellants.

(h) Choose the ODD one out from the following terms given and name the CATEGORY to which the others belong:
(i) Detergents, X-rays, sewage, oil spills

Answer: X-rays (Chemical pollutants)

Teacher's Note:
a) Detergents, sewage, and oil spills are all types of chemical pollutants that can contaminate water or soil. X-rays are a form of electromagnetic radiation, not a chemical pollutant.
b) Students need to categorize the given terms based on their nature or impact on the environment.

(ii) Lumen, muscular tissue, connective tissue, pericardium

Answer: Lumen (All others are connective tissues)

Teacher's Note:
a) Muscular tissue, connective tissue, and pericardium (a connective tissue sac around the heart) are all types of tissues or structures composed of tissues. Lumen refers to the inner open space or cavity of a tubular organ.
b) This question tests the understanding of anatomical terms and tissue types. Lumen is a space, not a tissue.

(iii) Dendrites, Medullary sheath, Axon, Spinal cord

Answer: Spinal cord (Parts of nerve cell)

Teacher's Note:
a) Dendrites, medullary sheath (myelin sheath), and axon are all parts of a single nerve cell (neuron). The spinal cord is a major part of the central nervous system, composed of many neurons.
b) Students should distinguish between components of a single neuron and a larger organ made of many neurons.

(iv) Centrosome.Cell wall, Cell membrane, Large vacuoles

Answer: Centrosome (Organelles in Plant cell)

Teacher's Note:
a) Cell wall, cell membrane, and large vacuoles are characteristic structures found in plant cells. The centrosome is primarily found in animal cells and lower plant forms, but typically absent in higher plant cells.
b) This question tests the knowledge of differences in cell organelles between plant and animal cells.

(v) Prostate gland, Cowper's gland, seminal vesicle, seminiferous tubules.

Answer: Seminiferous tubules (Others are Accessory glands in male reproductive system)

Teacher's Note:
a) The prostate gland, Cowper's gland (bulbourethral gland), and seminal vesicle are accessory glands that contribute fluids to semen. Seminiferous tubules are located within the testes and are responsible for spermatogenesis (sperm production), not accessory fluid secretion.
b) Students should differentiate between the structures involved in sperm production (seminiferous tubules) and those that produce seminal fluid (accessory glands).

SECTION - II (40 Marks)

Attempt any four questions from this Section

Question 2

(a) The diagram given below represents a stage during cell division.
Study the same and answer the questions that follow:

[Figure: A diagram of an animal cell undergoing cell division. Chromosomes are aligned at the equatorial plate. There are no cell walls. Spindle fibers are visible. The nuclear membrane is absent.]

(i) Identify whether it is a plant cell or an animal cell.
Give a reason in support of your answer.

Answer: Animals cell. Because it lacks cell-wall.

Teacher's Note:
a) Animal cells lack a cell wall and typically show a clear constriction (cleavage furrow) during cytokinesis, which is not explicitly shown here but the absence of a cell wall is a key identifier.
b) The presence of a cell wall is a defining characteristic of plant cells, and its absence indicates an animal cell.

(ii) Name the stage depicted in the diagram.
What is the unique feature observed in this stage?

Answer: Metaphase. Chromosomes lined up in one plane at equator.

Teacher's Note:
a) Metaphase is characterized by the alignment of all chromosomes along the metaphase plate (equatorial plate) of the cell.
b) Students should be able to identify the stages of mitosis based on the arrangement and behavior of chromosomes and spindle fibers.

(iii) Name the type of cell division that occurs during :
1. Replacement of old leaves by new ones.
2. Formation of gametes.

Answer:
1. Mitotic cell division
2. Meiosis (Reductional) cell division

Teacher's Note:
a) Mitosis is responsible for growth, repair, and replacement of somatic cells (like leaves), maintaining the same chromosome number. Meiosis is a reductional division that produces gametes with half the chromosome number.
b) Understanding the distinct roles of mitosis and meiosis in different biological processes is fundamental.

(iv) What is the stage that comes before the stage shown in the diagram?

Answer: Prophase comes before metaphase.

Teacher's Note:
a) The sequence of mitotic stages is Prophase, Metaphase, Anaphase, Telophase (PMAT).
b) Students should recall the correct chronological order of the phases of cell division.

(v) Draw a neat, labelled diagram of the stage mentioned in (iv) above keeping the chromosome number constant.

Answer:

[Figure: diagram to be added]

Prophase

Teacher's Note:
a) A diagram of prophase should show condensed chromosomes, the disappearance of the nuclear membrane, and the formation of spindle fibers.
b) Key labels for prophase include chromosomes (each with two sister chromatids), nuclear membrane (disappearing), and spindle fibers (forming).

(b) Mention the exact location of the following :
(i) Epididymis

Answer: Male reproductive system (or posterior surface of testis).

Teacher's Note:
a) The epididymis is a coiled tube located on the posterior surface of each testis in the male reproductive system, where sperm mature and are stored.
b) Students should be precise with anatomical locations, specifying "posterior surface of testis" for full accuracy.

(ii) Lacrimal gland

Answer: Eyes (or upper outer part of the orbit of the eye).

Teacher's Note:
a) Lacrimal glands are located in the upper outer region of each orbit (eye socket) and are responsible for producing tears.
b) Specifying "upper outer part of the orbit" is more precise than just "eyes."

(iii) Malleus

Answer: Middle ear

Teacher's Note:
a) The malleus is one of the three ossicles (malleus, incus, stapes) located in the middle ear, which transmit sound vibrations from the eardrum to the inner ear.
b) Students should know the names and locations of all three ossicles in the middle ear.

(iv) Hydathodes

Answer: Leaf of plants (or margins of leaves).

Teacher's Note:
a) Hydathodes are specialized pores, typically found on the margins or tips of leaves, through which guttation (exudation of water droplets) occurs.
b) It's important to specify "margins of leaves" for a more accurate location of hydathodes.

(v) Pulmonary semilunar valve

Answer: At the opening of pulmonary trunk in right ventricle

Teacher's Note:
a) The pulmonary semilunar valve is located at the exit of the right ventricle, guarding the opening into the pulmonary artery (pulmonary trunk).
b) Students should be able to locate all four heart valves and their specific positions between chambers and major arteries.

Question 3

(a) Given below are diagrams showing the different stages in the process of fertilisation of an egg. in the human female reproductive tract.
Study the diagrams and answer the questions:

[Figure: Four diagrams (A, B, C, D) showing stages of fertilization.
A: Zygote with two pronuclei fused.
B: Sperm entering egg, pronuclei forming.
C: Sperm approaching egg.
D: Unfertilized egg.]

(i) Arrange the letters given below each digram in a logical sequence to show the correct order in the process of fertilisation.

Answer: D-C-B-A

Teacher's Note:
a) The logical sequence of fertilization starts with an unfertilized egg (D), followed by sperm approaching (C), sperm entering and pronuclei forming (B), and finally the fusion of pronuclei to form a zygote (A).
b) Students should understand the chronological steps of fertilization from sperm-egg interaction to zygote formation.

(ii) Where does fertilisation normally take place?
What is 'Implantation' that follows fertilisation?

Answer: Ampullary - Isthmic junction in fallopian tubes
Implantation is a attachment of the developing foetus (blastocyst) to endometrium

Teacher's Note:
a) Fertilization typically occurs in the ampullary-isthmic junction of the fallopian tube. Implantation is the process where the blastocyst embeds itself into the uterine wall (endometrium) after reaching the uterus.
b) Students must know both the site of fertilization and the definition of implantation, which are key events in early human development.

(iii) Mention the chromosome number of the egg and zygote in humans.

Answer: Egg is haploid (23)
Zygote is diploid (46)

Teacher's Note:
a) The egg (ovum) is a haploid gamete with 23 chromosomes. Upon fertilization, the haploid sperm (23 chromosomes) fuses with the egg, forming a diploid zygote with 46 chromosomes.
b) Understanding the change in chromosome number from haploid gametes to a diploid zygote is fundamental to genetics and reproduction.

(iv) Explain the term 'Gestation'. How long does Gestation last in humans?

Answer: The intrauterine period of foetus in mother's body or the period from zygote to fully formed foetus in uterus period is gestation period. It is about 280 days (9 months + 7 days approximately)

Teacher's Note:
a) Gestation refers to the period of development of the embryo and fetus inside the mother's womb, from conception to birth.
b) Students should know the approximate duration of human gestation (around 280 days or 9 months and 7 days) and its definition.

(v) Draw a neat, labelled diagram of a mature human sperm.

Answer:

[Figure: diagram to be added]

Human Sperms

Teacher's Note:
a) A mature human sperm diagram should clearly show the head (containing acrosome and nucleus), middle piece (with mitochondria), and tail (flagellum).
b) Proper labeling of all parts and their functions (e.g., acrosome for penetration, mitochondria for energy, tail for motility) is important.

(b) A potted plant with variegated leaves was taken in order to prove a factor necessary for photosynthesis. The potted plant was kept in the dark for 24 hours and then placed in bright sunlight for a few hours. Observe the diagrams and answer the questions.

[Figure: A potted plant with variegated leaves. One leaf is labeled 'Leaf A' showing pale yellow and green regions. The setup is in bright sunlight.]

(i) What aspect of photosynthesis is being tested in the above diagram?

Answer: To show that chlorophyll is necessary for photosynthesis.

Teacher's Note:
a) Variegated leaves have both green (chlorophyll-containing) and non-green (chlorophyll-lacking) areas, allowing for a direct comparison of starch production in the presence and absence of chlorophyll.
b) This experiment is a classic demonstration of the necessity of chlorophyll for photosynthesis.

(ii) Represent the process of photosynthesis in the form of a balanced equation.

Answer: \(6CO_2 + 12H_2O \xrightarrow{\text{Light}} C_6H_{12}O_6 + 6O_2\uparrow + 6H_2O\)

Teacher's Note:
a) The balanced chemical equation for photosynthesis shows carbon dioxide and water as reactants, glucose and oxygen as products, with light energy and chlorophyll as necessary conditions.
b) Students must ensure the equation is correctly balanced and includes the conditions (light, chlorophyll) above the arrow.

(iii) Why was the plant kept in the dark before beginning the experiment?

Answer: To destarch the leaves.

Teacher's Note:
a) Keeping the plant in the dark for 24 hours ensures that any starch previously stored in the leaves is used up or translocated, providing a clean slate for testing new starch production.
b) Destarching is a critical preliminary step in photosynthesis experiments to ensure that any starch detected at the end of the experiment was newly synthesized.

(iv) What will be the result of the starch test performed on I eaf ‘A' shown in the diagram? Give an example of a plant with variegated leaves.

Answer: It will not turn blue. Example of plants with veriegated leaves is Oxalis species.

Teacher's Note:
a) The non-green (pale yellow) region of leaf 'A' lacks chlorophyll, so it cannot perform photosynthesis and thus will not produce starch. Therefore, it will not turn blue-black with iodine.
b) Common examples of plants with variegated leaves include Coleus, Croton, and Oxalis, which are often used in such experiments.

(v) Draw a neat labelled diagram of a chloroplast.

Answer:

[Figure: diagram to be added]

Chloroplast

Teacher's Note:
a) A chloroplast diagram should show the double membrane, stroma, grana (stacks of thylakoids), and stromal lamellae (fret).
b) Proper labeling of these structures is essential, as each plays a specific role in photosynthesis (e.g., grana for light reactions, stroma for dark reactions).

Question 4

(a) The diagram given below shows the internal structure of a spinal cord depicting a phenomenon. Studythe diagram and answer the questions:

[Figure: A diagram showing a cross-section of the spinal cord with a reflex arc. Label 1 points to the sensory neuron, 2 to the motor neuron, and 3 to the grey matter with the central canal.]

(i) Name the phenomenon that is depicted in the diagram. Define the phenomenon.

Answer: Reflex action
Definition - A quick, automatic, involuntary and often unconsicous action brought about when the receptors are stimulated by external or internal stimuli.

Teacher's Note:
a) The diagram illustrates a reflex arc, which is the neural pathway that mediates a reflex action, characterized by its speed, automaticity, and involuntary nature.
b) Students should remember the key characteristics of a reflex action and its importance in protecting the body from harm.

(ii) Give the technical term for the point of contact between the two nerve cells.

Answer: Synaptic - Junction

Teacher's Note:
a) The point of contact between two nerve cells (neurons) where nerve impulses are transmitted is called a synapse.
b) Students should understand that a synapse involves a presynaptic neuron, a synaptic cleft, and a postsynaptic neuron, facilitating chemical or electrical signal transmission.

(iii) Name the parts numbered 1, 2 and 3.

Answer:
1 = Sensory neuron
2 = Motor neuron
3 = Grey matter with central canal of spinal cord

Teacher's Note:
a) In a reflex arc, the sensory neuron carries impulses from the receptor to the CNS, and the motor neuron carries impulses from the CNS to the effector. Grey matter in the spinal cord contains cell bodies and interneurons.
b) Correctly identifying the components of a reflex arc (sensory neuron, motor neuron, grey matter) is crucial for understanding its pathway.

(iv) How does the arrangement of neurons in the spinal cord differ from that of the brain?

Answer: The grey matter is present in the cortex (outer side) consisting of cell bodies and white matter is present inside, which consists of myelinated axons in the brain.
In spinal cord, the grey matter (cell bodies) are present inside, while white matter (Myelinated axon) is present outside.

Teacher's Note:
a) In the brain, grey matter (neuron cell bodies) forms the outer cortex, and white matter (myelinated axons) is internal. In the spinal cord, this arrangement is reversed: grey matter is internal (H-shaped), and white matter is external.
b) Students should remember this key structural difference between the brain and spinal cord, which reflects their different functional organizations.

(v) Mention two ways by which the spinal cord is protected in our body.

Answer: Vertebral column, meninges and cerebrospinal fluid (CSF)

Teacher's Note:
a) The spinal cord is protected by the bony vertebral column, the three layers of meninges (dura mater, arachnoid mater, pia mater), and the cerebrospinal fluid (CSF) which acts as a shock absorber.
b) Students should be able to list at least two of these protective structures for the spinal cord.

(b) Give appropriate biological or technical terms for the following :
(i) Process of maintaining water and salt balance in the blood.

Answer: Osmoregulation

Teacher's Note:
a) Osmoregulation is the active regulation of the osmotic pressure of an organism's body fluids to maintain the homeostasis of the body's water content; it involves controlling the amount of water and salt.
b) This term is crucial for understanding kidney function and overall fluid balance in the body.

(ii) Hormones which regulate the secretion of other endocrine glands.

Answer: Trophic hormones (Secreted by hypothalamus and pituitary)

Teacher's Note:
a) Trophic hormones (also called tropins) are hormones that stimulate the activity and growth of other endocrine glands, such as TSH stimulating the thyroid or ACTH stimulating the adrenal cortex.
b) Students should understand the hierarchical control in the endocrine system, often involving the hypothalamus and pituitary gland secreting trophic hormones.

(iii) Movement of molecules of a substance from their higher concentration to lower concentration when they are in direct contact.

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, driven by the random motion of molecules.
b) This is a fundamental concept in biology, explaining the movement of gases, solutes, and other substances across membranes or within fluids.

(iv) The condition in which a pair of chromosomes carry similar alleles of a particular character.

Answer: Homozygous

Teacher's Note:
a) A homozygous individual has two identical alleles for a particular gene on homologous chromosomes (e.g., AA or aa).
b) Students should distinguish between homozygous (identical alleles) and heterozygous (different alleles) genotypes.

(v) The complex consisting of a DNA strand and a core of histones.

Answer: Nucleosomes

Teacher's Note:
a) Nucleosomes are the basic structural units of DNA packaging in eukaryotes, consisting of a segment of DNA wound around a core of eight histone proteins.
b) Understanding nucleosomes is key to comprehending how DNA is compactly organized within the cell nucleus.

(vi) The onset of menstruation in a young girl.

Answer: Menarche

Teacher's Note:
a) Menarche is the term for the first menstrual period in a female, marking the beginning of her reproductive life.
b) Students should know the specific terms related to the female reproductive cycle, such as menarche and menopause.

(vii) Squeezing out of white blood cells from the capillaries into the surrounding tissues.

Answer: Diapedesis

Teacher's Note:
a) Diapedesis is the process by which white blood cells (leukocytes) move out of capillaries and into surrounding tissues to fight infection or inflammation.
b) This process is a crucial part of the immune response, allowing immune cells to reach sites of injury or infection.

(viii) The fluid which surrounds the foetus.

Answer: Amniotic fluid

Teacher's Note:
a) Amniotic fluid is the protective fluid contained within the amniotic sac that surrounds the developing fetus in the uterus.
b) Students should understand the role of amniotic fluid in cushioning the fetus, regulating temperature, and allowing for fetal movement.

(ix) The relaxation phase of the heart.

Answer: Diastole

Teacher's Note:
a) Diastole is the phase of the heartbeat when the heart muscle relaxes and allows the chambers to fill with blood. Systole is the contraction phase.
b) Students should clearly distinguish between systole (contraction) and diastole (relaxation) in the cardiac cycle.

(x) The difference between he birth rate and the death rate.

Answer: Growth rate

Teacher's Note:
a) The natural growth rate of a population is calculated as the birth rate minus the death rate, indicating population change due to births and deaths.
b) This term is fundamental in population dynamics and understanding demographic changes.

Question 5

(a) The diagram given below is that of a structure present in a human kidney.
Study the same and answer the questions that follow:

[Figure: A diagram of a nephron. Label 1 points to the afferent arteriole leading into the glomerulus. Label 2 points to the collecting duct.]

(i) Name the structure represented in the diagram.

Answer: Nephron

Teacher's Note:
a) The diagram shows a nephron, which is the functional unit of the kidney responsible for filtering blood and forming urine.
b) Students should recognize the overall structure of a nephron, including its various parts like the glomerulus, Bowman's capsule, renal tubule, and collecting duct.

(ii) What is the liquid entering part '1' called?
Name two substances present in this liquid that are reabsorbed in the tubule.

Answer: (1) Glomerular filterate
(2) Glucose and Amino acids

Teacher's Note:
a) Part '1' represents the afferent arteriole, which brings blood to the glomerulus. The liquid that filters out into Bowman's capsule is called glomerular filtrate. Essential substances like glucose and amino acids are reabsorbed from this filtrate in the renal tubule.
b) Students should understand that glomerular filtrate contains both waste products and useful substances, and selective reabsorption ensures that vital nutrients are returned to the blood.

(iii) What is the fluid that comes to part '2' called?
Name the main nitrogenous waste in it.

Answer: (1) Urine
(2) Urea

Teacher's Note:
a) Part '2' represents the collecting duct, which receives the final fluid, urine, after filtration and reabsorption. The main nitrogenous waste product in urine is urea.
b) Students should know that urea is the primary nitrogenous waste in humans, formed in the liver and excreted by the kidneys.

(iv) Mention the three main steps involved in the formation of the fluid mentioned in (iii) above.

Answer: The 3 steps are
(1) Ultrafiltration
(2) Selective Reabsorption
(3) Tubular secretion

Teacher's Note:
a) Urine formation involves three distinct processes: ultrafiltration (in glomerulus), selective reabsorption (in renal tubule), and tubular secretion (in renal tubule).
b) Understanding these three steps is fundamental to comprehending how the kidneys regulate blood composition and produce urine.

(v) Name the substance which may be present in the fluid in part '2' if a person suffers from Diabetes mellitus.

Answer: Glucose

Teacher's Note:
a) In diabetes mellitus, blood glucose levels are abnormally high. When the glucose concentration in the glomerular filtrate exceeds the reabsorption capacity of the renal tubules, glucose appears in the urine.
b) The presence of glucose in urine (glycosuria) is a key diagnostic indicator of diabetes mellitus.

(b) Differentiate between the following pairs on the basis of what is indicated in the brackets.
(i) Leaf and Liver [form in which glucose is stored]

Answer:
Leaf- Starch
Liver - Glycogen

Teacher's Note:
a) Plants store excess glucose as starch, primarily in leaves and storage organs. Animals, including humans, store glucose as glycogen, mainly in the liver and muscles.
b) Students should know the different storage forms of carbohydrates in plants and animals.

(ii) ATP and AIDS [expand the abbreviations]

Answer:
ATP-Adenosine triphosphate
AIDS-Acquired Immunodeficiency Syndrome

Teacher's Note:
a) ATP is the primary energy currency of the cell. AIDS is a chronic, potentially life-threatening condition caused by the Human Immunodeficiency Virus (HIV).
b) Students should be able to correctly expand common biological and medical abbreviations.

(iii) Testosterone and Oestrogen [organ which secrets]

Answer:
Testosterone - Testis
Oestrogen - Ovaries

Teacher's Note:
a) Testosterone is the primary male sex hormone, secreted mainly by the testes. Oestrogen (estrogen) is the primary female sex hormone, secreted mainly by the ovaries.
b) Students should associate these key sex hormones with their respective primary endocrine glands.

(iv) Ureter and Urethra [function]

Answer:
Ureter - Tranport of urine from kidneys to urinary bladder.
Urethra - Transport of urine from urinary bladder to outside.

Teacher's Note:
a) The ureters are tubes that carry urine from the kidneys to the urinary bladder. The urethra is the tube that carries urine from the bladder out of the body.
b) Students often confuse these two terms; it's important to clearly distinguish their functions and anatomical pathways.

(v) Hypotonic solution and Hypertonic solution [condition of a plant cell when placed in them]

Answer:
Hypotonic solution-Turgid
Hypertonic solution-Flaccid

Teacher's Note:
a) When a plant cell is placed in a hypotonic solution, water enters the cell, causing it to become turgid (firm). In a hypertonic solution, water leaves the cell, causing it to become flaccid (limp) or plasmolyzed.
b) Understanding the effects of different tonicities on plant cells is crucial for comprehending osmosis and water relations in plants.

Question 6

(a) Given below is a diagram of a human blood smear.
Study the diagram and answer the questions that follow:

[Figure: A diagram of a human blood smear showing various blood components.
1: Red Blood Cell (RBC) - biconcave disc.
2: Neutrophil - multi-lobed nucleus.
3: Blood platelet - small, irregular fragment.
4: Blood plasma - the fluid matrix.]

(i) Name the components numbered '1' to '4'.

Answer:
1. RBC
2. Neutrophil
3. Blood platelets
4. Blood plasma

Teacher's Note:
a) This question requires identification of the major components of blood based on their typical appearance in a blood smear.
b) Students should be able to recognize RBCs (biconcave, anucleated), neutrophils (multi-lobed nucleus), platelets (small fragments), and plasma (the fluid matrix).

(ii) Mention two structural differences between the parts '1' and '2'.

Answer:
RBC
• Biconcave, disc shaped
• Do not have nucleas
Neutrophil
• Amoeboid
• Have 3-5 lobbed nucleas.

Teacher's Note:
a) RBCs are biconcave, anucleated, and lack most organelles, optimized for oxygen transport. Neutrophils are amoeboid, have a multi-lobed nucleus, and are phagocytic white blood cells.
b) Students should focus on distinct morphological features like shape, presence/absence of nucleus, and nuclear lobation when differentiating blood cells.

(iii) Name the soluble protein found in part ‘4' which forms insoluble threads during clotting of blood.

Answer: Fibrinogen

Teacher's Note:
a) Fibrinogen is a soluble plasma protein that, upon activation by thrombin, is converted into insoluble fibrin threads, forming the meshwork of a blood clot.
b) Students should understand the role of fibrinogen in the coagulation cascade and its transformation into fibrin.

(iv) What is the average lifespan of the component numbered ‘1'?

Answer: 120 days

Teacher's Note:
a) Red blood cells (RBCs) have an average lifespan of about 120 days, after which they are broken down in the spleen and liver.
b) Knowing the lifespan of RBCs is important for understanding their continuous production and destruction in the body.

(v) Component numbered ‘1' do not have certain organelles but are very efficient in their function. Explain.

Answer: RBCs do not have nucleas, endoplasmic reticulum and mitochondria. They are very efficient in carrying nutrients like glucose (which they cannot use, due to lack of mitochondria), can easily pass through the capillaries (lack of endoplasmic reticulum - endoskeleton)

Teacher's Note:
a) The absence of a nucleus, mitochondria, and endoplasmic reticulum in mature RBCs allows them to maximize space for hemoglobin, increasing oxygen-carrying capacity. Their biconcave shape also facilitates efficient gas exchange and flexibility to pass through capillaries.
b) Students should connect the structural adaptations of RBCs (lack of organelles, biconcave shape) directly to their functional efficiency in oxygen transport.

(b) Give biological explanations for the following:
(i) Education is very important for population control.

Answer: The married couples should be educated to delay birth of their first child, to space the second witha sufficient interval for proper up bringing and to stop the third.

Teacher's Note:
a) Education empowers individuals, especially women, leading to better awareness of family planning methods, delayed marriages, smaller family sizes, and improved health outcomes for mothers and children.
b) Education fosters responsible reproductive choices and helps break the cycle of high birth rates often associated with lack of awareness and resources.

(ii) The placenta is an important structure for the development of a foetus.

Answer: The placenta allows diffusion of food and oxygen from mother to foetus and that of nitrogenous waste and \(CO_2\) from foetus to mother.

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 developing fetus, while also acting as an endocrine gland.
b) Students should understand the dual role of the placenta in providing sustenance and removing waste, as well as its protective barrier function.

(iii) All the food chains begin with green plants.

Answer: Green plants are the only organisms that are able to synthesize food from \(CO_2\) and \(H_2O\) in presence of chlorophyll and sunlight. However, animals depend upon plants for food. Therefore, all food chains begin with green plants.

Teacher's Note:
a) Green plants are producers, capable of photosynthesis, converting light energy into chemical energy (food). All other organisms (consumers and decomposers) directly or indirectly depend on this energy.
b) This concept highlights the foundational role of autotrophs (green plants) as the base of nearly all terrestrial and aquatic food chains.

(iv) Plants growing in fertilized soil are often found to wilt if the soil is not adequately watered.

Answer: Plants growing in fertilized soil are often formed to wilt, if the soil is not adequately watered because of flaccidity or a decrease in turgor pressure exerted by the absorbed water on the cell wall of plants.

Teacher's Note:
a) Fertilized soil has a higher solute concentration (due to added salts) than unwatered soil. If not adequately watered, the soil solution can become hypertonic to the root hair cells, causing water to move out of the roots by osmosis, leading to wilting.
b) This phenomenon, known as "fertilizer burn," demonstrates the importance of maintaining a favorable water potential gradient for water absorption by plants.

(v) We should not put sharp objects into our ears.

Answer: We should not put sharp objects into out ears, as it may damage the ear drum.

Teacher's Note:
a) Inserting sharp objects into the ear canal can cause physical damage to the delicate structures of the ear, particularly the eardrum (tympanic membrane), leading to hearing loss or infection.
b) Students should be aware of the fragility of the ear structures and the risks associated with improper ear cleaning or insertion of foreign objects.

Question 7

(a) The diagram below represents a process in plants. The setup was placed in bright sunlight. Answer the following questions:

[Figure: A potometer setup. A potted plant is sealed in a container with its roots in water. A layer of oil is on top of the water. The container is placed on a weighing machine.]

(i) Name the physiological process depicted in the diagram.
Why was oil added to the water?

Answer: 1. Transpiration
2. Oil was added to the water to prevent its evaporative loss.

Teacher's Note:
a) The setup measures water loss from the plant, which is primarily due to transpiration. The oil layer prevents direct evaporation from the water surface, ensuring that all water loss measured is from the plant.
b) Students should understand the purpose of each component in an experimental setup, especially control measures like the oil layer.

(ii) When placed in bright sunlight for four hours, what do you observe with regard to the initial and final weight of the plant? Give a suitable reason for your answer.

Answer: Upon exposure to bright sunlight for four hours; the final weight will be lesser than the initial weight; because some water will be lost from the aerial parts of the plant by transpiration.

Teacher's Note:
a) Bright sunlight increases the rate of transpiration, leading to significant water loss from the plant's aerial parts, which reduces the overall weight of the setup.
b) This observation directly demonstrates the process of transpiration and its effect on plant water balance.

(iii) What happens to the level of water when this setup is placed in:
1. Humid conditions?
2. Windy conditions?

Answer:
1. No change in the level of water
2. The level of water drops.

Teacher's Note:
a) In humid conditions, the water potential gradient between the leaf and the atmosphere is reduced, slowing down transpiration, so water level change is minimal. In windy conditions, water vapor is quickly removed from the leaf surface, increasing the water potential gradient and thus increasing transpiration, causing the water level to drop.
b) Students should understand how environmental factors like humidity and wind speed affect the rate of transpiration.

(iv) Mention any three adaptations found in plants to overcome the process mentioned in (i).

Answer: The three adaptations found in plants to overcome transpiration are:
1. Sunken stomata: The stomata may be sunken or covered by hairs (eg. Nerium)
2. Narrow leaves: The leaves may become narrower to reduce surface area.
3. Fewer stomata: The number of stomata may be reduced.

Teacher's Note:
a) Plants, especially xerophytes, have evolved various adaptations to reduce water loss through transpiration, such as sunken stomata, reduced leaf surface area, and a thick cuticle.
b) Students should be able to list and explain these adaptations, linking them to water conservation strategies in plants.

(v) Explain the temm ‘Guttation'.

Answer: The leaves of certain plants exhibit droplets of water along their margins in the morning. This particularly happens in plants growing in warm humid conditions. A humid environment hampers transpiration while the roots continue to absorb water from the soil. This builds up a high hydrostatic pressure withinthe plant and “forces out” the excess water directly from the tips of veins in the leaf by a process called guttation.

Teacher's Note:
a) Guttation is the exudation of xylem sap (water droplets) from the margins or tips of leaves, typically occurring in humid conditions when transpiration is low but root pressure is high.
b) Students should differentiate guttation from dew and understand that it involves liquid water, not water vapor, and occurs through hydathodes.

(b) A pea plant which is homozygous for green pods which are inflated [GGII] is crossed with a homozygous plant for yellow pods which are constricted [ggii]. Answer the following questions;
(i) Give the phenotype and genotype of the F1 generation.
Which type of pollination has occurred to produce F1 generation?

Answer: (1) Phenotype ofF1 generation: Pea plants with green and inflated pods.
(2) Genotype ofF1 generation: GgIi
(3) Artificial cross pollination has occured to produce the F₁generation.

Teacher's Note:
a) This is a dihybrid cross. The F1 generation will be heterozygous for both traits (GgIi) and will express the dominant phenotypes: green pods and inflated pods.
b) Since the cross is specified between two distinct homozygous parents, it implies artificial cross-pollination to control the parentage.

(ii) Write the phenotypic ratio of the F2 generation.

Answer: The phenotypic ratio of the F₂generation is 9 : 3:3:1.

Teacher's Note:
a) For a dihybrid cross between two F1 heterozygotes (GgIi x GgIi), the classic Mendelian phenotypic ratio in the F2 generation is 9:3:3:1, representing the four possible combinations of dominant and recessive traits.
b) Students should remember this standard dihybrid ratio and be able to apply it to different trait combinations.

(iii) Write the possible combinations of the gametes that can be obtained if two F1 hybrid plants are crossed.

Answer: The possible combination of gametes that can be obtained if two F1 hybrid plants are crossed are as follows:
GI, Gi, gI, gi.

Teacher's Note:
a) An F1 hybrid plant with genotype GgIi can produce four types of gametes due to independent assortment: GI, Gi, gI, and gi.
b) This demonstrates Mendel's Law of Independent Assortment, where alleles for different traits segregate independently during gamete formation.

(iv) State Mendel's law of ‘Segregation of Gametes'.
What is the scientific name of the plant which Mendel used for his experiments on inheritance?

Answer: The two members of a pair of factors separate during the formation of gametes. This is the Mendel's law of 'Segregation of Gametes'.

Teacher's Note:
a) Mendel's Law of Segregation states that during gamete formation, the two alleles for a heritable character separate (segregate) from each other such that each gamete receives only one allele.
b) This law explains why offspring inherit one allele from each parent and is fundamental to understanding inheritance patterns.

(v) Pisum sativum

Answer: Pisum sativum

Teacher's Note:
a) Gregor Mendel conducted his groundbreaking genetics experiments using the garden pea plant, scientifically known as Pisum sativum.
b) Students should remember the scientific name of Mendel's experimental organism, written correctly in italics with the genus capitalized.