▶️ Answer/Explanation
Excretion is specifically defined as the removal of toxic metabolic waste products and substances that are in excess of what the organism requires.
Homeostasis refers to maintaining a stable internal environment, nutrition refers to obtaining food, and respiration refers to releasing energy — none of these match the description given.
✅ Answer: (A)
Homeostasis refers to maintaining a stable internal environment, nutrition refers to obtaining food, and respiration refers to releasing energy — none of these match the description given.
✅ Answer: (A)
▶️ Answer/Explanation
The concentrated glucose solution has a lower water potential than the onion cell’s cytoplasm, so water moves out of the cells by osmosis through the partially permeable cell membrane.
This loss of water causes the cell contents (cytoplasm and vacuole) to shrink away from the cell wall — a process called plasmolysis — which is what the “after” photograph shows.
✅ Answer: (D)
This loss of water causes the cell contents (cytoplasm and vacuole) to shrink away from the cell wall — a process called plasmolysis — which is what the “after” photograph shows.
✅ Answer: (D)
▶️ Answer/Explanation
The iodine test turning blue-black is a positive result specifically for starch; the Benedict’s test (negative, stays blue) rules out reducing sugars, and the Biuret test (negative, stays blue) rules out protein.
Since the emulsion/grease-spot test for fats also appears negative in the table, starch is the only nutrient confirmed present by this positive iodine result.
✅ Answer: (C)
Since the emulsion/grease-spot test for fats also appears negative in the table, starch is the only nutrient confirmed present by this positive iodine result.
✅ Answer: (C)
▶️ Answer/Explanation
At low temperatures (4 °C), the kinetic energy of enzyme and substrate molecules decreases, so they collide less frequently, reducing the rate of enzyme-catalysed reactions that cause food spoilage.
Enzymes are not denatured at 4 °C (denaturation requires high temperatures); they are simply slowed down, which is why refrigerated food can still eventually spoil.
✅ Answer: (A)
Enzymes are not denatured at 4 °C (denaturation requires high temperatures); they are simply slowed down, which is why refrigerated food can still eventually spoil.
✅ Answer: (A)
▶️ Answer/Explanation
In a leaf cross-section, the uppermost single-cell layer at the top of the diagram is the upper epidermis; it lacks chloroplasts and is covered by a waxy cuticle to prevent water loss and protect inner tissues.
Below the upper epidermis lies the palisade mesophyll (tightly packed cells with many chloroplasts), then the spongy mesophyll with air spaces, making it easy to identify P as the top layer.
✅ Answer: (C)
Below the upper epidermis lies the palisade mesophyll (tightly packed cells with many chloroplasts), then the spongy mesophyll with air spaces, making it easy to identify P as the top layer.
✅ Answer: (C)
▶️ Answer/Explanation
Dietary fibre is indigestible plant material (mainly cellulose) that adds bulk to the gut contents, stimulating the muscular contractions of peristalsis that move food through the intestine.
Without sufficient fibre, food moves too slowly through the large intestine, leading to constipation; fibre does not build tissue, bones, or supply iron — those are roles of protein, calcium/vitamin D, and iron minerals respectively.
✅ Answer: (C)
Without sufficient fibre, food moves too slowly through the large intestine, leading to constipation; fibre does not build tissue, bones, or supply iron — those are roles of protein, calcium/vitamin D, and iron minerals respectively.
✅ Answer: (C)
▶️ Answer/Explanation
The pulmonary artery is the vessel that carries blood from the heart to the lungs; elevated pressure in this artery is the condition being treated (pulmonary arterial hypertension).
The pulmonary vein carries blood back from the lungs to the heart, while the aorta and vena cava are systemic vessels — none of these carry blood toward the lungs as arteries do.
✅ Answer: (B)
The pulmonary vein carries blood back from the lungs to the heart, while the aorta and vena cava are systemic vessels — none of these carry blood toward the lungs as arteries do.
✅ Answer: (B)
▶️ Answer/Explanation
Cell division (1), protein synthesis (3), and temperature regulation (4) all require ATP energy from respiration — cell division needs energy to replicate DNA and separate chromosomes, protein synthesis uses ribosomes requiring energy, and maintaining body temperature requires metabolic heat production.
Oxygen diffusion (2) is a passive process driven solely by the concentration gradient and requires no energy input from respiration.
✅ Answer: (A)
Oxygen diffusion (2) is a passive process driven solely by the concentration gradient and requires no energy input from respiration.
✅ Answer: (A)
▶️ Answer/Explanation
The reflex arc pathway is: receptor → sensory neurone → relay neurone (in spinal cord/CNS) → motor neurone → effector; this pathway allows a fast, automatic response without involving the brain consciously.
The relay (connector) neurone is always in the middle — between the sensory and motor neurones — so the sequence must be sensory → relay → motor.
✅ Answer: (D)
The relay (connector) neurone is always in the middle — between the sensory and motor neurones — so the sequence must be sensory → relay → motor.
✅ Answer: (D)
▶️ Answer/Explanation
After pollination, the pollen grain germinates on the stigma and grows a pollen tube down through the style (the stalk connecting stigma to ovary) to reach the ovule inside the ovary.
The filament supports the anther, petals attract pollinators, and the stamen is the entire male organ — none of these are the channel through which the pollen tube travels.
✅ Answer: (D)
The filament supports the anther, petals attract pollinators, and the stamen is the entire male organ — none of these are the channel through which the pollen tube travels.
✅ Answer: (D)
▶️ Answer/Explanation
Since albinism is recessive (let \(b\) = albino allele, \(B\) = black allele), both black parents must carry one hidden \(b\) allele — making them both \(Bb\); the cross \(Bb \times Bb\) produces offspring in the ratio \(BB : Bb : bb = 1:2:1\), giving a \(\frac{1}{4}\) chance of albino (\(bb\)).
Only a heterozygous cross (\(Bb \times Bb\)) can produce an albino offspring from two visibly black parents, which corresponds to Punnett square B in the diagram.
✅ Answer: (B)
Only a heterozygous cross (\(Bb \times Bb\)) can produce an albino offspring from two visibly black parents, which corresponds to Punnett square B in the diagram.
✅ Answer: (B)
▶️ Answer/Explanation
The clues directly establish the chain: leaves (producer) → beetles (primary consumer/herbivore) → mice (secondary consumer, eating beetles) → owl (tertiary consumer).
Food chains always start with the producer and arrows point in the direction of energy flow, so the only correct sequence matching all four clues is: leaves → beetles → mice → owl.
✅ Answer: (B)
Food chains always start with the producer and arrows point in the direction of energy flow, so the only correct sequence matching all four clues is: leaves → beetles → mice → owl.
✅ Answer: (B)
▶️ Answer/Explanation
In the carbon cycle diagram, process X shows an arrow from atmospheric \(\text{CO}_2\) into plants/organic compounds; this is photosynthesis — the only process that removes \(\text{CO}_2\) from the atmosphere and fixes it into organic molecules.
Respiration, combustion, and decomposition all release \(\text{CO}_2\) back into the atmosphere (arrows pointing in the opposite direction), so X must be photosynthesis.
✅ Answer: (C)
Respiration, combustion, and decomposition all release \(\text{CO}_2\) back into the atmosphere (arrows pointing in the opposite direction), so X must be photosynthesis.
✅ Answer: (C)
▶️ Answer/Explanation
The experiment needs: a balance to weigh 5 g of magnesium, a measuring cylinder to measure 20 cm³ of acid, a beaker to hold the reaction mixture, and a stopwatch to time how long effervescence takes to stop.
No thermometer or gas syringe is required since the measurement is only of time (not temperature or gas volume), so the correct apparatus set is the one in option C.
✅ Answer: (C)
No thermometer or gas syringe is required since the measurement is only of time (not temperature or gas volume), so the correct apparatus set is the one in option C.
✅ Answer: (C)
▶️ Answer/Explanation
Sea water is a mixture (not a compound), so its components are not chemically combined and can be separated by physical means; it is a solution (homogeneous mixture), meaning the solute (NaCl) is uniformly distributed throughout the solvent (water).
The components of sea water — sodium chloride and water — each retain their own chemical properties (e.g., water’s boiling point is affected but NaCl can still be recovered), which is characteristic of a mixture rather than a compound.
✅ Answer: (C)
The components of sea water — sodium chloride and water — each retain their own chemical properties (e.g., water’s boiling point is affected but NaCl can still be recovered), which is characteristic of a mixture rather than a compound.
✅ Answer: (C)
▶️ Answer/Explanation
In a water molecule, oxygen (with 6 outer-shell electrons) forms two single covalent bonds with two hydrogen atoms (each with 1 electron), resulting in two bonding pairs and two lone pairs on oxygen — giving the characteristic bent shape shown in diagram A.
The correct dot-and-cross diagram must show oxygen with 2 shared pairs (one with each H) and 2 lone pairs, with each hydrogen having a full outer shell of 2 electrons after sharing.
✅ Answer: (A)
The correct dot-and-cross diagram must show oxygen with 2 shared pairs (one with each H) and 2 lone pairs, with each hydrogen having a full outer shell of 2 electrons after sharing.
✅ Answer: (A)
▶️ Answer/Explanation
Carbon has the electronic structure 2,4 — it has 4 electrons in its outer shell and needs 4 more to achieve a full outer shell of 8; hydrogen has 1 outer electron and needs 1 more to fill its shell of 2, so each hydrogen can form exactly one covalent bond.
Carbon therefore forms 4 covalent bonds, one with each of 4 hydrogen atoms: \(\text{C} + 4\text{H} \rightarrow \text{CH}_4\) (methane), giving carbon a complete outer shell of 8 electrons and each hydrogen a complete shell of 2 electrons.
✅ Answer: (D)
Carbon therefore forms 4 covalent bonds, one with each of 4 hydrogen atoms: \(\text{C} + 4\text{H} \rightarrow \text{CH}_4\) (methane), giving carbon a complete outer shell of 8 electrons and each hydrogen a complete shell of 2 electrons.
✅ Answer: (D)
▶️ Answer/Explanation
At the cathode (negative electrode): \(2\text{H}^+ + 2e^- \rightarrow \text{H}_2\) — hydrogen gas is produced because \(\text{H}^+\) ions from water are preferentially discharged over \(\text{Na}^+\) ions.
At the anode (positive electrode): \(2\text{Cl}^- \rightarrow \text{Cl}_2 + 2e^-\) — chlorine gas is produced because the high concentration of \(\text{Cl}^-\) ions means they are preferentially discharged over \(\text{OH}^-\) ions.
✅ Answer: (B)
At the anode (positive electrode): \(2\text{Cl}^- \rightarrow \text{Cl}_2 + 2e^-\) — chlorine gas is produced because the high concentration of \(\text{Cl}^-\) ions means they are preferentially discharged over \(\text{OH}^-\) ions.
✅ Answer: (B)
▶️ Answer/Explanation
Any reaction with a final temperature above 21 °C is exothermic (heat is released to the surroundings), and any reaction with a final temperature below 21 °C is endothermic (heat is absorbed from the surroundings).
By comparing each reaction’s final temperature to the initial 21 °C, the reactions can be correctly classified as exothermic or endothermic — row B correctly assigns all four reactions based on their temperature changes.
✅ Answer: (B)
By comparing each reaction’s final temperature to the initial 21 °C, the reactions can be correctly classified as exothermic or endothermic — row B correctly assigns all four reactions based on their temperature changes.
✅ Answer: (B)
▶️ Answer/Explanation
Decreasing the concentration of hydrochloric acid means fewer \(\text{H}^+\) ions are present in a given volume, so there are fewer successful collisions per second between acid particles and the calcium carbonate surface — this decreases the rate of reaction.
Options B and C (decreasing piece size / increasing surface area) increase the exposed surface for collision and speed up the reaction; increasing temperature (D) also increases reaction rate by giving particles more kinetic energy.
✅ Answer: (A)
Options B and C (decreasing piece size / increasing surface area) increase the exposed surface for collision and speed up the reaction; increasing temperature (D) also increases reaction rate by giving particles more kinetic energy.
✅ Answer: (A)
▶️ Answer/Explanation
Oxidation (in terms of oxygen) is defined as the chemical combination (bonding) of a substance with oxygen — for example, \(\text{2Mg} + \text{O}_2 \rightarrow \text{2MgO}\) is oxidation of magnesium.
Option B describes a physical mixture (not a chemical reaction), option C describes separation, and option D describes reduction (loss of oxygen) — none of these are oxidation.
✅ Answer: (A)
Option B describes a physical mixture (not a chemical reaction), option C describes separation, and option D describes reduction (loss of oxygen) — none of these are oxidation.
✅ Answer: (A)
▶️ Answer/Explanation
Carbon dioxide (\(\text{CO}_2\)) is a non-metal oxide that reacts with water to form carbonic acid: \(\text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{CO}_3\), classifying it as an acidic oxide.
Calcium oxide, lithium oxide, and sodium oxide are all metal oxides — they are basic oxides that react with acids to form salts and water, not acidic oxides.
✅ Answer: (B)
Calcium oxide, lithium oxide, and sodium oxide are all metal oxides — they are basic oxides that react with acids to form salts and water, not acidic oxides.
✅ Answer: (B)
▶️ Answer/Explanation
The flame test result (crimson/red flame) indicates the presence of lithium ions (\(\text{Li}^+\)), ruling out sodium (yellow flame); the silver nitrate test producing a white precipitate (soluble in dilute \(\text{NH}_3\)) indicates chloride ions (\(\text{Cl}^-\)), ruling out bromide (cream precipitate).
Combining both results — lithium cation + chloride anion — uniquely identifies compound P as lithium chloride (\(\text{LiCl}\)).
✅ Answer: (B)
Combining both results — lithium cation + chloride anion — uniquely identifies compound P as lithium chloride (\(\text{LiCl}\)).
✅ Answer: (B)
▶️ Answer/Explanation
Transition elements (e.g. iron, copper, nickel) are characterised by high density, high melting points (due to strong metallic bonding), good electrical conductivity, and the ability to form compounds with various colours due to their partially filled d-orbitals.
Low density is the opposite of what is expected — transition elements are notably dense metals; low density is a property of alkali metals such as lithium and sodium, not transition metals.
✅ Answer: (D)
Low density is the opposite of what is expected — transition elements are notably dense metals; low density is a property of alkali metals such as lithium and sodium, not transition metals.
✅ Answer: (D)
▶️ Answer/Explanation
The standard reactivity series places calcium above magnesium, which is above aluminium, which is above iron, which is above copper — so from highest to lowest: Ca > Mg > Al > Fe > Cu.
Option C (calcium → magnesium → iron → copper) correctly omits aluminium but maintains the right relative order for the four metals listed; only option C places calcium above magnesium and iron above copper without reversing any pair.
✅ Answer: (C)
Option C (calcium → magnesium → iron → copper) correctly omits aluminium but maintains the right relative order for the four metals listed; only option C places calcium above magnesium and iron above copper without reversing any pair.
✅ Answer: (C)
▶️ Answer/Explanation
Anhydrous cobalt(II) chloride paper is blue in the absence of water; when water molecules are absorbed, the cobalt(II) chloride hydrates and changes colour from blue to pink — this reaction is specific to water and is routinely used to test for the presence of water.
This test does not distinguish between acidic, alkaline, or neutral solutions, nor does it identify ethanol; it only confirms the presence of water molecules in the liquid.
✅ Answer: (D)
This test does not distinguish between acidic, alkaline, or neutral solutions, nor does it identify ethanol; it only confirms the presence of water molecules in the liquid.
✅ Answer: (D)
▶️ Answer/Explanation
Complete combustion means the fuel burns in excess oxygen, so all the carbon is fully oxidised to \(\text{CO}_2\) and all the hydrogen is oxidised to \(\text{H}_2\text{O}\): \(\text{C}_2\text{H}_5\text{OH} + 3\text{O}_2 \rightarrow 2\text{CO}_2 + 3\text{H}_2\text{O}\).
Incomplete combustion (insufficient oxygen) would produce carbon monoxide or carbon soot, but the question specifies complete combustion, so only \(\text{CO}_2\) and \(\text{H}_2\text{O}\) are produced.
✅ Answer: (C)
Incomplete combustion (insufficient oxygen) would produce carbon monoxide or carbon soot, but the question specifies complete combustion, so only \(\text{CO}_2\) and \(\text{H}_2\text{O}\) are produced.
✅ Answer: (C)
▶️ Answer/Explanation
Total distance \(= 5000 + 3000 = 8000\) m; total time \(= 1200 + 1800 = 3000\) s.
Average speed \(= \dfrac{8000}{3000} \approx 2.67 \approx 2.7\) m/s — note that average speed must use the total distance and total time for the whole journey, not the average of the two individual speeds.
✅ Answer: (B)
Average speed \(= \dfrac{8000}{3000} \approx 2.67 \approx 2.7\) m/s — note that average speed must use the total distance and total time for the whole journey, not the average of the two individual speeds.
✅ Answer: (B)
▶️ Answer/Explanation
From the diagram, the skydiver has a downward weight of 700 N and an upward air resistance of 300 N; since these forces act in opposite directions, the resultant \(= 700 – 300 = 400\) N, acting downward (in the direction of the larger force).
The resultant force is downward because weight (700 N) is greater than air resistance (300 N), meaning there is a net downward force causing the skydiver to accelerate downward.
✅ Answer: (A)
The resultant force is downward because weight (700 N) is greater than air resistance (300 N), meaning there is a net downward force causing the skydiver to accelerate downward.
✅ Answer: (A)
▶️ Answer/Explanation
Since the ball returns to its original height, the net change in gravitational potential energy is zero — the GPE gained going up equals the GPE lost coming down; the only reason the kinetic energy is less on return is because energy was lost to air resistance throughout the journey.
The energy lost \(= 12 – 8.0 = 4.0\) J, and since GPE is unchanged, all 4.0 J was dissipated as heat by air resistance — not 20 J, which would be the sum (an error in reasoning).
✅ Answer: (B)
The energy lost \(= 12 – 8.0 = 4.0\) J, and since GPE is unchanged, all 4.0 J was dissipated as heat by air resistance — not 20 J, which would be the sum (an error in reasoning).
✅ Answer: (B)
▶️ Answer/Explanation
Useful power \(P = \dfrac{\text{work done}}{\text{time}} = \dfrac{W \times d}{t}\); since weight \(W\) is already known, we additionally need the vertical distance \(d\) (to calculate work done \(= W \times d\)) and the time \(t\) taken to lift it.
Neither the mass (already accounted for by weight) nor the current/voltage of the motor (those give total power input, not useful output) are needed — only distance and time, which corresponds to row A in the table.
✅ Answer: (A)
Neither the mass (already accounted for by weight) nor the current/voltage of the motor (those give total power input, not useful output) are needed — only distance and time, which corresponds to row A in the table.
✅ Answer: (A)
▶️ Answer/Explanation
Air is a gas with particles that are very widely spaced and move randomly — there are very few particle-to-particle collisions to transfer thermal energy, making it an excellent thermal insulator (poor conductor).
Aluminium, copper, and iron are all metals containing free electrons that can rapidly carry kinetic energy from hot regions to cold regions, making them good thermal conductors; air has no free electrons and relies on slow molecular collision conduction.
✅ Answer: (A)
Aluminium, copper, and iron are all metals containing free electrons that can rapidly carry kinetic energy from hot regions to cold regions, making them good thermal conductors; air has no free electrons and relies on slow molecular collision conduction.
✅ Answer: (A)
▶️ Answer/Explanation
When light enters glass from air, it slows down and refracts toward the normal (angle of refraction < angle of incidence); when it exits through the parallel surface back into air, it speeds up and refracts away from the normal by the same amount.
Because the two surfaces are parallel, the exit ray is parallel to the original entry ray but laterally displaced — diagram C correctly shows this behaviour with the correct direction of bending at each interface.
✅ Answer: (C)
Because the two surfaces are parallel, the exit ray is parallel to the original entry ray but laterally displaced — diagram C correctly shows this behaviour with the correct direction of bending at each interface.
✅ Answer: (C)
▶️ Answer/Explanation
Across the electromagnetic spectrum, radio waves occupy the low-frequency, long-wavelength end; gamma rays are at the opposite extreme with the highest frequency and shortest wavelength.
Of the four options given — gamma (highest frequency), ultraviolet, infrared, and radio (lowest frequency) — radio waves have by far the lowest frequency, with wavelengths ranging from millimetres to kilometres.
✅ Answer: (D)
Of the four options given — gamma (highest frequency), ultraviolet, infrared, and radio (lowest frequency) — radio waves have by far the lowest frequency, with wavelengths ranging from millimetres to kilometres.
✅ Answer: (D)
▶️ Answer/Explanation
Since P is positive and Q is negative, they carry opposite charges and will experience an attractive force between them (unlike charges attract, like charges repel).
Objects become charged by the transfer of electrons only (protons cannot move as they are held in the nucleus); P lost electrons (becoming positive) and Q gained electrons (becoming negative) — row B in the table states attraction and electron transfer, which is correct.
✅ Answer: (B)
Objects become charged by the transfer of electrons only (protons cannot move as they are held in the nucleus); P lost electrons (becoming positive) and Q gained electrons (becoming negative) — row B in the table states attraction and electron transfer, which is correct.
✅ Answer: (B)
▶️ Answer/Explanation
Using Ohm’s Law: \(I = \dfrac{V}{R} = \dfrac{3.0}{60} = 0.05\ \text{A}\).
Converting to milliamps: \(0.05\ \text{A} \times 1000 = 50\ \text{mA}\); note that option A (0.050 mA) is 1000 times too small — a common unit-conversion error to avoid.
✅ Answer: (C)
Converting to milliamps: \(0.05\ \text{A} \times 1000 = 50\ \text{mA}\); note that option A (0.050 mA) is 1000 times too small — a common unit-conversion error to avoid.
✅ Answer: (C)
▶️ Answer/Explanation
In a parallel circuit, all branches share the same voltage as the battery — adding another parallel resistor does not change the voltage, so the voltmeter reading stays the same.
However, adding a third parallel branch lowers the total resistance \(\left(\frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}\right)\), so the total current drawn from the battery increases — the ammeter reading increases, corresponding to row D.
✅ Answer: (D)
However, adding a third parallel branch lowers the total resistance \(\left(\frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}\right)\), so the total current drawn from the battery increases — the ammeter reading increases, corresponding to row D.
✅ Answer: (D)
▶️ Answer/Explanation
Using the right-hand rule: point the right thumb in the direction of conventional current; the curled fingers show the direction of the magnetic field — for current into the page (represented by a cross symbol ✕), the field circles are clockwise when viewed from the front.
Diagram C shows concentric circular field lines in the clockwise direction around the wire, which is the correct pattern for a current directed into the page.
✅ Answer: (C)
Diagram C shows concentric circular field lines in the clockwise direction around the wire, which is the correct pattern for a current directed into the page.
✅ Answer: (C)
▶️ Answer/Explanation
Isotopes are atoms of the same element, so they must have the same atomic number — meaning the same number of protons; they differ only in their number of neutrons, which gives them different mass numbers.
Since both are neutral atoms of the same element, they also have the same number of electrons as protons — options A, B, and C are all incorrect because they change the proton count or electron count, which would make them different elements or ions respectively.
✅ Answer: (D)
Since both are neutral atoms of the same element, they also have the same number of electrons as protons — options A, B, and C are all incorrect because they change the proton count or electron count, which would make them different elements or ions respectively.
✅ Answer: (D)
▶️ Answer/Explanation
To find the half-life from the decay graph, identify the initial activity, find the time when it has fallen to half that value, and read off the time elapsed — from the graph, the activity halves every 2.0 years.
This can be verified by checking a second halving: if the activity halves again after another 2.0 years (i.e., at 4.0 years total), the value is one quarter of the original, which should be consistent with the graph curve shown.
✅ Answer: (B)
This can be verified by checking a second halving: if the activity halves again after another 2.0 years (i.e., at 4.0 years total), the value is one quarter of the original, which should be consistent with the graph curve shown.
✅ Answer: (B)