A variegated leaf (green and white patches) is kept in sunlight for a few hours, decolourised in warm alcohol and tested with iodine solution. Which parts turn blue-black?
Explanation: Only cells with chlorophyll can photosynthesise and store starch. Iodine turns blue-black with starch, so only the green patches change colour.
A pitcher plant grows well in nitrogen-poor soil because it traps insects. What does it mainly obtain from the digested insects?
Explanation: It still makes its own food by photosynthesis, but the trapped insects supply the nitrogen compounds that the soil lacks.
Rhizobium bacteria live in the root nodules of gram and pea plants. Their main contribution to the plant is to
Explanation: Rhizobium fixes atmospheric nitrogen into a usable form, while the plant gives the bacteria food and shelter. This partnership is called symbiosis.
Which pair correctly matches the organism with its mode of nutrition?
Explanation: Cuscuta (amarbel) takes ready-made food from its host, so it is a parasite. A mushroom feeds on dead and decaying matter, so it is a saprotroph.
In photosynthesis, 6 molecules of carbon dioxide react with 6 molecules of water. How many molecules of oxygen are released for each molecule of glucose formed?
Explanation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (in sunlight, with chlorophyll). Six oxygen molecules are released per glucose molecule.
Stomata on a leaf are surrounded by guard cells. Through the stomata, a leaf mainly
Explanation: Stomata let carbon dioxide in and oxygen out for photosynthesis, and water vapour escapes through them (transpiration).
A potted plant is kept in complete darkness for a week. Which statement is most likely to be true?
Explanation: Photosynthesis needs light to drive the reaction. Without light, the plant cannot prepare food and has to use up its stored food.
Farmers often grow a leguminous crop like peas between two wheat crops mainly to
Explanation: Legumes have Rhizobium in their root nodules that fix atmospheric nitrogen, which enriches the soil for the next crop.
The digestion of proteins begins in the
Explanation: Gastric juice contains hydrochloric acid and the enzyme pepsin, which starts protein digestion in the stomach. Carbohydrate digestion begins in the mouth.
Which sequence shows the correct path of food in humans?
Explanation: Food passes through the food pipe to the stomach, is absorbed in the small intestine, and water is absorbed in the large intestine.
The inner wall of the small intestine has millions of finger-like villi. Their main function is to
Explanation: Villi are rich in blood vessels and greatly increase the surface area, so digested food is absorbed into the blood quickly.
Amoeba catches food with pseudopodia. Digestion of the food then takes place in the
Explanation: The food is engulfed in a food vacuole, where digestive juices break it down. The undigested part is expelled from the cell surface.
Which digestive juice contains no enzymes but still helps in the digestion of fats?
Explanation: Bile from the liver breaks fat into tiny droplets so that enzymes can act on it. Saliva, gastric juice and pancreatic juice all contain enzymes.
When we chew a piece of bread for a few minutes, it slowly starts tasting sweet because
Explanation: Saliva contains the enzyme amylase, which begins the breakdown of starch (a carbohydrate) into sugar in the mouth.
How many teeth does a healthy adult normally have?
Explanation: A child has 20 milk teeth, which are replaced by 32 permanent teeth in an adult.
Cows chew cud because
Explanation: Ruminants quickly swallow grass, which is partially digested in the rumen. They later return this cud to the mouth and chew it thoroughly.
In the life cycle of the silk moth, which stage spins the cocoon?
Explanation: The caterpillar spins silk fibre from special glands around itself as a cocoon, and then turns into a pupa inside it.
Which pair contains only fibres that are proteins?
Explanation: Wool and silk are animal fibres made of protein. Cotton and jute are plant fibres; nylon and polyester are synthetic.
Washing sheared wool in tanks to remove grease, dust and dirt is called
Explanation: After shearing, the fleece is scoured. Sorting separates hair of different textures, and reeling is a silk process.
Wool used to make Pashmina shawls is obtained from the
Explanation: Pashmina comes from the fine underhair of the Kashmiri goat.
Taking out silk threads from cocoons is called
Explanation: The silk fibre of cocoons is loosened by heat and the threads are reeled off and twisted into yarn. Retting is used for jute.
Which is the correct order of stages in the life cycle of the silk moth?
Explanation: A silk moth lays eggs, from which caterpillars hatch. The caterpillar spins a cocoon and becomes a pupa, which later emerges as an adult moth.
During the processing of wool, the small fluffy fibres that are picked out of the hair after sorting are called
Explanation: After sorting, small fluffy fibres called burrs are picked out. The hair is then washed, dried, dyed and spun into yarn.
A liquid turns blue litmus paper red and has no effect on turmeric paper. The liquid is
Explanation: Acids turn blue litmus red and leave turmeric unchanged. A base would turn red litmus blue and turmeric paper red.
Milk of magnesia is taken for acidity because it
Explanation: Milk of magnesia is a base. It reacts with the excess hydrochloric acid to form a salt and water (neutralisation).
An ant sting injects formic acid. Which of these gives relief when applied to the skin?
Explanation: Calamine solution (zinc carbonate) is a base and neutralises the acid. Vinegar, lemon juice and tamarind are acidic.
China rose extract is used as an indicator. What colour does it turn in soap solution?
Explanation: China rose turns acidic solutions magenta and basic solutions green. Soap solution is basic, so it turns green.
A farmer's soil is too acidic for a crop. Which substance should be added to improve it?
Explanation: Slaked lime is a base and neutralises the acid in the soil. The other substances are acidic or would make the soil more acidic.
A colourless solution turns pink on adding a few drops of phenolphthalein. The solution is
Explanation: Phenolphthalein is colourless in acidic and neutral solutions and turns pink in a basic solution.
When hydrochloric acid reacts completely with sodium hydroxide, the products are
Explanation: HCl + NaOH → NaCl + H₂O. The reaction between an acid and a base gives a salt and water.
Which household substance is basic in nature?
Explanation: Baking soda solution turns red litmus blue. Lemon juice, curd and vinegar are acidic.
Iron nails are kept in three test tubes: (1) dry air, (2) boiled water covered with a layer of oil, (3) tap water open to air. In which will the nails rust?
Explanation: Rusting needs both oxygen and moisture. Tube 1 has no water, and tube 2 has no dissolved oxygen. Tube 3 has both.
Which of the following is a chemical change?
Explanation: In curdling, milk changes into curd and whey, which are new substances that cannot be turned back into milk. The others are physical changes.
Coating iron with a layer of zinc to protect it from rusting is called
Explanation: Zinc protects the iron from air and moisture. It is used for iron pipes, buckets and fencing.
An iron nail is dipped in copper sulphate solution for about half an hour. The nail turns brownish and the blue solution turns
Explanation: Iron displaces copper. Copper deposits on the nail (brown) and iron sulphate, which is pale green, forms in the solution.
Vinegar is added to baking soda and the gas released is passed through lime water. What happens?
Explanation: Carbon dioxide reacts with lime water (calcium hydroxide) to form a milky white precipitate of calcium carbonate.
When a candle burns, which of these changes take place?
Explanation: Wax melts near the flame (physical). The wax vapour burns to form carbon dioxide and water vapour (chemical).
Large crystals of copper sulphate can be obtained from its hot saturated solution by
Explanation: As the saturated solution cools slowly, the dissolved substance separates as crystals. This is called crystallisation.
Which pair contains two chemical changes?
Explanation: Ripening and burning produce new substances. Freezing, boiling, melting and dissolving change only the state or form.
Yeast is added to dough to make bread rise. The dough rises because yeast respires without oxygen and releases
Explanation: Yeast breaks down sugar without oxygen, forming alcohol and carbon dioxide. The gas bubbles make the dough swell.
During a sprint, muscle cells get too little oxygen and respire anaerobically. The substance that builds up and causes cramps is
Explanation: Anaerobic respiration in muscle cells breaks glucose down only partially, forming lactic acid and a small amount of energy.
When we breathe in, the diaphragm
Explanation: This enlarges the chest cavity and lowers the pressure inside, so air rushes into the lungs.
A potted plant is over-watered so that the soil is completely filled with water. The plant may die because
Explanation: Roots respire using oxygen from the air spaces in the soil. Waterlogging fills these spaces with water.
Which statement about respiration in muscle cells is correct?
Explanation: Aerobic respiration breaks glucose down completely (to carbon dioxide and water) and releases much more energy. In muscles, anaerobic respiration ends with lactic acid.
At rest, a healthy adult breathes about
Explanation: The breathing rate rises during exercise because the body needs more oxygen.
Earthworms breathe mainly through their
Explanation: Oxygen dissolves in the moisture on the earthworm's skin and diffuses into the blood.
Air enters a cockroach's body through tiny openings on its sides called
Explanation: Spiracles open into a network of air tubes (tracheae) that carry air to all body parts.
Which component of blood helps in clotting at a cut and stops bleeding?
Explanation: Platelets stick together at a wound and help form a clot that seals the cut.
Which blood vessel carries oxygen-rich blood?
Explanation: The pulmonary vein carries oxygenated blood from the lungs to the heart. The pulmonary artery carries deoxygenated blood to the lungs.
Which chamber of the human heart pumps oxygen-rich blood to the whole body?
Explanation: The left ventricle has the thickest wall and pushes oxygenated blood into the aorta. The right ventricle pumps blood only to the lungs.
In plants, water and minerals absorbed by the roots are carried to the leaves by the
Explanation: Xylem vessels carry water and minerals upward, pulled by the loss of water vapour from the leaves (transpiration). Phloem carries food.
The main nitrogenous waste excreted in human urine is
Explanation: The kidneys filter urea, excess water and salts out of the blood to form urine. Birds and reptiles excrete uric acid.
The normal pulse rate of a healthy adult at rest is about
Explanation: The pulse is the throb of an artery as the heart pumps blood. It equals the heartbeat rate, about 72 per minute at rest.
The red pigment haemoglobin, which carries oxygen, is found in
Explanation: Haemoglobin in red blood cells combines with oxygen in the lungs and releases it to the body cells.
Which of these is NOT an excretory organ in humans?
Explanation: Kidneys remove urea, skin removes sweat and lungs remove carbon dioxide. The stomach digests food.
Small plantlets grow from the notches of a Bryophyllum leaf that falls on wet soil. This method of reproduction is called
Explanation: New plants grow from a vegetative part (the leaf) without seeds or spores. Budding is seen in yeast.
After fertilisation in a flower, the ovule and the ovary develop into
Explanation: The fertilised ovule becomes the seed containing the embryo, while the ovary becomes the fruit that protects the seeds.
Which seed or fruit is adapted for dispersal by water?
Explanation: The coconut has a fibrous, buoyant coat. Maple is dispersed by wind, Xanthium by animals (hooks) and balsam by the bursting of the fruit.
Which of these flowers is bisexual (has both stamens and a pistil)?
Explanation: Rose has both male and female parts. Papaya, cucumber and maize have unisexual flowers.
A bee carries pollen from a flower of one mango tree to a flower of another mango tree. This is
Explanation: Pollen was transferred between flowers of different plants. Fertilisation happens later, when a male gamete fuses with an egg in the ovule.
Bread mould and ferns reproduce by producing tiny
Explanation: Spores are tiny reproductive units enclosed in a protective coat. They germinate into new plants in favourable conditions.
A small bulb-like projection grows on a yeast cell, breaks off and becomes a new yeast cell. This method is called
Explanation: In budding the bud grows from the parent cell and later separates to live independently.
A bus covers the first 30 km at 60 km/h and the next 30 km at 30 km/h. What is its average speed for the whole 60 km?
Explanation: Time = 30/60 + 30/30 = 0.5 + 1 = 1.5 h. Average speed = 60 km ÷ 1.5 h = 40 km/h. It is not the simple average of the two speeds.
The distance–time graph of a toy car is shown. What is the speed of the car during the last 2 seconds (from 4 s to 6 s)?
Explanation: From 4 s to 6 s the distance changes from 20 m to 60 m: 40 m in 2 s, so the speed is 20 m/s. From 2 s to 4 s the car is at rest.
A simple pendulum makes 30 oscillations in 1 minute. Its time period is
Explanation: Time period = total time ÷ number of oscillations = 60 s ÷ 30 = 2 s.
A cyclist rides at 36 km/h. What is this speed in m/s?
Explanation: 36 km/h = 36 × 1000 m ÷ 3600 s = 10 m/s.
A train 150 m long passes a signal pole in 10 s. What is its speed in km/h?
Explanation: The train covers its own length: 150 m ÷ 10 s = 15 m/s. Then 15 × 18/5 = 54 km/h.
Which of these speeds is the greatest?
Explanation: 72 km/h = 20 m/s, 1.2 km/min = 72 km/h = 20 m/s and 25 m/s = 90 km/h. So 25 m/s is the greatest.
Two trains are 200 km apart and move towards each other at 60 km/h and 40 km/h. After how long do they meet?
Explanation: Their distance closes at 60 + 40 = 100 km/h. Time = 200 ÷ 100 = 2 hours.
Which instrument in a vehicle records the distance travelled?
Explanation: An odometer shows the total distance covered. The speedometer shows the speed at that moment.
The wire used in an electric fuse should have
Explanation: When the current becomes too large, the fuse wire heats up and melts, breaking the circuit and protecting the appliances.
Which change makes an electromagnet stronger?
Explanation: More turns (and more current, with a soft iron core) increase the magnetic effect. Wood and copper are not magnetic, and fewer cells give less current.
Two identical bulbs are connected in series with one cell as shown. If Bulb 1 fuses, what happens to Bulb 2?
Explanation: A series circuit has only one path. When one bulb fuses, the circuit is broken and no current flows, so both bulbs go off.
In the circuit symbol of a cell, the longer line represents the
Explanation: The longer thin line is the positive terminal and the shorter thick line is the negative terminal.
Which effect of electric current is used in electroplating?
Explanation: When current passes through a conducting solution, chemical changes take place. In electroplating, metal from the solution is deposited on the object.
Which material is generally used as the heating element of an electric heater?
Explanation: Nichrome is an alloy with high resistance and a high melting point, so it gets red hot without melting.
A miniature circuit breaker (MCB) is used in houses to
Explanation: An MCB works like a fuse but switches off the circuit when the current is too large, and it can be switched on again.
When current flows through a wire placed near a compass needle, the needle gets deflected. This shows the
Explanation: A current-carrying wire produces a magnetic field, which deflects the compass needle.
A ray of light strikes a plane mirror so that it makes an angle of 30° with the surface of the mirror. What is the angle of reflection?
Explanation: The angle of incidence is measured from the normal: 90° − 30° = 60°. The angle of reflection equals the angle of incidence, so it is 60°.
Two plane mirrors are placed at 90° to each other and a candle is placed between them. How many images are formed?
Explanation: Number of images = 360°/angle − 1 = 360°/90° − 1 = 3.
Vehicles use a convex mirror as a rear-view mirror because it
Explanation: A convex mirror always forms an erect, smaller virtual image and lets the driver see a large area behind.
Which of these words looks exactly the same in a plane mirror placed to its right (left–right reversal)?
Explanation: Only letters that are symmetrical about a vertical line look unchanged. M and O are symmetrical, but D and P are not.
A girl walks towards a plane mirror at 2 m/s. At what speed does her image approach her?
Explanation: The image is as far behind the mirror as she is in front. When she moves 2 m closer, her image also moves 2 m closer to the mirror, so the gap between them closes at 2 + 2 = 4 m/s.
The splitting of white light into its seven colours is called
Explanation: A prism splits white light into violet, indigo, blue, green, yellow, orange and red. A rainbow is formed by the same process in water drops.
A lens can focus sunlight on paper to burn it. This lens must be
Explanation: A convex lens is thicker in the middle and converges parallel rays to a point.
The image formed by a plane mirror is
Explanation: A plane mirror image cannot be caught on a screen (virtual). It is upright, the same size as the object, and laterally inverted.
In a forest ecosystem, which of these is a producer?
Explanation: Trees make their own food by photosynthesis, so they are producers. Deer are herbivores, tigers are carnivores and fungi are decomposers.
Which is a correct forest food chain?
Explanation: The arrow points from the organism that is eaten to the one that eats it, starting with a producer.
Fallen leaves and dead animals in a forest are converted into nutrient-rich humus by
Explanation: Decomposers break down dead matter and return the nutrients to the soil.
Large-scale cutting of forests (deforestation) increases which gas in the atmosphere?
Explanation: Fewer trees means less carbon dioxide is absorbed in photosynthesis. Burning or decaying wood also releases CO₂.
Which of the following is NOT a benefit of forests?
Explanation: Tree roots bind the soil and help prevent erosion, so forests reduce erosion rather than increase it.
The uppermost layer of a forest, formed by the crowns of tall trees, is called the
Explanation: The canopy receives most of the sunlight, and shrubs and herbs grow in the shade below it.
Which statement describes the role of forests in the water cycle?
Explanation: Trees take up water through roots and lose it as water vapour through transpiration, adding moisture to the air and helping cloud formation.
Solid sludge settled during sewage treatment is decomposed by anaerobic bacteria. The useful gas produced can be used as
Explanation: The sludge is decomposed in a separate tank without oxygen, producing biogas that can be used for cooking or to generate electricity.
Which is the correct order of steps in a sewage treatment plant?
Explanation: Large objects are removed by bar screens, then sand and grit settle. Solids settle in the tank and the clear water is disinfected with chlorine.
Chlorine is added to treated water mainly to
Explanation: Chlorination disinfects the water before it is released.
In places without a sewerage system, toilet waste is treated in a septic tank. The waste is decomposed there by
Explanation: Anaerobic bacteria in the tank break down the human waste. The liquid soaks into the soil and gases escape through a vent pipe.
Which of these diseases is spread mainly by contaminated water?
Explanation: Cholera, typhoid and hepatitis A spread through contaminated water. Malaria and dengue are spread by mosquitoes.
Cooking oil and grease should not be poured down the drain because they
Explanation: Oil and grease harden in pipes, block the flow and harm the bacteria that clean wastewater. They should be disposed of in the dustbin.
Which household practice helps to reduce water pollution?
Explanation: Chemicals, medicines and paints should never enter water bodies. Kitchen waste can be turned into compost.