CBSE Class 10 Biology Life Processes MCQs Set 14

Answer: (c) A is true, but R is false.

Explanation:
1. Autotrophs get carbon (as CO₂) and energy (light) through photosynthesis, so A is true.
2. They do prepare their own food, so R is false.

Teacher's Note:
1. Autotroph = self-feeder.
2. Heterotrophs depend on others for food.

Answer: (b) conduction of air

Explanation:
1. The bronchi are tubes that carry air from the trachea into the lungs.
2. Gas exchange occurs only in the alveoli.

Teacher's Note:
1. Bronchi conduct air; alveoli exchange gases.
2. Oxygenation takes place in the alveolar capillaries.

Answer: (c) Light energy is converted into chemical energy

Explanation:
1. In photosynthesis chlorophyll absorbs light energy.
2. This is stored as chemical energy in the glucose molecules.

Teacher's Note:
1. Photosynthesis: light energy to chemical energy.
2. Respiration releases this chemical energy again.

Answer: (b) They avoid collapse of air passage

Explanation:
1. The rings of cartilage in the trachea are stiff and keep the windpipe open.
2. Thus the air passage does not collapse when air pressure drops inside.

Teacher's Note:
1. Cartilage rings keep the trachea open.
2. The epiglottis stops food from entering the trachea.

Answer: (d) light is necessary for photosynthesis

Explanation:
1. The black paper stops light from reaching the covered part of the leaf, while air (CO₂) and chlorophyll are still available.
2. If the covered part gives no starch test but the uncovered part does, it shows that light is necessary for photosynthesis.

Teacher's Note:
1. In such experiments only one factor is changed at a time; here it is light.
2. Starch is tested with iodine solution.

Answer: (c) They convert carbon dioxide and water into carbohydrates in the absence of sunlight

Explanation:
1. Autotrophs need sunlight and chlorophyll to make carbohydrates from CO₂ and water.
2. Statement (c) says this takes place in the absence of sunlight, which is wrong.

Teacher's Note:
1. Photosynthesis requires light.
2. Autotrophs are producers.

Answer: (c) production of carbon dioxide

Explanation:
1. Yeast in the dough ferments sugar anaerobically.
2. The CO₂ released forms bubbles, which make the dough rise.

Teacher's Note:
1. Yeast fermentation gives ethanol + CO₂.
2. The alcohol evaporates on baking.

Answer: (d) lactic acid

Explanation:
1. During vigorous running the muscles respire anaerobically.
2. Pyruvate is converted into lactic acid, whose accumulation causes cramps.

Teacher's Note:
1. Lactic acid is the byproduct of anaerobic respiration in muscles.
2. Rest allows oxygen to break it down.

Answer: (b) respiration

Explanation:
1. Respiration is the oxidation of food, mainly glucose, inside the cells to release energy.
2. Digestion occurs in the alimentary canal, outside the cells.

Teacher's Note:
1. Respiration is a cellular process.
2. Energy is stored as ATP.

Answer: (b) transpiration

Explanation:
1. Plants lose excess water as vapour through stomata by transpiration.
2. Perspiration (sweating) is shown by animals.

Teacher's Note:
1. Plants transpire; animals perspire.
2. Transpiration also cools the plant.

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. Mucus protects the stomach lining from the acid, so without it the lining may be damaged; A is true.
2. HCl is secreted by the gastric glands, so R is true, but R does not tell how mucus protects the lining.

Teacher's Note:
1. Mucus coats the stomach wall.
2. The reason given is only a related fact.

Answer: (c) A is true, but R is false.

Explanation:
1. Cellulose is digested slowly, so herbivores need a long small intestine, and A is true.
2. Food rich in cellulose is difficult to digest, so R is false.

Teacher's Note:
1. Herbivore: long small intestine; carnivore: short small intestine.
2. Cellulose digestion needs more time.

Answer: (c) A is true, but R is false.

Explanation:
1. The liver is the largest gland in the body and secretes bile, so A is true.
2. Salivary amylase is secreted by the salivary glands, not the liver, so R is false.

Teacher's Note:
1. Liver: bile; salivary glands: salivary amylase.
2. Bile has no enzymes.

Answer: (c) Secreted by liver and stored in gall bladder

Explanation:
1. Bile is secreted by the liver cells.
2. It is stored in the gall bladder and released into the small intestine when fatty food arrives.

Teacher's Note:
1. Liver makes bile; gall bladder only stores it.
2. The bile duct is just the tube that carries it.

Answer: (b) Test tube X: no change in colour; test tube Y: turns blue-black

Explanation:
1. Saliva contains salivary amylase, which breaks down starch in test tube X, so no starch is left to give a colour with iodine.
2. Test tube Y has no saliva, so its starch remains and turns blue-black with iodine.

Teacher's Note:
1. Iodine gives a blue-black colour only with starch.
2. This activity shows that saliva digests starch.

Answer: (b) Small intestine

Explanation:
1. The small intestine has millions of villi that give a very large surface area.
2. Digested food is absorbed here into the blood.

Teacher's Note:
1. Small intestine: digestion and absorption of food.
2. Large intestine: absorption of water.

Answer: (c) Mouth

Explanation:
1. In the mouth, food is chewed and mixed with saliva.
2. Salivary amylase in the saliva begins the digestion of starch, so digestion starts in the mouth.

Teacher's Note:
1. Digestion of starch starts in the mouth, of proteins in the stomach, and is completed in the small intestine.
2. Do not confuse digestion with absorption.

Answer: (c) Stomach

Explanation:
1. Pepsin, secreted in the gastric juice, breaks proteins into smaller peptides in the acidic medium of the stomach.
2. No protein-digesting enzyme acts in the mouth or oesophagus.

Teacher's Note:
1. Protein digestion begins in the stomach and ends in the small intestine.
2. Starch digestion begins in the mouth.

Answer: (d) Stomata

Explanation:
1. Stomata are tiny pores on the surface of leaves.
2. Gases for respiration and photosynthesis diffuse in and out through them.

Teacher's Note:
1. Stomata are in leaves; lenticels are in woody stems.
2. Guard cells control the stomatal opening.

Answer: (c) is anaerobic and produces carbon dioxide

Explanation:
1. Yeast respires without oxygen and forms ethanol and CO₂.
2. It does not form lactic acid and does not depend on darkness.

Teacher's Note:
1. Yeast fermentation: ethanol + CO₂.
2. Lactic acid is formed in muscles.

Answer: (c) Ethanol + Carbon dioxide + Energy

Explanation:
1. In plants and yeast, anaerobic respiration converts pyruvate to ethanol and carbon dioxide with release of energy.
2. Lactic acid is produced in animal muscles.

Teacher's Note:
1. Plants/yeast: ethanol + CO₂. Animal muscle: lactic acid.
2. Complete oxidation gives CO₂ + water.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. Birds and mammals are warm-blooded and keep their body temperature constant, which needs a lot of energy.
2. Separating oxygenated and deoxygenated blood gives an efficient supply of oxygen for this high energy need, so R explains A.

Teacher's Note:
1. Four-chambered heart keeps the two kinds of blood apart.
2. More oxygen supply means more respiration and more energy.

Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Explanation:
1. The septum separates the left and right sides, so the two types of blood do not mix; A is true.
2. Valves do allow one-way flow, so R is true, but they do not prevent mixing.

Teacher's Note:
1. Septum prevents mixing; valves prevent backflow.
2. Two different functions.

Answer: (c) A is true, but R is false.

Explanation:
1. Arteries carry oxygenated blood except the pulmonary artery, so A is true.
2. The pulmonary vein carries oxygenated blood from the lungs, so R is false.

Teacher's Note:
1. Pulmonary vein: oxygenated blood to heart.
2. Pulmonary artery: deoxygenated blood to lungs.

Answer: (a) towards the lungs

Explanation:
1. The right ventricle pumps deoxygenated blood through the pulmonary artery to the lungs.
2. There it takes up oxygen.

Teacher's Note:
1. Right ventricle sends blood to the lungs.
2. Left ventricle sends blood to the body.

Answer: (d) increased blood oxygen-carrying efficiency

Explanation:
1. A four-chambered heart keeps oxygenated and deoxygenated blood completely separate.
2. The body therefore receives blood rich in oxygen, so oxygen supply is more efficient.

Teacher's Note:
1. Four chambers: separate blood streams.
2. It suits warm-blooded animals.

Answer: (b) pure blood always

Explanation:
1. The pulmonary veins bring oxygenated (pure) blood from the lungs to the left atrium.
2. This is always the case.

Teacher's Note:
1. Pulmonary vein: oxygenated. Pulmonary artery: deoxygenated.
2. Pure blood means oxygenated blood.

Answer: (c) Ventricles

Explanation:
1. The ventricles pump blood out of the heart to the lungs and to the whole body.
2. They need stronger muscles, so their walls are thicker than the walls of the atria, which only receive blood.

Teacher's Note:
1. Thick wall = more pumping work.
2. The left ventricle has the thickest wall.

Answer: (a) artery

Explanation:
1. Arteries carry blood away from the heart to the various organs of the body.
2. Veins bring blood back, and capillaries link the two.

Teacher's Note:
1. Artery = away from the heart.
2. Remember: A for artery and away.

Answer: (b) erythrocytes

Explanation:
1. Erythrocytes (red blood cells) contain haemoglobin, which carries oxygen.
2. Most of the oxygen is carried by haemoglobin rather than plasma.

Teacher's Note:
1. Erythrocytes = RBCs.
2. Leucocytes = WBCs; thrombocytes = platelets.

Answer: (d) Difference in the ion concentration creates a gradient for water movement

Explanation:
1. Root cells actively take up ions from the soil.
2. The resulting difference in ion concentration creates a water gradient, so water moves into the root by osmosis.

Teacher's Note:
1. Active ion uptake comes first, water follows by osmosis.
2. This builds the root pressure.

Answer: (b) blood pressure

Explanation:
1. The pressure exerted by blood on the walls of the blood vessels is called blood pressure.
2. It is measured in mm of Hg with a sphygmomanometer.

Teacher's Note:
1. Normal BP is 120/80 mm of Hg.
2. It is higher in arteries than in veins.

Answer: (a) Both A and R are true, and R is the correct explanation of A.

Explanation:
1. These processes together keep the body alive and maintained, so A is true.
2. R is true and gives the reason for A, since life would stop without them.

Teacher's Note:
1. Life processes keep the body going.
2. They need a continuous supply of energy.

Answer: (a) Tubule

Explanation:
1. Blood is filtered in the glomerulus and Bowman's capsule.
2. In the tubular part, useful substances are selectively reabsorbed by the surrounding blood capillaries.

Teacher's Note:
1. Filtration: glomerulus. Reabsorption: tubule.
2. Ureter is outside the nephron.

Answer: (c) excretion

Explanation:
1. The kidneys filter the blood and form urine, removing nitrogenous wastes such as urea.
2. Therefore they belong to the excretory system.

Teacher's Note:
1. Kidney, ureter, bladder and urethra form the excretory system.
2. Each kidney has about a million nephrons.