CBSE Class 10 Biology Life Processes MCQs Set 12

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

Explanation:
1. Oil blocks the stomata, so CO₂ cannot enter the leaf.
2. Less CO₂ lowers the rate of photosynthesis, so R explains A.

Teacher's Note:
1. Stomata are the gates for CO₂ entry.
2. Blocking them affects both photosynthesis and transpiration.

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

Explanation:
1. Our body takes in food and oxygen and gives out waste and heat, so it exchanges both matter and energy; A is true.
2. A closed system does not exchange matter, so R is false: the body is an open system.

Teacher's Note:
1. Open system exchanges matter and energy.
2. Closed system exchanges energy only.

Answer: (b) Parasitic nutrition

Explanation:
1. A parasite lives on or inside a living host and takes food from it without killing it.
2. Saprotrophs feed on dead matter.

Teacher's Note:
1. Parasites: Cuscuta, tapeworm, lice, Plasmodium.
2. Saprotrophs: fungi on dead matter.

Answer: (c) haemoglobin

Explanation:
1. Haemoglobin in the red blood cells combines with oxygen in the lungs to form oxyhaemoglobin.
2. It releases oxygen to the tissues.

Teacher's Note:
1. Haemoglobin = oxygen carrier.
2. Urea is a waste product.

Answer: (c) diffusion

Explanation:
1. In unicellular organisms the whole cell surface is in contact with the surroundings.
2. Materials simply diffuse in and out, so no transport organs are needed.

Teacher's Note:
1. Diffusion is enough for small single cells.
2. Multicellular organisms need transport systems.

Answer: (d) a fungi, Rhizopus

Explanation:
1. Fungi such as Rhizopus (bread mould) secrete digestive enzymes on the food outside their body.
2. They then absorb the digested food; this is saprophytic nutrition.

Teacher's Note:
1. Saprophytes digest food outside the body; parasites feed on a living host.
2. Cuscuta and tapeworm are parasites; Rhizobium fixes nitrogen.

Answer: (c) Intestinal juice

Explanation:
1. Intestinal juice contains enzymes that complete the digestion of all three food types in the small intestine.
2. Carbohydrates become glucose, proteins amino acids, and fats fatty acids and glycerol.

Teacher's Note:
1. Gastric juice acts only on proteins.
2. Bile salts emulsify fats but have no enzyme.

Answer: (b) Yeast, mushroom, bread mould

Explanation:
1. Yeast, mushroom and bread mould are fungi with saprophytic nutrition.
2. They pour out enzymes on the dead organic matter, digest it outside the body and then absorb the digested food.

Teacher's Note:
1. Saprophytes digest food outside the body.
2. Green plants are autotrophs; amoeba and paramecium digest food inside the cell.

Answer: (d) Photosynthesis

Explanation:
1. Photosynthesis builds glucose, a complex molecule, from simple CO₂ and water, so it is anabolic.
2. Digestion and respiration break complex molecules down (catabolism), and transpiration is loss of water vapour.

Teacher's Note:
1. Anabolism = building up; catabolism = breaking down.
2. Photosynthesis is the main anabolic life process in plants.

Answer: (c) oxygen

Explanation:
1. In photosynthesis the oxygen released comes from the splitting of water.
2. So the oxygen gas molecules given out will carry the radioactive isotope.

Teacher's Note:
1. Oxygen released in photosynthesis comes from water, not CO₂.
2. Isotopes are used as tracers.

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

Explanation:
1. The small intestine has numerous villi, so A is false.
2. Villi increase the surface area for absorption, so R is true.

Teacher's Note:
1. Villi are the fingerlike projections lined with blood vessels.
2. They are largest in number in the small intestine.

Answer: (c) it increases surface area for absorption of food

Explanation:
1. The long, coiled small intestine with its villi provides a very large surface area.
2. This helps in complete absorption of the digested food.

Teacher's Note:
1. Length plus villi give more absorption area.
2. The intestine does not store food.

Answer: (b) Stomach and small intestine

Explanation:
1. Pepsin begins protein digestion in the stomach.
2. Trypsin and other enzymes of the pancreatic and intestinal juices complete it in the small intestine.

Teacher's Note:
1. Protein digestion: stomach plus small intestine.
2. The mouth has no protein-digesting enzyme.

Answer: (b) Mucus

Explanation:
1. The gastric glands secrete mucus along with HCl and pepsin.
2. Mucus coats the inner wall of the stomach and protects it from the acid.

Teacher's Note:
1. Without mucus, the acid would corrode the stomach lining and cause ulcers.
2. Pepsin is an enzyme, not a protective layer.

Answer: (b) digest cellulose present in the food

Explanation:
1. A cow is a herbivore and eats grass, which is rich in cellulose.
2. Its large, special stomach and long small intestine allow cellulose to be digested, which a lion does not need.

Teacher's Note:
1. Herbivores have a longer small intestine because cellulose takes longer to digest.
2. Carnivores have a shorter one because meat is easy to digest.

Answer: (d) proteins, fats and carbohydrates

Explanation:
1. Pancreatic juice contains trypsin for proteins, lipase for fats and amylase for carbohydrates.
2. So it helps in the digestion of all three.

Teacher's Note:
1. The pancreas is the most important digestive gland.
2. Pancreatic juice enters the small intestine.

Answer: (d) Trypsin digests proteins and lipase digests emulsified fats droplets

Explanation:
1. Trypsin is a protein-digesting enzyme, and lipase breaks down emulsified fat droplets.
2. Bile first emulsifies the fats and then lipase acts on them.

Teacher's Note:
1. Trypsin = proteins; lipase = fats; amylase = starch.
2. Emulsification by bile gives lipase a large surface to act on.

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

Explanation:
1. Most animals respire aerobically, but their muscles sometimes get too little oxygen and then produce lactic acid anaerobically.
2. So R explains why aerobic animals are not entirely aerobic.

Teacher's Note:
1. Muscle cells switch to anaerobic respiration in vigorous exercise.
2. Lactic acid causes cramps.

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

Explanation:
1. In large organisms most cells are not in contact with the surroundings, so diffusion alone is insufficient and special organs are needed; A is true.
2. The greater oxygen requirement is the reason, so R explains A.

Teacher's Note:
1. Large body size means large oxygen need.
2. Lungs, gills and trachea are the respiratory organs.

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

Explanation:
1. Plants have low energy needs, so they need little gaseous exchange.
2. Diffusion through stomata and lenticels is enough, so R explains A.

Teacher's Note:
1. Stomata in leaves and lenticels in stems are enough for exchange.
2. Animals need respiratory organs because of higher demands.

Answer: (c) alcohol, CO₂ and 2 ATP

Explanation:
1. In the absence of oxygen yeast converts glucose into ethanol (alcohol) and CO₂.
2. Only 2 ATP are produced, much less than the 36 to 38 ATP in aerobic respiration.

Teacher's Note:
1. Anaerobic respiration is less efficient.
2. Lactic acid forms in muscles, not yeast.

Answer: (c) carbon dioxide

Explanation:
1. Exhaled air contains carbon dioxide.
2. CO₂ reacts with lime water, calcium hydroxide, forming insoluble calcium carbonate that makes it milky.

Teacher's Note:
1. Lime water turning milky is the test for CO₂.
2. Ca(OH)₂ + CO₂ → CaCO₃ + H₂O.

Answer: (a) cytoplasm

Explanation:
1. Without oxygen, pyruvate cannot enter the mitochondria for complete breakdown.
2. It is converted to lactic acid in the cytoplasm of the muscle cell, which causes cramps.

Teacher's Note:
1. Glycolysis and anaerobic conversion both occur in the cytoplasm.
2. Muscle cramps after heavy exercise are due to lactic acid.

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

Explanation:
1. Haemoglobin is the respiratory pigment of human blood, so A is true.
2. It combines with oxygen and carries it to tissues; this role makes it a respiratory pigment, so R explains A.

Teacher's Note:
1. Respiratory pigment = oxygen carrier.
2. It is present in RBCs.

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

Explanation:
1. The normal value is 120 mm of Hg systolic and 80 mm of Hg diastolic, so A is true.
2. A sphygmomanometer does measure blood pressure, so R is true, but the instrument does not explain the normal value.

Teacher's Note:
1. Both statements are separate facts.
2. Systolic pressure is higher than diastolic pressure.

Answer: (d) Food is transported from a region where it is produced to other parts of the plants

Explanation:
1. In phloem, food made in the leaves (source) is moved to the parts that need it (sinks), such as roots, fruits and growing tips.
2. Movement can therefore be in both upward and downward directions.

Teacher's Note:
1. Phloem transport is multi-directional.
2. Xylem transport is only upward.

Answer: (a) Xylem

Explanation:
1. Xylem consists of vessels and tracheids that carry water and minerals upward from the roots.
2. Phloem carries food.

Teacher's Note:
1. Xylem: water and minerals. Phloem: food.
2. Both tissues together form the vascular bundle.

Answer: (a) xylem

Explanation:
1. Xylem is the vascular tissue that carries water and dissolved minerals from the roots upward.
2. Phloem carries food, and stomata are pores in the leaf.

Teacher's Note:
1. Xylem for water, phloem for food.
2. Chloroplast is a cell organelle, not a tissue.

Answer: (c) Lymph

Explanation:
1. Lymph is a colourless fluid that flows in lymph vessels.
2. It carries digested fat and drains excess fluid from the tissue spaces back to the blood.

Teacher's Note:
1. Lymph is a second transport fluid.
2. Plasma is a part of blood, not a separate fluid.

Answer: (c) Shedding of yellow leaves

Explanation:
1. Plants store solid wastes in the old leaves, bark and fruits.
2. They are removed when the old leaves are shed.

Teacher's Note:
1. Other plant wastes: gums, resins, latex in old xylem.
2. Gases leave through stomata.

Answer: (a) 120/80 mm of Hg

Explanation:
1. The normal blood pressure of a healthy adult is about 120 mm of Hg (systolic) over 80 mm of Hg (diastolic).
2. The other values are higher or lower than this normal value.

Teacher's Note:
1. Systolic is the pressure when the ventricles contract; diastolic when they relax.
2. 120/80 is the standard normal value.

Answer: (c) (II) and (III)

Explanation:
1. (I) is false: the left atrium receives oxygenated blood from the lungs through the pulmonary vein.
2. (II) is true and (III) is true.
3. (IV) is false: the aorta arises from the left ventricle, not from the left atrium.

Teacher's Note:
1. Right side handles deoxygenated blood, left side handles oxygenated blood.
2. Aorta starts from the left ventricle.

Answer: (b) (ii) and (iii)

Explanation:
1. Plants absorb nitrogen from the soil as inorganic nitrates and nitrites, and organic urea can also be taken up.
2. They cannot use atmospheric nitrogen directly, and proteins are too large to be absorbed.

Teacher's Note:
1. Nitrogen is needed for proteins.
2. Rhizobium fixes atmospheric nitrogen for pulses.

Answer: (c) 180 L daily

Explanation:
1. About 180 litres of filtrate are formed daily in the kidneys by filtration of blood.
2. Most of it is reabsorbed and only about 1–2 litres leave the body as urine.

Teacher's Note:
1. 180 L filtered daily; only 1–2 L passes out as urine.
2. Selective reabsorption returns the rest to the blood.

Answer: (a) exosmosis

Explanation:
1. Urea at a high concentration makes the soil solution more concentrated than the cell sap.
2. Water then moves out of the root cells by exosmosis, and the plant wilts and dies.

Teacher's Note:
1. Water moves towards the more concentrated side.
2. Excess fertiliser can harm plants.