CBSE Class 10 Biology Life Processes MCQs Set 13

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

Explanation:
1. Photosynthesis absorbs light energy, so it is endothermic and A is true.
2. Energy is absorbed and stored, not released; R is false.

Teacher's Note:
1. Photosynthesis stores energy; respiration releases it.
2. Endothermic means absorbs energy.

Answer: (d) conversion of pyruvate to lactic acid

Explanation:
1. During strenuous activity the muscles do not get enough oxygen.
2. Pyruvate is then converted to lactic acid, whose build-up causes painful cramps.

Teacher's Note:
1. Ethanol is formed in yeast, lactic acid in muscles.
2. Massage and rest remove the lactic acid.

Answer: (b) starch

Explanation:
1. Plants convert excess glucose into starch for storage.
2. Animals store glycogen.

Teacher's Note:
1. Starch is a plant reserve; glycogen is an animal reserve.
2. Starch is tested with iodine.

Answer: (a) water

Explanation:
1. During the light reaction, light energy splits water molecules into hydrogen and oxygen.
2. The oxygen is released to the atmosphere, so it comes from water.

Teacher's Note:
1. This splitting of water is called photolysis.
2. Carbon dioxide supplies the carbon for glucose.

Answer: (d) all of the above

Explanation:
1. Autotrophs make their own food by photosynthesis.
2. For this they need carbon dioxide and water as raw materials, chlorophyll to trap light, and sunlight as the source of energy, so all the given things are required.

Teacher's Note:
1. Autotrophic nutrition needs four things: CO₂, water, chlorophyll and sunlight.
2. Green plants, algae and some bacteria are autotrophs.

Answer: (d) breakdown of fats

Explanation:
1. Bile salts break large fat globules into very small droplets.
2. This is called emulsification of fats and helps lipase to act.

Teacher's Note:
1. Emulsification applies only to fats.
2. It is done by bile.

Answer: (b) Stomata

Explanation:
1. Oxygen formed in the chloroplasts diffuses out of the leaf.
2. It leaves through the stomatal pores.

Teacher's Note:
1. Stomata: gaseous exchange in leaves.
2. Guard cells only control the opening.

Answer: (c) Nitrogen

Explanation:
1. Proteins are made of amino acids that contain nitrogen.
2. Plants absorb nitrogen as nitrates and nitrites.

Teacher's Note:
1. Nitrogen is the characteristic element of proteins.
2. Carbon dioxide is a compound, not an element.

Answer: (a) Lungs → pulmonary vein → left atrium → left ventricle → aorta → body cells

Explanation:
1. Oxygenated blood leaves the lungs by the pulmonary vein and enters the left atrium.
2. It goes to the left ventricle, which pumps it into the aorta to all body cells.

Teacher's Note:
1. Left side of the heart carries oxygenated blood.
2. Aorta takes blood to the body; vena cava brings it back.

Answer: (d) Bilirubin

Explanation:
1. Lipase digests fats, amylase digests starch and trypsin digests proteins, so all three are enzymes.
2. Bilirubin is a yellow bile pigment formed from the breakdown of haemoglobin, not an enzyme.

Teacher's Note:
1. Names of enzymes usually end in -ase (trypsin and pepsin are older exceptions).
2. Bile contains salts and pigments, but no enzymes.

Answer: (a) A and B

Explanation:
1. Salivary amylase breaks starch into maltose and chewing increases the surface area, so A and B are correct.
2. Saliva does not emulsify fats and teeth only break food into small pieces without making molecules soluble.

Teacher's Note:
1. Mechanical digestion by teeth; chemical digestion by enzymes.
2. Emulsification is done by bile.

Answer: (b) chyme

Explanation:
1. The stomach churns the food with gastric juice into a semi-liquid acidic mixture.
2. This mixture is called chyme.

Teacher's Note:
1. Bolus is the chewed food from the mouth.
2. Chyme goes into the small intestine.

Answer: (c) stomach and pancreas

Explanation:
1. Pepsin is secreted by the gastric glands of the stomach.
2. Trypsin is secreted by the pancreas and acts in the small intestine.

Teacher's Note:
1. Both digest proteins, but in different organs.
2. Pepsin needs acid; trypsin needs an alkaline medium.

Answer: (d) Carbohydrates

Explanation:
1. Saliva contains salivary amylase and pancreatic juice contains pancreatic amylase.
2. Both enzymes digest starch, which is a carbohydrate.

Teacher's Note:
1. Amylase = starch (carbohydrate) digesting enzyme.
2. Minerals do not need digestion.

Answer: (d) Ptyalin

Explanation:
1. Pancreatic juice contains trypsin, amylase and lipase.
2. Ptyalin is the old name of salivary amylase, which is secreted by the salivary glands.

Teacher's Note:
1. Ptyalin = salivary amylase.
2. Pancreatic juice contains pancreatic amylase, not ptyalin.

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

Explanation:
1. Aerobic respiration releases far more energy than anaerobic respiration, so A is true.
2. R reverses the numbers: aerobic respiration gives about 38 ATP and anaerobic gives 2 ATP, so R is false.

Teacher's Note:
1. Aerobic: about 38 ATP; anaerobic: 2 ATP.
2. Check the numbers in reason statements.

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

Explanation:
1. Yeast and some other organisms form ethanol and CO₂ from pyruvate without oxygen, so A is true.
2. The process takes place in the cytoplasm in the absence of oxygen, so R is false.

Teacher's Note:
1. Anaerobic means without oxygen.
2. Mitochondria are needed only for aerobic breakdown of pyruvate.

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

Explanation:
1. In aerobic respiration glucose is oxidised to CO₂ and water, so A is true.
2. Glucose is a carbohydrate, not a protein, so R is false.

Teacher's Note:
1. Glucose: simple carbohydrate.
2. Proteins are made of amino acids.

Answer: (b) alveoli of lungs

Explanation:
1. The alveoli are thin-walled air sacs surrounded by blood capillaries.
2. Oxygen diffuses into the blood and CO₂ diffuses out of the blood in the alveoli only.

Teacher's Note:
1. Trachea, larynx and throat are only air passages.
2. Alveoli give a large surface area for gas exchange.

Answer: (d) thick and dry surface

Explanation:
1. A good respiratory surface is thin, moist, has a large area and is richly supplied with blood vessels.
2. A thick and dry surface hinders diffusion of gases.

Teacher's Note:
1. Gases diffuse across moist, thin surfaces.
2. Alveoli are an example.

Answer: (a) liberation of oxygen

Explanation:
1. Respiration takes in oxygen and gives out CO₂ and energy.
2. Oxygen is liberated in photosynthesis, not in respiration.

Teacher's Note:
1. Respiration: O₂ in, CO₂ and energy out.
2. Photosynthesis liberates O₂.

Answer: (a) Location: aerobic – cytoplasm; anaerobic – mitochondria

Explanation:
1. Complete aerobic breakdown of pyruvate takes place in the mitochondria, while anaerobic respiration takes place in the cytoplasm.
2. So row (a) has the locations interchanged.

Teacher's Note:
1. Anaerobic respiration occurs only in the cytoplasm.
2. Aerobic respiration releases much more ATP.

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

Explanation:
1. Blood pressure is the pressure exerted by the blood on the walls of the arteries, so A is true.
2. It is measured with a sphygmomanometer, so R is true, but the instrument does not explain why BP is arterial pressure.

Teacher's Note:
1. Both statements are facts, but R only tells how it is measured.
2. Normal BP of an adult is about 120/80 mm of Hg.

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

Explanation:
1. Both vessels carry blood to the heart, so they are veins and A is true.
2. The pulmonary vein carries oxygenated blood while the vena cava carries deoxygenated blood, so R is true, but it does not explain why both are veins.

Teacher's Note:
1. Veins carry blood towards the heart.
2. Pulmonary vein is the exception in oxygen content.

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

Explanation:
1. Pulse rate is the number of heart beats per minute and varies with the condition of the heart, so R is true.
2. Hence the doctor can judge the health of the heart from it, and R explains A.

Teacher's Note:
1. Normal heart rate of an adult is about 72 beats per minute.
2. A stethoscope is used to hear the heart sounds.

Answer: (b) capillaries

Explanation:
1. Capillaries are thin-walled, one-cell-thick vessels that link arteries to veins.
2. Exchange of materials between blood and cells takes place through them.

Teacher's Note:
1. Artery, capillary, vein is the path.
2. Sieve tubes belong to plant phloem.

Answer: (b) It helps the plant to maintain temperature on hot sunny days

Explanation:
1. Evaporation of water from the leaves cools the plant, as sweating cools us.
2. Transpiration also creates the pull that moves water upward.

Teacher's Note:
1. Benefits: cooling, upward water movement, mineral transport.
2. Food is moved by the phloem, not by transpiration.

Answer: (c) suffer from water and mineral shortage

Explanation:
1. The xylem carries water and minerals from the roots to the leaves.
2. If it is blocked, both water and minerals fail to reach the shoot.

Teacher's Note:
1. Xylem: water and minerals. Phloem: food.
2. Carbohydrates are made in the leaves and move by phloem.

Answer: (a) A and B

Explanation:
1. Statements A and B are correct: CO₂ enters for photosynthesis and O₂ enters for respiration.
2. Statement C is wrong because in transpiration water vapour is lost through the stomata, not taken in.

Teacher's Note:
1. Transpiration = loss of water vapour.
2. Stomata are the gas gates of leaves.

Answer: (c) Dialysis

Explanation:
1. In dialysis, blood passes through a machine with a semipermeable membrane.
2. Nitrogenous wastes such as urea are filtered out into a dialysing fluid, and the clean blood returns to the patient.

Teacher's Note:
1. The dialysis machine acts as an artificial kidney.
2. It is used in kidney failure.

Answer: (a) To sustain the high-pressure blood from the heart

Explanation:
1. Blood leaves the heart under high pressure.
2. Thick, elastic walls of the arteries withstand this pressure.

Teacher's Note:
1. One-way flow in veins is ensured by valves.
2. Gas exchange occurs through thin capillary walls.

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

Explanation:
1. The kidneys are the main excretory organs, so A is true.
2. They remove excess water and nitrogenous wastes, which is why they are the main organs; R explains A.

Teacher's Note:
1. Excretion = removal of nitrogenous wastes.
2. Kidneys also keep water balance.

Answer: (d) nephron

Explanation:
1. Each kidney contains about a million tiny filtering units called nephrons.
2. The ureter and urethra are tubes, and the neuron is a nerve cell.

Teacher's Note:
1. Nephron = structural and functional unit of the kidney.
2. Neuron is the nerve cell; do not confuse the two.

Answer: (c) Glucose: present; protein: absent; salts: present

Explanation:
1. The glomerular filtrate contains small molecules such as glucose, amino acids, salts and urea.
2. Large protein molecules cannot pass through the filter, so protein is absent.

Teacher's Note:
1. Filtration is size-based.
2. Glucose is later reabsorbed in the tubule.

Answer: (d) Ureter

Explanation:
1. A pair of ureters carries urine from the kidneys to the urinary bladder.
2. The urethra carries urine from the bladder out of the body.

Teacher's Note:
1. Ureter: kidney to bladder. Urethra: bladder to outside.
2. Nephron is the filtering unit.