CBSE Class 10 Biology Life Processes MCQs Set 28

Answer: (d) Ribs are pushed upward and outward

Explanation:
1. During exhalation the ribs move downward and inward.
2. Moving upward and outward happens during inhalation.

Teacher's Note:
1. The diaphragm relaxes and rises to its dome shape.
2. The chest volume decreases and air is pushed out.

Answer: (d) (b) and (d)

Explanation:
1. (a) is wrong: during inhalation the ribs move up and out and the diaphragm flattens.
2. (c) is wrong: haemoglobin has a very high affinity for oxygen.
3. (b) and (d) are correct.

Teacher's Note:
1. Alveoli number in millions and give a huge surface area.
2. Gas exchange is by diffusion along concentration differences.

Answer: (a) Bicarbonates

Explanation:
1. About 70 per cent of CO₂ is carried as bicarbonate in the plasma.
2. About 23 per cent is carried by haemoglobin and a small part is dissolved.

Teacher's Note:
1. CO₂ is more soluble in water than oxygen.
2. The enzyme carbonic anhydrase helps in its conversion.

Answer: (d) Haemoglobin

Explanation:
1. Haemoglobin in the red blood cells combines with oxygen to form oxyhaemoglobin.
2. It carries about 97 per cent of the oxygen.

Teacher's Note:
1. Plasma is the liquid part of blood.
2. Leucocytes and lymphocytes are white blood cells for defence.

Answer: (a) His breathing rate and heartbeat will increase

Explanation:
1. At high altitude the air has less oxygen.
2. The body compensates by breathing faster and pumping blood faster.

Teacher's Note:
1. With time the body also makes more red blood cells.
2. This is called acclimatisation.

Answer: (a) Blood circulation

Explanation:
1. William Harvey (1628) described the circulation of blood in the body.
2. He showed that the heart pumps blood through a closed system of vessels.

Teacher's Note:
1. Harvey is called the father of modern physiology.
2. Blood clotting and respiration were studied by others.

Answer: (b) Leucocytes

Explanation:
1. DNA is present in the nucleus.
2. Mature human red blood cells and platelets have no nucleus, but leucocytes do.

Teacher's Note:
1. Serum is the liquid part of blood after clotting and has no cells.
2. DNA from white blood cells identifies a person.

Answer: (d) Thromboplastin

Explanation:
1. Platelets release thromboplastin when a vessel is injured.
2. It starts the clotting process by converting prothrombin to thrombin.

Teacher's Note:
1. Heparin is an anticlotting substance.
2. Prothrombin and fibrinogen are plasma proteins.

Answer: (d) Internal valves

Explanation:
1. Veins have valves that prevent backflow of blood.
2. Arteries have thicker walls and carry blood away from the heart; they do not have valves.

Teacher's Note:
1. Blood in veins flows at low pressure.
2. Valves are especially useful in the legs.

Answer: (a) Capillary

Explanation:
1. Capillaries are microscopic vessels with walls one cell thick.
2. Exchange of materials between blood and tissues occurs through them.

Teacher's Note:
1. Arteries divide into arterioles and then capillaries.
2. Capillaries join to form venules and then veins.

Answer: (d) They have thick elastic walls without valves, blood flows under high pressure, and they carry blood away from the heart to different parts of the body

Explanation:
1. Arteries carry blood away from the heart under high pressure.
2. They have thick elastic walls and no valves.

Teacher's Note:
1. The first option describes veins in part but with wrong features.
2. Elastic walls withstand the pressure from each heartbeat.

Answer: (c) Smooth muscle not under voluntary control

Explanation:
1. Artery walls have smooth (involuntary) muscle.
2. We cannot control it consciously.

Teacher's Note:
1. Cardiac muscle is striated and involuntary.
2. Skeletal muscle is striated and voluntary.

Answer: (d) Mammals

Explanation:
1. Mammals and birds have two atria and two ventricles.
2. Fishes have two chambers, amphibians three and most reptiles three.

Teacher's Note:
1. The four chambers keep oxygenated and deoxygenated blood completely separate.
2. This supports the high energy needs of warm-blooded animals.

Answer: (d) Superior and inferior vena cava

Explanation:
1. The venae cavae bring deoxygenated blood from the body to the right atrium.
2. The pulmonary veins go to the left atrium.

Teacher's Note:
1. The aorta carries blood out from the left ventricle.
2. The pulmonary artery carries blood out from the right ventricle.

Answer: (a) Right atrium and right ventricle

Explanation:
1. The tricuspid valve has three flaps and guards the opening between the right atrium and right ventricle.
2. It prevents backflow of blood into the right atrium.

Teacher's Note:
1. The left side has the bicuspid valve.
2. Both are called atrioventricular valves.

Answer: (c) Pericardium

Explanation:
1. The heart lies in a double-layered sac called the pericardium.
2. The fluid inside protects it from shock.

Teacher's Note:
1. Peritoneum lines the abdomen and pleura covers the lungs.

Answer: (b) SA node

Explanation:
1. The sino-atrial (SA) node is a patch of special muscle tissue that starts each heartbeat.
2. It sets the rate of the heart.

Teacher's Note:
1. The AV node passes the impulse on to the ventricles.
2. An artificial pacemaker is used if the SA node fails.

Answer: (c) Initiate the heartbeat

Explanation:
1. The pacemaker generates the electrical impulse that begins each heartbeat.
2. It does not control the supply of blood to the heart itself.

Teacher's Note:
1. The heartbeat is myogenic, i.e. it begins in the heart muscle.
2. Nerves and hormones only change the rate.

Answer: (a) In the wall of the right atrium

Explanation:
1. The SA node lies in the wall of the right atrium near the opening of the superior vena cava.
2. It is therefore called the pacemaker of the heart.

Teacher's Note:
1. The AV node is on the septum between the atria and ventricles.
2. The right atrium receives blood from the body.

Answer: (c) Exit of blood from the ventricles

Explanation:
1. Systole is contraction of the heart chambers.
2. Ventricular systole pushes blood out of the ventricles into the arteries.

Teacher's Note:
1. Diastole is relaxation, when the heart fills with blood.
2. One cardiac cycle has both systole and diastole.

Answer: (a) Oxygen

Explanation:
1. In the lungs, oxygen diffuses into the blood and CO₂ diffuses out.
2. The blood leaving the lungs is therefore richer in oxygen.

Teacher's Note:
1. The blood entering the lungs is rich in CO₂.
2. The exchange is in the alveoli.

Answer: (c) Venous blood

Explanation:
1. The fish heart receives deoxygenated (venous) blood from the body.
2. It pumps it to the gills for oxygenation, so only venous blood passes through it.

Teacher's Note:
1. Oxygenated blood goes from the gills directly to the body.
2. Such a heart is called a venous heart.

Answer: (b) semilunar; open

Explanation:
1. When the ventricles contract, the AV valves close to stop backflow into the atria.
2. The semilunar valves open to let blood into the aorta and pulmonary artery.

Teacher's Note:
1. The 'lub' sound is closing of the AV valves.
2. The 'dub' sound is closing of the semilunar valves.