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A Level Biology: Transport in mammals MCQs — Biology

31 multiple-choice questions on A Level Biology: Transport in mammals from Biology, each with the correct answer and, where available, a teacher's explanation. Read through them to revise the chapter, then practise the same questions one by one to test yourself.

1. Elastic arteries such as the aorta have many elastic fibres so that they

  1. exchange substances
  2. stretch and recoil to smooth out pressure surges
  3. can constrict to control flow
  4. have valves

Answer: B) stretch and recoil to smooth out pressure surges

Explanation: Elastic recoil maintains pressure. AS & A Level Biology · Topic 8 Transport in Mammals · 8.1 The circulatory system

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2. The Bohr shift is important because

  1. haemoglobin binds CO₂ better
  2. less oxygen reaches muscles
  3. more oxygen is released in actively respiring tissues
  4. blood pH increases

Answer: C) more oxygen is released in actively respiring tissues

Explanation: More O₂ is unloaded where CO₂ is high. AS & A Level Biology · Topic 8 Transport in Mammals · 8.2 Transport of oxygen and carbon dioxide

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3. A band of non-conducting tissue between the atria and ventricles

  1. closes the valves
  2. speeds up conduction
  3. acts as the pacemaker
  4. prevents the excitation wave passing directly to the ventricles

Answer: D) prevents the excitation wave passing directly to the ventricles

Explanation: It forces the signal through the AVN. AS & A Level Biology · Topic 8 Transport in Mammals · 8.3 The heart

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4. The Bohr shift describes how

  1. temperature has no effect
  2. high CO₂ concentration lowers haemoglobin's affinity for oxygen
  3. low CO₂ lowers affinity
  4. chloride ions raise affinity

Answer: B) high CO₂ concentration lowers haemoglobin's affinity for oxygen

Explanation: Curve shifts right with more CO₂. AS & A Level Biology · Topic 8 Transport in Mammals · 8.2 Transport of oxygen and carbon dioxide

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5. The atrioventricular node delays the impulse so that

  1. the SAN can recover
  2. the atria finish contracting before the ventricles contract
  3. blood flows back into the atria
  4. the ventricles contract first

Answer: B) the atria finish contracting before the ventricles contract

Explanation: The delay lets ventricles fill. AS & A Level Biology · Topic 8 Transport in Mammals · 8.3 The heart

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6. Most carbon dioxide is transported in the blood as

  1. hydrogencarbonate ions in plasma
  2. carbaminohaemoglobin
  3. oxyhaemoglobin
  4. dissolved CO₂

Answer: A) hydrogencarbonate ions in plasma

Explanation: About 85% as HCO₃⁻. AS & A Level Biology · Topic 8 Transport in Mammals · 8.2 Transport of oxygen and carbon dioxide

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7. Veins have valves to

  1. exchange gases
  2. prevent backflow of low-pressure blood
  3. increase pressure
  4. filter plasma

Answer: B) prevent backflow of low-pressure blood

Explanation: Valves stop backflow. AS & A Level Biology · Topic 8 Transport in Mammals · 8.1 The circulatory system

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8. Water's high specific heat capacity allows blood to

  1. dissolve oxygen better
  2. carry proteins
  3. clot
  4. transport heat while resisting temperature change

Answer: D) transport heat while resisting temperature change

Explanation: Blood distributes heat. AS & A Level Biology · Topic 8 Transport in Mammals · 8.1 The circulatory system

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9. The tendinous cords (chordae tendineae)

  1. supply the heart with blood
  2. separate the two sides
  3. prevent AV valves turning inside out
  4. conduct impulses

Answer: C) prevent AV valves turning inside out

Explanation: They anchor the valve flaps. AS & A Level Biology · Topic 8 Transport in Mammals · 8.3 The heart

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10. The chloride shift is

  1. movement of Cl⁻ out of red cells
  2. binding of Cl⁻ to haemoglobin
  3. movement of Cl⁻ into red cells as HCO₃⁻ moves out, maintaining charge balance
  4. movement of O₂ into plasma

Answer: C) movement of Cl⁻ into red cells as HCO₃⁻ moves out, maintaining charge balance

Explanation: Electrical neutrality is maintained. AS & A Level Biology · Topic 8 Transport in Mammals · 8.2 Transport of oxygen and carbon dioxide

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11. The oxygen dissociation curve of haemoglobin is S-shaped because

  1. binding of the first O₂ makes it easier for further O₂ to bind
  2. haemoglobin has only one binding site
  3. oxygen dissolves in plasma
  4. CO₂ competes for haem

Answer: A) binding of the first O₂ makes it easier for further O₂ to bind

Explanation: Cooperative binding. AS & A Level Biology · Topic 8 Transport in Mammals · 8.2 Transport of oxygen and carbon dioxide

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12. Heart valves open and close because of

  1. hormones
  2. differences in blood pressure on either side
  3. muscles attached to valves
  4. nerve impulses

Answer: B) differences in blood pressure on either side

Explanation: Valves respond passively to pressure. AS & A Level Biology · Topic 8 Transport in Mammals · 8.3 The heart

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13. Carbonic anhydrase catalyses the reaction between

  1. hydrogen ions and chloride
  2. oxygen and haemoglobin
  3. carbon dioxide and water
  4. glucose and oxygen

Answer: C) carbon dioxide and water

Explanation: It forms carbonic acid. AS & A Level Biology · Topic 8 Transport in Mammals · 8.2 Transport of oxygen and carbon dioxide

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14. Which blood vessel carries oxygenated blood from the left ventricle?

  1. Aorta
  2. Pulmonary artery
  3. Pulmonary vein
  4. Vena cava

Answer: A) Aorta

Explanation: The aorta supplies the body. AS & A Level Biology · Topic 8 Transport in Mammals · 8.1 The circulatory system

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15. The semilunar valves close when

  1. pressure in the arteries exceeds pressure in the ventricles
  2. the AVN fires
  3. atrial pressure rises
  4. ventricles contract

Answer: A) pressure in the arteries exceeds pressure in the ventricles

Explanation: Backflow is prevented in diastole. AS & A Level Biology · Topic 8 Transport in Mammals · 8.3 The heart

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16. Which structure acts as the pacemaker of the heart?

  1. Atrioventricular node
  2. Purkyne tissue
  3. Sinoatrial node
  4. Bundle of His

Answer: C) Sinoatrial node

Explanation: The SAN initiates each heartbeat. AS & A Level Biology · Topic 8 Transport in Mammals · 8.3 The heart

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17. Purkyne tissue conducts excitation

  1. from the ventricles to the SAN
  2. to the coronary arteries
  3. to the apex of the ventricles so they contract from the bottom upwards
  4. across the atria

Answer: C) to the apex of the ventricles so they contract from the bottom upwards

Explanation: Ventricles contract upwards, pushing blood out. AS & A Level Biology · Topic 8 Transport in Mammals · 8.3 The heart

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18. Haemoglobinic acid is formed when

  1. haemoglobin combines with oxygen
  2. CO₂ binds to iron
  3. chloride binds haemoglobin
  4. haemoglobin combines with hydrogen ions

Answer: D) haemoglobin combines with hydrogen ions

Explanation: HHb forms as H⁺ binds Hb. AS & A Level Biology · Topic 8 Transport in Mammals · 8.2 Transport of oxygen and carbon dioxide

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19. The left ventricle wall is thicker than the right because it

  1. receives blood from the lungs
  2. has to pump blood to the lungs
  3. has more valves
  4. pumps blood around the whole body at high pressure

Answer: D) pumps blood around the whole body at high pressure

Explanation: Systemic circulation needs high pressure. AS & A Level Biology · Topic 8 Transport in Mammals · 8.3 The heart

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20. Why does water return to the capillary at the venous end?

  1. lymph pushes it in
  2. red cells pump water in
  3. Plasma proteins lower the water potential of the blood
  4. hydrostatic pressure is very high

Answer: C) Plasma proteins lower the water potential of the blood

Explanation: Osmosis back into the capillary. AS & A Level Biology · Topic 8 Transport in Mammals · 8.1 The circulatory system

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21. Muscular arteries control the flow of blood to organs by

  1. using valves
  2. contracting or relaxing the smooth muscle in their walls
  3. stretching
  4. filtering plasma

Answer: B) contracting or relaxing the smooth muscle in their walls

Explanation: Vasoconstriction and vasodilation. AS & A Level Biology · Topic 8 Transport in Mammals · 8.1 The circulatory system

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22. Tissue fluid forms at the arterial end of a capillary because

  1. hydrostatic pressure forces fluid out
  2. veins pull fluid out
  3. water potential is high in the blood
  4. plasma proteins leave the blood

Answer: A) hydrostatic pressure forces fluid out

Explanation: Pressure filters plasma. AS & A Level Biology · Topic 8 Transport in Mammals · 8.1 The circulatory system

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23. At the pO₂ in the lungs, haemoglobin is

  1. about 50% saturated
  2. saturated with CO₂
  3. nearly fully saturated
  4. unable to bind oxygen

Answer: C) nearly fully saturated

Explanation: High pO₂ gives about 97% saturation. AS & A Level Biology · Topic 8 Transport in Mammals · 8.2 Transport of oxygen and carbon dioxide

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24. Capillaries are adapted for exchange because their walls are

  1. elastic
  2. one cell thick (endothelium only)
  3. thick and muscular
  4. lined with valves

Answer: B) one cell thick (endothelium only)

Explanation: Short diffusion distance. AS & A Level Biology · Topic 8 Transport in Mammals · 8.1 The circulatory system

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25. Which cell develops into a macrophage?

  1. Neutrophil
  2. Lymphocyte
  3. Monocyte
  4. Erythrocyte

Answer: C) Monocyte

Explanation: Monocytes become macrophages in tissues. AS & A Level Biology · Topic 8 Transport in Mammals · 8.1 The circulatory system

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