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Biology 20

Biology 20 · Worksheets

Circulation and gas exchange

Ten questions of mixed difficulty, covering Circulation. Print it, or work through it on screen — the answer key starts on its own page.

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Circulation and gas exchange

Biology 20 · maddyhelps.com

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  1. In the pulmonary circuit, blood travels

    1. a) from the right ventricle to the lungs and back to the left atrium
    2. b) from the lungs to the body and back
    3. c) from the right atrium to the lungs and back to the right ventricle
    4. d) from the left ventricle to the body and back to the right atrium

  2. Arteries are defined as vessels that

    1. a) carry oxygenated blood
    2. b) exchange gases with tissues
    3. c) carry blood away from the heart
    4. d) carry blood towards the heart

  3. Gas exchange in the alveoli happens by

    1. a) active transport using ATP
    2. b) osmosis
    3. c) diffusion down partial pressure gradients
    4. d) bulk flow through valves

  4. The chamber with the thickest muscular wall is the

    1. a) left ventricle
    2. b) right ventricle
    3. c) left atrium
    4. d) right atrium

  5. Actively exercising muscle produces acid and heat, which cause hemoglobin to

    1. a) take up carbon dioxide instead
    2. b) stop carrying oxygen
    3. c) bind oxygen more tightly
    4. d) release oxygen more readily where it is most needed

  6. Plasma differs from the formed elements of blood in that plasma is

    1. a) the portion containing red blood cells
    2. b) the same thing as serum plus cells
    3. c) the clotting fraction only
    4. d) the liquid portion, carrying dissolved proteins, nutrients and wastes

  7. Valves in the heart and veins

    1. a) produce blood cells
    2. b) increase blood pressure
    3. c) filter the blood
    4. d) prevent blood from flowing backwards

  8. Exchange of gases, nutrients and wastes with tissues happens in the

    1. a) veins
    2. b) capillaries
    3. c) arteries
    4. d) arterioles

  9. The heartbeat is initiated by the

    1. a) aorta
    2. b) brain
    3. c) atrioventricular node
    4. d) sinoatrial node

  10. The human heart has

    1. a) four chambers: two atria and two ventricles
    2. b) three chambers
    3. c) four ventricles
    4. d) two chambers

Answer key · Circulation and gas exchange

Biology 20 · maddyhelps.com

  1. a) from the right ventricle to the lungs and back to the left atrium — The pulmonary circuit is the short loop to the lungs; the systemic circuit is the long loop to everything else. Blood passes through the heart twice per complete journey.
  2. c) carry blood away from the heart — The definition is direction, not oxygen content. The pulmonary artery carries deoxygenated blood, and the pulmonary vein carries oxygenated blood — both exceptions to the usual pattern.
  3. c) diffusion down partial pressure gradients — Oxygen is at higher partial pressure in the alveolus than in the blood, and carbon dioxide the other way round, so each moves down its own gradient. No energy is spent on the exchange itself.
  4. a) left ventricle — It has to push blood around the entire body, while the right ventricle only has to reach the lungs. Wall thickness follows the pressure needed, not the volume pumped — both ventricles move the same volume.
  5. d) release oxygen more readily where it is most needed — Lower pH and higher temperature shift the oxygen–hemoglobin curve to the right, so hemoglobin gives up its oxygen more easily. The tissue working hardest changes its own local conditions to get a bigger share.
  6. d) the liquid portion, carrying dissolved proteins, nutrients and wastes — Formed elements are the cells and platelets; plasma is the fluid they float in, about 55% of blood by volume and mostly water. Nearly everything dissolved in blood travels in the plasma.
  7. d) prevent blood from flowing backwards — They are one-way flaps that close when pressure would push blood the wrong way. In veins, where pressure is low, they are what lets blood in the legs return upwards at all.
  8. b) capillaries — Capillary walls are one cell thick and the network is so fine that no cell is far from one. Arteries and veins are transport pipes — their walls are far too thick for exchange.
  9. d) sinoatrial node — The SA node in the right atrium fires on its own and sets the pace, which is why a heart continues beating when removed from the body. Nerves and hormones adjust that rate but do not create it.
  10. a) four chambers: two atria and two ventricles — Atria receive blood and ventricles pump it out. Four chambers keep oxygenated and deoxygenated blood completely separate, which is what makes a high-pressure double circuit possible.