The heart and double circulation — return questions key

1. CR1 · Return

Model answer. C. The coronary arteries branch over the outside of the heart and into its wall. Like other arteries that supply a working muscle, they carry oxygenated blood, and they supply the heart muscle itself, which contracts all the time. Row A puts them inside the chambers, row B gives the job of the pulmonary artery, and row D gives them deoxygenated blood, which could not keep the working muscle supplied with oxygen.

A full answer includes

• I chose row C.
• I did not choose row A: the blood inside the chambers cannot reach the muscle cells deep in the wall.

Also accept

• C

Watch for

• “Row A: they are inside the heart's chambers.” — The blood inside the chambers is pumped straight through and cannot reach the cells deep in the thick wall. The coronary arteries run over the outside and into the muscle.
• “Row B: they carry deoxygenated blood to the lungs.” — That is the pulmonary artery's job. The coronary arteries carry oxygenated blood to the heart muscle.
• “Row D: they carry deoxygenated blood to the heart muscle.” — The muscle cells need oxygen for respiration, so the coronary arteries bring them oxygenated blood. The blood becomes deoxygenated only after the muscle cells have taken its oxygen.

2. CR2 · Return

Model answer. Blood is pumped away from the heart in arteries and returns to the heart in veins. Oxygen does not decide the name: the pulmonary artery carries deoxygenated blood.

A full answer includes

• I chose: arteries carry blood away from the heart; veins carry blood back to it.
• I did not choose the statement about oxygenated and deoxygenated blood.

Also accept

• arteries away from the heart; veins back to it

Watch for

• “Arteries carry oxygenated blood; veins carry deoxygenated blood.” — The pulmonary artery carries deoxygenated blood and the pulmonary vein oxygenated blood. Only the direction decides.
• “Veins carry blood away from the heart; arteries carry blood back to it.” — That swaps them. Arteries carry blood away from the heart, as the aorta does; veins bring it back.
• “Arteries carry blood to the lungs; veins carry blood to the rest of the body.” — Both kinds go to the lungs and to the body: the pulmonary artery takes blood to the lungs and the pulmonary vein brings it back.

3. CR3 · Return

Model answer. B. The plastic pump does the heart's job: it makes the blood move. Its four valves open one way and shut when blood starts to flow back, so the blood flows one way only. The patient's own blood vessels still carry the blood round the body. So the circulatory system is still a system of blood vessels with a pump and valves that make the blood flow one way.

A full answer includes

• I chose row B.
• I did not choose row C: a pump alone pushes blood backwards as well as forwards.

Also accept

• B

Watch for

• “Row A: the valves make the blood move and the pump keeps it flowing one way.” — That swaps the jobs. Valves only open and shut; the pump pushes the blood.
• “Row C: the pump both moves the blood and keeps it flowing one way.” — Without valves, a pump pushes blood backwards as well as forwards. The valves shut when blood starts to flow back, so it can only go forwards; that is why the artificial heart has four of them.
• “Row D: the blood vessels make the blood move.” — The vessels only carry the blood. The push that moves it comes from the pump.

4. BR1 · Return

Model answer. The blood leaks from the right ventricle back into the right atrium, so the faulty valve lies between them: the atrioventricular valve of the right side. It should shut when the ventricle contracts. The semilunar valve of the right side lies at the foot of the pulmonary artery, and the two valves of the left side are on the other side of the septum.

A full answer includes

• I chose the atrioventricular valve of the right side.
• I did not choose the semilunar valve of the right side: it lies between the ventricle and the pulmonary artery.

Also accept

• the atrioventricular valve of the right side

Watch for

• “The semilunar valve of the right side.” — That valve lies at the foot of the pulmonary artery. A leak there would let blood flow back from the artery into the ventricle as it relaxes, not into the atrium.
• “The atrioventricular valve of the left side.” — The left valves are on the other side of the septum. Blood leaking into the right atrium has passed the atrioventricular valve of the right side.
• “The semilunar valve of the left side.” — That valve is at the foot of the aorta; a leak there sends blood back into the left ventricle.

5. BR2 · Return

Model answer. When the atria contract they squeeze the last of the blood through the open atrioventricular valves into the ventricles. The ventricles are relaxed, so the semilunar valves stay shut.

A full answer includes

• I chose: the atria push blood into the ventricles; the semilunar valves stay shut.
• I did not choose that the atria push blood into the arteries.

Also accept

• blood into the ventricles; semilunar valves shut

Watch for

• “The atria push blood straight into the aorta and the pulmonary artery.” — The arteries leave the ventricles, not the atria. The atria fill the ventricles.
• “The atria and the ventricles contract together, and all the valves open.” — The atria contract first, then the ventricles. All four valves are never open together, or blood would flow back.
• “The atrioventricular valves shut, and the blood flows back into the veins.” — The atrioventricular valves stay open while the atria contract, so the blood is squeezed down into the ventricles.

6. BR3 · Return

Model answer. (a) The left ventricle's wall (14 mm) is more than five times as thick as the left atrium's (2.5 mm), and it makes a pressure ten times as high (15 kPa against 1.5 kPa). The atrium only pushes blood a short way, into the ventricle just below it, so a low pressure and little muscle are enough. The ventricle pumps blood out of the heart and all round the body, which needs a high pressure, so it has much more muscle, which contracts with more force. (b) In a healthy heart the septum is a solid wall with no holes. Blood from the right ventricle goes along the pulmonary artery to the lungs and comes back to the left atrium. The septum keeps the deoxygenated blood of the right side from mixing with the oxygenated blood of the left side, so the blood pumped to the body is fully oxygenated.

A full answer includes

• (a) I wrote that the ventricle's wall is several times thicker: 14 mm against 2.5 mm.
• (a) I wrote that the ventricle makes a pressure ten times higher: 15 kPa against 1.5 kPa.
• (a) I wrote that the atrium pushes blood only into the ventricle just below it.
• (a) I wrote that the ventricle pumps blood out of the heart, all round the body.
• (b) I wrote that the septum has no holes: it is a solid wall between the two sides.
• (b) I wrote that blood from the right ventricle goes to the lungs before it reaches the left side.
• (b) I wrote that the septum keeps oxygenated and deoxygenated blood from mixing, so the body gets fully oxygenated blood.
• I did not write that the atrium's wall is thin because it holds less blood.

Also accept

• (a) the ventricle makes a far higher pressure (15 against 1.5 kPa) to pump blood round the body; the atrium only fills the ventricle below; (b) the septum is a solid wall: blood reaches the left side by way of the lungs, and oxygenated and deoxygenated blood stay apart

Watch for

• “(a) The atrium holds less blood, so it needs a thinner wall.” — The thickness matches the pressure each chamber must make, not the volume it holds.
• “(b) Blood passes from the right side to the left side through the valves.” — The valves lie between each atrium and the ventricle below it, on the same side. Blood reaches the left side only by way of the lungs.

7. DR1 · Return

Options as numbered on the pupil sheet: 1 — the systemic circulation; 2 — the pulmonary circulation.

Model answer. The pulmonary circulation is the loop from the right ventricle to the lungs and back to the left atrium: the vessel out of the right ventricle (the pulmonary artery), the capillaries around the air sacs and the vessel from the lungs to the left atrium (the pulmonary vein). The systemic circulation is the loop from the left ventricle round the rest of the body and back to the right atrium: the coronary arteries, which branch from the aorta to the heart muscle, the artery to the liver and the veins from the legs.

A full answer includes

• I matched the coronary arteries to the systemic circulation.
• I matched the capillaries around the air sacs to the pulmonary circulation.
• I matched the vessel from the lungs to the left atrium to the pulmonary circulation.
• I matched the artery to the liver to the systemic circulation.
• I matched the vessel out of the right ventricle to the pulmonary circulation.
• I matched the veins from the legs to the systemic circulation.
• I did not match the coronary arteries to the pulmonary circulation because they lie close to the lungs.

Also accept

• pulmonary: the capillaries around the air sacs, the vessel from the lungs to the left atrium, the vessel out of the right ventricle; systemic: the coronary arteries, the artery to the liver, the veins from the legs

Watch for

• “The coronary arteries belong to the pulmonary circulation, because they lie close to the lungs.” — The coronary arteries branch from the aorta, which the left ventricle fills, and supply the heart muscle: they are part of the systemic circulation.
• “The vessel from the lungs to the left atrium is systemic, because it carries oxygenated blood.” — Oxygen does not decide. It carries blood from the lungs back to the heart, so it is part of the pulmonary circulation.

8. DR2 · Return

Model answer. A fish's heart pumps blood to the gills; from there it flows straight to the body and back to the heart. It passes through the heart once on each trip: a single circulation.

A full answer includes

• I chose: heart → gills → body → heart, a single circulation.
• I did not call this route a double circulation.

Also accept

• heart, gills, body, heart; single

Watch for

• “Heart → gills → heart → body → heart: a double circulation.” — That route would be a double circulation. In a fish the blood goes from the gills straight to the body.
• “Heart → body → gills → heart: a single circulation.” — The fish's heart pumps blood to the gills first; the body gets the blood after it has taken in oxygen.
• “Heart → gills → body → heart: a double circulation.” — The route is right, but the blood passes through the heart only once on each trip, so the circulation is single.

9. DR3 · Return

Model answer. The capillaries in the lungs have very thin walls next to the air spaces. A lower pressure protects them from damage and stops fluid being pushed out into the air spaces, while the left ventricle still sends blood to the body at a high pressure.

A full answer includes

• I chose: the thin-walled capillaries of the lungs could be damaged by a higher pressure.
• I did not choose that the right ventricle's thinner wall is the advantage: it is why the pressure is lower.

Also accept

• protects the thin lung capillaries (fluid not pushed into the air spaces)

Watch for

• “The right ventricle has a thinner wall, so it cannot make a higher pressure.” — That is true, but it is the reason the pressure is lower, not why a lower pressure is an advantage.
• “The lungs need far less blood each minute than the rest of the body does.” — The lungs receive all the blood that goes round the body, every minute.
• “A lower pressure makes the blood flow faster through the capillaries of the lungs.” — A lower pressure pushes blood more slowly, not faster.