Answers · The heart and double circulation

A pump, pipes and valves — answer key

Check meaning, not exact wording. These are teaching points, not official Cambridge marks.

1. CQ1 · Practice

Options as numbered on the pupil sheet: 1 — the blood; 2 — a valve; 3 — the septum; 4 — the heart; 5 — the blood vessels.

Model answer. The pump makes the water move, as the heart pumps the blood. The pipes carry the water, as the blood vessels carry the blood. The flap lets water through one way only, as a valve does for the blood. The water is the liquid that goes round, like the blood. So the circulatory system is a system of blood vessels with a pump and valves that keep the blood flowing one way.

A full answer includes

I matched the electric pump to the heart.
I matched the plastic pipes to the blood vessels.
I matched the rubber flap to a valve.
I matched the water to the blood.
I did not match the rubber flap to the septum.

Also accept

pump: the heart; pipes: the blood vessels; flap: a valve; water: the blood

Watch for

“The rubber flap matches the septum, because both hold a liquid back.” — The septum is a fixed wall between the two sides of the heart; it never opens. A flap that opens one way and shuts the other is a valve.
“The pipes match the heart, because the water passes through them.” — Blood passes through the heart too, but the heart is the pump. The tubes that carry the blood all round the body are the blood vessels.
“The electric pump matches the valves.” — Valves only open and shut. The heart's muscle makes the blood move, as the pump does.

2. CQ2 · Practice

Model answer. D is the left ventricle. The heart is drawn from the front, so its left side is on the right of the page; the left ventricle is the lower chamber there, with the thickest wall, and the aorta (J) leaves it.

A full answer includes

I chose D.
I did not choose C: the heart is seen from the front, so C, on the left of the page, is the right ventricle.

Also accept

Watch for

“C, because it is on the left of the drawing.” — The diagram is seen from the front, so the heart's left side is on the right of the page. C is the right ventricle.
“B, the space at the top right.” — B is an atrium, with a thin wall. The ventricles are the lower spaces.
“A, the space at the top left.” — A is an atrium too, on the heart's right side. The left ventricle is a lower space, on the heart's left side.

3. CQ3 · Practice

Options as numbered on the pupil sheet: 1 — the vena cava; 2 — a vein in the leg; 3 — an artery in the leg; 4 — capillaries in the leg muscle.

Model answer. The blood leaves the heart in arteries, so an artery in the leg comes first. In the muscle it flows through tiny capillaries. A vein in the leg then carries it back towards the heart, and the vena cava, the large vein, brings it into the heart.

A full answer includes

I put the artery in the leg first.
I put the capillaries in the muscle between the artery and the vein.
I put the vein in the leg after the capillaries.
I put the vena cava last.
I did not put a vein before the capillaries.

Also accept

an artery in the leg; capillaries in the leg muscle; a vein in the leg; the vena cava

Watch for

“A vein carries the blood down to the leg, and an artery brings it back.” — That swaps them. Arteries carry blood away from the heart, and veins bring it back.
“The vena cava comes first, because it is the largest vessel.” — Size does not decide. The vena cava brings blood back into the heart, so it is a vein and comes last.

4. CQ4 · Practice

Options as numbered on the pupil sheet: 1 — left ventricle; 2 — coronary artery; 3 — muscular wall; 4 — septum; 5 — right atrium; 6 — left atrium; 7 — one-way valve.

Model answer. A is the right atrium (top left of the page, because the heart is seen from the front) and E the septum between the two sides. F is a one-way valve: its flaps lie between the left atrium and the left ventricle. H is one of the coronary arteries, which run over the outside of the heart and supply its muscle with blood, and L is the thick muscular wall of the left ventricle.

A full answer includes

I matched A to the right atrium.
I matched E to the septum.
I matched F to a one-way valve.
I matched H to a coronary artery.
I matched L to the muscular wall.
I did not match L to the septum.

Also accept

A right atrium; E septum; F one-way valve; H coronary artery; L muscular wall

Watch for

“A is the left atrium because it is on the left.” — The diagram is seen from the front, so the heart's right side is on the left of the page.
“H is a vein bringing blood back into the heart.” — H runs over the outside of the muscle: it is a coronary artery, which supplies the heart muscle itself.
“L is the septum.” — The septum (E) runs down the middle, between the two sides. L is the outer wall of muscle around the left ventricle.

5. CQ5 · Practice

Model answer. With the valves in place, the inlet valve shuts when the bulb is squeezed and the outlet valve shuts when it springs back, so the water can only move one way. Without valves, squeezing pushes water out of both tubes and springing back draws it in through both, so the water only moves back and forth and is not moved along. The heart works in the same way: its muscle is the pump, and its valves make the blood flow one way.

A full answer includes

I wrote that squeezing would push water out of both tubes, backwards as well as forwards.
I wrote that springing back would draw water in through both tubes.
I wrote that the water would only move back and forth, so it would not be moved along.
I did not write that the valves push the water.

Also accept

squeezing pushes water out of both tubes and springing back draws it in through both, so it moves back and forth; valves make the flow one way

Watch for

“The pump would still move the water, only more slowly.” — Without valves, the water pushed forwards by each squeeze is drawn back by each spring-back, so almost none is moved along.
“The valves push the water.” — The squeezed bulb pushes the water. The valves only stop it flowing the wrong way.

6. CQ6 · Practice

Model answer. P (the pulmonary artery) carries blood away from the heart to the lungs, and R (the aorta) carries blood away from the heart to the body, so both are arteries. Q and S bring blood back to the heart: they are veins.

A full answer includes

I chose P.
I chose R.
I did not choose Q: it brings blood back to the heart, so it is a vein.

Also accept

P and R

Watch for

“Q and R, because they carry bright red, oxygenated blood.” — The name depends on direction, not oxygen. Q brings blood back to the heart, so it is a vein; P takes dark red blood away, so it is an artery.
“S, because it is a large vessel joined to the heart.” — Size does not decide. S brings blood back to the heart from the body, so it is a vein.
“Only R, the aorta.” — R is an artery, but so is P: it carries blood away from the heart to the lungs.

7. CT1 · Apply

Model answer. Arteries carry blood away from the heart. The umbilical arteries carry blood away from the baby's heart, out to the placenta, so they are arteries, even though their blood is deoxygenated.

A full answer includes

I wrote that the umbilical arteries carry blood away from the baby's heart.
I wrote that the direction of flow decides the name.
I did not write that arteries must carry oxygenated blood.

Also accept

away from the (baby's) heart; direction, not oxygen, decides

Watch for

“They should be called veins, because their blood is deoxygenated.” — A vessel is an artery when it carries blood away from the heart, whatever its oxygen. The pulmonary artery is another example.

8. CT2 · Apply

Model answer. (a) Rod 2 is in the aorta. It ends in the ventricle with the much thicker wall, which is the left ventricle, and the aorta is the artery that leaves the left ventricle. Rod 1 is in the pulmonary artery, which leaves the right ventricle. (b) Squeeze each ventricle between finger and thumb: the left one feels firmer, because its muscular wall is much thicker.

A full answer includes

(a) I identified the artery as the aorta.
(a) I wrote that rod 2 ends in the left ventricle, the ventricle with the thicker wall.
(a) I wrote that the aorta leaves the left ventricle.
(b) I suggested squeezing each ventricle: the left one feels firmer, because its wall is thicker.
I did not use the side of the heart that was facing me.

Also accept

(a) the aorta: rod 2 is in the left ventricle (the thicker wall), and the aorta leaves the left ventricle; (b) squeeze each ventricle: the left one feels firmer

Watch for

“(a) The pulmonary artery, because it is the largest artery.” — The aorta is the largest artery, and it leaves the left ventricle, the one with the thicker wall. The pulmonary artery leaves the right ventricle.
“(b) See which ventricle is on the left as the heart lies on the tray.” — A loose heart can lie either way up, and seen from the front its left side is on your right. Use a feature of the heart itself.

9. CT3 · Apply

Model answer. The flaps work as valves. When the tube contracts, they close the openings, so the squeezed blood cannot escape back out through them; it can only flow forwards. Like a mammal's heart, the insect's heart is a pump with valves that make the blood flow one way.

A full answer includes

I wrote that the flaps act as valves.
I wrote that they stop blood being pushed back out through the openings when the tube contracts.
I wrote that the blood then flows one way, forwards to the head.
I did not write that the flaps push the blood.

Also accept

valves; stop blood flowing back out of the openings, so it flows one way (forwards)

Watch for

“The flaps push the blood forwards.” — The muscle of the tube pushes the blood. The flaps only stop it flowing out the wrong way.

10. CT4 · Apply

Options as numbered on the pupil sheet: 1 — coronary artery; 2 — right ventricle; 3 — muscular wall; 4 — left ventricle; 5 — one-way valve; 6 — septum.

Model answer. W is the septum, the wall of muscle down the middle. X are the flaps of a one-way valve, held by thin cords, between the right atrium and the right ventricle. Y is the right ventricle: the heart is seen from the front, so its right side is on the left of the picture. Z is the thick muscular wall of the left ventricle, the thickest wall of the heart. A real heart is harder to read than a diagram: look for the same shapes.

A full answer includes

I matched W to the septum.
I matched X to a one-way valve.
I matched Y to the right ventricle.
I matched Z to the muscular wall.
I did not match Y to the left ventricle.

Also accept

W septum; X one-way valve; Y right ventricle; Z muscular wall

Watch for

“Y is the left ventricle, because it is on the left of the picture.” — The heart is seen from the front, so its right side is on the left of the picture; the thicker wall (Z) belongs to the left ventricle.
“X is a coronary artery.” — Coronary arteries run over the outside of the heart. X are pale flaps inside, tied by cords: a valve.