The heart and double circulation — final check key

1. CK1 · Final check

Options as numbered on the pupil sheet: 1 — right ventricle; 2 — muscular wall; 3 — coronary artery; 4 — left atrium; 5 — left ventricle; 6 — right atrium; 7 — one-way valve; 8 — septum.

Model answer. 1 is the left atrium and 2 the right ventricle: the heart is seen from the front, so its left side is on the right of the page. 3 is the septum, the wall of muscle between the two ventricles. 4 is a one-way valve: its flaps, held by thin cords, lie between the right atrium and the right ventricle. 5 is a coronary artery running over the outside of the heart near the base of the aorta, and 6 the thick muscular wall of the left ventricle.

A full answer includes

• I matched 1 to the left atrium.
• I matched 2 to the right ventricle.
• I matched 3 to the septum.
• I matched 4 to a one-way valve.
• I matched 5 to a coronary artery.
• I matched 6 to the muscular wall.
• I did not match 2 to the left ventricle.
• I did not match 6 to the septum.

Also accept

• 1 left atrium; 2 right ventricle; 3 septum; 4 one-way valve; 5 coronary artery; 6 muscular wall

Watch for

• “2 is the left ventricle because it is on the left.” — The heart is seen from the front, so the left of the page is the heart's right side. 2 is the right ventricle, with the thinner wall.
• “6 is the septum.” — The septum (3) is the wall between the two ventricles. 6 is the outer wall of muscle around the left ventricle.
• “5 is a vein bringing blood back into a chamber.” — 5 runs over the outside of the heart muscle and does not open into a chamber: it is a coronary artery, which supplies the heart muscle itself.
• “4 is the septum, because it lies between two spaces.” — The septum (3) is a solid wall between the two ventricles. 4 is a pair of thin flaps between an atrium and a ventricle: a one-way valve.

2. CK2 · Final check

Model answer. (a) The pupil has swapped the jobs. The heart is the pump: its muscle contracts and pushes the blood. The valves only open and shut; they stop the blood flowing backwards, so it flows one way round the body. (b) They are veins, because they carry blood back to the heart. Only the direction of flow decides.

A full answer includes

• (a) I wrote that the heart is the pump: its muscle pushes the blood.
• (a) I wrote that the valves stop the blood flowing backwards, so it flows one way.
• (b) I wrote that the jugular vessels are veins.
• (b) I wrote that they bring blood back to the heart.
• I did not use the oxygen in the blood to decide.

Also accept

• (a) the heart pumps, the valves stop backflow; (b) veins: they bring blood back to the heart

Watch for

• “(b) They are arteries, because they are large vessels in the neck.” — Size and place do not decide. These vessels bring blood back to the heart, so they are veins.
• “(a) The statement is right: valves move the blood.” — Valves have no muscle and push nothing. They only open and shut, so the blood flows one way.

3. BK1 · Final check

Model answer. (a) M lies between the right atrium and the right ventricle, so it is an atrioventricular valve. (b) N is at the foot of the pulmonary artery, where it leaves the right ventricle, so it is a semilunar valve. (c) The ventricles are contracting: the atrioventricular valve M is shut, so blood cannot go back into the atrium, and the semilunar valve N is open, so blood is pushed into the pulmonary artery. (d) Next the ventricles relax. The pressure in them falls, so the semilunar valves shut and stop blood flowing back from the arteries; the atrioventricular valves open and blood flows from the atria into the ventricles.

A full answer includes

• (a) I identified M as an atrioventricular valve.
• (b) I identified N as a semilunar valve.
• (c) I stated that the ventricles are contracting.
• (c) I explained that M is shut, so blood cannot flow back into the atrium.
• (c) I explained that N is open, so blood is pushed out into the pulmonary artery.
• (d) I described the muscle of the ventricles relaxing.
• (d) I described the semilunar valves shutting.
• (d) I described the atrioventricular valves opening, so blood flows from the atria into the ventricles.
• I did not write that the valves contract.

Also accept

• (a) atrioventricular; (b) semilunar; (c) ventricles contracting, M shut, N open; (d) ventricles relax, semilunar valves shut, atrioventricular valves open, ventricles fill

Watch for

• “(b) N is an atrioventricular valve because it is on the right side of the heart.” — Each side has both kinds. N sits at the foot of an artery, so it is a semilunar valve.
• “(c) The atria are contracting.” — When the atria contract, the atrioventricular valves are open so that blood can pass into the ventricles. M is shut.
• “(d) The valves contract to shut.” — Only the muscle of the chamber walls contracts. The valves open and shut because of the pressure on each side.

4. BK2 · Final check

Model answer. (a) Wall thickness matches the pressure a chamber must make. The right ventricle pumps blood only to the lungs, close by, at a lower pressure; the left ventricle pumps blood all round the body, which needs a much higher pressure, so it has more muscle. The oxygen in the blood does not decide it. (b) The atria do contract: they squeeze blood into the ventricles just before the ventricles contract. They push it only a short way, so a low pressure and a thin wall are enough.

A full answer includes

• (a) I wrote that the thickness depends on the pressure the ventricle makes, not on the oxygen in its blood.
• (a) I wrote that the right ventricle pumps blood only to the lungs, close by, at a lower pressure.
• (a) I wrote that the left ventricle pumps blood all round the body at a higher pressure, so it needs more muscle.
• (b) I wrote that the atria do contract.
• (b) I wrote that the atria push blood only a short way, into the ventricles just below, so a thin wall is enough.
• I did not write that the left ventricle pumps more blood than the right.

Also accept

• (a) thickness matches pressure: right pumps only to the nearby lungs, left round the whole body; (b) the atria do contract, but only push blood into the ventricles below

Watch for

• “(a) The left ventricle is thicker because it holds more blood.” — Both ventricles pump the same volume; the left one pumps it at a higher pressure.
• “(b) The atria are thin because blood flows into them by itself.” — Blood does flow in from the veins, but the atria also contract to finish filling the ventricles. A low pressure is enough for that short push.

5. BK3 · Final check

Model answer. (a) Person 2. In person 1 the right ventricle holds deoxygenated blood (74 %) and the left ventricle oxygenated blood (97 %): the septum keeps them apart. In person 2 the two values are close (84 % and 89 %): oxygenated and deoxygenated blood have mixed through the septum. (b) The left ventricle pumps blood to the body. In person 2 this blood carries only 89 % of the most it could, instead of about 97 %, so less oxygen reaches the body's cells for respiration.

A full answer includes

• (a) I chose person 2.
• (a) I wrote that person 2's two ventricles have close values, 84 % and 89 %, so their blood has mixed.
• (b) I wrote that the left ventricle pumps blood to the body.
• (b) I wrote that person 2's blood for the body carries less oxygen: 89 % against 97 %.
• (b) I wrote that the body's cells get less oxygen for respiration.
• I did not choose person 1 because of the low 74 % in the right ventricle.

Also accept

• (a) person 2; (b) the blood sent to the body carries less oxygen (89 %, not 97 %), so the cells get less oxygen for respiration

Watch for

• “Person 1, because 74 % in the right ventricle is too low.” — The right ventricle should hold deoxygenated blood from the body, so a lower value there is normal. A septum that works keeps the two values far apart.

6. DK1 · Final check

Model answer. (a) A fish's blood passes through two sets of capillaries on each trip: first in the gills, where it takes in oxygen, then in the body's organs. Its circulation is single because the blood passes through the heart only once on each trip. (b) The cell flows in veins to the vena cava and into the right atrium, then into the right ventricle, which pumps it along the pulmonary artery to the lungs. It comes back along the pulmonary vein to the left atrium: this loop is the pulmonary circulation. The left ventricle pumps it into the aorta, and an artery takes it to the kidney: the loop from the left ventricle round the body and back to the right atrium is the systemic circulation. On the way the cell passes through the heart twice.

A full answer includes

• (a) I wrote that the fish's blood passes through two sets of capillaries on each trip, in the gills and in the body's organs.
• (a) I wrote that "single" means the blood passes through the heart once on each trip.
• (b) I wrote that the cell returns in veins to the vena cava and the right atrium.
• (b) I wrote that the right ventricle pumps it to the lungs.
• (b) I wrote that it returns from the lungs to the left atrium.
• (b) I named the loop from the right ventricle to the lungs and back to the left atrium as the pulmonary circulation.
• (b) I wrote that the left ventricle pumps it into the aorta, and an artery takes it to the kidney.
• (b) I named the loop from the left ventricle round the body and back to the right atrium as the systemic circulation.
• I did not write that the cell passes through the lungs twice.

Also accept

• (a) two sets of capillaries (gills, then body); single = once through the heart; (b) kidney → veins → vena cava → right atrium → right ventricle → lungs → left atrium (pulmonary) → left ventricle → aorta → kidney (systemic), twice through the heart

Watch for

• “(b) In a mammal the blood goes through the lungs twice.” — It goes through the heart twice and the lungs once on each trip round the body.
• “(a) The statement is right: the gills are the fish's only capillaries.” — Every organ of a fish's body has capillaries too. The blood passes through those of the gills and then those of the body.

7. DK2 · Final check

Model answer. (a) The left ventricle pumps blood into the aorta at a high pressure, but the right ventricle pumps blood into the pulmonary artery at a much lower pressure. Blood flows from a higher pressure to a lower one, so it flows from the aorta into the pulmonary artery. (b) The extra blood from the aorta goes on to the lungs, so more blood, at a higher pressure, is pushed through the lung capillaries. Their thin walls can be damaged, and fluid is pushed out into the air spaces, which makes gas exchange harder. Normally the double circulation keeps the blood in the lungs at a low pressure.

A full answer includes

• (a) I wrote that the left ventricle pumps blood into the aorta at a high pressure.
• (a) I wrote that the right ventricle pumps blood into the pulmonary artery at a lower pressure.
• (a) I wrote that blood flows from the higher pressure to the lower pressure.
• (b) I wrote that more blood, at a higher pressure, reaches the lungs.
• (b) I wrote that the lung capillaries have thin walls, which this higher pressure can damage.
• (b) I wrote that fluid is pushed out of the capillaries into the air spaces.
• I did not write that the blood flows this way because the aorta's blood is oxygenated.

Also accept

• (a) the aorta (left ventricle) is at a higher pressure than the pulmonary artery (right ventricle), and blood flows from high to low pressure; (b) more blood at a higher pressure reaches the thin lung capillaries: damage, fluid into the air spaces

Watch for

• “(a) The blood flows that way because the aorta's blood is oxygenated, and the lungs need oxygen.” — Blood moves from a higher pressure to a lower one. The oxygen it carries does not push it.
• “(b) The lungs would get too much oxygen.” — Oxygen is not the problem: the extra blood arrives at a higher pressure and can damage the thin capillaries.