AQA GCSE Combined Science: Trilogy Biology Paper 1 (Higher), 2023: Question 3

✅ Correct answer

• The heart pumps blood in two circuits: one to the lungs and one to the rest of the body.
• Blood passes through the heart twice in one complete journey around the body.
• Mark scheme wording you could use: right ventricle pumps blood to the lungs and left ventricle pumps blood around / to the body .

💡 Key knowledge

• Double circulation = pulmonary circuit + systemic circuit.
• Pulmonary circuit: heart → lungs → heart.
• Systemic circuit: heart → body → heart.

🧠 Exam technique

• To get both marks, mention both circuits or say blood goes to the lungs and the body.
• “Two loops” or “blood passes through the heart twice” are good shorthand.
• Use the word double to show you understand the idea, not just the path.

❌ Common errors

• Saying only “blood goes around the body” = incomplete.
• Mixing up chambers: the right side sends blood to the lungs; the left side sends blood to the body.
• Writing “oxygenated and deoxygenated blood mix” is not what this question is asking.

✅ Correct answer

Right atrium.

💡 Key knowledge

• The pacemaker is a group of cells that controls the heartbeat.
• It is found in the right atrium.

🧠 Exam technique

• Give the exact chamber name.
• “Upper right chamber” is helpful, but the best answer is right atrium.

❌ Common errors

• Saying “right ventricle” — that is incorrect.
• Just writing “in the heart” is too vague for the mark.

✅ Correct answer

Pulmonary artery.

💡 Key knowledge

• The pulmonary artery carries deoxygenated blood from the heart to the lungs.
• Important exception: arteries usually carry oxygenated blood, but the pulmonary artery is different.

🧠 Exam technique

• Use the vessel name, not just “the artery”.
• Remember: artery = away from the heart, but oxygen level is not always the same thing.

❌ Common errors

• Aorta — carries oxygenated blood to the body.
• Coronary artery — supplies the heart muscle.
• Pulmonary vein — carries oxygenated blood from lungs to heart.

✅ Correct answer

• Veins have valves to prevent backflow of blood / prevent blood flowing in the wrong direction.
• This is because blood in veins is at lower pressure than in arteries, so it can flow backwards more easily.

💡 Key knowledge

• Low pressure in veins means the blood needs help moving back to the heart.
• Arteries do not need valves because blood is pushed out of the heart at high pressure.

🧠 Exam technique

• You need two linked points for full marks: valves stop backflow + veins are low pressure.
• It helps to write it as a cause and effect sentence.
• Example full-mark answer: Veins have valves to prevent backflow because blood in veins is at lower pressure than in arteries.

❌ Common errors

• Saying only “to stop blood going backwards” may get one mark, but not the second unless pressure is mentioned.
• Writing that arteries have valves is incorrect.
• “Blood travels more slowly in veins” can help, but lower pressure is the strongest exam phrase.

✅ Correct answers — any two

• The lumen in a vein is wider than in an artery.
• The wall of a vein has a thinner layer of muscle than an artery.
• The wall of a vein has a thinner layer of elastic tissue than an artery.

💡 Key knowledge

• Arteries need thicker muscle and elastic tissue because blood is under higher pressure.
• Veins carry blood at lower pressure, so their walls are thinner and their lumen is wider.

🧠 Exam technique

• Answers must be comparative: vein is wider/thinner than artery.
• Use the correct terms: lumen, muscle, elastic tissue.
• You only need two valid differences for full marks.

❌ Common errors

• Just saying “veins have thinner walls” may earn at most one mark if not compared properly.
• Referring to “cell wall” is wrong — blood vessels are not plant cells.
• Talking about valves here would not help, because the question says do not refer to valves.

✅ Must-know facts

• Double circulation = heart → lungs → heart and heart → body → heart.
• Pacemaker = right atrium.
• Deoxygenated blood vessel = pulmonary artery.
• Veins have valves because blood is at lower pressure.
• Veins vs arteries: wider lumen, thinner muscle, thinner elastic tissue.

🧠 One-sentence exam method

For 1-mark questions, give the exact term. For 2-mark explanations, write two linked points: what happens and why it happens.