S2 Science: Respiration, Circulation And Excretion (Paper 4 (error Clinic))

S2 Science: Respiration, Circulation and Excretion (Paper 4 (error clinic))

2026-11-14

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Tutor Prep Guide · Respiration and gas exchange, features of alveoli, blood components and the three vessel types, the four heart chambers and double circulation, kidney filtration and reabsorption, dialysis and sweat

S2 Science: Respiration, Circulation and Excretion (Paper 4 (error clinic))

This paper corrects ten common errors about respiration, circulation and excretion, covering respiration versus breathing, plant respiration, the pulmonary artery, venous blood, red and white cells, the two sides of the heart, kidney function, sweat and alveolar surface area.

Direct answers　Respiration is a chemical reaction inside cells, plants respire day and night, the pulmonary artery carries deoxygenated blood, venous blood simply has less oxygen, red cells have no nucleus, platelets clot blood, the right heart serves the lungs, the kidney removes urea and regulates the blood, sweat and urine differ in concentration, and many alveoli give the large surface area.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	20
Difficulty mix	Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1
Chapter	Chapter: S2 Science: Respiration, Circulation and Excretion
Level	S2

02　Questions (10 items)

FoundationRespiration is said to be simply breathing in and out. What is wrong?
FoundationPlants are said to respire only in daylight. What is wrong?
FoundationAll arteries are said to carry oxygenated blood. What is wrong?
IntermediateVein blood is said to mean blood full of waste. What is wrong?
IntermediateMature red blood cells are said to have a nucleus and to divide. What is wrong?
IntermediateWhite blood cells are said to clot blood. What is wrong?
ChallengeThe right side of the heart is said to pump blood round the body. What is wrong?
ChallengeThe kidney is said merely to remove surplus water. What is wrong?
ChallengeSweat and urine are said to have similar composition. What is wrong?
Error redoThe large alveolar surface area is said to come from the lungs being big. What is wrong?

03　Answers and one-line notes

#	Answer	One-line note
1	Breathing only moves air; respiration is the chemical breakdown of glucose to release energy inside cells	One is a mechanical action and the other a chemical reaction, and mixing them up spoils every question about energy.
2	Plants respire day and night; it is only photosynthesis that is faster in the day	Respiration runs all the time to keep the plant alive, which is why plants also need oxygen.
3	The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs, which is the exception	An artery is defined by blood flowing away from the heart, not by how much oxygen it carries.
4	Vein blood simply carries less oxygen; whether it holds waste depends on which vein it is	For example the renal vein does hold less urea, but ordinary venous blood still carries nutrients.
5	Mature red cells have no nucleus and cannot divide, so they have a limited life and must be replaced by bone marrow	Losing the nucleus leaves more room for haemoglobin, so oxygen transport is more efficient.
6	Clotting is done by platelets, while white cells engulf pathogens and make antibodies	Both belong to the defence system but their jobs differ, and questions often swap them on purpose.
7	The right side pumps to the lungs and the left side to the body, and the left ventricle has the thickest wall	Remember blood goes from the right heart to the lungs and only after returning to the left heart is it sent round the body.
8	It also removes nitrogenous waste such as urea and regulates salt, water and acidity	Removing water alone would not need such complex filtration and reabsorption structures.
9	Sweat is mainly water with a little salt and a trace of urea, while urine has a much higher urea concentration	In dehydration sweating falls but waste must still leave, so the urine becomes more concentrated.
10	The key is the huge number of alveoli, which fold a limited volume into an enormous surface	For the same volume, splitting it into millions of small sacs gives far more surface than one hollow space.

04　What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

For respiration and circulation questions ask three things: whether the question is about structure, process or numbers, which way the air or blood is moving, and whether the units have been converted correctly.Tutor Registration →

Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.