Immunity, blood & circulation — questions and answers
5 high-yield, syllabus-aligned questions on Immunity, blood & circulation, covering 16 individually creditable mark points. Each one shows the answer that scores full marks under our guide, which phrase earns which mark, and a common incomplete answer — so you can see the difference rather than guess at it.
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Every question and solution is reviewed by examiners versed in WAEC and JAMB, each with more than thirty years of experience.
Mark allocations are TopMarks’ own, written against the published syllabus and Chief Examiners’ reports. They are a guide to how these answers are usually credited, not an official marking scheme.
State4 marks
State four functions of blood.
TopMarks model answer
Blood transports oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs. It transports digested food, hormones and excretory waste such as urea to the kidneys. It defends the body against disease by means of white blood cells and antibodies. It clots at a wound to prevent further loss of blood and the entry of pathogens, and it distributes heat, helping to regulate body temperature.
Suggested marking guide
1Transport of respiratory gases
2Transport of food, hormones or excretory waste
3Defence against disease
4Clotting or heat distribution
Why it scores
Four marks, four different kinds of function — transport of gases, transport of solutes, defence, and clotting or temperature. Listing four transported substances is one function repeated four times, and the mark scheme will credit it once.
A common incomplete answer
“Blood carries oxygen and carbon dioxide around the body and fights disease.”
What it costs: Two marks of four. Gas transport and defence are credited; the transport of food, hormones and urea is missing, and so is clotting or temperature regulation.
Explain the difference between natural and artificial immunity, giving one example of each.
TopMarks model answer
Natural immunity is acquired without medical intervention. It is active when a person makes their own antibodies after recovering from an infection such as measles, and passive when antibodies pass from mother to child across the placenta or in breast milk. Artificial immunity is acquired through medical intervention. It is active in vaccination, where a weakened or killed antigen stimulates the body to make its own antibodies, and passive when ready-made antibodies are injected in an antiserum.
Suggested marking guide
1Natural active — antibodies made after an infection
This is a two-by-two question hiding inside a one-line instruction: natural and artificial, each of which is active or passive. Four marks tells you there are four boxes to fill. Candidates who see only two categories can score at most half.
A common incomplete answer
“Natural immunity is obtained after you recover from an infection, and artificial immunity comes from vaccination.”
What it costs: Two marks of four. Both statements are correct and credited, but the passive forms — antibodies from the mother, and injected antiserum — are not mentioned at all.
Key ideas to include: active immunity, passive immunity, antibodies, antigen, vaccination, antiserum, placenta.
Explain2 marks
Explain why blood flows in one direction only in the veins.
TopMarks model answer
Veins contain semi-lunar valves along their length which open to let blood flow towards the heart and close when the blood tends to flow backwards, so backflow is prevented. The contraction of the surrounding skeletal muscles squeezes the vein and pushes the blood forward through the open valves.
Suggested marking guide
1Valves prevent backflow
2Contraction of surrounding muscles pushes blood along
Why it scores
The first mark is not for the word “valve” — it is for what the valve DOES. Naming a structure without giving its action is the commonest way an “explain” question is under-answered. The second mark, for the muscle pump, is the one almost nobody gives.
A common incomplete answer
“Because veins have valves that stop the blood going back.”
What it costs: One mark of two. The valve and its action are both credited, but the role of the surrounding muscles in pushing the blood forward is missing.
State three differences between an artery and a vein.
TopMarks model answer
An artery carries blood away from the heart while a vein carries blood towards the heart. An artery has a thick, muscular and elastic wall with a narrow lumen, whereas a vein has a thin wall and a wide lumen. Arteries have no valves except at the base of the aorta and the pulmonary artery, while veins have semi-lunar valves along their length.
Suggested marking guide
1Direction of blood flow relative to the heart
2Thick wall and narrow lumen versus thin wall and wide lumen
3Valves along veins but not along arteries
Why it scores
Notice that the direction mark is about the HEART, not about oxygen. The pulmonary artery carries deoxygenated blood, so “arteries carry oxygenated blood” is not a safe difference and examiners penalise it. Define arteries and veins by direction, never by the gas they carry.
A common incomplete answer
“Arteries carry oxygenated blood and veins carry deoxygenated blood.”
What it costs: Nothing safely. This is the classic trap: the pulmonary artery carries deoxygenated blood and the pulmonary vein carries oxygenated blood, so the statement is false as a general difference.
Key ideas to include: away from the heart, towards the heart, lumen, elastic wall, semi-lunar valves.
Explain3 marks
Explain how bleeding from a small cut is stopped.
TopMarks model answer
When a blood vessel is cut, platelets collect at the wound and release the enzyme thrombokinase. In the presence of calcium ions and vitamin K, thrombokinase converts the soluble plasma protein prothrombin into thrombin. Thrombin then converts soluble fibrinogen into insoluble fibrin threads, which form a mesh that traps red blood cells and forms the clot that seals the wound.
Suggested marking guide
1Platelets release thrombokinase
2Prothrombin becomes thrombin, needing calcium or vitamin K
3Fibrinogen becomes fibrin, which traps cells to form a clot
Why it scores
This is a named-sequence question, and the marks follow the sequence. Each mark needs BOTH names of a conversion — prothrombin to thrombin, fibrinogen to fibrin. Writing only the product ("fibrin forms") shows you know the end but not the process, and the mark scheme wants the process.
A common incomplete answer
“Platelets release an enzyme which makes fibrin form a clot over the wound.”
What it costs: One mark of three. The platelets and enzyme are credited, but the prothrombin-to-thrombin step is skipped entirely and fibrinogen is never named as the source of the fibrin.
Key ideas to include: platelets, thrombokinase, prothrombin, thrombin, fibrinogen, fibrin, calcium, vitamin K.
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