IGCSE Biology | Practice Test — Answers | 25 Questions
Section A — Recall
Questions 1–10 | Definitions, facts, and naming
1.
List the four components of blood.
Answer
Red blood cells, white blood cells, platelets, plasma
2.
State the function of red blood cells.
Answer
Transport oxygen from the lungs to body cells.
3.
Name the red protein found inside red blood cells that allows them to carry oxygen.
Answer
Haemoglobin
4.
Name the two types of white blood cell you need to know for IGCSE.
Answer
Lymphocytes and phagocytes
5.
State the function of lymphocytes.
Answer
Produce antibodies that target and destroy specific pathogens.
6.
State the function of phagocytes.
Answer
Engulf and digest pathogens.
7.
State the function of platelets. Refer to fibrinogen and fibrin in your answer.
Answer
- Platelets cause blood to clot at a wound site.
- They trigger the conversion of soluble fibrinogen (a plasma protein) into insoluble fibrin.
- Fibrin forms a mesh that traps blood cells, creating a clot that seals the wound.
- This prevents blood loss and stops pathogens from entering the body.
8.
Name four substances transported by plasma.
Answer
Any four from:
Blood cells | Ions | Glucose | Amino acids | Hormones | Carbon dioxide | Urea | Vitamins | Plasma proteins
9.
What is the name of the fluid that surrounds body cells in the spaces between them?
Answer
Tissue fluid
10.
Give one substance that moves from tissue fluid into body cells, and one substance that moves from body cells into tissue fluid.
Answer
- Into body cells: any one of — oxygen, glucose, amino acids, hormones
- Out of body cells: any one of — carbon dioxide, urea
Section B — Application
Questions 11–20 | Short explanations and scenarios
11.
Explain why it is an advantage for red blood cells to have no nucleus.
Answer
- Having no nucleus means there is more space inside the cell for haemoglobin.
- More haemoglobin means the cell can carry more oxygen per cell.
- This makes red blood cells more efficient at their function of oxygen transport.
12.
A student examines a blood smear under a microscope. They see a small cell with a large, round nucleus that fills almost the entire cell, with only a thin ring of cytoplasm visible around it.
- (a) Identify this type of white blood cell.
- (b) State the function of this cell.
Answer
(a)
Lymphocyte
(b)
Produces antibodies that target specific pathogens.
Exam tip: The large round nucleus filling the cell is the key feature that identifies a lymphocyte. A phagocyte has a lobed or irregular nucleus with more cytoplasm visible.
13.
Describe how a phagocyte destroys a pathogen that enters the body.
Answer
- The phagocyte surrounds and engulfs the pathogen.
- The pathogen is then digested inside the phagocyte.
14.
Explain why a blood clot at a wound site helps to prevent infection as well as blood loss.
Answer
- When a blood vessel is damaged, fibrin forms a mesh that seals the wound.
- The clot creates a physical barrier at the surface of the wound.
- This barrier blocks pathogens from entering the body through the open wound.
- It also stops blood from leaving the damaged vessel, preventing further blood loss.
15.
Name three substances transported by plasma. For each one, state where it comes from and where it is going.
Answer
Any three correct examples. Model answer:
- Glucose — from the small intestine (absorbed after digestion) → to all body cells (used in respiration)
- Carbon dioxide — from body cells (waste product of respiration) → to the lungs (breathed out)
- Urea — from the liver (produced from breakdown of excess amino acids) → to the kidneys (removed in urine)
16.
Explain how the way lymphocytes fight pathogens is different from the way phagocytes fight pathogens.
Answer
- Lymphocytes fight pathogens using a chemical method — they produce antibodies, which are proteins that attach to specific pathogens. The antibodies mark the pathogen for destruction or make it harmless.
- Phagocytes fight pathogens using a physical method — they engulf the pathogen directly, surrounding it and digesting it with enzymes inside the cell.
Key difference: Lymphocytes = antibodies (indirect, chemical). Phagocytes = engulfing (direct, physical).
17.
Tissue fluid does not contain red blood cells or large plasma proteins. Explain why these substances cannot pass from the blood into the tissue fluid.
Answer
- Tissue fluid forms when plasma is pushed out through the walls of the capillaries.
- The capillary wall acts as a filter — only small molecules can pass through the tiny gaps between the cells of the wall.
- Red blood cells are too large to pass through the capillary wall, so they remain in the blood.
- Large plasma proteins are also too large to pass through, so they stay dissolved in the blood plasma.
18.
Describe how tissue fluid is formed from blood in the capillaries.
Answer
- Blood in the capillaries is under pressure (higher at the arterial end).
- This pressure forces water and small dissolved substances — such as glucose, oxygen, ions, and amino acids — out through the thin capillary wall.
- This fluid collects in the spaces surrounding body cells and becomes tissue fluid.
- Red blood cells and large plasma proteins are too large to pass through the wall and remain in the blood.
19.
A patient has a small cut that bleeds for a very long time without stopping. Suggest which blood component may not be functioning correctly. Explain your answer.
Answer
Platelets are not functioning correctly (or there are too few platelets).
- Platelets trigger blood clotting by causing soluble fibrinogen to be converted into insoluble fibrin.
- If platelets are absent or not working, fibrin cannot form.
- Without fibrin, no clot develops at the wound site, so bleeding continues.
20.
Explain why oxygen moves from tissue fluid into body cells rather than in the opposite direction.
Answer
- Body cells continuously use oxygen in respiration.
- This means the concentration of oxygen inside the cells is low.
- The concentration of oxygen in the tissue fluid (which receives oxygen from the blood) is higher.
- Substances move by diffusion from high concentration to low concentration.
- So oxygen diffuses from the tissue fluid (high concentration) into the body cells (low concentration).
Section C — Challenge
Questions 21–25 | Multi-part and extended answers
21.
This question is about identifying blood cells under the light microscope.
- (a) Describe the appearance of a red blood cell as seen on a prepared slide under a light microscope.
- (b) Describe how you would distinguish a lymphocyte from a phagocyte when looking at them under a microscope. Refer to the nucleus and the cytoplasm in your answer.
- (c) Red blood cells appear paler in the centre than at the edges when viewed under a microscope. Explain why.
Answer
(a) Appearance of a red blood cell
- Small, round, pinkish/red cell
- Biconcave disc shape — flattened, with a dip on both sides
- Pale centre with a darker, deeper pink edge
- No visible nucleus
- Present in very large numbers compared to white blood cells
(b) Distinguishing lymphocyte from phagocyte
- Lymphocyte: large, round nucleus that fills most of the cell; only a very thin ring of cytoplasm is visible around the nucleus.
- Phagocyte: lobed or irregular-shaped nucleus; significantly more cytoplasm visible; the cell is generally larger overall.
(c) Why red blood cells appear pale in the centre
- Red blood cells have a biconcave disc shape — they are thinner in the centre and thicker at the edges.
- The pink colour comes from haemoglobin inside the cell.
- Because the cell is thinner at the centre, there is less haemoglobin there.
- Less haemoglobin means less colour — so the centre appears paler when light passes through.
22.
This question is about blood components and their functions.
- (a) State the four components of blood and give the function of each.
- (b) A patient is found to have no platelets in their blood. Describe two consequences this would have for the patient’s health. Explain each consequence.
- (c) Fibrinogen is a plasma protein that is always dissolved in the blood. Explain why it is important that fibrinogen stays soluble in normal blood, but becomes insoluble (as fibrin) only at a wound site.
Answer
(a) Four components and functions
- Red blood cells — transport oxygen from the lungs to all body cells
- White blood cells — defend the body against pathogens (lymphocytes produce antibodies; phagocytes engulf pathogens)
- Platelets — cause blood clotting by triggering the conversion of fibrinogen to fibrin, sealing wounds to prevent blood loss and pathogen entry
- Plasma — transports blood cells, ions, glucose, amino acids, hormones, carbon dioxide, urea, vitamins, and plasma proteins around the body
(b) Consequences of having no platelets
- Consequence 1 — Uncontrolled bleeding: Platelets trigger the clotting reaction. Without them, fibrinogen cannot be converted to fibrin and no clot forms. Any cut or damaged blood vessel would bleed continuously, leading to severe blood loss.
- Consequence 2 — Increased risk of infection: Without a clot forming at a wound, the wound remains open. Pathogens can enter the body freely through the wound site, increasing the risk of serious infection.
(c) Why fibrinogen must stay soluble normally
- Fibrinogen is dissolved in the plasma, so it flows freely through the blood vessels without blocking anything.
- If fibrinogen converted to insoluble fibrin inside the blood vessels, it would form clots inside the vessels.
- These internal clots would block blood flow, which could be very dangerous or fatal.
- The conversion to fibrin is triggered only at a damaged blood vessel by the platelets, so clotting happens where it is needed — at the wound — and not elsewhere in the blood.
23.
This question is about plasma and the substances it transports.
- (a) Name all nine substances transported by plasma.
- (b) Describe the complete journey of glucose from food to a body cell. In your answer, name the component of blood that carries it and explain how it reaches the cell from the blood.
- (c) Urea is transported in the plasma. State where urea is produced and where it is taken. Explain why urea must be removed from the blood.
Answer
(a) All nine substances transported by plasma
Blood cells • Ions • Glucose • Amino acids • Hormones • Carbon dioxide • Urea • Vitamins • Plasma proteins
(b) Journey of glucose from food to a body cell
- Food is digested in the small intestine and glucose is absorbed into the blood through the intestine wall.
- Glucose dissolves in the plasma and is carried in the blood to the capillaries near body cells.
- At the capillaries, blood pressure pushes plasma out through the capillary wall, forming tissue fluid. Glucose passes into this tissue fluid.
- Glucose is used by the body cells in respiration, so its concentration inside the cells is lower than in the tissue fluid.
- Glucose therefore diffuses from the tissue fluid (high concentration) into the body cell (low concentration).
(c) Urea — production, destination, and removal
- Produced in: the liver (from the breakdown of excess amino acids)
- Transported to: the kidneys
- The kidneys filter urea out of the blood and it is removed from the body in urine.
- Urea must be removed because it is a waste product — if it builds up in the blood it becomes toxic and harmful to body cells.
24.
This question is about the transfer of substances between blood, tissue fluid, and body cells.
- (a) Explain how tissue fluid forms from blood in the capillaries. In your answer, state which substances can pass through the capillary wall and which cannot.
- (b) Name two substances that move from tissue fluid into body cells. For each one, explain why it moves in this direction.
- (c) Name two waste substances that move from body cells into tissue fluid. For each one, explain why it moves in this direction.
- (d) Describe what happens to tissue fluid after it has exchanged substances with the surrounding body cells.
Answer
(a) Formation of tissue fluid
- Blood arrives at capillaries under pressure (highest at the arterial end).
- This pressure forces water and small dissolved substances out through the thin capillary wall into the spaces around body cells — this becomes tissue fluid.
- Can pass through: water, glucose, oxygen, amino acids, ions, hormones, carbon dioxide — these are small enough to fit through the capillary wall.
- Cannot pass through: red blood cells and large plasma proteins — they are too large and remain in the blood.
(b) Two substances entering body cells from tissue fluid
- Oxygen: body cells use oxygen in respiration, so the concentration inside cells is lower than in tissue fluid. Oxygen diffuses from tissue fluid (high) into cells (low).
- Glucose: body cells use glucose in respiration, so the concentration inside cells is lower than in tissue fluid. Glucose diffuses from tissue fluid (high) into cells (low).
(c) Two waste substances leaving body cells into tissue fluid
- Carbon dioxide: produced in cells as a waste product of respiration, so the concentration inside cells is higher than in tissue fluid. CO2 diffuses from cells (high) into tissue fluid (low).
- Urea: produced in cells from the breakdown of amino acids, so the concentration inside cells is higher than in tissue fluid. Urea diffuses from cells (high) into tissue fluid (low).
(d) What happens to tissue fluid after exchange
- At the venous end of the capillary, blood pressure is lower. Most of the tissue fluid is reabsorbed back into the capillary, carrying waste products (CO2, urea) into the blood.
25.
A doctor tests a patient’s blood and finds that the patient has very few red blood cells and very few white blood cells, but a normal number of platelets.
- (a) Predict one symptom this patient would show because of their low red blood cell count. Explain your answer using your knowledge of red blood cell function.
- (b) Explain the effect of the low white blood cell count on the patient’s ability to fight infection. Refer to both lymphocytes and phagocytes in your answer.
- (c) The patient’s platelet count is normal. Explain what this means for the patient’s ability to stop bleeding from a cut.
Answer
(a) Symptom from low red blood cell count
- Symptom: The patient would feel very tired and lacking in energy (or feel breathless).
- Red blood cells carry oxygen from the lungs to body cells, where oxygen is used in respiration to release energy.
- With very few red blood cells, less oxygen is delivered to the body cells.
- Cells cannot respire as efficiently, so less energy is produced — the patient feels constantly tired even without physical activity.
(b) Effect of low white blood cell count on immunity
- Fewer lymphocytes means fewer antibodies are produced. The body cannot recognise and neutralise specific pathogens as quickly or effectively. The patient will struggle to fight off specific infections and may become ill more easily.
- Fewer phagocytes means fewer pathogens are engulfed and destroyed. Pathogens that enter the body can survive and multiply for longer before being removed.
- Overall, the patient’s immune system is severely weakened. They are at much greater risk of serious infection from pathogens that a healthy person would fight off easily.
Exam tip: When a question says “refer to both lymphocytes and phagocytes,” make sure you write a separate point for each one. A combined answer will not earn full marks.
(c) Normal platelets — effect on clotting
- Because the patient’s platelet count is normal, blood clotting will work normally.
- When a blood vessel is cut, platelets will gather at the wound and trigger the conversion of fibrinogen to fibrin.
- Fibrin will form a clot that seals the wound, stopping bleeding in the usual way.
- The patient is not at increased risk of excessive bleeding from cuts.
