Transport questions

Transport syllabus

Questions on transport can test recall, calculations, explanations, diagrams, data handling and practical skills. You should be able to:

• 2.51 explain why unicellular organisms can rely on diffusion for transport.
• 2.52 explain why multicellular organisms need transport systems.
• 2.53 describe phloem transport of sucrose and amino acids.
• 2.54 describe xylem transport of water and mineral ions from the roots.
• 2.55B explain how root hair cells absorb water.
• 2.56B define transpiration as evaporation of water from a plant’s surface.
• 2.57B explain how humidity, wind speed, temperature and light intensity affect transpiration.
• 2.58B investigate environmental factors affecting transpiration from a leafy shoot.
• 2.59 describe red blood cells, white blood cells, platelets and plasma.
• 2.60 explain plasma’s role in transporting carbon dioxide, digested food, urea, hormones and heat.
• 2.61 link red blood cell shape, lack of a nucleus and haemoglobin to oxygen transport.
• 2.62 explain phagocytosis and the production of specific antibodies by lymphocytes.
• 2.63B explain vaccination, memory cells and the faster, larger antibody response to later infection.
• 2.64B explain the role of platelets in clotting, preventing blood loss and pathogen entry.
• 2.65 describe the structure and function of the heart.
• 2.66 explain changes in heart rate during exercise and under adrenaline.
• 2.67 explain risk factors for coronary heart disease.
• 2.68 relate artery, vein and capillary structure to function.
• 2.69 describe circulation through the heart, lungs, liver and kidneys, including the main blood vessels.

How to answer transport questions

1. Trace the named substance through the relevant organs, tissues and cells in the correct order.
2. Link structural adaptations to diffusion distance, surface area, concentration gradient or transport rate.
3. Use balanced biological equations where required and distinguish respiration from breathing.
4. When explaining a data trend, quote evidence and connect it to the underlying biological process.

Transport example questions and worked answers

These examples show how information in a diagram, graph or experimental context becomes part of a complete exam answer.

Example 1: Evaluating a transpiration experiment

Adapted from June 2019, Paper 2B · Question 2(c)

Question 1

A student uses this method to investigate the role of leaves in transpiration.

• remove four leaves from a plant
• cover the upper surface of one leaf with petroleum jelly
• cover the lower surface of one leaf with petroleum jelly
• cover both surfaces of one leaf with petroleum jelly
• keep one leaf uncovered
• measure the mass of each leaf
• suspend the leaves for several hours in air

After several hours, the student measures the mass of each leaf again.

The graph shows his results.

The student concludes that transpiration occurs mainly from the upper surface of leaves. Evaluate this conclusion.

Final answer

I disagree with the conclusion. The leaf with its upper surface covered loses more mass than the leaf with its lower surface covered, so most mass is lost from the lower surface. Stomata are found on the lower surface.

Mark scheme points

1. M1 States that mass is lost from the lower surface or when the upper surface is covered; alternatively, little or least mass is lost from the upper surface or when the lower surface is covered.
2. M2 States that stomata are on the lower surface, or that there are few or no stomata on the upper surface.
3. M3 Disagrees with the student's conclusion.

Explanation

Compare the decrease in mass for the leaves: more mass is lost when the upper surface is covered than when the lower surface is covered. This indicates that most mass is lost from the exposed lower surface. Stomata, through which water vapour leaves the leaf during transpiration, are mainly on the lower surface. Therefore, the results do not support the student's conclusion that transpiration occurs mainly from the upper surface.

Common mistakes

• The examiner report notes that candidates often struggled to describe the results: refer to mass lost and identify the lower surface (or the leaf with its upper surface covered), rather than writing only about water loss.

Example 2: Explaining damage to heart muscle

Adapted from January 2020, Paper 2B · Question 3(b)

Question 2

The human heart pumps blood when its muscle tissue contracts.

Diagram 1 shows a human heart and a cross-section through its ventricles.

Ventricle muscle tissue is damaged if the blood supply is reduced.

Diagram 2 shows the damaged part of a human heart and a cross-section through its ventricles.

Explain the cause of the change in the appearance of the muscle tissue in diagram 2.

Final answer

A coronary artery is blocked, so less blood, oxygen and glucose reach the ventricle muscle. This reduces aerobic respiration and energy release, causing muscle cells to die; the ventricle wall therefore has less muscle and appears thinner.

Mark scheme points

Any 3 of these points are needed for the 3 marks:

1. M1 The coronary artery is blocked or less blood passes through it.
2. M2 The ventricle muscle receives less oxygen or glucose.
3. M3 Less respiration occurs, or less energy / ATP is produced.
4. M4 Muscle cells or tissue die.
5. M5 The ventricle wall is thinner or has less muscle.

Explanation

The coronary arteries supply blood to the heart muscle. If one is blocked, less blood reaches the ventricle muscle, so it receives less oxygen and glucose. These are needed for aerobic respiration, which releases energy for the muscle cells. If the supply is too low, muscle cells can die, leaving less muscle in the ventricle wall and changing its appearance.

Common mistakes

• The examiner report noted that fewer candidates named the coronary artery. Identify this vessel and state that blood flow to the ventricle muscle is reduced.
• “The heart dies” alone is ignored; refer specifically to muscle-cell or tissue death, or to the thinner ventricle wall.

Practise Transport questions

Build a focused practice set from this part of the Edexcel IGCSE Biology syllabus.