12.1 Transport systems

Mass transport Over large distances in organisms, efficient supply of materials is

provided by mass transport (the bulk movement of substances

through transport systems).

The transport systems of larger organisms are intimately linked with

specialised exchange systems, whose main function is to maintain

concentration gradients.

Mammalian heart The structure and function of the heart, including the atria and

ventricles, atrioventricular and semilunar valves. The cardiac cycle

related to the maintenance of blood flow through the heart.

Candidates should be able to relate pressure and volume changes

in the heart and aorta to events in the cardiac cycle.

Blood vessels The structure of arteries, arterioles, veins and capillaries related to

their functions.

Exchange of materials The main substances transported by the blood system, and the sites

at which exchange occurs.

The loading, transport and unloading of oxygen in relation to the

oxygen haemoglobin dissociation curve, and the effects of pH and

carbon dioxide concentration.

Tissue fluid The relationship between blood, tissue fluid, lymph and plasma.

The role of the lymph system in the return of tissue fluid to the

blood system.

12.2 The control of breathing and


Control of ventilation The role of the medulla in the brain and of the stretch receptors in

the lungs in the maintenance of breathing.

The role of the medulla in the brain and of the receptors in the

lungs, aortic bodies and carotid bodies in the response of the

breathing system to increased muscular activity.

Control of heartbeat The role of the sinoatrial node, the atrioventricular node and the

bundle of His in the maintenance of the heartbeat.

The role of the medulla, pressure receptors and chemoreceptors in

the walls of the aorta and carotid sinuses in the response of the

heart to increased muscular activity.

12.3 Energy and exercise

Energy sources Glucose, glycogen and triglycerides as sources of energy for muscle


ATP as the immediate energy source.

Comparison of aerobic and anaerobic respiration as sources of ATP

for muscle contraction, in terms of amounts of energy produced

and products. (Biochemical details of pathways are not required.)

Muscle fatigue Muscle fatigue in terms of increase in blood lactate and decrease in

blood pH.

The fate of lactate.

12.4 The transport of substances in


Root structure Structure of a primary root, to include root hairs, endodermis,

xylem and phloem. The distribution of these tissues and their

adaptations for function.

Uptake and the transpiration


Uptake of water and ions from the soil.

Pathway of transport of water from root hairs to stomata, including

apoplast and symplast pathways in the root.

Transpiration, and the effects of light, temperature, humidity and

air movement.

The roles of root pressure and cohesion–tension in moving water

through the xylem.

Xerophytes Structural adaptations that reduce the rate of transpiration in

xerophytic plants, related to survival in dry conditions.

Translocation Phloem as the tissue that transports organic substances.

The mass flow hypothesis for the mechanism of translocation in


Experimental evidence The use of radioactive tracers and ringing experiments to determine

the movement of ions and organic substances through plants.

Candidates should be able to interpret evidence from tracer and

ringing experiments and to evaluate the evidence for and against the

mass flow hypothesis.