Transport and Circulation
What you must understand
In mammals, blood travels in a double circulation: right side of the heart to the lungs, left side to the body. Know the heart chambers, valves, arteries, veins and capillaries, and the direction of flow. Blood contains red cells (haemoglobin carries oxygen), white cells (defence), platelets (clotting) and plasma (transport of dissolved substances).
Learn the blood vessel adaptations: arteries have thick elastic walls and narrow lumens; veins have thin walls and valves; capillaries are one cell thick for exchange. Understand how the heart rate changes with exercise and how the nervous system controls it.
In plants, xylem transports water and minerals upward (dead, hollow cells; transpiration pull) and phloem transports sugars (living cells; translocation). Transpiration is affected by light, temperature, humidity and wind.
Traps examiners set
- Mixing up the sides of the heart - the left ventricle is thickest because it pumps to the whole body.
- Saying arteries always carry oxygenated blood - the pulmonary artery carries deoxygenated blood.
- Confusing xylem and phloem direction and contents.
- Describing transpiration as "plants sweating" without linking to water loss through stomata.
Worked rule of thumb
Use a two-column table in your head: vessel type → wall thickness, lumen, valves, direction of flow. For plant transport, remember "xylem up, phloem both ways" and link each to the tissue's cell structure.