ZIMSEC O Level · Biology · Form 3, Form 4
Plants
- Xylem: dead, hollow, lignified vessels carrying water and minerals up from roots.
- Phloem: living cells carrying sucrose and amino acids (translocation) both ways.
- Water enters root hairs by osmosis, moves across the root, up the xylem (pulled by transpiration), and leaves as vapour through stomata.
- Transpiration increases with temperature, wind and light, and decreases with humidity. Measure it with a potometer.
Humans: the heart and circulation
- Double circulation: right side pumps deoxygenated blood to the lungs; left side pumps oxygenated blood to the body. The left ventricle wall is thickest.
- Valves (bicuspid, tricuspid and semilunar) prevent backflow.
- Arteries: thick, elastic, muscular walls; high pressure. Veins: thinner walls, valves, low pressure. Capillaries: one cell thick, for exchange.
Blood
- Red cells: haemoglobin carries oxygen; no nucleus; biconcave shape.
- White cells: phagocytes engulf pathogens; lymphocytes make antibodies.
- Platelets: clotting. Plasma: transports CO₂, glucose, urea, hormones.
Exam tip: The pulmonary artery is the only artery carrying deoxygenated blood – a favourite exam question.
Check yourself
- Why is the left ventricle wall thicker than the right?
- State the function of valves in veins.
- Name the tissue that transports sugars in plants.
Show answers
- It pumps blood around the whole body at higher pressure, not just to the lungs.
- They prevent the backflow of blood.
- Phloem.
Questions about this topic (0)
No questions about this topic yet.
Sign in or create a free account to join in.