(a) State one function of each of the following structures: (i) Arteries (ii) Capillaries (iii) Veins (iv) Xylem (v) Phloem (b) Describe the changes that ta...

(a) One function of each structure

• (i) Arteries: carry blood at high pressure away from the heart to the body organs.
• (ii) Capillaries: allow exchange of materials (oxygen, food, carbon dioxide, wastes) between the blood and the body cells.
• (iii) Veins: carry blood at low pressure back to the heart (their valves prevent backflow).
• (iv) Xylem: conducts water and dissolved mineral salts from the roots up to the leaves (and gives support).
• (v) Phloem: conducts (translocates) manufactured food such as sucrose from the leaves to other parts of the plant.

(b) Changes in the composition of blood as it passes through the

• (i) Lungs: blood gains oxygen and loses carbon dioxide (becomes oxygenated).
• (ii) Liver: excess glucose is removed and stored as glycogen so blood sugar is regulated; amino acids are deaminated so urea is added; toxins are removed; blood may gain heat.
• (iii) Kidneys: urea, excess salts and water are removed, so the blood leaving is purified of nitrogenous waste.
• (iv) Small intestine: blood gains digested food such as glucose, amino acids, vitamins and mineral salts (it becomes rich in nutrients after a meal).

(c) Cellular components of blood

1. Red blood cells (erythrocytes)
2. White blood cells (leucocytes)
3. Platelets (thrombocytes)