Give reasons:

(a) Ventricles have thicker muscular walls than atria.

(b) Transport system in plants is slow.

(c) Circulation of blood in aquatic vertebrates differs from that in terrestrial vertebrates.

(d) During the daytime, water and minerals travel faster through xylem as compared to the night.

(e) Veins have valves whereas arteries do not.

(a) Ventricles have thicker muscular walls than atria because ventricles have to pump blood to various distant organs of the body under high pressure, whereas atria only receive blood or pump it into the ventricles directly below them.

(b) The transport system in plants is slow because plants are stationary (do not move) and have a large proportion of dead cells (such as sclerenchyma and mature xylem elements) in many of their tissues. Consequently, they have very low energy needs.

(c) Circulation in aquatic vertebrates (like fish) differs from terrestrial vertebrates because fish have a two-chambered heart where blood is pumped to the gills, oxygenated, and sent directly to the rest of the body (single circulation). Terrestrial vertebrates have three- or four-chambered hearts where blood passes through the heart twice during each complete cycle (double circulation) to ensure efficient separation of oxygenated and deoxygenated blood.

(d) During the daytime, water and minerals travel faster through xylem because the stomata are open, making transpiration very active. The transpiration pull acts as the major driving force for the upward movement of water. At night, when stomata are closed, transpiration pull is negligible, and transport relies mainly on the slower process of root pressure.

(e) Veins have valves whereas arteries do not because arteries carry blood away from the heart under high pressure, which naturally keeps the blood flowing in one direction. Veins carry blood back to the heart under much lower pressure, so they require valves to prevent the backflow of blood and ensure it flows only towards the heart.