Watching blood flow
Blood flows round the body in a closed system of vessels, pumped by the heart. Activity 6.3 lets you watch it.
Activity 6.3 — blood flowing in capillaries
Wrap a small live fish or a tadpole in wet cotton wool, leaving the tail free. Lay it on a glass slide and look at the thin tail under the low power of a microscope. Return the animal to water quickly.
The observation
Blood cells move in single file along very narrow vessels, the capillaries, that join bigger vessels.
Arteries
Carry blood away from the heart
Capillaries
Exchange substances with the cells
Veins
Carry blood back to the heart