Digestion, the heart and blood

The idea

Enzymes are biological catalysts with an active site that fits one substrate (lock and key). Amylase breaks starch into sugars, proteases break proteins into amino acids, and lipases break lipids into fatty acids and glycerol. Bile, made in the liver, neutralises stomach acid and emulsifies fats. The heart's right side pumps blood to the lungs; the left side pumps it to the body. Blood is plasma carrying red cells, white cells and platelets.

1. Match each enzyme to its substrate and products.
2. Trace blood through the heart.
3. Link each blood vessel or blood part to its function.

Watch out Bile is not an enzyme: it emulsifies fats, increasing their surface area for lipase.