(a) Define enzymes. (b) State six characteristics of enzymes. (c) Describe the role of pancreatic juice in the digestion of carbohydrates and proteins in a ...

(a) Definition of enzymes

Enzymes are organic catalysts, made of protein, produced by living cells, which speed up the rate of biochemical reactions without themselves being used up or altered in the process.

(b) Six characteristics of enzymes

1. They are proteins in nature.
2. They are specific in action (each enzyme acts on one substrate or type of reaction).
3. They are required in very small quantities.
4. They are not used up in the reaction, so they can be used again (catalysts).
5. Their activity is affected by temperature and is destroyed (denatured) by high temperature.
6. Their activity is affected by pH; each works best at an optimum pH.

(Also acceptable: their action can be reversible; their activity is affected by substrate concentration.)

(c) Role of pancreatic juice in digestion of carbohydrates and proteins

Pancreatic juice is poured into the duodenum and contains several enzymes:

• Pancreatic amylase digests starch (carbohydrate) into maltose.
• Trypsin (secreted as inactive trypsinogen and activated by enterokinase) digests proteins and peptones into smaller peptides and amino acids.

The juice is also alkaline, providing the correct pH for these enzymes to work.

(d) Form in which carbohydrate is stored

(i) In animals: glycogen (in the liver and muscles).
(ii) In plants: starch.

(e) Saprophytic nutrition of Rhizopus

Rhizopus (bread mould) feeds saprophytically on dead organic matter such as bread. It grows fine thread-like hyphae; the root-like rhizoids penetrate the food and secrete digestive enzymes onto it. These enzymes digest the food externally (extracellular digestion), breaking down starch and proteins into soluble substances. The soluble products are then absorbed through the hyphae into the fungus and used for energy and growth, while excess food is stored.