CCEA GCSE Biology 1.4 Enzymes and Digestion Exam Questions

About CCEA GCSE Biology 1.4 Enzymes and Digestion

Enzymes and Digestion sits in CCEA GCSE Biology Unit 1 and combines how enzymes work with how food is digested and absorbed. You need to explain enzyme action using the active site and the lock and key model, describe the effects of temperature and pH, and carry out the prescribed practical on temperature and enzyme activity. You then apply this to the digestive system: where amylase, protease and lipase act, what bile does and how the ileum is adapted for absorption. It links to food tests, diffusion and the circulatory system. Examiners commonly test denaturation explanations, interpreting rate graphs and calculating rate as 1 / time.

What you need to know

• How enzymes work Enzymes are proteins that act as biological catalysts, speeding up reactions without being used up. The substrate fits into the active site, which has a specific shape that is complementary to the substrate (lock and key model), forming an enzyme-substrate complex.
• Temperature and pH Activity increases with temperature up to an optimum because molecules move faster and collide more often. Above the optimum the active site changes shape and the enzyme is denatured, so the substrate no longer fits. Each enzyme also has an optimum pH; pepsin in the stomach works best at an acidic pH.
• Prescribed practical: temperature and enzymes Mix amylase and starch at different temperatures in water baths and take samples at regular intervals into iodine on a spotting tile. Record the time until the iodine stays orange-brown (no starch left). Rate can be calculated as 1 / time.
• Digestive enzymes Amylase (from salivary glands and the pancreas) breaks down starch into maltose. Protease (from the stomach and pancreas) breaks down proteins into amino acids. Lipase (from the pancreas) breaks down fats into fatty acids and glycerol.
• Bile Bile is made in the liver and stored in the gall bladder. It neutralises stomach acid, giving alkaline conditions for enzymes in the small intestine, and emulsifies fats into small droplets, increasing the surface area for lipase.
• The ileum and villi Small soluble products are absorbed in the ileum. Villi give a large surface area, have walls one cell thick for a short diffusion distance, and have a good blood supply (capillaries) that keeps a steep concentration gradient. Lacteals absorb fatty acids and glycerol.

Common mistakes in 1.4 Enzymes and Digestion

• Writing that enzymes are killed at high temperatures. Enzymes are not living; they are denatured because the active site changes shape.
• Saying that bile is an enzyme or that it digests fat. Bile emulsifies fat, which increases the surface area for lipase to act on.
• Explaining a faster rate at higher temperature without mentioning more collisions between enzyme and substrate molecules.
• Stating that starch is broken down directly to glucose by amylase. At GCSE, amylase breaks starch into maltose.
• Saying villi have thin walls without linking it to a shorter diffusion distance and faster absorption.

Try three 1.4 Enzymes and Digestion exam-style questions