WJEC GCSE Biology 1.3 Digestion and the Digestive System in Humans Exam Questions

About WJEC GCSE Biology 1.3 Digestion and the Digestive System in Humans

Digestion in Unit 1 explains why large insoluble food molecules must be broken down into small soluble ones that can be absorbed into the blood. You need the enzymes that digest starch, proteins and fats, the food tests for starch, glucose and protein, and the roles of the organs of the digestive system. The topic also covers peristalsis, bile, absorption in the small intestine and the use of Visking tubing as a model gut. It finishes with a balanced diet and the health effects of too much sugar, fat and salt. It builds on 1.1, and examiners often test food test results and the energy in food practical.

What you need to know

• Breakdown of food Carbohydrases break starch into sugars (glucose); proteases break proteins into amino acids; lipases break fats into fatty acids and glycerol. The products are small and soluble enough to be absorbed.
• Food tests Iodine solution turns from orange-brown to blue-black with starch. Benedict's reagent, heated, turns from blue to green, yellow or brick red with glucose. Biuret reagent turns from blue to purple with protein.
• Organs and peristalsis Know the roles of the mouth, stomach, pancreas, small intestine, large intestine and liver. Peristalsis is waves of muscle contraction that push food along the gut.
• Bile Bile is made in the liver, stored in the gall bladder and released into the small intestine. It emulsifies fats into small droplets, increasing the surface area for lipase.
• Absorption Soluble products are absorbed through the wall of the small intestine into the blood. Visking tubing can model the gut but does not have villi, blood flow or active transport.
• Diet and energy A balanced diet contains protein, carbohydrate, fat, minerals (e.g. iron), vitamins (e.g. vitamin C), fibre and water. Foods contain different amounts of energy, and excess energy is stored as fat. Investigating the energy content of foods by burning them under water is a specified practical.

Common mistakes in 1.3 Digestion and the Digestive System in Humans

• Saying bile is an enzyme or that it digests fat. Bile emulsifies fat, which increases the surface area for lipase to act on.
• Writing that Benedict's test turns red straight away. The solution must be heated, and the colour goes from blue through green and yellow to brick red depending on how much sugar is present.
• Stating that digestion happens so food can be used for energy. The key reason is that large insoluble molecules must be broken down into small soluble ones that can be absorbed.
• Forgetting the limitations of the energy in food practical. Much heat is lost to the surroundings and the food may not burn completely, so the value is lower than the true energy content.

Try three 1.3 Digestion and the Digestive System in Humans exam-style questions