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Junior Certificate Biology Chapter 2 – The Digestive System The digestive system in humans is group of organs working together to break down food. Liver Produces bile to break down fats. Small intestine Produces enzymes and carries out the final breakdown of the food. Food is absorbed into the bloodstream here. Large intestine Water passes back into the bloodstream from here producing solid waste. Anus Waste food is released through here. Mouth oesophagus Liver Small intestine Stomach Large intestine Anus Organ Function Mouth Food is mixed with saliva and chewed. Amylase enzyme breaks down the starch. Oesophagus A tube which brings the food from the mouth to the stomach by muscular action. Stomach Churns the food and mixes it with digestive juices and acid. Acid kills bacteria. Pancreas The five stages of Nutrition 1. Ingestion – taking in food. 2. Digestion – breaking down the food by chewing and churning or by enzyme. 3. Absorption – passing of food into the blood stream. 4. Assimilation – this is where body cells use the food for energy, growth and repair. 5. Egestion – getting rid of waste food through the anus. Physical digestion of food The physical digestion of food is carried out by (i) muscle action, the stomach and intestinal walls crush the food by squashing it, or (ii) crushing, using teeth to cut and grind the food. Produces digestive enzymes. 1 G. Nugent Junior Certificate Biology There are four types of teeth. Incisors A second enzyme called maltase then breaks down the maltose into glucose. Sharp flat front teeth used to cut food. Canines Pointed teeth for tearing food. Premolars Flat back teeth for grinding food Mandatory experiment; To show the action of amylase enzyme on starch. A B water at 37oC Molars Larger flat back teeth for grinding food. Chemical digestion Chemical digestion involves the use of special chemicals, called enzymes, to breakdown the large food molecules (proteins, fats and carbohydrates) into smaller ones. An enzyme can be defined as a biological catalyst. A catalyst is a chemical which speeds up a chemical reaction without itself being used up. Starch only Starch and amylase enzyme 1. In test tube A put starch only. 2. In test tube B put some starch and a few drops of amylase enzyme solution. 3. Place both in a beaker of warm water. The enzyme works best in warm conditions. 4. After 10 minutes, take out a small amount of A and B and test them with iodine solution. 5. ‘A’ will turn blue/ black due to the presence of starch. 6. ‘B’ will not change the colour of the iodine because the enzyme has converted all of the starch to maltose. 7. Test both test tubes with Benedict’s solution. 8. A shows no reaction to it. 9. B changes the blue benedict’s solution to brick red. This shows that test tube B now contains sugar. This must be due to the presence of the enzyme. How enzymes work The substance acted-on by the enzyme is called the substrate. The substance formed by the enzyme action is called the product. The enzyme works by grabbing a substrate molecule, breaking it down and then releasing the products when they are formed. An example of this is amylase enzyme. It grabs starch molecules, breaks them down into maltose molecules and then releases them. 2 G. Nugent