specification - digestion and the digestive system in humans

• digestion - the breakdown of large molecules into smaller molecules so they can be absorbed for use by body cells
• the digestion of larger insoluble molecules into their soluble products which can then be absorbed
• fats made up of fatty acids and glycerol
• proteins made up of amino acids
• starch (a carbohydrate) made up of a chain of glucose molecules
• starch using iodine solution: brown to blue/black
• glucose using Benedict’s reagent: blue to brick red
• protein using biuret solution: blue to violet
• Carbohydrase: starch to glucose
• Protease: protein to amino acids
• Lipase: fats and oils (lipids) to fatty acids and glycerol
• the structure of the human digestive system and associated structures: the mouth, oesophagus, stomach, liver, gall bladder, bile duct, pancreas, small intestine, large intestine, anus
• Mouth - starch digestion begins by carbohydrase/ amylase in saliva
• Stomach - secretes protease
• Pancreas - secretes lipase, proteases and carbohydrase into the small intestine
• Small intestine - continued digestion of carbohydrates to glucose, proteins to amino acids, fats to fatty acids and glycerol and absorption of digested molecules
• Large intestine - absorption of water
• Liver - secretes bile
• Understand the action of contraction and relaxation of muscles in peristalsis in forcing food through the digestive system.
• Bile emulsifies large droplets of fat into small droplets to increase the surface area for enzyme action.
• Bile also increases the pH in the small intestine to the optimum pH for lipase activity.
• The small intestine has a relatively large surface area, created by villi, which contain blood vessels.
• The small intestine has a rich blood supply which maintains a steep diffusion gradient
• Visking tubing can be used as a model gut but as it has no blood supply cannot maintain a diffusion gradient.
• glycerol from fats provide energy
• glucose from carbohydrate provides energy or is stored as glycogen]
• amino acids from digested proteins are needed to build proteins in the body
• the dietary nutrients and water necessary to maintain good health will vary with age and activity levels
• Iron is needed for the production of haemoglobin,
• vitamin C is needed to maintain healthy tissue and fibre provides bulk in the digestive system
• Water is an essential part of many body functions and processes
• energy from food, when it is in excess, is stored as fat by the body
• The energy content of food eaten must be balanced with energy needs since excess energy will be stored as fat by the body
• Excess stored fat leads to obesity.
• Excess sugar can lead to type 2 diabetes, obesity, tooth decay.
• Excess fat can lead to obesity, heart disease and circulatory disease
• Excess salt (sodium) can lead to high blood pressure.
• Different foods have different energy contents. The energy content of a food can be released when you set it alight. When you hold a burning food underneath a known volume of water, the temperature increase can be measured. A simple calculation can then be used to estimate the amount of energy stored within the food.
• Investigation of the energy content of foods -

  A) thermometer

  B) boiling tube

  C) clamp stand

  D) water

  E) mounted needle

  F) burning food

  
• Method of Investigation of the energy content of foods


  1. Measure 20cm3 of water into a boiling tube

  2. Clamp the boiling tube to the clamp stand

  3. Record the temperature of the water using a thermometer

  4. Choose a piece of food and record its mass

  5. Place food onto a mounted needle

  6. Hold the food in the Bunsen burner flame, until it catches alight

  7. As soon as the food is alight, hold it under the boiling tube of water. Keep the flame directly underneath the tube

  8. Hold the food in this position until it has burnt completely. If the flame goes out, but the food is not completely burnt, quickly light it again using the Bunsen burner and hold it directly underneath the boiling tube

  9. When the food has burned completely, and the flame has gone out, immediately record the temperature of the water

  10. Repeat steps 1-9 for other foods