B3 Organisation and the Digestive System

• the liver produces bile
• bile contains bile salts which emulsify fats (break them down)
• organs are a collection of tissues
• tissues are a group of cells with similar structures and functions working together
• the pancreas makes hormones to control blood sugar levels and enzymes that digest food.
• The food you take in and eat is made up of large insoluble molecules. They need to be broken down into smaller soluble molecules that can be absorbed by blood and used in cells. 
• The small intestine is adapted to have a very large surface area and is covered in villi, to increase the rate of active transport and diffusion. It also has a very good blood supply and short diffusion distances.  
• the liver produces bile
• the stomach breaks down large insoluble molecules into smaller soluble ones
• the small intestine is the site of absorption of food into blood and also breaks down large molecules into smaller ones
• large intestine is where water is absorbed for undigested food
• carbohydrates provide the fuel needed for the reactions of life
• all carbs are made from sugars
• carbs made from one unit of sugar (glucose) or two units of sugar (sucrose) are called simple sugars
• carbs made from long chains of sugar units bonded together are complex carbs
• lipids can be fats (solids) or liquids (oil)
• all lipids are insoluble in water
• protein molecules are made from long chains of amino acids, joined together by special bonds
• the bonds that hold protein molecules together are very sensitive to temperature and pH, if these exceed optimum conditions, the protein will denature
• enzymes are built from proteins
• If we are testing something for starch, we would add iodine. If starch is found, the iodine would go from yellow/red to blue/black. 
• If we are testing for glucose, we would add benedict's solution to the food in a test tube, place in the water bath and once out, if a positive result is obtained, the solution will turn from blue to brick red. 
• If we are testing for lipids, we would add ethanol and if we receive a positive result, the solution will turn cloudy. 
• If we are testing for proteins, you would add biuret. If protein is found, the solution will go from blue to purple. 
• Salivary glands produce saliva which contains an enzyme called amylase. This breaks down carbohydrates (starch) into sugars such as maltose, sucrose and lactose.
• A catalyst speeds up a reaction but is not used up in the reaction so can be used repeatedly.
• Enzymes are large protein molecules.
• The long chains of amino acids are folded to produce a molecule with an active site that has a unique shape so it can bind to a specific substrate.
• The substrate of the reaction that is to be catalysed fits into the active site of the enzyme. Once in place, the substrate and the active site bind together. The reaction then takes place rapidly and the products are released from the surface of the enzyme.
• The reactions that take place in cells happen at a relatively low temperature. The rate of enzyme-controlled reactions increase as the temperature increases.  
• after 40 degrees, the protein structure of the enzymes can break so the folded protein chain unravels, causing the active site to change shape so it will no longer fit the substrate (denature)
• Enzymes that break down carbohydrates are called carbohydrase. Starch is most common and is broken down into sugars in your mouth and your small intestine. This reaction is catalysed by an enzyme called amylase. 
• The digestion of protein foods are catalysed by protease enzymes. Proteases are produced by your stomach, pancreas and small intestine.
• Lipids (fats and oils) are broken down into fatty acids and glycerol in the small intestine. The reaction is catalysed by lipase enzymes, which are made in your pancreas and small intestine. 
• digestion is the breaking down of large insoluble molecules into smaller soluble molecules. this happens so food molecules can be absorbed into the blood
• the small intestine has villi for a larger surface area to speed up the movement of digested food molecules into the bloodstream
• amylase is produced in the small intestine, the salivary gland and the pancreas
• protease is produced in the small intestine, the pancreas and the stomach
• lipase is produced in the pancreas and the small intestine
• HCl is also produced in the stomach, it is very acidic to kill off pathogens and create optimum pH for protease