01/10/2016 Food and Digestion W Richards Worthing High School

Why do we need food? We need to consume a balanced diet which contains a variety of food in the proportions shown in the diagram. The body needs: Carbohydrates which provide energy. Proteins for repair and growth. Vitamins and minerals to keep the body healthy.

01/10/2016 Food types Type Found in Uses Carbohydrates Fats Proteins Vitamins Minerals Fibre Water Bread, potatoes, cereal Cream, butter, milk, oil Meat, fish, eggs Vegetables, cereal Meat, milk, cereal Fruit + veg, cereal Water! Energy A store of energy Building and repairing cells Keep things “ticking over” Strong teeth etc 75% of the body is water Keeps you regular!

What do carbohydrates provide? Starchy foods contain carbohydrates, which are made of long chains of identical small sugar molecules. Carbohydrate 1 Sugar molecule

The body has to break these large food molecules up into smaller pieces. The small sugar molecules are very useful. The body can use them to make… This energy is used to make the body work. ENERGY What do carbohydrates provide?

What do proteins provide? As with carbohydrates, proteins are made of chains of chemicals. However, instead of the chain containing identical molecules, in protein these molecules are different. Protein is made up of chains of amino acids. There are over 20 different kinds of amino acid. Protein is used to allow the body to grow and to repair the body.

01/10/2016 Food tests 1 To investigate what happens in digestion we need to be able to test for different foods. Here are two simple tests: 1)The test for starch: Drop some iodine onto the food. If the iodine turns BLUE/BLACK then STARCH is present. 2)The test for simple sugars (e..g glucose) Boil the food with some Benedict’s solution. If an orange “precipitate” appears then the food contains simple sugars Iodine

01/10/2016 Food tests 2 1)The test for protein: Add 5cm3 of dilute sodium hydroxide followed by 5cm3 of dilute copper sulphate. If protein is present it will produce a purple colour. 2)The test for fats: Shake the food with about 10cm3 of ethanol in a test tube. Pour some of the solution into a tube containing water. If fat is present the water will turn cloudy white.

01/10/2016 The digestive system The whole point of digestion is to break down our food so that we can get the bits we need from it… The main foods affected are CARBOHYDRATES – these are broken down into GLUCOSE

Food is firstly broken down (mechanical breakdown) into smaller parts by the teeth in the mouth. It is then mixed with saliva and swallowed. Mechanical digestion

Food enters the stomach, which is basically a muscular bag, filled with hydrochloric acid (HCl). Two things happen here: Chemical breakdown of the food. Microbes are destroyed. food enters from the gullet cross section of stomach digested food leaves muscle tissue The stomach

The small intestine Food enters the small intestine from the stomach. It passes along the small intestine where the soluble food is taken into the blood through the walls.

01/10/2016 The small intestine This is where the “small parts” are absorbed into our blood stream… Glucose gets absorbed into the blood Everything else passes into the large intestine

The large intestine The remains of the food are then passed on to large intestine (colon). All that is left is waste material and water. The body will want to leave the waste material within the digestive system but the water is valuable and so it is re-absorbed here. The waste material is passed to the rectum where it is stored until it leaves the body through the anus.

Why breakdown large molecules into smaller ones? The body must go through mechanical and chemical digestion to convert large insoluble molecules into smaller soluble ones. Carbohydrate molecule Protein molecule (folded up) Fat molecule This is because smaller molecules can pass through the walls of the small intestine and then dissolve into the blood stream. Larger molecules cannot do this. Sugar

Enzymes Enzymes are chemicals which break the larger molecules down into smaller molecules. There are three types of enzymes that you need to know about.

Enzymes Carbohydrase chops carbohydrates into smaller sugar molecules. The three types of enzymes are: Protease cuts proteins into the soluble amino acids. Lipase breaks fats down into the smaller fatty acids and glycerol.

Proteins are digested in the stomach by an enzyme called Protease. This enzyme needs to work in an acidic environment. Protease breaks proteins (chains of different molecules) down into up to 20 different amino acids (four of which are shown). Proteins digestion Protease Folded up protein chain Amino acids

Carbohydrates are chains of identical sugar molecules. The enzyme called Carbohydrase breaks the chemical bonds between the individual sugar molecules (called glucose) as part of digestion. Starch/ carbohydrates Carbohydrase Long carbohydrate Small sugar

Fats Fats are digested in two stages: Firstly bile (released by the gall bladder) allows the fat to “mix” with water by breaking the fat up into smaller droplets. This is called emulsification. Secondly, an enzyme called Lipase breaks the fats down into the smaller fatty acid molecules and glycerol. Bile Lipase + Fat Fatty acid Glycerol

01/10/2016Enzymes Enzymes are chemicals produced by the body to help _______. When they react with food they break it down into ______ pieces which can then pass into the ______: Carbohydrase breaks _______ (a carbohydrate) down into glucose: Protease breaks _______ down into amino acids: Lipase breaks fats (_____) down into fatty acids and glycerol: Words – blood, lipids, proteins, digestion, starch, smaller