GCSE Diet, Digestion and Enzymes

• They are made of carbon, hydrogen and oxygen They are made up of large molecules (e.g. starch, cellulose and glycogen) which are polymers (=made up of chains) of simple sugars e.g. glucose, fructose. Starch from glucose, glycogen from glucose

• They are made of carbon, hydrogen, oxygen and nitrogen • They are made up of chains (polymers) of amino acids

• (fats and oils) • They are made of carbon, hydrogen and oxygen • They are made up of fatty acids and glycerol

• Get a piece of food and break it up with a pestle and mortar • Transfer the ground food to a beaker and add some distilled water • Give the mixture a good stir with a glass rod to dissolve some of the food • Filter the solution suing a funnel lined with filtered paper to get rid of the solid bits of food

• The food sample is placed on a spotting tile. • A drop of yellow-brown iodine solution is added to the starch. • The positive result turns blue-black and the negative result turns brown • The iodine solution reacts with the starch to form a blue-black colour • Starch is insoluble but the test will work on a solid sample of food or a food sample

• Glucose is a reducing sugar • Add 2cm^3 of distilled water to a test tube • Add a small piece of your food sample • Add a bung and shake • Add 5 drops of Benedict’s Reagent to the tube • Heat the tube in a boiling water bath for 4 mins • Results are a scale. Blue=none then it goes: green, yellow, orange, brick red (most)

• Add 2cm^3 of water to a test tube • Add a small piece of your food sample • Add a bung and shake the tube • Add biuret solution to the sample and mix it by shaking it • Positive results = blue->purple, negative result = stays blue

• Fats and oils are insoluble in water but will dissolve in ethanol • Place one drop of lipids in a test tube • Add 2cm^3 ethanol and then shake the tube to dissolve the lipid • The solution is poured into a test tube that is about three quarters full with cold water * A cloudy emulsion forms on top of the water as ethanol dissolves in the water and the lipid is left behind as a suspension of tiny droplets

• Enzymes are biological catalysts. Catalysts speed up chemical reactions without being used up in the reaction. • The molecule that an enzyme acts on is called a substrate. Each enzyme has a small area on its surface called an active site, which is where the substrate attaches to. • The substrate fits into the active site of the enzyme. A substrate will only fit into the active site of a particular enzyme. The active site has to be complimentary with the substrate. (Lock and key model). This means that enzymes are specific - they will catalyse only one reaction. 1. The substrate enters the enzyme’s active site 2. The bind together to form an enzyme-substrate complex 3. Chemical reaction happens 4. Products are released after being broken down

• In humans, the optimum temperature of enzymes in the body is 37C (body temp). • As the temperature of the surroundings of an enzyme get closer to 37, the rate of reaction increases as it gives the molecules move KE so they collide more often so reactions occur more frequently. • Above the optimum temperature, something different happens. Enzymes are made up of proteins and proteins break down by heat. • From 40C upward, the enzyme becomes denatured. Denaturing changes the shape of the active site so the substrate can no longer fit into it. Denaturing is permanent - the enzyme will no longer catalyse the reaction. • Google what a graph of temperature on enzymes should look like.

• The pH around the enzyme is important. The pH inside cells is neutral, 7 and most enzymes have evolved to work best at this pH. • At the extremes of the pH scale, enzyme activity decreases. • The pH where the enzymes work best is called its optimum temperature (where rate of reaction is fastest) and the pH can denature an enzyme. Denaturing changes the shape of the active site so the substrate can no longer fit into it. Denaturing is permanent - the enzyme will no longer catalyse the reaction. • For some enzymes like those in the stomach, extremely acidic pHs do not denature it as it is used to a low pH. • Google what a graph of pH on enzymes should look like.

• The digestive enzyme amylase breaks starch down into the sugar maltose. If the speed at which the starch disappears is recorded, we get a measure of the activity of the amylase. • Spots of iodine solution are placed in the dips of a spotting tile. Using a syringe, 5cm^3 of starch suspension is placed in a boiling tube and 5cm^3 of amylase solution into another tube using a different syringe. The beaker is filled with water at 20C. Both boiling tubes are places in the beaker of water for 5 minutes and the temperature is recorded. • The amylase solution is then poured into the starch suspension, leaving the tube containing the mixture in the water bath. Immediately a small sample of the mixture is removed from the tube with a pipette and added to the first drop of iodine solution on the spotting tile. The colour of the iodine solution is recorded. • A sample of the mixture is taken every 30 seconds for 10 minutes and tested for starch as above until the iodine solution remains yellow, showing that all of the starch has been used up. • The experiment is repeated maintaining the water bath at different temperatures between 20C and 60C (going up by 10 each time except for one that is at body temp). • The rate of reaction can be calculated from the time taken for the starch to be fully broken down as shown by the colour change from blue-black to yellow. The rate is found by dividing the volume of the starch (5cm^3) by the time to get x cm^3/min. • Google what a graph of temperature on enzymes should look like.

• Appropriate proportions of water, vitamins, minerals, proteins, lipids, carbohydrates and dietary fibre

• They are the body’s main ‘fuel’ for supplying cells with energy - the provide energy. • Found in pasta, rice, sugar.

• Helps with growth an repair of tissues • Found in meat and fish

• Energy store, provides insulation (under the skin) • Found in dairy products (butter, milk, cheese etc.), oily fish

• Making a chemical in the retina, also protects the surface of the eye • Deficiency = night blindness, damaged corner of eye • Found in fish liver oils, liver, butter, margarine, carrots

• Sticks together cells lining surfaces such as the mouth • Deficiency = scurvy • Found in fresh fruit and vegetables

• Helps bones absorb calcium and phosphate • Deficiency = rickets, poor teeth • Found in fish liver oils, also made in skin in sunlight

• Making teeth and bones • Found in dairy products, fish, bread, vegetables

• Part of haemoglobin in red blood cells, helps carry oxygen • Found in red meat, liver, eggs, some vegetables (e.g. spinach)

• Nearly every bodily function needs water. We need a constant supply of water to replace water lost through urinating, breathing and sweating • Found in food and drink

• Aids the movement of food through the gut by giving the muscles in the gut something to push against as the food is moved through the intestine • Found in wholemeal bread and fruit. It is mostly cellulose.

• Activity level - active people need more energy than people who sit about all day • Age - children (above 6) and teenagers need more energy than older people as they need energy to grow and they are generally more active • Pregnancy - pregnant women need more energy than other omen as they need to provide the energy for their babies to develop