c) Biological Molecules
2.5 identify the chemical elements present in carbohydrates proteins and lipids (fats and oils)
Carbohydrates: Carbon Hydrogen Oxygen

Proteins: Carbon Hydrogen Oxygen Nitrogen
Lipids: Carbon Hydrogen Oxygen

2.6 describe the structure of carbohydrates, proteins and lipids as large molecules made up from smaller basic units
Carbohydrates: large molecules (eg. starch and glycogen) are made from simple sugars (eg. glucose)
Proteins: large molecules are made up of amino acids
Lipids: large molecules are made up of fatty acids and glycerol

2.7 describe the tests for glucose and starch
Test for glucose/reducing sugar:

• Add Benedict's reagent to the sample of food
• Heat it (with out boiling) in a water bath
• If glucose is present it will form a coloured precipitate

Test for starch:

• Add iodine solution to the sample
• If starch is present it will turn from an orange/brown colour to a blue/black colour

2.8 understand the role of enzymes as biological catalysts in metabolic reacions

Enzymes are biological catalysts whose purpose is too speed up metabolic reactions, without them, the reactions in our body would be too slow to sustain life.

Catalyst: a substance that increases the speed of a reaction, without being changed or used up

Enzymes are REACTION SPECIFIC because the active site only fits one specific substrate.

2.9 understand how the functioning of enzymes can be affected by changes in temperature, including changes due to change in active site

• At first, the higher the temperature, the faster the reaction because, since the temperature is higher, the enzymes ans substrates have more energy, which causes them to move around faster and causes a higher collision rate. And therefore a faster reaction
• If it gets too warm, the enzyme's active site changes shape, which means the enzyme-substrate complex can no longer be formed. The enzyme is now denatured (an irreversible change). Therefore the rate decreases rapidly
• Each enzyme has it's own optimum temperature - in humans it is 37 degrees Celsius (body temperature)

TRIPLE CONTENT: 2.10 understand how the functioning of enzymes can be affected by changes in active site caused by changes in pH

• If the pH is too high or too low, it interferes with the bonds holding the enzymes together and the active site deforms and the enzyme becomes denatured. Which rapidly slows down the rate of reaction.
• Each enzyme has a different optimum pH eg pepsin breaks down protein in the stomach and has a optimum pH of 2

2.11 describe experiments to investigate how enzyme activity can be affected by changes in temperature

You can measure how fast a product appears:

• Catalase catalyses the breakdown of hydrogen peroxide into water and oxygen
• You would put the hydrogen peroxide and a source of catalase (eg raw potato slices) into a conical flask or boiling tube. 
• You would attach a gas syringe to the boiling tube/conical flask using a delivery tube.
• You would put the boiling tube/conical flask into a water bath at a set temperature eg 30C
• You would wait about ten minutes and then measure how much oxygen has been produced
• Run a series of experiments at different temperatures (eg 20C, 40C, 50C, 60C) to see how it affects the catalase enzyme
• CONTROL VARIABLES: to make it a fair test keep the enzyme concentration, the pH and the volume of hydrogen peroxide solution the same

You can also measure how fast a substrate disappears:

• Amylase catalyses the breakdown of starch to maltose
• You would put the starch solution and amylase solution into a boiling tube and place it into a water bath at a set temperature eg 30C
• Each minute you would sample the mixture using a pipette and putting a drop of it onto a spotting tile and adding iodine solution
• Once the iodine no longer turns blue-black - starch is no longer present and you can stop the experiment
• Repeat for other temperatures eg 20C, 40C, 50C and 60C
• CONTROL VARIABLES: to make it a fair test keep the enzyme concentation, pH and the volume of starch solution the same.