Section 2 c) Specfication

2.5 identify the chemical elements present in carbohydrates, proteins and lipids (fats and oils)

In carbohydrates and lipids, there are CHO: Carbon, Hydrogen and Oxygen.
In proteins, there are CHON: Carbon, Hydrogen, Oxygen and Nitrogen.

2.6 describe the structure of carbohydrates, proteins and lipids as large molecules made up from smaller basic units: starch and glycogen from simple sugar; protein from amino acids; lipid from fatty acids and glycerol

Starch and glycogen are carbohydrates that are polymers, their monomers being simple sugars (monosaccharides) such as glucose: C6H12O6

Proteins are made of amino acids, which join together to form unique shapes and combinations, important for each protein to have its own properties.

Lipids are made up of fatty acids and glycerol, in this structure:

2.7 describe the tests for glucose and starch

Starch: Test using iodine solution. If it changes from brown-orange to blue-black, there is starch present.

Glucose: heat with Benedict's solution. It will turn red if positive.

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

Enzymes work with the lock and key model. They are a certain shape that allows substrates to fit in, then bond together or break apart in the active site. It speeds up the reaction. They are useful in digestion, enzymes such as protease break up proteins, amylase breaks up starch into glucose,

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

The active site of the enzyme is the most important part of it. It allows the enzyme to take part in metabolic reactions, however if it is put in conditions that are too far from the optimum it can be damaged. In high temperatures, the shape of the active site can be changed, rendering the enzyme useless. The enzyme is denatured.

This curve depicts the way temperature affects enzymes:

Beyond the optimum temperature, the enzyme is denatured. Leading up to the optimum temperature, the enzyme activity increases due to increasing kinetic energy of the particles which increases the rate of collisions.

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

Extreme change in pH can also cause the enzyme to be denatured. This varies depending on the optimum pH of the enzyme, but a very extreme pH will denature any enzyme. 

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

1. Place test tubes containing the same mixture of amylase and starch in water baths of different temperatures with regular temperature intervals (e.g. 20℃, 30℃, 40℃, 50℃, 60℃, 70℃)
2. Take a sample from each at regular time intervals (every 30 seconds) and test for starch with iodine
3. Record which sample was the first to not test positive for starch.
From this, you can see how long it took for the enzyme to break down the starch. It can be graphed to determine the optimum temperature.