1. Most organisms are active in a limited temperature range.
a) Identify the role of enzymes in metabolism, describe their chemical composition and use a simple model to describe their specificity on substrates.
Metabolism is the total of all the physical and chemical reactions which occur in an organism. All chemical reactions are controlled by enzymes.
Enzymes are:
Biological catalysts that change the speed of chemical reactions by altering the activation energy (amount of energy required for a chemical reaction to occur) of a chemical reaction
Chemically unchanged at the end of the reaction and can be reused
Specific – they will only catalyse one type of chemical reaction
Made inside cells. Some work inside cells (intracellular enzymes) and some work outside cells (extracellular enzymes)
Made of proteins folded into specific shapes – these specific shapes are determined by the amino acids forming a 3D shape by forming chains that fold over each other in a specific pattern.
How do enzymes work?
1. The substrate (chemical that needs to be broken down) binds to the active site (usually 3 or 4 amino acids, this is the area that catalyses the chemical reaction) of the enzyme.
2. This forms an enzyme-substrate complex
3. A chemical reaction occurs and two new products are formed from the substrate. The enzyme is unchanged at the end of the reaction and can be used again.
NB: this process can also occur backwards where two substances bind to the active site of the enzyme then the chemical reaction occurs joining the two original substances to make a new substrate.
Common enzymes in the body:
Lactase: breaks down lactose in milk
Urease: creates urea
Protease: breaks down protein
Lipase: breaks down lipids
Amylase: breaks down carbohydrates
Model for the ‘Lock and Key’ Theory

Model for the ‘Induced Fit’ Theory

b) Identify the pH as a way of describing the acidity of a substance pH < 7 is acidic pH = 7 is neutral pH > 7 is basic/alkaline
Extreme pH changes from the optimum level at which enzymes work can denature the enzymes – change the shape of the active site of the enzyme preventing substrates from binding to the active site

c) Identify data sources, plan, choose equipment or resources and perform a first-hand investigation to test the effect of: - increased temperature
Effect of Temperature on Enzyme Activity
Aim: to investigate the effect of a change in temperature on the activity of catalase.
Hypothesis: At 39°C, the activity of catalase will be high and most efficient. Below 39°C, the activity of catalase will be low and above 39°C, there will be no activity of catalase.
Equipment List:
5 large beakers for water baths
Bunsen burner
Wire gauze
10 test tubes
Scalpel
5mL H2O2
Detergent in dropper bottle
Ruler

Risk Assessment: Hot plate could burn you so do not touch the hotplate while it is on or soon after it has been turned off. H2O2 is toxic so do not drink or spill on body and wear safety glasses. If a burn or spillage occurs, notify the teacher immediately.
Method:
1) Prepare five water baths at approximately the following temperatures (by using ice or boiling water in a beaker) –
5°C (A)
25°C (B) (room temperature)
39°C (C) (approximate body temperature for most animals)
80°C (D)
100°C (E)
2) Place 5mL of H2O2 in each of the five test tubes (labelled A, B, C, D and E) and place a test tube in each water bath. Add one drop of detergent to each to stabilise the foam.
3) Cut five small pieces of liver the same size (no bigger than a pea) and put one piece in each of the five dry test tubes. Mark these test tubes A, B, C, D and E.
4) Place one of each of the five test tubes containing liver into each of the five water baths and allow the liver to reach the same temperature as the water bath (approximately 2 minutes). (You should now have 2 test tubes in each water bath).
5) When the temperatures have stabilised, pour the H2O2 into the