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How does temperature affect rate of enzyme catalysed reaction?

As temperature increases, rate of reaction increases up to a maximum rate, after which the rate decreases dramatically (faster than it increased).


Why is the graph shaped like this?

- As temperature increases towards optimum, enzyme and substrate molecules gain more kinetic energy and more collisions happen, so more substrate-enzyme complexes form.
- When temperature surpasses optimum, enzyme gets denatured so less is available to catalyse reaction, so rate of reaction decreases.


What is the action of lipase enzymes on lipids (triglycerides)?

Breaks them down into fatty acids and glycerol.


What is the independent variable?



What is the dependent variable?

Time taken for phenolphthalin to decolourise.


What variables need to be controlled?

- Volume and concentration of lipids added (volume/type of milk added).
- Volume and concentration of NaHCO3 added.
- Volume and concentration of lipase added.
- Type of lipase added.


What variable are not controlled and what effects may they have on the results?

- pH, as the end-point of the experiment is determined by the pH change. This may affect the rate of reaction as it changes (decreases throughout experiment).


What are the limitation of the experiment?

- pH not controlled.
- Milk fat not properly emulsified, so each sample may contain different concentration of fats.
- Due to improper emulsification, the milk fat may solidify/ clump more easily at lower temperatures, which decreases surface area - volume ratio and thus rate of reaction.
- Microorganisms growing in test tube may also affect results, especially at warmer temperatures.
- Human reaction time will account for a delay between decolourisation and stopping stop watch.
- Judgment as to when to count the phenolphthalin as 'decolourised' may vary between experiments/people.


What precautions need to be taken?

- Ensure all milk samples come from same milk bottle, beaker as fat concentration varies form bottle to bottle.
- Ensure milk is well shaken so fat is as well emulsified as can be.
- Repeat experiment several times to improve reliability (by identifying and eliminating outliers).
- Leave the solution (without lipase) in the water bath and allow temperature of mixture to reach desired temperature before beginning experiment.


What is the benefit of having lipases that work efficiently at low temperatures?

- Lipases are usually found in biological washing powers where they are used to remove grease stains.
- The lower the operating temperature of the lipase, the lower the washing temperature, which will save energy and cost.