Starter quiz
- In most reactions, what will an increase in temperature result in?
- An increase in the rate of a reaction ✓
- A decrease in the rate of a reaction
- No change to the rate of a reaction
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- What type of microscopic organisms carry out decomposition?
- animals
- plants and fungi
- humans and plants
- bacteria and fungi ✓
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- In enzyme catalysed reactions, how will an increase in temperature affect the rate of the reaction?
- The reaction will increase as the temperature increases
- The reaction increases until the enzyme starts to denature - the reaction slows ✓
- The enzyme works at the same rate whatever the temperature
- The rate slows down as the temperature increases
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- What is meant by the 'optimum' temperature in an enzyme catalysed reaction?
- When the enzyme is working fastest ✓
- When the enzyme is becoming denatured
- When there are small numbers of collisions between the enzyme and substrate
- When there is no substrate left for the enzyme to break down
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- Why are moisture levels important in the rate of decomposition?
- Decomposers need water to carry out respiration
- Decomposers need water in order to photosynthesise
- Decomposers are aquatic organisms - they live in water
- Decomposers secrete enzymes to break down organic matter and this requires water ✓
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- What happens to manure (animal waste) that is put onto a field by a farmer?
- Manure is broken down by the plants that grow in the soil.
- The manure gets washed into the soil by rainfall.
- The manure is broken down by decomposers. ✓
- Nothing - it just helps to replace soil which may have been eroded.
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Exit quiz
- In an experiment to determine the effect of temperature on the rate of decomposition by an enzyme, it takes 5 seconds for the indicator to reach the end point. What is the rate of the reaction?
- 5
- 1
- 0.5
- 0.2 ✓
- 0.02
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- A range of equipment and chemicals are used in the experiment to determine the effect of temperature on the rate of decomposition by an enzyme. Match the words with their function in the experiment.
- lipase⇔enzyme (works on lipids) ✓
- Cresol red⇔indicator (used to measure the end point) ✓
- lipids⇔found in milk (the substrate) ✓
- fatty acids⇔the product (decreases pH of the solution) ✓
At which of the following points are enzymes being denatured?- a
- b
- c ✓
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- Point b in the graph is known as the enzyme's optimum temperature. Which of the following statements explains what is happening at point 'b'?
- The active sites of the enzymes are changing as it becomes denatured.
- The number of collisions between enzymes & substrate are most frequent. ✓
- There are fewer collisions taking place between the enzyme and substrate.
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- What is the name of the part of the enzyme that the substrate needs to collide with for a reaction to take place?
- 'active site' ✓
- How does keeping food such as meat or fish in the fridge help to slow the rate of decomposition?
- The fridge door prevents oxygen from getting into the fridge.
- The low temperature of the fridge slows enzyme activity. ✓
- The fridge helps to dry the food.
- The low temperature increases the number of bacteria
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Worksheet
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Presentation
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Video
Lesson Details
Key learning points
- Calculate rate of reaction where rate = 1/time taken to reach the end point.
- Plot a graph of results (x-axis = temperature and y-axis = rate, or time taken to reach end point).
- Interpret the results and evaluate how well they support the hypothesis.
- Explain the results using ideas about the effect of temperature on the rate of enzyme activity.
Common misconception
As pH increases above the optimum, enzymes denature and reaction rate falls; but this is not what happens at pHs below the optimum, so the graph and explanation resemble temperature.
The process of denaturing an enzyme is explored in detail, and a graph of reaction rate is explained carefully to make it clear that the changes to rate occur above and below the optimum pH.
Keywords
Rate - The rate is how quickly something takes place. The rate of a reaction is a measure of how much change occurs per unit of time.
End point - The point at which a reaction is complete, often indicated by a change in colour of an indicator.
Hypothesis - A precise, measurable and testable statement based on observations about how something works.
Active site - The part of an enzyme where the substrate binds.
Denature - A permanent change in the shape of an enzyme which stops it from working.
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