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8. Phenolphthalein is an indicator - Edexcel - GCSE Biology - Question 9 - 2016 - Paper 1
Question 9
8. Phenolphthalein is an indicator. It is pink in alkaline solutions and turns colourless as the pH decreases. It can be used to measure the activity of the enzyme ... show full transcript
Worked Solution & Example Answer:8. Phenolphthalein is an indicator - Edexcel - GCSE Biology - Question 9 - 2016 - Paper 1
Step 1
Explain why phenolphthalein turns colourless when lipase breaks down the lipids.
Answer
Phenolphthalein turns colourless when lipase breaks down lipids because lipase breaks down triglycerides into fatty acids and glycerol. The released fatty acids decrease the pH of the solution, causing the phenolphthalein to change from pink to colourless as it is sensitive to pH levels.
Step 2
Describe the effect of temperature on the activity of lipase, as shown in Figure 10.
Answer
Figure 10 shows that the activity of lipase increases with temperature up to a peak around 40°C, where the rate of activity is at its highest. Beyond this temperature, the enzyme activity declines, indicating that high temperatures can denature the enzyme, leading to reduced activity.
Step 3
Explain why the activity of lipase changes above a temperature of 40°C.
Answer
The activity of lipase changes above 40°C because enzymes are proteins that have an optimal temperature range for their activity. As the temperature exceeds this optimum, the enzyme's structure begins to denature, altering its active site. This alters the enzyme's ability to bind to its substrate, resulting in decreased activity.
Step 4
Calculate the rate of amylase enzyme activity for the 10% starch solution.
Answer
To calculate the rate of amylase activity, we can take the average time taken from the five tests:
ext{Average time} = rac{120 + 125 + 110 + 115 + 118}{5} = 118.6 ext{ seconds}
Then, the rate of activity can be expressed as:
ext{Rate} = rac{1 ext{ (substrate breakdown)}}{ ext{Average time (s)}} = rac{1}{118.6} ext{ units per second} ext{ (approximately 0.0084 units/s)}.
Step 5
State one other variable that the student should have controlled during this investigation.
Answer
One variable that should have been controlled is the temperature at which the experiment was conducted. Keeping the temperature constant ensures that it does not affect the rate of enzyme activity.
Step 6
Explain why enzymes can only catalyse specific reactions.
Answer
Enzymes can only catalyse specific reactions because of their unique active sites, which are structured to fit specific substrates, much like a key fits into a lock. This specificity arises from the enzyme's three-dimensional shape, which is determined by its amino acid sequence. Only the correct substrate (the reactant that an enzyme acts on) that matches the active site can bind and undergo the chemical reaction.