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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
Answer
Phenolphthalein acts as a pH indicator. When lipase breaks down lipids, fatty acids are produced, which lower the pH of the solution. As the pH decreases and becomes more acidic, phenolphthalein transitions from pink to colourless. This change indicates the breakdown of lipids by lipase.
Step 2
Describe the effect of temperature on the activity of lipase, as shown in Figure 10.
Answer
The graph in Figure 10 indicates that the activity of lipase increases as temperature rises, reaching a peak at around 40°C. Beyond this temperature, the activity declines. This suggests that lipase is most active at its optimal temperature, but higher temperatures lead to denaturation, reducing enzyme activity.
Step 3
Explain why the activity of lipase changes above a temperature of 40°C.
Answer
Above 40°C, the activity of lipase decreases due to denaturation, which occurs when the enzyme's structure is altered. High temperatures disrupt the hydrogen bonds and other interactions that maintain the enzyme's three-dimensional shape, preventing it from binding to its substrate effectively.
Step 4
Calculate the rate of amylase enzyme activity for the 10% starch solution.
Answer
To calculate the rate of amylase activity, we first need to determine the average time taken across all tests. The times recorded are 120s, 125s, 110s, 115s, and 118s. The average time is given by:
ext{Average time} = rac{120 + 125 + 110 + 115 + 118}{5} = 118.6 ext{ seconds}
The rate of activity can be calculated as the reciprocal of the average time (since rate is defined as the inverse of time taken):
ightarrow 0.00843 ext{ s}^{-1}$$Step 5
Step 6
Explain why enzymes can only catalyse specific reactions.
Answer
Enzymes can only catalyse specific reactions due to their unique active sites, which are complementary in shape to their specific substrates. This specificity is similar to a lock and key model, where only the correct key (substrate) fits into the lock (enzyme). As a result, enzymes facilitate specific biochemical reactions, thereby ensuring proper metabolic regulation.