Question

Q3.

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 lipase on the breakdown of lipids.
Samples of milk containing phenolphthalein were incubated with lipase at different temperatures.
The time taken for the phenolphthalein to turn colourless was recorded and used to calculate the rate of
enzyme activity.
Figure 10 shows these results.
0.9
rate of lipase
activity/
arbitrary units
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1-
0-
0
30
40
temperature / °C
Figure 10
xplain why phenolphthalein turns colourless when lipase breaks down the lipids in milk.
10
20
50
60
be the effect of temperature on the activity of lipase, as shown in Figure 10.

Answer 1

Step-by-step explanation:

Phenolphthalein turns colorless when lipase breaks down the lipids in milk due to the change in pH during the enzymatic reaction. Lipase is an enzyme that catalyzes the hydrolysis of lipids (fats) into their component fatty acids and glycerol. During this process, lipase acts on the ester bonds in lipids, breaking them down.

Phenolphthalein is a pH indicator that changes color depending on the acidity or alkalinity of the solution. It is pink in alkaline (basic) solutions and colorless in acidic solutions. As lipase breaks down the lipids in milk, it releases fatty acids. The presence of fatty acids lowers the pH of the solution, making it more acidic. As a result, phenolphthalein, which is sensitive to pH changes, turns colorless.

In Figure 10, the graph shows the effect of temperature on the activity of lipase. As the temperature increases, the rate of lipase activity also increases. This is indicated by the higher values on the y-axis (rate of lipase activity) at higher temperatures on the x-axis (temperature in °C).

Typically, enzyme activity increases with temperature up to an optimal temperature. This is because higher temperatures increase the kinetic energy of the molecules, including both the enzyme and substrate, leading to more frequent collisions and faster reaction rates. However, beyond the optimal temperature, the activity of the enzyme may decrease or denature due to the disruption of its structure by excessive heat.

Based on Figure 10, the rate of lipase activity initially increases as the temperature rises, reaching a peak around 50°C, and then starts to decrease. This suggests that there is an optimal temperature at which lipase functions most efficiently. Beyond this temperature, the enzyme may start to denature, causing a decline in its activity.

It's worth noting that enzyme activity can be affected by other factors such as pH, substrate concentration, and the presence of inhibitors or activators. In this case, the experiment focused on studying the effect of temperature on the activity of lipase using phenolphthalein as an indicator.