Temperature / °C Benedict's test colour after heating 10 green 25 orange 37 brick-red 60 blue The table below shows an investigation into lactose-free milk....
Question 1 Report
| Temperature / °C | Benedict's test colour after heating |
|---|---|
| 10 | green |
| 25 | orange |
| 37 | brick-red |
| 60 | blue |
The table below shows an investigation into lactose-free milk. Lactase enzyme was added to equal volumes of milk in separate tubes. The tubes were kept at different temperatures for ten minutes. Benedict's test was then used to estimate the amount of glucose formed. A colour nearer to brick-red shows more reducing sugar. The pH and volume of milk were kept the same in every tube.
| Temperature / °C | Benedict's test colour after heating |
|---|---|
| 10 | green |
| 25 | orange |
| 37 | brick-red |
| 60 | blue |
(a) Name the substrate acted on by lactase in milk. [1]
(b) Describe the result at 37 °C. [1]
(c) Explain why little or no glucose was formed at 60 °C. [2]
(d) State one variable that was controlled in this test. [1]
Answer Details
(a) Lactase acts on the substrate lactose. [1]
(b) At 37 °C, Benedict’s solution became brick-red. This indicates the greatest amount of reducing sugar, including glucose, was formed. [1]
(c) At 60 °C, the high temperature denatures lactase. Its active site changes shape, so lactose cannot bind to form enzyme-substrate complexes. Little or no glucose is therefore produced. [2]
(d) One controlled variable was the pH. Other acceptable examples include volume of milk, volume or concentration of lactase, time, or volume of Benedict’s solution. [1]
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