When testing a leaf for starch, why is it first placed in boiling water?
When testing a leaf for starch, why is it first placed in boiling water?
- A) to extract the chlorophyll
- B) to remove colour from the leaf
- C) to dissolve the starch
- D) to stop chemical reactions
Correct Answer: D) to stop chemical reactions
Explanation
When testing a leaf for starch, it is first placed in boiling water to stop chemical reactions that may interfere with the test. When the leaf is boiled, it denatures the enzymes that are responsible for breaking down starch. This prevents the breakdown of starch and ensures that we can accurately test for the presence of starch in the leaf. Boiling water does not extract chlorophyll or remove colour from the leaf. It may dissolve some of the pigments in the leaf, but this is not the main reason for boiling the leaf. Although boiling water can dissolve starch, this is not the reason why the leaf is boiled. In fact, boiling water can cause the starch granules to burst, which can lead to inaccurate results. Therefore, the correct option is D - to stop chemical reactions that may interfere with the test. It is important to note that the test for starch involves using iodine solution, which reacts with starch to produce a blue-black color. Overall, boiling the leaf before testing for starch is a crucial step in ensuring accurate results. This helps to prevent interference from enzymes and other chemical reactions that may affect the outcome of the test.