Starch is mixed with amylase at pH 4, 7 and 10. After 2 minutes only the pH 7 tube no longer turns the iodine solution blue-black. What conclusion can be drawn?
Answer and explanation
Correct answer: A. Amylase works best near pH 7
- Step 1: Blue-black iodine shows starch is still present.
- Step 2: Only the pH 7 tube had no starch left, so amylase is most active near pH 7.
Answer
Amylase works best near pH 7.
Why not the others: Amylase works best at pH 4: the pH 4 tube still had starch. Amylase is destroyed at pH 7: starch has been digested there. Iodine digests starch: iodine is only an indicator.
Practise more Skills and Applying Knowledge.
Free questions with an explanation for every one, and full timed National 5 (Scotland) mock tests.
More Skills and Applying Knowledge questions
- A scientist records the dry mass of seedlings grown with and without fertiliser. Which is the dependent variable?
- Why is a control experiment included in an investigation?
- Repeating an experiment several times and calculating a mean improves what?
- The table shows the mass of a potato cylinder in different salt solutions. The mass change is +4% at 0.0 M, 0% at 0.2 M, and −6% at 0.4 M. A…
- A cell has a mass of 4 µg and divides by mitosis. Its two daughter cells each have a mass of 2 µg. A new cell grows to a mass of 4 µg before…
- A section of DNA has 30% adenine. What percentage of the bases are guanine?