5 (a) Apple trees show genetic variation - Edexcel - GCSE Biology Combined Science - Question 5 - 2023 - Paper 1

The term for an observable characteristic is D phenotype.

The type of reproduction that produces genetically identical organisms is asexual reproduction.

One advantage of growing genetically identical apple trees is that they will produce fruit with desired qualities, ensuring uniformity in taste and appearance.

One disadvantage is that they may be susceptible to diseases, which can spread quickly through genetically identical specimens.

To find the optimum pH of an enzyme that breaks down starch, follow these steps:

1. Prepare a series of buffer solutions at a range of pH levels (e.g., pH 4, 5, 6, 7, 8, 9).
2. Add equal volumes of starch solution to each pH buffer.
3. Introduce a fixed amount of the enzyme solution to each mixture.
4. Incubate the mixtures at a constant temperature.
5. After a specified time, add iodine solution to each mixture and observe the color change.
6. The pH that shows the least color change (indicating starch breakdown) is the optimum pH for the enzyme.

This enzyme would not work at pH 10 because enzymes have specific pH ranges in which they are most active, known as the optimum pH. At pH levels significantly away from this optimum, the enzyme's active site may denature, leading to a loss of its functional shape and, consequently, its catalytic activity.