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 the fruit will have desired qualities, such as consistent taste. A disadvantage is that these trees can be susceptible to a disease, which could spread rapidly due to their genetic similarity.

To determine the optimum pH for an enzyme that breaks down starch, prepare a series of buffer solutions with varying pH values (for example, pH 4, 5, 6, 7, 8, 9). Add a fixed amount of starch solution to each buffer solution. Introduce the enzyme solution to each mixture and incubate at a constant temperature. After a set time, add iodine solution to each sample to test for the presence of starch. The solution that shows no blue-black color indicates the optimum pH for enzyme activity.

The enzyme would not work at pH 10 because enzymes have an optimum pH range in which they function best. At pH levels significantly different from their optimum, the enzyme's active site can become altered, reducing its ability to bind to the substrate and thus inhibiting its catalytic activity.