Use the information and the graph below to answer the following question. Scientists wanted to student the effect of water temperature on the swimming speed of goldfish. They set up and experiment in which they raised populations of goldfish in two different environments. Population 1 was raised at 5°C. Population 2 was raised at 25°C. All other variables were constant in both aquariums. The results of this experiment are shown in the graph below.

Which of these is most affected in the cells of the goldfish when the water temperature is lowered?

enzyme activity

DNA base sequence

pH level

salt concentration