Choose A if the statement applies to asexual reproduction, or S if it applies to sexual reproduction.

• It produces offspring that are genetically identical to the parent.
• It requires the fusion of male and female gametes.

A student investigates the effect of temperature on the reproduction rate of yeast.

This is the student's method:

• Put yeast suspension with glucose in four different test tubes.
• Place the tubes in an incubator kept at $15^{\circ }C$.
• Repeat this process with test tubes at $25^{\circ }C$ and $35^{\circ }C$.
• Leave the tubes for 24 hours under the same conditions.
• After 24 hours, measure the concentration of yeast cells (in millions per mL) in each tube.

The table shows the student's results:

(i) What is the independent variable in this investigation?

Identify the temperature where the mean concentration of yeast cells is the same as the mode for the four test tubes.

• $15^{\circ }C$
• $25^{\circ }C$
• $35^{\circ }C$

The student thinks that there is a problem with their data at $35^{\circ }C$, which has made the calculated mean inaccurate. Explain how the student could improve their investigation to obtain a more accurate mean.

The student has concluded that extremely high temperatures slow down yeast reproduction. Explain how high temperatures slow the reproduction rate of yeast. Refer to enzymes and respiration in your answer.

The student also concluded that $25^{\circ }C$ is the optimum temperature for yeast reproduction. Their teacher states they need to extend the experiment to confirm this. Describe how the student should extend their experiment.