Explain how the structure of phospholipid molecules allows for the formation of plasma membranes.

The permeability of plasma membranes can be investigated using beetroot. Beetroot cells contain a red pigment within their vacuoles. This pigment leaks out of the cells only when the plasma membrane becomes damaged or more permeable.

Some students investigated the effect of temperature on the permeability of plasma membranes in beetroot cells.

The students used a valid method, which is outlined below:

• Equal-sized cylinders of beetroot were cut and washed.
• The cylinders were each immersed in an equal volume of distilled water inside a test tube.
• The tubes were placed in water baths at six different temperatures for a set time of 20 minutes.
• After this time, the solution was stirred and the absorbance measured using a colorimeter.
• The procedure was replicated three times at each temperature.

The students recorded their results in the format shown below:

• $20^{\circ }C$ -- $0.00,0.00,0.00$; average = $0.00$
• $30^{\circ }C$ -- $0.02,0.01,0.03$; average = $0.02$
• $40^{\circ }C$ -- $0.12,0.14,0.13$; average = $0.13$
• $50^{\circ }C$ -- $0.45,0.43,0.44$; average = $0.44$
• $60^{\circ }C$ -- $0.78,0.76,0.77$; average = $0.77$
• $70^{\circ }C$ -- $0.91,0.93,0.92$; average = $0.92$

Present the students' results in an appropriate table.

The students concluded that the red pigment began to leak out of the beetroot cells at temperatures above $30^{\circ }C$. Suggest and explain why a high temperature causes the red pigment to leak out of the beetroot cells.

Outline how the students could modify their investigation to get a more accurate value for the temperature at which the red pigment begins to leak out of the beetroot cells.