It is not possible to observe membranes directly, so this investigation is an indirect study of the effects of different substances and treatments on living beetroot cells. Beetroot cells have been chosen for this activity because each beetroot cell has a large central vacuole bounded by a membrane (Figure 1). Contained in the vacuole is the red pigment anthocyanin, which gives the beetroot its typical colour. The whole beetroot cell is also surrounded by the cell membrane. If the two membranes remain intact the anthocyanin cannot escape into the surrounding environment. If the membranes are stressed or damaged, the red colour can leak out. The cell wall surrounding plant cells provides a structure to the plant. It does not have a role in controlling the movement of substances into and out of cells.
The cell membrane is the same in both plants and animals, therefore you will be able to apply the knowledge you gain from this investigation to both plants and animals.
Figure 1 Location of anthocyanin in a plant cell.
Part 1: Effects of temperature
The aim of this experiment is to investigate the effect of different temperatures on the cell membrane.
Bunsen burner, tripod and wire gauze
250 mL beaker thermometer: 100–110ºC
10 mL measuring cylinder marking pen or sticky labels dissecting needle fine forceps
8 test tubes test-tube racks or 500 mL beaker to hold eight test tubes access to freezer and refrigerator washed beetroot slices: at least 40 in 100 mL beaker of water
1 Use forceps to collect at least 40 beetroot slices in a 100 mL beaker of water.
2 Use a marking pen or sticky labels to mark eight test tubes with the temperatures listed in Table 1. Stand the test tubes in either test-tube racks or a 500 mL beaker.
3 Put five beetroot slices in the test tube labelled ‘–5ºC’ and place