Biology: Cell Membrane and Test Tube

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EXPERIMENT ONE- BIOLOGY MODEL Answers
TO DETERMINE THE EFFECT OF CHEMICALS AND TEMPERATURE ON MEMBRANE DESTRUCTION AND PERMEABILITY IN BEETROOT (Beta vulgaris)

Introduction

The cell membrane is made up primarily of phospholipids and proteins which contribute to its selectively permeable nature. The function and permeability of the cell membrane depends on its intact structure. When destroyed, the permeability of the cell membrane is disrupted causing cellular contents to leak out. The cell membrane can be destroyed by physical damage, chemicals and high temperature. When cells are cut, the cell membranes are mechanically ruptured. High temperature disrupts the structure of proteins and certain chemicals such as fat solvents dissolve the phospholipids, leading to damage of the membrane and therefore increased permeability.

Beetroot contains a red pigment called betacyanin, which is located in the large central vacuole of the beetroot cells. The vacuole is enclosed by a single membrane called the tonoplast and the whole cell is enclosed by the cell membrane made up of phospholipids and proteins. Betacyanin will remain inside the vacuoles of intact cells. However, if the membranes are damaged, betacyanin will leak out and produce a red/dark pink colour in the surrounding water. Cut cylinders of beetroot are used in this experiment. The beetroot cylinders were repeatedly washed following cutting until not more colour appeared in the wash water.

Materials

1. Washed cylinders of beetroot (1 cm in diameter, 4 cm long) in distilled water 2. 3 x test tubes
3. 1 x test tube containing distilled water, cyclohexane and a cylinder of beetroot, labelled TT4. 4. Test tube rack
5. A bottle containing 8 ml distilled water
6. A bottle containing 8 ml 50% acetone
7. A bottle containing 8 ml 100% acetone
8. Permanent marker pen
9. 1x sheet graph paper

Experimental procedure

1. Using the permanent marker pen, label the empty test tubes TT1, TT2, and TT3. 2. Prepare these 3 test tubes as follows (see Table 1):
Pour the distilled water into TT1.
Pour the 50% acetone into TT2.
Pour the 100% acetone into TT3.
3. Place all tubes in the test tube rack.
4. Immediately place a washed cylinder of beetroot in TT1, TT2 and TT3. 5. Shake test tubes 1-4 gently for a few seconds.
6. After 15 minutes observe the colour of the solution in each test tube.

Table 1: Solvents in Test Tubes 1-4
TEST TUBES| Test tube 1 (TT1)| Test tube 2 (TT2)| Test tube 3 (TT3)| Test tube 4 (TT4)| SOLVENTS| Distilled water | 50% Acetone| 100% Acetone| Distilled water + Cyclohexane|

SECTION 1
a.

At the start of the experiment, the distilled water surrounding the washed cylinders of beetroot appeared clear in colour. Why? Choose the correct answer by ticking the appropriate box. i.

Betacyanin is not soluble in water. ii. Betacyanin is soluble in organic solvents only.
iii.

Damaged cells were empty of betacyanin after repeated washing,

and no further cell membrane damage occurred.
iv. All the above.
(0.5 mark)

b. Which test tube represents the control? Choose the correct answer by ticking the appropriate box.

TT1 | TT2| TT3| TT4|
(0.5 mark)

c. Based on the colour of the solution in TT2 and TT3, where was betacyanin more soluble? Choose the correct answer by ticking the appropriate box.

50% acetone| 100% acetone|

(0.5 mark)

d. In TT4 which layer represents water? Choose the correct answer by ticking the appropriate box.

Upper

Lower
(0.5 mark)

e. Why was the water coloured in TT4 but NOT in TT1? Choose the correct answer by ticking the appropriate box....
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