2.7 Required practical 4

Question 1

What is the theory being tested

Answer 1

• Cell surface membranes are made up of a phospholipid bilayer, making them selectively permeable
• Permeability can be changed by different variables, e.g. temperature and concentrations of solvents, like ethanol

Question 2

What is used for this experiment and why

Answer 2

• Beetroot cells are used which contain a purple pigment called betalain
• When the permeability is increased, more pigment leaks out of the cells

Question 3

How is permeability measured in this experiment

Answer 3

By the amount of pigment leaked from the beetroot cells into an aqueous solution using a colorimeter

Question 4

How do higher temperatures affect the permeability

Answer 4

• The higher the temperature, the higher the permeability
• At higher temperatures, the phospholipids have more energy which causes them to move more which creates more gaps
• At very high temperatures, proteins in the membrane denature (as heat damages bonds in tertiary structure), which creates gaps in the membrane so molecules can pass through more easily

Question 5

How do lower temperatures affect the permeability

Answer 5

• The lower the temperature, the lower the permeability
• Phospholipids have little energy, so pack closer together which restricts molecules passing through the membrane (rigid)

Question 6

What happens at very low temperatures (to the permeability)

Answer 6

Ice crystals can form which can pierce the membrane, increasing permeability

Question 7

How does ethanol affect the membrane

Answer 7

Causes membrane to rupture, releasing the betalain pigment from the cell

Question 8

How does the concentration of ethanol affect the permeability

Answer 8

• As concentration of ethanol increases, permeability increases
• Higher concentrations cause more disruption to the membrane, causing more gaps to form which allow molecules to pass through easier

Question 9

Describe a method for this practical

Answer 9

1. Cut beetroot into 6-10 identical cubes using a scalpel
2. Wipe/rinse to clean off any pigment released as a result
3. Place each of the cubes of beetroot in an equal volume of distilled water
4. Place each test tube in a water bath at a range of temperatures (30-80 degrees)
5. Leave samples for 20 minutes - the pigment will leak out of the beetroot
6. Set the colorimiter to a blue filter and zero using a cuvette with distilled water
7. Filter each sample into a cuvette using filter paper
8. Measure the absorbance for each solution. A higher absorbance indicates higher pigment concentration, and hence a more permeable membrane

Question 10

What are the risks associated with this practical

Answer 10

• Scalpel
• Broken glass
• Hot liquids
• Ethanol

Question 11

What are the risks associated with broken glass and scalpel

Answer 11

Cuts from a sharp object

Question 12

What are the risks associated with hot liquids

Answer 12

Scalding

Question 13

What are the risks associated with ethanol

Answer 13

Irritant/flammable.

Question 14

What are the precautions for the scalpel

Answer 14

• Cut away from fingers
• Use forceps to hold sample while cutting
• Keep scalpel away from edge of desk

Question 15

What are the precautions for broken glass

Answer 15

• Take care when handling glassware
• Keep away from edge of desk

Question 16

What are the precautions for ethanol

Answer 16

• Wear eye protection
• Keep away from naked flames

Question 17

What are the precautions for hot liquids

Answer 17

• Handle with care
• Use tongs to remove boiling tubes from water bath
• Wear eye protection
• Keep away from edge of desk