Practical 5 - Investigation into the permeability of cell membranes using beetroot

Question 1

Permeability

Answer 1

How much substance can crops a membrane in a particular amount of time

Question 2

Method for this practical

Answer 2

1-Cut 5 pieces of beetroot, 1cm long, from the cylinders provided
2- Wash under running water to remove the pigment released from cells during cutting
3- test tube with 5cm3 distilled water into a water bath to equilibrium for 5 minutes
4- 1 piece of beetroot into each test tube for 30 minutes
5- After 30 minutes, shake the test tubes gently to ensure pigment is well mixed and remove beetroot cones
6- Describe the depth of colour (white card behind can help)
7- Use a colorimeter to respond to a blue/green filter (wavelength 530nm) and measure absorbance/percentage transmission of each tube

Question 3

How long do we cut all of the beetroot slices and why is it important that they’re all cut the same?

Answer 3

1cm, to have no affect on the amount of betalain passing through the membrane

Question 4

How is the water bath controlled?

Answer 4

Thermostatically

Question 5

How much water do we place into each test tube and what type of water is this?

Answer 5

5cm3 distilled water

Question 6

Why do we wash running water over the beetroot before starting the real testing?

Answer 6

To remove the pigment released from cells during cutting

Question 7

What type of data does a colorimeter give and why is this useful?

Answer 7

Quantitate - more accurate

Question 8

Which filter do we set the colorimeter to?

Answer 8

The blue/green filter (520nm wavelength)

Question 9

What does the colorimeter measure?

Answer 9

Absorbance/percentage transmission

Question 10

Draw and label a beetroot cell

Answer 10

(Check notes)

Question 11

What’s the name of the bright coloured pigment found in the vacuole of the beetroot cell?

Answer 11

Betalain

Question 12

Where is betalain found in the beetroot cell?

Answer 12

In the vacuole

Question 13

Describe betalain

Answer 13

-bright coloured purple pigment
-water soluble

Question 14

How does betalain exit the cell?

Answer 14

Has to diffuse down a concentration gradient

Question 15

Independent variable - definition and what was it in this practical?

Answer 15

The variable that WE change
Temperature of the water bath

Question 16

Dependant variable - definition and what was it in this practical?

Answer 16

The variable that we measure
Light absorbance (a.u.)

Question 17

Unit of light absorbance

Answer 17

A.u

Question 18

Control variables - definition and what were they in this practical?

Answer 18

Things to remain constant
Surface area of the beetroot and temperature of the water bath

Question 19

2 hazards involved in this practical

Answer 19

Sharp scalpel
Water bath is over 60 degrees

Question 20

Risk involved with a sharp scalpel

Answer 20

Cutting or piercing the skin

Question 21

Risk involved with water baths being over 60 degrees

Answer 21

Scalding

Question 22

Over which temperatures does the water impose a risk of scalding?

Answer 22

60 degrees

Question 23

Control measure of a sharp scalpel

Answer 23

Cut downwards onto a white tile

Question 24

Control measure of the water baths being over 60 degrees

Answer 24

Ensure that beaker water baths are set up so they’re stable
Use test tube holders to move the test tubes

Question 25

How many times should we repeat this practical and why?

Answer 25

3 times
Improves reliability
Identify anomalies
Calculate a mean

Question 26

Why is it important to calculate a mean?

Answer 26

Reduces the affects of anomalous data

Question 27

What is the conclusion from this practical?

Answer 27

The higher the temperature, the higher the permeability (higher light absorbance)

Question 28

How come the light absorbance is higher in the samples in higher temperatures which have higher permeability?

Answer 28

They’re darker, and dark colours absorb more light

Question 29

What’s the reason for higher temperatures giving higher permeability (up to 40 degrees Celsius)?

Answer 29

Higher temperatures = increase in kinetic energy = phospholipids, proteins and pigment in the molecule move more
This creates gaps that the pigment can diffuse out of the cell through

Question 30

What’s the reason for higher temperatures giving higher permeability (above 40 degrees Celsius)?

Answer 30

Protein components of the membrane begin to denature + the cell membrane becomes fully permeable to the pigment if all of the proteins denature
This forms large pores that the betalain pigment can diffuse through easily

Question 31

At what point would the cell membrane become fully permeable?

Answer 31

If all of the proteins denature due to the very high temperatures (above 40 degrees Celsius)

Question 32

What’s the only part of the cell that denatures to allow betalain to diffuse through the membrane?

Answer 32

Proteins

Question 33

What do proteins do at higher temperatures?

Answer 33

Denature, so that the cell membrane become fully permeable to the betalain

Question 34

Which two factors can cause pigment to diffuse out of a cell’s membrane?

Answer 34

Acid (denatures proteins)
Ethanol (dissolves phospholipids and fatty acids)

Question 35

What does acid do to proteins?

Answer 35

Denatures them

Question 36

What can denature proteins?

Answer 36

Acid

Question 37

What does ethanol do to phospholipids/fatty acids?

Answer 37

Dissolves them

Question 38

What can ethanol dissolve?

Answer 38

Phospholipids/fatty acids

Question 39

What can dissolve phospholipids/fatty acids?

Answer 39

Ethanol

Question 40

What does acid denature?

Answer 40

Proteins