Mr Brown's Cwk Practical Test

Question 1

1. Create a table to show your results - 2 marks

Answer 1

Table shoud include similar data as follows:

Temperature (°c) - 30, 45, 60, 80

Estimated concentration of Betalain (%) - e.g. 0.3, e.g. 0.45, e.g. 0.5, e.g. 1.0

Question 2

2. Present your data in a suitable graph on the graph paper attatched - 4 marks

Answer 2

• The graph needs to be a line graph; curved or point to point - curved -> needs to start a little bit before the first plot
• Graph title: “A graph to show the effect of temperature on the permeablilty of Betroot Cell Membranes (where Betalain concentration acts as an indicator)”
• X-axis (on the bottom) needs to be “Temperature (°c)” and the Y-axis along the side needs to be “Estimated concentration of Betalain (%)”
• Both axis need to be scaled correctly: Y-axis depends on concentration estimates (e.g. goes up in 0.1s from 0.1 to 1.0) and X-axis needs to start from 20 (with a squiggle before it) up to 80
• Data needs to be plotted accurately (corresponding to results table)
• The plot for 80% needs to be higher than 30% and 40%

Question 3

3. Describe the effect that changing the temperature had on the concentration of Betalain in the test tubes

Answer 3

As the temperature increased the (estimated) concentration of Betalain also increased, depicting a non linear relationship - the curve on the graph gets steeper as the temperature increases. The graph and results table also illustrate that the increase is much greater at higher temperatures.

-Use of figures from graph/table to support this (data needed from at least 2 points)…

Question 4

4. Use your graph to estimate the concentration of Betalain obtained at 50°c - *1 mark *

Answer 4

Use curved line on graph to estimate the concentration of Betalain obtained at 50°c

e.g. 0.46%

Question 5

5. Why were the Beetroot discs rinsed before they were immersed in water of different temperatures at the start?

Answer 5

We needed to rinse the Beetroot discs before they were immersed in water of different temperatures at the start for a number of reasons.

1. Firstly, the water and discs were coloured - this would have affected the colour of the water at the end of the investigation which would have altered the results.
2. Secondly, to cut the Betroot samples into discs we used a scalpel, which in turn opened the vacuoles of the cut cells. This would have affected the results as there would be Betalain in the samples that had not come through the membrane.
3. Lastly, the rinsing was also needed to remove the excess Betalain as if the pigment leaked rather than coming across the membrane it would give an overestimate.

Question 6

6. Explain what is meant by partially permeable

Answer 6

Cell surface membranes (and also the membranes within cells) are partially permeable - they let some substances pass through but not others. The permeability of a membrane is determined by the phospholipids and proteins. For example, the centre of the bilayer is hydrophobic (water-repelling) so the membrane doesn’t allow water-soluble substances (like ions) through it - it acts as a barrier to these dissolved substances.

Question 7

7. Why does more pigment escape at higher temperatures?

Answer 7

At higher temperatures the membranes are damaged/broken down or made more permeable (as the phospholipids become more fluid). As well as this, the proteins in the membranes are denatured (tertiary structure is destroyed e.g. the hydrogen bonds between the R groups). Lastly, at higher temperatures the Betalain molecules have more kinetic energy.

Question 8

8. Describe 3 limitations in this procedure and their effects

Answer 8

1. It was difficult to match the colours of those in my test tubes against those in the test tubes of standard/know concentrations, so it was difficult to estimate the concentration of Betalain in my test tubes.
2. The Betroot discs did not have a uniform thickness, so all the discs did not have the same surface area nor the same amount of cells.
3. The Betroot discs were not in the water for an equal amount of time, so some results might show too much or too little Betalain released.

Question 9

9. Name a variable that has been controlled in this experiment

Answer 9

The number of discs at each temperature and the volume of water added.

Question 10

10. Why are large, water soluble molecules unable to pass through membranes by simple diffusion?

Answer 10

This is because the phospholipid tails/ fatty acids of the membrane’s bilayer are hydrophobic (water-repelling) and so the membrane acts as a barrier to water-soluble substances. Also, some molecules are too large so it is difficult for the molecules fo fit between the gaps in the phospholipids. Due to these factors, the large dissolved (in water) substances are unable to pass through membranes by simple diffusion, and so require facilitated diffusion (using carrier proteins).

*Other points include the concentration of Betalain inside the vacuole was higher than outside the vacuole. And the vacuole is surrounded by a membrane. *

Question 11

11. How might large water soluble molecules be transported into a vacuole?

Answer 11

Large water-soluble molecules are unable to pass through membranes by simple diffusion, and so require facilitated diffusion (using carrier proteins) or active transport.

Carrier proteins move large water-soluble molecules into the cell, down their concentration gradient. Firstly, a large molecule attatches to a carrier protein in the membrane. The protein then changes shape and this moves the molecule across the membrane, releasing it on the other side.

Active transport uses energy (from ATP - a common source of energy used in the cell) to move molecules across plasma membranes, against a concentration gradient - this process also involves carrier proteins.