How does temperature affect the permeability of a cell membrane in a beetroot.

Introduction:

The purpose of the cell membrane is to control the transport of substances moving into and out of the cell. It is made of a phospholipid bilayer that has proteins floating in it. The proteins span the membrane and touch both the inside and outside of the cell. The cell membrane is between 6-8 nanometers (nm) thick and made up of many different molecules. These are shown in the diagram below.

The phospholipid bilayer is the basic structure of the membrane. The fatty acid tails are non-polar; this means it is difficult for polar molecules or ions to pass through them as they act as a barrier to most water-soluble substances. The molecules move in and out of the cell through diffusion, osmosis and active transport. Diffusion is the net movement of molecules from a high concentration to a low concentration.

In the cells of a beetroot plant a substance called anthocyanin is contained in the plasma membrane. The anthocyanin gives the beetroot its purple appearance. If the cell membrane becomes damaged then the anthocyanin “bleeds” from the cell like a dye. This characteristic of beetroot will be used in this experiment. The experiment is to test the effects of temperature on the cell membrane. The molecules in the membrane move using kinetic energy. As the temperature increases the molecules gain more kinetic energy and diffuse faster. Temperature also causes the lipids of the membrane to be more fluid. It also causes the proteins to denature. However as the proteins denature and the lipids become liquid like, bigger gaps emerge so larger molecules can diffuse more freely. As the proteins denature the protein channels will increase in size so that more hydrophilic molecules can diffuse through in a shorter space of time.

Surface area of beetroot:

The surface area of the beetroot is to be the same for each of the segments. The diagram below shows the shape of the segments:

1 2

Cylinder

Surface area is worked out using the following formula:

Area of end 1 + Area of end 2 + area of sides (cylinder shape)

πr2+πr2+(2πr)h

Height = 1cm

Radius = 0.5

π0.52+π0.52+(2π0.5) 1

= 2(π0.52)+2(2π0.5)

= 1.570796327…+6.283185307…

=7.853981643…

=7.85cm2 (3 significant figures)

Variables:

Apparatus:

Risk assessment:

During the experiment I must be careful when handling the hot water as it may scald. When using a bunsen burner I must be careful not to burn myself on the flame and leave it on the safety flame or off when not using it.

I must push the cork borer into the beetroot away from the body, holding the beetroot at an angle where the cork borer will not touch.

When using the scalpel to cut the beetroot I must be careful to avoid cutting my ...

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Apparatus:

Risk assessment:

I must push the cork borer into the beetroot away from the body, holding the beetroot at an angle where the cork borer will not touch.

When using the scalpel to cut the beetroot I must be careful to avoid cutting my fingers or hands.

Safety goggles should be worn at all times. To protect my eyes from flying objects or splashes.

I shall also tie back my hair and not wear lose clothing which might catch on fire.

Prediction:

I expect the concentration of anthocyanin to increase as the temperature of the water is increased. This is because an increase in temperature will damage and denature the proteins in the plasma membrane this will cause the substances inside the membrane to be released and leak into the surrounding liquid. The proteins in the cell membrane are at a tertiary level, which means that there are globular in shape as, in the picture below.

When the proteins are heated the hydrogen bonds (in red) are broken. This allows the anthocyanin and other substances from inside the membrane to escape. The higher the temperature the quicker the proteins will denature so the more anthocyanin will be able to escape.

Method:

Collect equipment
Set up the bunsen burner, tripod, gauze and beaker with 150ml of water.
Place 3 test tubes filled with 10ml of water in the water baths to heat, using the thermometer to measure the heat of the water. I am using 3 test tubes at once so the experiment will be quicker as I can do three results at once.
Using cork borer remove a cylinder out of the beetroot.
Place on white tile and cut into 1cm long cylinders.
Rinse the beetroot and roll dry on paper towel.
Place the cylinders in the test tubes, one per test tube.
Leave for 10 minutes
After 10 minutes, remove the beetroot from the test tube. And shake the mixture. This will distribute the colour equally.
Remove 3ml of the liquid using a pipette and place in cuvette.
Place the cuvette in the colorimeter and test the light transmission. Using a blue filter.
Record the result in table.
Repeat steps 3-12 at each temperature.

Results to show how temperature affects the permeability of a cell membrane in a beetroot.

All my results are given to 1 decimal place.

Analysis:

As you can see from this table I have a few anomalous results. I have highlighted the inconsistent results in red. These are the results that are the extremes from the averages. The reasons for these extremes will be explained later in my evaluation.

My secondary results from the lab tech. are as follows these are to two significant figures:

Graphs:

On graph 1 I have plotted my results.

On graph 2 I have plotted my secondary results.

On graph 3 I have plotted a calibration curve.

On graph 4 I have plotted pigment and temperature.

The experiment has confirmed my prediction that the higher the temperature the more pigment will be released. As when the heat from the water denatured the proteins in the cell membrane the hydrogen bonds are broken changing the shape of the protein allowing the anthocyanin to diffuse into the surrounding water. This caused the colour of the water to darken as the pigment was released. As the temperature increased more anthocyanin could be released in the 10 minutes allowed to release the pigment into the water.

A copy of the graph using my results is below.

As you can see from this graph my results give a definite negative correlation this means that the percentage of transmission becomes lower as the temperature increases. This backwards “S” shape means that at a certain temperature (between 50 and 60) there is a sharp increase in the speed at which the proteins denature. This is because between the temperatures of 30 and 40 °C the diffusion increases as the beetroot reaches it’s optimum diffusion levels. However at 45 °C the proteins in the membranes denature causing the holes in the membrane to expand. This allows more pigment out. So between 50 and 60 °C the membrane becomes more fluid with more gaps in the membrane allowing more pigment to escape. While still diffusing at a fast rate. Between 60 and 70 °C the membrane is still being denatured but not with such a sharp increase in speed. The pigment is still diffusing rapidly and there are more spaces in the membrane.

My secondary set of results came from the schools lab. technicians experiment. These have a different range than my results as they go up in unequal steps. These results start at 17°C but range up to 70 °C. As you can see from graph 2 there is one point in which a steep decrease is seen. Many of the results in this are very close together.

Calibration is the process of determining the absolute values. The calibration curve is to see the proportion of pigment that has been released from beetroot. This is used so that we can relate the figures to known standards. This calibration curve is showing the lower the % pigment the higher the transmission.

Evaluation:

My experiment gave me good results over all as they gave me a set of results that confirmed my prediction. There were however a few anomalous results. This could have been caused by inaccuracies in my method.

Teacher Reviews

Here's what a teacher thought of this essay

Ross Robertson

24th of Jun 2013

This report of an investigation into the effect of temperature on membrane permeability in beetroot tissue is well-structured and clearly written. Some sections, notably the variables and evaluation, are especially well written, both in table form which make it easy for the reader to follow. There are, however, a number of ways in which the report could be improved: [1] The hypothesis (referred to as a prediction) needs to be stated at the end of the introduction. It needs to be clear and testable, linking the IV and DV. [2] The purpose of the technician's results needs to be more clearly explained. They are presented as something of a bolt-on to the writer's own results. [3] Identification of anomalies needs more care. In view of there only being 3 replicates, it is very difficult to identify any anomalies. However, these are relatively minor criticisms and overall, this is a good piece of GCSE coursework which would gain the higher grades. 4 stars

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