Investigate the Effect of Temperature on Cell Membranes and Membrane Structure

Investigate the Effect of Temperature on Cell Membranes and Membrane Structure

If you read a recipe for cooked beetroot it will usually recommend

that you don’t remove the outer skin of the beetroot and don’t cut off

al the stalk and root if you want to avoid getting lots of red dye in

the cooking water. Beetroot contains red pigments called betalains,

located within the cell vacuole. Normally the pigments can’t pass

through membranes but they leak out when the beetroot is cooked.

Aim – The aim of this practical is to use beetroot to examine the

effect of the temperature on cell membranes and relate the effects

observed to membrane structure. To function correctly a cell needs to

be able to control transport across the partially permeable cell

membrane.

Theory – To understand how the red pigment leaks out of the beetroot

it is essential that we understand the molecular Structure of a plasma

membrane.

A membrane is a phospholipid bilayer. This means that it has two

layers of molecules called phospholipids. Each of these phospholipid

molecules

has two parts:

• A 'head' that will mix with water but not with fat (i.e. it is

hydrophilic)

• Two 'tails' that will mix with fat but not with water (i.e. they are

hydrophobic).

In the phospholipid bilayer, the hydrophilic heads are always on the

outside of the membrane. The hydrophobic tails are always on the inside

of the membrane. Alone, this arrangement of phospholipids would form

a barrier to water and to water-soluble substances. However, other

molecules are scattered among the phospholipids. These include lipids

(including cholesterol in the membranes of animals), proteins and

polysaccharides. The proteins in membranes are of special interest to

us. This is because they have a number of important functions. Proteins

function as:

• Carriers for water-soluble molecules (such as glucose)

• Channels for ions (such as sodium and chloride ions)

• Pumps, which use energy to move water-soluble molecules and ions

• Receptors, which enable hormones and nerve transmitters to bind to

specific cells

• Recognition sites, which identify a cell as being of a particular

type

• Enzymes, which speed up chemical reactions at the edge of the

membrane

The ways that substances move across cell membrane are

1. Diffusion

2. Active transport

3. Faci...

... middle of paper ...

...ees Celsius. Because at 30 degrees

Celsius I would have presumed that the membrane would have been fairly

stable. However my graph shows the contrary. This might be due to

sources of error in my experiment.

Experiments - I have successfully gained my results that back my

hypothesis. However the results have limitations and some sources of

error. The size of the beetroot is essential. In my experiment I used

a ruler and cork bore to measure out the same size beetroot. The cork

borer was a a good aid as it ensured that the beetroot had the same

diameter. However using a ruler could present possible error. Due to

the surface area to volume ratio.

As the test tubes were taken out of the water bath and placed the in

the colorimeter the temp reduced by a few degrees. This small error

could of change the results by 0.5 percent inaccuracy. This is because

of insufficient equipment.

I understand this experiment is only on a small scale but to gain

better results each test tube going up in 10 degrees Celsius so we can

tell the point of denaturing more accurately, however I feel that I my

experiment showed breath of how a membrane functions under temperature

change.