Why does the colour leak out of a cooked beetroot?

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Biology – Ms Gordilier                 Christian Fowler

                28th November 2007

Why does the colour leak out of a cooked beetroot?

Aim:

To investigate the effect of temperature on membrane structure on a beetroot

Hypothesis:

I predict that diffusion will be at its highest at 70.

Null Hypothesis:

There will be no relationship found between the rate of diffusion and the temperature rise in the beetroot.

Rationale:

All cells have a cell membrane that forms the outer limit of the cell. Bacteria, fungi, and plant cells have a cell wall outside this, but it is considered to be quite distinct and outside the cell. Cell membranes are also found inside the cells of plant and animal cells as part of membrane bound organelles [1].

For a cell to function correctly it needs to be able to control transport across its surface membrane. Molecules and ions move across membranes by diffusion, osmosis, active transport, exocytosis, and endocytosis.

When observing a cell surface membrane, we can see that it has a bilayer, which appears as two distinct lines. This bilayer is made up of two layers of phospholipids [2].

A phospholipid is made up of the hydrophilic head and the hydrophobic tails. The hydrophobic tails are made of fatty acids and the hydrophilic heads are made up of a glycerol group and a phosphate group where X can be a variety of chemical groups [2].

The phosphate head of the molecule is polar, which means that the sharing of the electrons within this part of the molecule is not quite even and so one end becomes slightly positive and the rest is slightly negative. This makes the phosphate head attract other polar molecules, like water, and it is therefore hydrophilic. The fatty acid tails are non-polar and therefore hydrophobic. When added to water phospholipids either form a layer on the surface with their hydrophobic tails directed out of the water, or they arrange themselves into spherical clusters called micelles to avoid contact between the hydrophobic tails and water [2].

Phospholipids that make up the cell surface membrane form a bilayer with all the hydrophilic heads pointing outwards and the hydrophobic tails facing inwards avoiding any contact with water on either side of the membrane. [2].

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Diffusion is the movement of molecules or ions from an area of their high concentration to an area of their low concentration. Diffusion will continue until the substance is evenly spread throughout the whole volume. Small-uncharged particles diffuse across the cell membrane, passing between the lipid molecules as they move down the concentration gradient. Small molecules like, oxygen and carbon dioxide, can diffuse rapidly across the cell membrane. Carbon Dioxide is polar but its small size allows rapid diffusion [2].

Cell surface membrane is not simply a phospholipid bilayer. It also contains proteins, cholesterol, glycoproteins, and glycolipids. Some ...

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