1.4.5 Describe how membrane structure can be investigated practically, e.g. by the effect of alcohol concentration or temperature on membrane permeability.

effect of temperature on membrane structure:

- as temperature increases, phospholipids become more fluid, allowing molecules to leak from the cell.

-  plants containing pigment within the cytoplasm and/or vacuole can be used to test this idea:

• cut equal sized pieces of tissue
• rinse under running water to remove all pigment which could have leaked out of the vacuole due to the damaged membrane.
• place 5cm3 of distilled water in 8 boiling tubes into a water bath maintained at 0, 10, 20, 30, 40, 50, and 60 degrees. leave for 5 minutes until the water reaches the required temperature.
• place the pieces into each of the boiling tubes maintained at the temperature above. leave for 30 minutes in the water bath. 
• remove the pieces carefully from the tubes and shake to disperse the pigment. 
• assess amount of pigment lost using a colorimeter to measure a absorbance to transmission vale of the solution
• the higher the absorbance reading, the more pigment released, the higher the permeability of the membrane.

- below 0 degree celsius  the membrane is rigid because phospholipids don't have much energy and are thus packed closely together, channel and carrier proteins deform, increasing permeability of membrane.

- between 0-45 degree celsius, the phospholipids can move around (aren't as tightly packed) so the membrane is partially permeable and increase in temp. increases the movement of phospholipids which increases the permeability of the membrane.

- above 45 degree celsius the bilayer starts to melt, the channel an carrier proteins deform and water inside cell expands putting pressure on the membrane. this increases the permeability of the membrane. 

effect of alcohol on membrane structure.

- the phospholipids in membranes dissolve when disrupted by alcohol since alcohol is non-polar/ organic solvent, causing pigment to leak (increasing permeability).