Factors affecting membrane structure 5.2

Question 1

what is the overarching function of membranes

Answer 1

Membranes control the passage of different substances into and out of cells (and organelles).

Question 2

How does an increase in temperature effect the structure of a cell-surface membrane and its compenents

Answer 2

When temperature is increased the phospholipids will have more kinetic energy and will move more. This makes a membrane more fluid and it begins to lose its structure. If temperature continues to increase the cell will eventually break down completely

This loss of structure increases the permeability of the membrane, making it easier for particles to cross it

Carrier and channel proteins in the membrane will be denatured at higher temperatures. These proteins are involved in the transport across the membrane so as they denature, membrane permeability will be affected

Unlike proteins, membranes are not denatured by high temperatures when they lose their structure they should be described as disputed or destroyed

Question 3

how is water essential for the formation of the phospholipid bilayer

Answer 3

non-polar tails of the phospholipids are orientated away from the water, forming a bilayer with the hydrophobic core. The charged phosphate heads interact with water, helping to keep the bilayer intact

Question 4

how do membranes interact with less polar or non polar solvents to effect the structure

Answer 4

Organic non-polar solvents will dissolve membranes, disrupting cells.
This is why alcohols are used in antiseptic wipes.
The alcohols dissolve the membranes of bacteria in a wound, killing them and reducing the risk of infection

Question 5

How can non-polar alcohol molecules effect the structure of cell-membranes

Answer 5

The non-polar alcohol molecules can enter the cell membrane ( if ingested in an alcoholic drink) and the presence of these molecules between the phospholipids disrupts the membrane.
When the membrane is disrupted it becomes more fluid and more permeable.

Question 6

explain the steps of the experiment investigating permeability

Beetroot cells

Answer 6

5 small pieces of beetroot of equal size were cut using a cork borer.
The beetroot pieces were thoroughly washed in running water, they were then placed in 100ml of distilled water in a water bath.
The temperature of the water bath was increased in 10°C intervals.
Samples of the water containing the beetroot were taken 5 minutes after each temperature was reached.
The absorbing of each sample is measured using a colorimeter with a blue filter.
The experiment was done 3 times, each time with fresh beetroot pieces and a mean calculated for each temperature.
Then plot the points on a graph