Gas Exchange, Cell Membranes & Transport (Edexcel A (SNAB) A Level Biology)

The diagram below shows part of a plasma membrane. 

Complete the table below by writing the letter from the diagram which refers to each part of the membrane.

Give a function of the structure labelled V in the diagram in part (a).

Plasma membranes such as the one seen in the diagram in part (a), are often described as having a fluid-mosaic structure.

Explain why they are described this way.

Structures X and Y from the diagram in part (a) form a phospholipid. Collectively, these phospholipids form the phospholipid bilayer of the cell surface membrane.

State three functions of this phospholipid bilayer.

A student investigated the effect of different concentrations of sodium chloride on the mass of beetroot tissue. A few large beetroots were peeled and cut into strips. The strips were weighed before being placed in beakers containing sodium chloride solutions of different concentrations (0%, 2%, 4%, 6%, 8% and 10%). Three strips were placed in each covered beaker.

The strips were left in the beakers for 24 hours after which they were removed, blotted dry and weighed again.

The mean percentage change in mass was calculated for each sodium chloride solution.

The following graph shows the results of the investigation.

Apart from repeating the experiment, explain one improvement that could be made to this investigation.

(2)

At which point on the graph was the rate of osmosis the highest? 

(1)

Deduce a suitable conclusion for this investigation by using the information given at part (a).

Pickled beetroot is a popular side dish around the world. Beetroot pieces are added to a brine consisting of white vinegar containing acetic acid. This results in the pickling brine turning a deep red colour.

Explain why this happens.

When investigating membrane structure and permeability using beetroot, a colorimeter is used to determine the amount of pigment in different samples.

Which of the following is not correct regarding the use of a colorimeter? 

Some scientists investigated the uptake of magnesium ions in rice plants. They divided the plants into two groups and placed their roots in solutions containing radioactive magnesium ions.

Group Y: plants had a substance that inhibited respiration added to the solution

Group Z: plants did not have the respiratory inhibitor added to the solution

The scientists calculated the total mass of magnesium ions absorbed by the plants every 5 minutes.

Their results are shown in the graph below:

Calculate the ratio of the mean rate of uptake of magnesium ions in the first 20 minutes to the mean rate of uptake of magnesium ions in the second 20 minutes for group Z plants.

Using the graph in part (a), calculate the rate of uptake of magnesium ions for group Y plants after 40 minutes.

Provide suitable units for your answer.

Explain the results of the investigation by using the information provided in the graph at part (a).

State two differences between the processes of facilitated diffusion and active transport.

In the 1930's, Hugh Davson and James Danielli proposed a model of the cell surface membrane.

The diagram below shows this model.

Compare and contrast the Davson-Danielli model of the cell surface membrane with the fluid mosaic model.

As technology advanced, scientists could construct a more accurate model of the cell surface membrane which led to the rejection of the Davson-Danielli model.

Describe two such advancements.

Structure X in the diagram at part (a) are the components that form the cell surface membrane.

Explain how the properties of X contribute to this.

Cholesterol forms an important part of the cell surface membrane.i)

Which of the following correctly describes the role of cholesterol in the cell membrane?