Cell Membranes and Transport

Name the structures labelled A, B and C in Fig. 1.1.

A ______
B ______
C ______

Draw an arrow on Fig. 1.1 to show the movement of a molecule across the membrane into the cell by facilitated diffusion.

Explain how the fluidity of the membrane would change if the proportion of unsaturated fatty acids in the phospholipid bilayer increased.

The R-groups of amino acids give them different properties.

Suggest how the properties of the R-groups of the amino acids at position 1 of P may differ from the R-groups of the amino acids at position 2.

The Visking tubing used by the student was not permeable to sucrose.

Explain the results shown in Table 3.1.

When red blood cells are placed in water they are destroyed by bursting.

The student also investigated how red blood cells are affected by immersion in solutions of sodium chloride of different concentration. Blood samples of the same volume were added to solutions of sodium chloride in separate test-tubes.

After 10 minutes, the student took $0.1\ \text{cm}^3$ of the blood samples from the test-tubes and estimated the percentage of red blood cells that had burst in each blood sample.

Fig. 3.2 shows the student’s results.

Describe and explain the effects on red blood cells of immersion in different concentrations of sodium chloride as shown in Fig. 3.2.

Explain why the different concentrations of sucrose result in different mean percentage changes in mass of potato tissue.

State how the graph is used to estimate the water potential of the potato tissue.

With reference to Fig. 3.2, describe the effect of increasing the concentration of sucrose solution on the mass of potato cylinders.

Explain why there was a change in mass for the potato cylinders in $0.6\ \text{mol dm}^{-3}$ sucrose solution.

State what is meant by the term fluid mosaic.

State the thickness of a cell surface membrane.

List four features of cell surface membranes of eukaryotic cells that are not visible in Fig. 6.1.

1 ______

2 ______

3 ______

4 ______

Describe what is meant by the term fluid mosaic.

In 1934, the biologists Davson and Danielli published their suggestion for the structure of the cell surface membrane, as shown in Fig. 1.1.

They suggested that the membrane was a phospholipid bilayer with a layer of hydrophilic protein on both surfaces.

State one way in which the Davson-Danielli structure is similar to the fluid mosaic structure and one way in which it differs from the fluid mosaic model.

similarity

difference

One way in which substances can cross cell membranes is by active transport.

Describe the mechanism of active transport.

High temperature can damage cell membranes. One factor contributing to this damage is the denaturation of membrane proteins.

Describe how proteins become denatured at high temperature and explain how this could lead to damaging cell membranes.

State the functions of structures P, Q and R.

P

Q

R

Circle the width of the membrane shown as W in Fig. 5.1.

$17.0\;\mu\text{m} \qquad 1.7\;\mu\text{m} \qquad 0.7\;\mu\text{m} \qquad 70.0\;\text{nm} \qquad 17.0\;\text{nm} \qquad 7.0\;\text{nm} \qquad 0.7\;\text{nm}$

Membranes, such as the cell surface membrane, are described as having a fluid mosaic structure.

Explain what is meant by the term fluid mosaic.

Aquaporins are membrane channel proteins in plant and animal cells. They permit the movement of water across membranes. Explain why they are necessary.

Complete Table 1.1 to show the transport mechanisms across cell surface membranes and examples of materials transported.

Table 1.1

Each transport mechanism across cell surface membranes has a characteristic set of features.

In each of the boxes below, state one example of a transport mechanism that matches the pathway shown.

In the box below, draw a labelled diagram of a section through a cell surface membrane to show how the above components are organised within the membrane.

The diagram should include other named components of the membrane.

Label the inner and outer surfaces of the membrane.

Suggest why ‘fluid mosaic’ is an appropriate term to use to describe membrane structure.

Use a label line and the appropriate letter to label each of the following on Fig. 1.1.

P protein for active uptake of potassium ions

Q protein for facilitated diffusion of polar molecules

R receptor site for a hormone

S hydrophilic heads of phospholipids on the internal surface of the membrane

T molecule that modifies the fluidity of the membrane

Some cells take in bacteria by endocytosis.

Explain how endocytosis occurs at a cell surface membrane.