Cell Membranes and Transport

The diagram shows the dimensions of two blocks of agar. The diagram has been drawn to scale.

The blocks of agar were stained pink with a pH indicator. In acidic conditions, the pink pH indicator becomes colourless.

The two blocks of agar were placed in a beaker of acid at the same time. As the acid diffused into the blocks, the blocks became colourless.

What is the surface area to volume ratio of the block that became completely colourless first?

Options

A   $0.58 : 1$
B   $0.67 : 1$
C   $1.50 : 1$
D   $1.71 : 1$

The graph shows how the rate of facilitated diffusion of substance X across a cell surface membrane changed as the concentration of substance X increased. All conditions, except for the concentration of substance X, were kept constant. Temperature was maintained at $15\ ^{\circ}\text{C}$.

Which statement about the rate of facilitated diffusion is correct?

Options

A   The rate of facilitated diffusion of substance X at Q will increase if the temperature is increased to $20\ ^{\circ}\text{C}$.
B   The rate of facilitated diffusion of substance X at P will increase if the concentration of ATP is increased.
C   The rate of facilitated diffusion of substance X at Q will increase if the concentration of substance X is increased.
D   The rate of facilitated diffusion of substance X at P will increase if the length of time over which the rate is measured is increased.

A molecule of oxygen diffuses from the air in an alveolus to haemoglobin in a red blood cell.

Assuming that the molecule crosses cellular layers by passing through cells, rather than between cells, what is the minimum number of phospholipid layers that the molecule of oxygen must pass through?

Options

A   5
B   6
C   8
D   10

The cell surface membrane structure is described as a ‘fluid mosaic’.

What correctly describes the ‘mosaic’ part of the cell surface membrane?

Options

A   the different patterns that are obtained by the moving phospholipid molecules
B   the random distribution of cholesterol molecules within the phospholipid bilayer
C   the regular pattern produced by the phospholipid heads and membrane proteins
D   the scattering of the different proteins within the phospholipid bilayer

A student immersed a plant tissue in solution S.

For the next 30 minutes, the student used a microscope to observe the cells in the plant tissue.

During this time, the cytoplasm of the cells shrunk and no longer pushed up against the cell wall. In many cells, a space appeared between the cytoplasm and the cell wall.

Which statements are correct conclusions from these observations?

1 The water potential in solution S was more negative than the water potential in the cytoplasm of the cells at the start of the experiment.
2 Without a cell wall to provide support, it is likely that many of the cells would have burst.
3 The clear space between the cell wall and the cytoplasm of many of the cells was filled with air.

Options

A   1 and 3
B   1 only
C   2 and 3
D   2 only

Water potentials were measured inside a leaf cell, in the air spaces of the leaf and in the atmosphere.

Which values of water potential ($\Psi$) would allow water to move from the leaf to the atmosphere?

Options

Cell membranes become less fluid as the temperature decreases.

Bacteria and yeast cannot regulate their cell temperatures.

How do bacteria and yeast maintain the fluidity of their cell membranes when the temperature decreases?

1 They increase the numbers of unsaturated fatty acids in their phospholipid molecules.
2 They increase the numbers of saturated fatty acids in their phospholipid molecules.
3 They increase the numbers of cholesterol molecules in their cell membranes.

Options

A   1 and 3
B   1 only
C   2 and 3
D   2 only

Samples X, Y and Z are epidermal tissues cut from an onion. Each epidermal tissue was immersed in one of three different concentrations of a salt solution for 30 minutes.

A student observed each tissue sample with a light microscope. Then the student estimated the concentration of each salt solution using a scale.

The diagram shows the scale. P, Q and R represent the estimated concentration of the three salt solutions.

The photomicrographs show the appearance of the tissues in samples X, Y and Z.

Which row shows the estimated concentrations of the salt solutions in which samples Y and Z were immersed?

Options

The graph shows the results of an osmosis investigation using potato tissue.

What is the concentration of sodium chloride solution that has the equivalent water potential to this potato tissue and what is correct about the movement of water at that point?

Options

A   $0.37\ \text{mol dm}^{-3}$ and no net movement of water
B   $17\ \text{mol dm}^{-3}$ and net movement of water out of the potato tissue
C   $0\ \text{mol dm}^{-3}$ and no net movement of water
D   $0.9\ \text{mol dm}^{-3}$ and net movement of water into the potato tissue

Some agar was coloured pink using a pH indicator. The pink agar was then used to make three agar cubes with different dimensions.

The cubes were placed in a beaker and covered with $0.1\ \text{mol dm}^{-3}$ hydrochloric acid. The temperature of the experiment was standardised at $20\ ^{\circ}\text{C}$.

Hydrochloric acid diffused into the agar cubes causing the cubes to become colourless.

What is the surface area to volume ratio of the agar cube that became colourless in the least amount of time?

Options

A   $0.33:1$
B   $0.83:1$
C   $1.2:1$
D   $3.0:1$