Membranes

Which one of the following is not a major component of the cell surface membrane?

• glycolipid

• glycoprotein

• cholesterol

• triglyceride

If two sucrose solutions of different concentrations are separated by a partially permeable membrane, which one of the following will occur?

• The solute will diffuse from the more concentrated to the less concentrated solution.

• Both solute and solvent will diffuse until equilibrium is reached.

• The volume of the less concentrated solution will increase.

• The volume of the less concentrated solution will decrease.

Potassium cyanide interferes with the formation of ATP. The use of potassium cyanide reduces the rate at which molecules of a certain chemical enter the cell.

Select the process by which the molecules would normally enter the cell.

• 
  simple diffusion

• 
  facilitated diffusion

• 
  osmosis

• 
  active transport

Which of these has the highest water potential?

• 
  5% sucrose solution

• 
  10% sucrose solution

• 
  20% sucrose solution

• pure water

What will happen if a red blood cell is placed in a solution with a more negative water potential?

• becomes turgid

• 
  bursts due to osmosis

• 
  shrinks due to osmosis

• stays the same

The water potential of a plant cell is -400 kPa. The cell is put in a solution with a water potential of -600 kPa. Which one of the following happens to the cell?

• 
  the cell bursts

• 
  the cell becomes turgid

• 
  the cell wall shrinks

• 
  the cell becomes plasmolysed

A sample of blood, added to a saline solution with a less negative water potential than the cell contents, results in a uniform red colour in the solution which is unaffected by centrifugation.

Which one of the following explains this result?

• 
  Haemoglobin has diffused through the erythrocyte membrane into the solution.

• Water has entered erythrocytes by osmosis. As the cells are now less dense than the solution, they will not sediment on centrifugation.

• Water has left the cells by osmosis, causing them to shrink and become too small to sediment on centrifugation.

• Water has entered the erythrocytes by osmosis, causing them to swell and burst and the haemoglobin is released into the solution.

Three plant cells, X, Y and Z, are in contact with each other. Their water potentials are shown in the table

• 
  X to Y   X to Z   Y to Z

• 
  Z to X   Z to Y   X to Y

• 
  X to Z   Y to X   Y to Z

• 
  Y to X   Z to Y   X to Z

Which diagram shows the appearance of a plant cell with an original ψ of -1.2 MPa after being placed in a solution as shown?

• A

• B

• C

• D

The graph shows how the concentration of a substance affects its rate of absorption into a cell.

Substance F enters by simple diffusion, substance G by facilitated diffusion.

Why does the curve for substance G level off above a certain concentration?

• 
  equilibrium is reached with the concentration of G being the same inside and outside of the cell

• 
  ATP becomes depleted

• 
  the membrane becomes impermeable to G above a certain concentration

• 
  carrier molecules are saturated