Membrane Transport

Standard Level

Transport Types Simple Diffusion Facilitated Diffusion Active Transport Osmosis Tonicity Osmotic Effects

SL Content Statements

B1.1.13

Ability of non-polar steroids to pass through the phospholipid bilayer
Include oestradiol and testosterone as examples. Students should be able to identify compounds as steroids from molecular diagrams.
B2.1.3

Simple diffusion across membranes
Use movement of oxygen and carbon dioxide molecules between phospholipids as examples of simple diffusion across membranes.
B2.1.5

Movement of water molecules across membranes by osmosis and the role of aquaporins
Include an explanation in terms of random movement of particles, impermeability of membranes to solutes and differences in solute concentration.
B2.1.6

Channel proteins for facilitated diffusion
Students should understand how the structure of channel proteins makes membranes selectively permeable by allowing specific ions to diffuse through when channels are open but not when they are closed.
B2.1.7

Pump proteins for active transport
Students should appreciate that pumps use energy from ATP to transfer specific particles across membranes and therefore that they can move particles against a concentration gradient.
B2.1.8

Selectivity in membrane permeability
Facilitated diffusion and active transport allow selective permeability in membranes. Permeability by simple diffusion is not selective and depends only on the size and hydrophilic or hydrophobic properties of particles.
D2.3.2

Water movement from less concentrated to more concentrated solutions
Students should express the direction of movement in terms of solute concentration, not water concentration. Students should use the terms “hypertonic”, “hypotonic” and “isotonic” to compare concentration of solutions.
D2.3.3

Water movement by osmosis into or out of cells
Students should be able to predict the direction of net movement of water if the environment of a cell is hypotonic or hypertonic. They should understand that in an isotonic environment there is dynamic equilibrium rather than no movement of water.
D2.3.4

Changes due to water movement in plant tissue bathed in hypotonic and hypertonic solutions
AOS: Students should be able to measure changes in tissue length and mass, and analyse data to deduce isotonic solute concentration. Students should also be able to use standard deviation and standard error to help in the analysis of data. Students are not required to memorise formulae for calculating these statistics. Standard deviation and standard error could be determined for the results of this experiment if there are repeats for each concentration. This would allow the reliability of length and mass measurements to be compared. Standard error could be shown graphically as error bars.
D2.3.5

Effects of water movement on cells with a cell wall
Include the development of turgor pressure in a hypotonic medium and plasmolysis in a hypertonic medium.
D2.3.6

Effects of water movement on cells that lack a cell wall
Include swelling and bursting in a hypotonic medium, and shrinkage and crenation in a hypertonic medium. Also include the need for removal of water by contractile vacuoles in freshwater unicellular organisms and the need to maintain isotonic tissue fluid in multicellular organisms to prevent harmful changes.
D2.3.7

Medical applications of isotonic solutions
Include intravenous fluids given as part of medical treatment and bathing of organs ready for transplantation as examples.

Membrane Transport

Standard Level

SL Content Statements

B1.1.13

Ability of non-polar steroids to pass through the phospholipid bilayer

Include oestradiol and testosterone as examples. Students should be able to identify compounds as steroids from molecular diagrams.

B2.1.3

Simple diffusion across membranes

Use movement of oxygen and carbon dioxide molecules between phospholipids as examples of simple diffusion across membranes.

B2.1.5

Movement of water molecules across membranes by osmosis and the role of aquaporins

Include an explanation in terms of random movement of particles, impermeability of membranes to solutes and differences in solute concentration.

B2.1.6

Channel proteins for facilitated diffusion

Students should understand how the structure of channel proteins makes membranes selectively permeable by allowing specific ions to diffuse through when channels are open but not when they are closed.

B2.1.7

Pump proteins for active transport

Students should appreciate that pumps use energy from ATP to transfer specific particles across membranes and therefore that they can move particles against a concentration gradient.

B2.1.8

Selectivity in membrane permeability

Facilitated diffusion and active transport allow selective permeability in membranes. Permeability by simple diffusion is not selective and depends only on the size and hydrophilic or hydrophobic properties of particles.

D2.3.2

Water movement from less concentrated to more concentrated solutions

Students should express the direction of movement in terms of solute concentration, not water concentration. Students should use the terms “hypertonic”, “hypotonic” and “isotonic” to compare concentration of solutions.

D2.3.3

Water movement by osmosis into or out of cells

Students should be able to predict the direction of net movement of water if the environment of a cell is hypotonic or hypertonic. They should understand that in an isotonic environment there is dynamic equilibrium rather than no movement of water.

D2.3.4

Changes due to water movement in plant tissue bathed in hypotonic and hypertonic solutions

D2.3.5

Effects of water movement on cells with a cell wall

Include the development of turgor pressure in a hypotonic medium and plasmolysis in a hypertonic medium.

D2.3.6

Effects of water movement on cells that lack a cell wall

D2.3.7

Medical applications of isotonic solutions

Include intravenous fluids given as part of medical treatment and bathing of organs ready for transplantation as examples.