Membrane transport

Topic 1.4

Essential idea: Membranes control the composition of cells by active and passive transport.


1.4.U1 Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport.

Diffusion is the passive movement of particles from a region of high concentration to a region of low concentration while facilitated diffusion requires the presence of an intregal membrane protein. Osmosis is the passive movement of water molecules, across a partially permeable membrane, from our region of low solute concentration to a region of high solute concentration. Active transport requires the use of ATP to move particles from a region of low concentration to a region of high concentration.

Membrane Transport Explained

1.4.U2 The fluidity of membranes allows materials to be taken inot cells by endocytosis or released by exocytosis.

Vesicles are used to transport material within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane. Place the mouse pointer on numbers 1 to 5 on the figure below for the explanation of how the material is secreted from the cell and 6 to 7 for how a material is taken into a cell.

How membrane fluidity allows for shape change, endocytosis and exocytosis?

Explanation membrane fluidity

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Vesicles link Vesicles animation
Endomembrane System in a Cell 1 2 3 4 5 6 7


1.4.A1 Structure and function of sodium-potassium pumps for active transport and potassium channels for facilitated diffusion                      in axons

Active Transport: sodium-potassium pump

Explanation of active transport

Facilitated Diffusion: potassium channel

Explanation of facilitated diffusion

1.4.A2 Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm                      to prevent osmosis

Explanation of osmolarity

Does water move into or out of the human cell?

Place your mouse on the figure to view answers

Practice questions on osmolarity


1.4.S1 Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions

Pre-lab: For Your Information

Explanation of tonicity related to osmolarity

Lab: How to Information

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Go to Internal Assessment: Data Collection and Processing
Go to Internal Assessment: Conclusion and Evaluation
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