Cell membranes and transport

Learning objectives

Describe the fluid mosaic model, explaining how hydrophobic and hydrophilic interactions create the phospholipid bilayer, and where proteins, cholesterol, glycolipids and glycoproteins sit within it.

Explain how phospholipids, cholesterol, glycolipids, proteins and glycoproteins contribute to membrane stability, fluidity and permeability, to transport through channel and carrier proteins, to cell signalling as receptors and to cell recognition as antigens.

Outline cell signalling from start to finish: release of a specific signalling molecule (ligand), its journey to target cells, and its binding to a complementary cell surface receptor that sets off a specific response inside the cell.

Describe and explain simple diffusion, facilitated diffusion, osmosis, active transport, endocytosis and exocytosis, including which processes need ATP and which need transport proteins.

Calculate surface area to volume ratios of simple 3-D shapes to show that the ratio falls as size increases, and investigate diffusion and osmosis using agar blocks, Visking (dialysis) tubing and plant tissue.

Explain water movement in terms of water potential and its different effects on animal cells (lysis, crenation) and plant cells (turgor, plasmolysis), and estimate the water potential of a plant tissue from mass or length changes in a series of solutions.