Fluid mosaic membranes & cell signalling

Every cell is wrapped in a thin, living skin, and in this lesson we build that skin up piece by piece. We meet the fluid mosaic model of the cell surface membrane and name every component — the phospholipid bilayer with its hydrophilic heads and hydrophobic tails, cholesterol, glycolipids, proteins and glycoproteins. We see what the whole membrane is for (a partially permeable barrier that controls entry and exit and lets cells recognise one another), then give each part its own specific job: phospholipids form the barrier, cholesterol steadies its fluidity, channel proteins form selective pores, carrier proteins change shape to ferry substances, receptors listen for chemical messages and antigens act as identity badges. Finally we outline cell signalling — a signalling molecule such as a hormone released from one cell, binding a complementary receptor on a target cell and triggering a specific response, using adrenaline as our worked example. We finish with the beetroot practical that lets you actually see membrane damage as leaked pigment.