Transcript TRANSPORT
TRANSPORT Cell Membrane ** The cell membrane controls the passage of materials into and out of the cell. • Cell membranes are semi-permeable • Cell membranes are made of phospholipids (fats) and proteins – The fat molecules have hydrophilic (water-loving) heads and hydrophobic (water-hating) tails. – The fat molecules form a double layer with heads out and tails in – Proteins are embedded in the phospholipid bilayer • See pg. 145 (biozone) Phospholipid Bilayer http://www.bio.davidson.edu/people/macampbell/111/membswf/membranes.swf Passive Transport • Movement of materials without using energy • Particles move along a concentration gradient from high concentration to low concentration • There are 2 types of passive transport: – Diffusion – Osmosis Diffusion • All particles of matter are constantly moving at random. • Diffusion is the movement of particles down a concentration gradient until evenly distributed. – Example: if someone sets off a stink bomb in one corner of the room, the smell will gradually move to fill the room evenly or food colouring – Raise your hand when…….. • The rate of diffusion varies depending on: – – – – Size of molecules (small-fast, big-slow) Temperature (warm-fast, cool-slow) State of matter (gas-fast, liquid-slow) Concentration gradient (steep-fast, gentleslow) – Distance involved (short-fast, long-slow) – Surface Area involved (large-fast, smallslow) • Facilitated diffusion occurs when a substance is helped across a membrane by a protein-carrier Osmosis • Osmosis is the movement of water molecules from an area of high water concentration to an area of low water concentration through a semi-permeable membrane. • Example: If you have a 5% salt solution on one side (95% water) and a 15% salt solution (85% water) on the other side, the water will move from the 5% solution side to the 15% solution side. • Osmoregulation is the control of water in a cell. – If a plant cell loses water, it becomes flaccid (floppy) and the cytoplasm pulls away from the cell wall. This is plasmolysed. – If a plant cell gains water, it swells and becomes turgid (stiff). – Since animal cells have no cell wall, if they have too much water they burst. This is called lysed.