Structure and Function Cell Membranes Structure and Function

Animal Cell Membrane

Semi-permeable Membranes Lipid membranes are semi-permeable, also called selectively permeable Water moves across the membrane freely Ions (charged particles) do not move across the membrane freely Many large molecules do not move across the membrane freely

Passive Transport Diffusion – the movement of substances from an area of higher concentration to an area of lower concentration Osmosis – the movement of water from an area of higher water content to an area of lower water content

Active Transport The movement of a substance against the concentration gradient (from lower concentration to higher concentration Active transport requires the use of energy

Membrane proteins play an important role in passive and active transport

Very large molecules may be taken in by endocytosis

Exocytosis secretes substances