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