How substances move into and out of the cell Cell Membranes How substances move into and out of the cell

Objectives: 1. Identify the main functions of the cell membrane 2. Describe what happens during diffusion 3. Explain the processes of osmosis, facilitated diffusion, and active transport

Cell Membrane Regulates what enters and leaves the cell and also provides protection and support In: food and water, Out: waste Lipid bilayer = strong, flexible barrier Lipids – hydrophobic tails face each other Proteins – some are channels and pumps Carbohydrates – attached to surface of some proteins for recognition

Diffusion Moves substances across the membrane without use of energy The cytoplasm inside of cells is a solution (liquid mixture of substances) Substances dissolved in liquid = solutes

Diffusion Concentration = amount of solute per volume of solution (example: g/L) Molecules are moving, and diffuse from high concentration to low concentration = diffusion Equilibrium = same concentration of solute throughout solution

Osmosis Membranes are “selectively permeable” = some substances can pass through, others cannot Osmosis = the diffusion of water through a selectively permeable membrane (through proteins called “aquaporins”) Water moves in both directions, but the net movement is in the direction of the most solute particles

Osmosis

Osmosis Osmotic pressure is handled in a number of ways… Cells are surrounded by isotonic solution (blood) Cells are surrounded by a cell wall (plants) Cells use a contractile vacuole to pump excess water out of the cell (single-celled organisms)

Movement of Substances Across the Membrane Protein channels allow substances to cross that normally could not Ions, sugars, salts, etc. Net movement from higher to lower concentration No energy required Movement against the concentration gradient Requires energy input “Pumps” (for small molecules or ions) Endocytosis = taking in large amount of material by folding inward Exocytosis = removal of large amounts of material by a vacuole fusing with the membrane Facilitated Diffusion Active Transport