Transport through the Cell Membrane A. Passive Transport passive transport is the movement of molecules through the cell membrane without cellular energy there are 3 types: diffusion; osmosis; and facilitated diffusion

1. Diffusion molecules are in constant motion diffusion is the process by which particles move naturally from an area of HIGH concentration to an area of LOW concentration until a dynamic equilibrium is reached (no net movement) [high] [low] this is called moving “with the concentration gradient” small molecules diffuse through the phospholipids of the cell membrane (e.g. O2, CO2, H2O, alcohol, small lipids)

Factors that affect diffusion concentration. of particles ( conc.,  rate of diffusion) temperature. of particles ( temp.,  rate of diffusion) pressure ( pressure,  rate of diffusion) agitation ( movement,  rate of diffusion)

2. Osmosis Three types of membranes: impermeable permeable osmosis is the diffusion of water through a semi- permeable membrane Three types of membranes: impermeable permeable semi-permeable Which membrane is most like a cell membrane?

Three terms for solutions: Solute: the dissolved substance, e.g. salt Solvent: able to dissolve things, e.g. water Solution: mixture of solvent and solute Three types of solutions: Hypertonic solution: the solution surrounding the cell has a higher [solute] than the cell’s cytoplasm, water moves out of the cell Hypotonic solution: the solution surrounding the cell has a lower [solute] than the cell’s cytoplasm, water moves into the cell Isotonic solution: the [solute] is the same in the cell’s cytoplasm and in the solution surrounding the cell

What will happen to red blood cells placed in a salt water solution?

It depends on the type of solution they are placed in. Hypertonic Isotonic Hypotonic More water diffused out of the cells Water diffused equally in and out of the cells More water diffused into the cells

Turgor pressure the rigid cell wall of plant cells prevents them from bursting when they are filled with water water in vacuoles causes an outward push called turgor pressure plant cells swollen with water are said to be turgid Plasmolysis when plant cells are placed in a salt solution, the cells shrink, this is called plasmolysis

3. Facilitated Diffusion some molecules are too large or are hydrophilic, and cannot pass through the phospholipids transport proteins assist these molecules through the cell membrane (e.g. glucose) transport protein transport occurs with the concentration gradient (no energy is required)

B. Active Transport active transport is the movement of molecules through the cell membrane against the concentration gradient using transport proteins [low] [high] this process requires the use of cellular energy (ATP) transport proteins are highly selective (e.g. Na+/K+ pump)

Active vs. Passive Transport Facilitated Diffusion Active Transport Diffusion

C. Transport by Vesicles a) Endocytosis: transport of material into a cell by means of vesicles cell engulfs material by folding a portion of its membrane around it energy is required 3 types of endocytosis: 1. phagocytosis, cell eating; movement of large molecules and whole cells into the cell’s interior

2. pinocytosis: cell drinking; transport of liquids into vesicles inside cell 3. receptor-mediated endocytosis: molecules bind to receptors on cell’s surface and are folded into vesicles within the cell

b) Exocytosis: transport of macromolecules (e.g. hormones) out of a cell by means of vesicles made by the Golgi complex; energy is required

Work on review in the booklet