Cell Walls

Movement Through the Plasma Membrane Selective permeability allows intracellular fluid to differ from extracellular fluid nutrients enter, wastes exit intracellular concentrations of substances must be maintained within norms

Passive transport processes 1. solutes, solvents, and solutions 2. diffusion: movement of solute molecules from areas of high concentration to areas of low concentration. a. concentration gradient: measure of the difference in solute concentrations between two points

b. may involve membrane channels

3. osmosis a. diffusion of water across a selectively permeable membrane b. water diffuses from low [solute] to high [solute]

c. osmotic pressure: pressure created by movement of water across a membrane - cell walls can allow cells to withstand

Tonicity Hypotonic solutions have a lower concentration of solutes than cytoplasm lysis

Tonicity Hypotonic solutions Hypertonic solutions have a lower concentration of solutes than cytoplasm lysis Hypertonic solutions have a higher concentration of solutes than cytoplasm crenation

Tonicity Hypotonic solutions Hypertonic solutions Isotonic solutions have a lower concentration of solutes than cytoplasm lysis Hypertonic solutions have a higher concentration of solutes than cytoplasm crenation Isotonic solutions concentration of solutes is the same as cytoplasm

Selective Transport Mechanisms Facilitated Diffusion 1. Moves molecules with the gradient through membrane protein. 2. Requires a specific transport protein.

Active Transport 1. Moves solutes against the gradient. 2. Results in increased [solutes] on one side of membrane. 3. Requires energy input (ATP) and a transport protein.

Bulk Transport Endocytosis is an energy-requiring process cell “takes-in” substances can involve pseudopodia a membrane-bound vesicle is formed

Endocytosis Subtypes: 1. phagocytosis pseudopodia large vesicles formed contents of vesicle digested

Endocytosis Subtypes: 2. pinocytosis invagination of cell membrane takes in liquid material smaller vesicles

Exocytosis 1. products “packaged” into transport (secretory) vesicles 2. vesicles fuse with cell membrane 3. contents “spilled” outside of cell (secretion)

Membrane Proteins Used in Communication Receptor proteins (on surface) 1. recognize specific molecules (like hormones) 2. receptor often changes shape 3. causes a change in cell activity (signal transduction)

Membrane Proteins Used in Communication Gated channels 1. gated (may be open or closed) 2. allow passage of ions (current) 3. used in neurons and muscle cells