Cellular Transport

Diffusion Maintaining homeostasis Cell membranes help organisms maintain homeostasis by controlling what substances may enter or leave cells. Passive Transport- substances can cross the cell membrane without any input of energy

Diffusion Molecular motion Molecules are in constant motion because they have kinetic energy (brownian motion) Molecular motion is random Molecules tend to move from areas where they are more concentrated to areas where they are less concentrated

Diffusion- movement of molecules from area of higher concentration to area of lower concentration Concentration gradient- difference in the concentration of molecules across a distance So, molecules tend to move “down” their concentration gradient Diffusion will eventually cause the molecules to be in equilibrium Equilibrium- concentration of molecules will be the same throughout the space the molecules occupy

Diffusion Simple diffusion- diffusion of substances across the cell membrane without the help of membrane proteins Facilitated diffusion- the movememt of molecules across the cell membrane is assissted by specific proteins in the membrane Used to move large molecules, polar molecules, ions Carrier proteins- used in facilitated diffusion

Osmosis Osmosis- the process by which water moleucles diffuse across a cell membrane from high to low concentration Form of passive transport (does not requir energy)

Direction of Osmosis Depends on relative concentration of solutes on the two sides of the membrane Hypotonic- describes solution with solute concentration lower than concentration inside cell (water diffuses in) Hypertonic- describes solution with solute concentration higher than concentration in cell (water diffuses out) Isotonic- describes solution with solute concentration equal to concentration in cell (water diffuses in and out at same rate)

How osmosis affects living cells

Active transport Active transport- when cells move materials from area of lower concentration to an area of higher concentration, “against” the concentration gradient (requires energy, ATP)

Cell membrane pumps Carrier proteins – “pumps”- moving from low to high concentration Sodium-potassium pump- transports Na+ ions and K+ ions up their concentration gradient Helps create electrical impulses that are important in animal cells (nerve cells)

Movement in vesicles Endocytosis- process by which cells ingest external fluid, macromolecules, and large particles, including other cells by forming a vesicle Pinocytosis- involves transport of solutes or fluids Phagocytosis- movement of large particles or cells

Exocytosis- process by which a substance is released from the cell through a vesicle