Biology 8 Cell Transport/Exchange

passive transport

movement of materials using a concentration gradient (w/o energy)

active transport

movement of materials using energy (ion pumps), typically against the concentration gradient

molecules able to cross cell membrane

oxygen, carbon dioxide, and nitrogen

why can’t large/polar molecules cross the cell membrane?

polar molecules don’t interact the hydrophobic tails of the phospholipids in the bilayer of the cell membrane

large molecules can't squeeze through small pores of the membrane

concentration gradient

difference in the concentration of a substance (drives diffusion)

diffusion

the process of particles moving from high to low concentration, typically across a cell membrane

spontaneous process

a process which doesn't require energy from the cell

osmosis

the movement of water across a membrane to equalize solute concentration on both sides

direction of water movement in osmosis

from hypotonic solution to hypertonic solution

hypertonic

solution which is more concentrated

hypotonic

solution which is more dilute

isotonic solution

when the concentrations of the solutions are equal

why are cells always hypotonic to water?

cells are filled with salt, sugar, and protein

osmotic pressure

result of the difference in concentration across the membrane

facilitated diffusion

movement of molecules across the cell membrane with the help of proteins

molecular transport

active transport which moves small molecules and ions

endocytosis

material is engulfed by the cell through pockets of cell membrane, which forms a vesicle

phagocytosis

a type of endocytosis, which is done with large particles. It requires a lot of energy

pinocytosis

type of endocytosis that involves the uptake of small particles and liquids (“cell drinking”)

how does pinocytosis occur?

pockets in the cell membrane fill with liquid and separate to form a vesicle.

exocytosis

process by which a cell releases large amounts of material from the cell

how does exocytosis occur?

vesicle fuses with the membrane, which releases its contents

active vs passive transport

active transport requires energy (ATP), while passive transport doesn’t

semi-permeable membrane

allows cell to maintain homeostasis