Unit 4 : Cell Transport

lipid bilayer

• the organization of phospholipids in a membrane, with the hydrophilic phosphate group head facing outward and the hydrophobic lipid tail facing inward.

fluid mosaic model

• describes the structure of cell membranes. cell membranes are made of many different types of molecules (phospholipids, proteins, glycoproteins, glycolipids, and cholesterol). unless they are anchored, they are free to move around in the cell membrane.

passive transport

• transport of material that does NOT require energy. always moves material with the concentration gradient, from a greater concentration to a lesser concentration.

• diffusion: movement of particles from a greater concentration until they are equal. SMALL, NONPOLAR MOLECULES can diffuse directly across the cell membrane when they are moving WITH the concentration gradient.

• facilitated diffusion: diffusion of molecules through protein channels, SMALL, POLAR MOLECULES need protein channels to travel across the cell membrane when they are moving WITH the concentration gradient because the cell membrane in non-polar and does not like to interact with polar molecules.

• osmosis: diffusion of water through a semi-permeable membrane.

active transport

• transport of material requiring the use of energy. moves materials against the concentration gradient, from a lower concentration to a higher concentration.

• ion pumps: protein channels that move ions (charged particles) against the concentration gradient. requires energy

• endocytosis: how cells bring large molecules (such as proteins) into a cell. the cell engulfs the material and brings it inside the cell in a vesicle. requires energy because it moves large amounts of cytoplasm and cell membrane.

  • phagocytosis: engulfing really large material or cells

  • pinocytosis: engulfing smaller but still large enough not to be able to move through the membrane

• exocytosis: how cells release large molecules (such as proteins) out of a cell. vesicles fuse with the cell membrane, expelling the material from the cell. requires energy because it moves large amounts of cytoplasm and cell membrane.

concentration gradient

• going from higher concentration to a lower concentration

dynamic equilibrium

• when concentration of particles is equal on both sides of the membrane, but particles continue to move but there is no net change in concentration

most likely transport for the following molecules

• large molecules

  • into: endocytosis

  • out of: exocytosis

• polar molecules

  • with gradient: facilitated diffusion

  • against gradient: active transport

• small, nonpolar molecules

  • with gradient: simple diffusion directly through the membrane

  • against gradient: active transport

selectively permeable membrane

• a membrane that allows for the transport of some materials through it but not others

how cells respond to being in different types of solutions

• hypertonic: when placed in hypertonic solutions, plant and animal cells shrivel

• isotonic: when place in isotonic solutions, animal cells and plant cells behave normally

• hypotonic: when placed in a hypotonic solution, animal cells swell and may burst, whereas plant cells are protected by their cell walls.

role of vesicle sin cell transport

• vesicles are used in both endocytosis and exocytosis. in endocytosis, engulfed material is brought into the cell in vesicles. in exocytosis, vesicles fuse to the cell membrane to expel material out of the cell.

definitions

• hypotonic: when comparing two solutions, hypotonic solutions are the solutions with the lower amount of solute.

• isotonic: when comparing two solutions, isotonic solutions have equal concentration of solute

• hypertonic: when comparing two solutions, hypertonic solutions are the solutions with the higher amount of solute (hypertonic solutions are more concentrated)

• osmotic pressure: during osmosis, water will always move to the side of the membrane that is hypertonic (contains more solute). this puts pressure on that side of the membrane.