Unit 3 Part 2: Cell Transport

cell walls

• support, shape, protect

• porous: H20, CO2, etc. can go through

  • helps plants stay upright

cell membrane

double-layered sheet w/lipid bilayer

lipid bilayer

• hydrophilic head on outside, hydrophobic (fatty acid) tail that is oily and keeps water out

• makes membranes flexible w/strong baarrier

• controls what comes in/out of cell

in the membrane, proteins…

are embedded and have channels and pumps that move bigger things through the membrane

in the membrane, carbohydrates…

attach to many proteins, serve as “IDs”

fluid mosaic model

• proteins move around and there are many different molecules in the membrane, giving it this name

  • membrane is semipermeable (some big/highly charged things can’t go through)

cell analogy

cells are like nations with regulated borders

cells need to keep

the same internal conditions (homeostasis)

diffusion

• cytoplasm has many dissolved substances in it

• particles move randomly from high to low concentration until equilibrium is reached

• particles will keep moving, but maintain equilibrium after it’s reached

• random movement of particles, meaning it doesn’t require energy (PASSIVE)

facilitated diffusion

• small molecules w/no charge (dissolve in lipids) can pass through molecules, but bigger ones need help

• specialized proteins act as channels and there are 100s of types

  • no extra energy from cell used

How does water pass through cell?

• example of facilitated diffusion

• because the inside of bilayer is hydrophobic, water channels proteins called aquaporins let water pass through them

osmosis

• diffusion of water through selectively permeable membrane

• higher to lower concentration - movement of water molecules only

hypotonic

• below strength - lower concentration

hypertonic

• above strength - higher concentration

isotonic

same strength - same concentration

strength

amount of solute

osmotic pressure

• net movement of water into/out of cell

osmotic pressure in animal cells

can cause cells to shrink/swell/burst

cells are hypertonic to

• fresh water (much less concentrated)

• can burst, but most cells are bathed in blood/isotonic fluids

osmotic pressure in plant cells

• changes central vacuole size

• cell wall helps it hold shape (to an extent)

isotonic solution in cells

• same inner/outer concentration of solutes

• h20 molecules move in both directions

• normal sized animal cell/plant vacuole

hypertonic solution in cell

• solution solute concentration is greater than cell

• net movement out of cell → shrinkage

  • shrunken animal cell, shrunken plant vacuole/membrane

hypotonic solution in cell

• solution solute concentration < cell

• Net movement into cell = swelling

  • swollen/burst animal cell, swollen plant vacuole/membrane

active transport

movement of materials against a concentration difference/forces of diffusion, requires energy

molecular active transport (protein pumps)

• ions like Ca+, K+, Na+ moved by pumplike proteins

• changes in shape play a role

• considerable amount of cell energy used

bulk transport

• different forms depending on material size/shape

  • endocytosis (pino/phagocytosis), exocytosis)

endocytosis

• taking material in through pockets of cell membrane

• pocket breaks from membrane → vesicle/vacuole forms

• used for large molecules, food clumps, entire cells

pinocytosis

• type of endocytosis

• take liquid from environment

• pockets form on membrane, fill w/liquid, become vacuoles w/i cell

phagocytosis

• type of endocytosis

• cytoplasm extensions surround particle, package in food vacuole and engulf it

• amoeba use this for food, white bloods cells do this to eat damaged cells

exocytosis

releasing material - vacuole membrane and cell membrane fuse, contents are forced out

• ex: water removal by contractile vacuole

protein pumps - active transport

• atp pumps sm. molecules/ions across membrane

• proteins change shape - bind w/substances on one side of membrane, release on the other