Ch. 3 Part 2
Cell Transport
Movement Across Cell Membranes
• Cell membranes are a barrier, but substances
must be able to get in and out
• 5 main methods of transport
– Simple diffusion
– Osmosis
– Facilitated diffusion
– Active transport
– Vesicles
Simple Diffusion
• Molecules move from an area of high
concentration to an area of low concentration
(H → L)
• Through cells – only lipid-soluble molecules
(steroids) or very small molecules (O2, H2O,
CO2) can do this
• Only stop when equilibrium is reached
Simple Diffusion
Osmosis
• Diffusion of water
• Water is always looking to keep a balance
between inside and outside the cell
• 3 types of solutions result in osmosis
– Hypotonic
– Hypertonic
– Isotonic
Osmosis
• Hypotonic
– Concentration of solute is higher outside the cell than inside the
cell
– Water moves inward to balance
– Cell size increases – animal cells can burst (lysis)
• Hypertonic
– Concentration of solute is lower outside the cell than inside the
cell
– Water moves outward to balance
– Cell size decreases – shrivel up (crenation)
• Isotonic
– Concentration of solute is equal inside and outside
– Water moves, but the balance remains
– Cell size does not change
Osmosis
Facilitated Diffusion
• Same as diffusion with help (facilitated)
• This help is done by proteins
• 2 types of proteins
– Channel proteins
• Form a pore or channel where ions can pass through
• Many channels are gated and can be closed
– Carrier proteins
• Has a binding site for a specific molecule
• Can move substances in and out
Facilitated Diffusion
Active Transport
• Forces molecules to go from one side to the
other, against concentrations
• Must be performed with proteins
• Must have energy to occur
• Example:
– Sodium-potassium pump
Active Transport
• Sodium-potassium pump
– Essential for neural impulses
to be sent
– Pumps 3 sodium out of the
cell
– Pumps 2 potassium into the
cell
– This helps maintain the
correct gradient of ions
Vesicles
• Exocytosis
– Removes large molecules out of the cell by using
vesicles (pouches)
• Endocytosis
– Brings large molecules into the cell using vesicles
– Pinocytosis – cell drinking
– Phagocytosis – cell eating
Vesicles
Transport Summary
• Active transport
– Moves materials from low to high
– Goes against the concentration gradient
– Energy required
• Passive transport
– Moves materials from high to low
– Goes with the concentration gradient
– No energy required
Which is which?
• Which types of transport are passive or
active?
• Which types of transport use proteins?
• Simple diffusion?
• Osmosis?
• Facilitated diffusion?
• Active transport?
• Vesicles?