Download 3.4 Diffusion and Osmosis

3.4 Diffusion and Osmosis
KEY CONCEPT Materials move across membranes
because of concentration differences.
3.4 Diffusion and Osmosis
Passive transport:
• Does not require energy input from a cell.
•Movement of molecules across the cell
membrane.
• There are two types of
passive transport.
• diffusion
• osmosis
3.4 Diffusion and Osmosis
Diffusion and osmosis are types of passive
transport.
Diffusion:
• Results from the natural motion of
particles which collide & scatter.
• Molecules diffuse down a
concentration gradient.
• Concentration gradient is the
difference in concentration between 2
locations.
• Movement of molecules from high
concentration to low concentration.
Ex. Tie-dye
3.4 Diffusion and Osmosis
Diffusion and osmosis are types of passive
transport.
Osmosis:
• is the diffusion of water molecules across a
semipermeable membrane.
• Water travels where there is not much water.
• Remember: the higher concentration of dissolved
particles you have, the lower the concentration of water.
3.4 Diffusion and Osmosis
Diffusion and osmosis are types of passive transport.
• There are three types of solutions.
• isotonic
•
hypertonic
•
hypotonic
•
•
These types of solutions are comparisons.
Isotonic: the outer solution has the same concentration of
dissolved particles as the cell.
•
•
Hypertonic: the outer solution has a higher concentration of
dissolved particles than in the cell.
•
•
Water flows out of the cell, may shrivel or die.
Hypotonic: the outer solution has a lower concentration of
dissolved particles than the cell.
•
•
Water moves in & out of cell at equal rate.
Water flows into the cell, swelling & may burst.
Some animals are adapted to living in hypotonic solutions
by removing excess water.
“What will happen to a houseplant if you water it with salt
water (a hypertonic solution)?”
3.4 Diffusion and Osmosis
Some molecules can only diffuse through transport
proteins.
• Some molecules cannot easily diffuse across the
cell membrane.
• Facilitated diffusion:
• is diffusion through
transport proteins.
•Requires NO energy
from the cell.
•Molecules move down
concentration gradient.
•Most only allow certain
ions/molecules to pass
•Some act as enzymes
& change shape
“Why are transport proteins needed in the cell membranes?”