Passive Transport
• transport of molecules across the cell
membrane that does not require energy!
• 3 Types:
1) Diffusion
2) Osmosis
3) Facilitated Diffusion
1. Diffusion
• Diffusion = the movement of particles from an area
where they are more concentrated to an area where
they are less concentrated
• Type of passive transport; does NOT require energy!
• HIGH TO LOW
http://student.ccbcmd.edu/courses/bio141/lecg
uide/unit3/eustruct/passive_flash.html
2. Osmosis
• The cell membrane is permeable to water;
water can move freely through it.
• Osmosis is the diffusion of water across the
cell membrane.
http://www.stolaf.edu/peopl
e/giannini/flashanimat/trans
port/osmosis.swf
http://www.nclark.net/osmosisPocus.gif
• Examples:
• If you place a cell into a solution where the
concentration of solute (salt or sugar) is HIGHER
in the solution than in the cell, then water will
move _________________ the cell.
• Picture:
• If you place a cell into a solution where the
concentration of solute (salt or sugar) is LOWER
in the solution than in the cell, then water will
move _________________ the cell.
• A cell has lots of sugars and salts inside it.
• If you place it in pure water, which way would
the water flow?
_____________________________
• In animal cells, it would continue until the cell
burst!
• In plant cells, the cell wall would keep it from
bursting.
Turgor pressure:
is the pressure on the cell walls
from the amount of water
moving into or out of the cell.
• A cell has lots of sugars and salts inside it.
• However, if you placed it in pure sugar or salt,
which way would water flow?
________________________________
• The animal cell shrivels, and the plant cell’s
cytoplasm is pulled away from the cell wall. This is
called plasmolysis.
3. Facilitated Diffusion
• Facilitated means to “help”
• Some molecules (like glucose) are way too big to
diffuse through the plasma membrane.
• These molecules move through membrane
proteins that have a hole in the middle.
• These proteins are called channel proteins.
• This is still diffusion! Molecules can only move
across the membrane to an area of lower
concentration.