Cell Transport - CP
1)Homeostasis- maintenance of a stable internal environment - Biological Balance
Cell membrane controls homeostasis for cells by allowing only some things in and out
2) What Gets through
Generally, small molecules can enter fast. Molecules that mix with lipids (lipid solvents) can enter fast because they can dissolve their way through the membrane
Digestion- makes molecules small enough to enter cells
Cells store small molecules by bonding them- too large-can't escape
3) Diffusion-
Molecules are always moving
They tend to move from areas of higher to lower concentration
This is called diffusion- the movement of molecules from areas of higher concentration to areas of lower concentration
When the molecules are evenly spread out, they keep moving in all directions equally-They have reached equilibrium
4) Passive Transport-
When molecules move into or out of a cell by diffusion it is called passive transport because the cell does not use any of its own energy to make it happen.
The most common molecule to diffuse in/out of cells is water
The diffusion of water through a cell membrane is called osmosis
5) Three Osmotic Situations a cell might be in
a) Cells in Isotonic solution- the % or water inside and outside the cell are equal
water enters and leaves at equal rates
examples- blood cells in blood, body cells in lymph, Ringer's solution
b) Cells in Hypotonic Solution- the % of water outside the cell is greater than inside-
water enters faster than it leaves (high to low).
Pressure can build up- Turgor Pressure
cell might burst- cytolysis
examples- plants create hypotonic solution around their cells when the roots absorb water and send it into the rest of the plant- cell wall prevents bursting
Cells becomes more rigid- helps non-woody parts of plants- leaves etc.
If there is not enough water- loss of turgor pressure- plant wilts
One celled organisms in fresh water have to pump water out to prevent bursting
This is done by the contractile vacuole.
Fresh water fish- water enters through the gills- Is pumped out by the kidneys
Penicillin- weakens cell wall of bacteria- turgor pressure bursts cell
c) Cells in Hypertonic Solution- the % of water inside the cell is greater than outside.
Water leaves faster than it enters.
cell shrivels- plasmolysis
Examples- Root Burn, Salt Cured meat
Salt water gargle
6) Facilitated Diffusion- protein molecules in the membrane speed up diffusion for certain molecules
These proteins are called "carrier proteins" This still requires no cell energy- Passive transport
7) Active Transport-
Molecules move in/out of a cell from areas of lower concentration to higher concentration
This requires that the cell use energy
This uses proteins called "membrane pumps"
8) Bulk Transport
Large pieces or large amounts move in/out of a cell
Examples- WBC and Ameba surround large objects by changing shape - phagocytosis
Contractile vacuole pumps out large amounts of water