CELL TRANSPORT
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
A) small molecules can enter faster
Digestion- makes molecules small enough to enter cells
Store small molecules by bonding them- can't escape
B) molecules that mix with lipids (lipid solvents) can enter fast because they can dissolve their way through the membrane
C) particles with charges (ions) enter more slowly
3) Diffusion-
All 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
The difference in concentration is called a concentration gradient- going from high to low conc is "moving with the gradient"
When the molecules are evenly spread out, they keep moving in all directions equally-They have reached equilbirium
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) Osmotic Situations
A is ISOTONIC to B- equal % of water in A and B
A is HYPOTONIC to B - higher % of water in A than B
A is HYPERTONIC to B- lower % of water in A than B
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- 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 bacteria cell walls- turgor pressure causes cell to burst
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, don't drink salt water
6) Facilitated Diffusion- protein molecules (carrier proteins) in the cell membrane speed up the diffusion process- this is still passive transport
7) Active Transport
The cell uses energy to make molecules move from low to high - "against the conc gradient" This is done by proteins in the membrane called membrane pumps
example- the Na-K Pump Moves sodium and potassium into nerve and muscle cells
8) Bulk Transport
Moving large quantities or large particles in/out of cell
Endocytosis /exocytosis
Examples - Endo- Phagocytosis-cells change shape and surround large particles
Ameba feeds this way WBC catch bacteria this way
Exo -Contractile vacuole- removes large amounts of water all at once
Golgi are involved in exocytosis- helping to release large amounts of proteins