Transport across a membrane notes
G1. CELL MEMBRANE:
3. Cell Membrane:
Fluid Mosaic Model:
- double layer of phospholipids
- protien molecules imbedded in and throughout the double layer
3. Cell Membrane:
Fluid Mosaic Model:
- double layer of phospholipids
- protien molecules imbedded in and throughout the double layer
Proteins - help to move stuff through the membrane
- receptor sites that influences cell metabolism.
- Some compounds (proteins, carbohydrate, lipids) are attached to outer surface of the membrane, sometimes glycolipids, glycoprotiens etc.
- These act as cell "fingerprints" or "identity factors"
G2. - G5 MOVEMENT ACROSS A CELL MEMBRANE
Selectively Permeable
- some things can pass through it, other cannot
- depends upon size etc.
- selects in 6 ways :
1) Diffusion : - particles moving from an area of greater concentration towareds an area of lesser concentration until it is equally distributed.
Increase rate by:
- increasing temperature
- increase surface area
- changes in shape of molecules
- changes in concentrations
-decrease size of molecules
- receptor sites that influences cell metabolism.
- Some compounds (proteins, carbohydrate, lipids) are attached to outer surface of the membrane, sometimes glycolipids, glycoprotiens etc.
- These act as cell "fingerprints" or "identity factors"
G2. - G5 MOVEMENT ACROSS A CELL MEMBRANE
Selectively Permeable
- some things can pass through it, other cannot
- depends upon size etc.
- selects in 6 ways :
1) Diffusion : - particles moving from an area of greater concentration towareds an area of lesser concentration until it is equally distributed.
Increase rate by:
- increasing temperature
- increase surface area
- changes in shape of molecules
- changes in concentrations
-decrease size of molecules
Examples:
- alcohols (can disolve in phospholipids)
- gases (O2, CO2)
- water **This is called osmosis
2) Osmosis:
defined as:
- The net movement of water molecules from the area of greater concentration of water to the area of lesser concentration of water until it is evenly distributed
- must be across a selectively permeable membrane
- Water passes through the membrane, solutes (sugars, proteins, larger molecules) cannot.Water molecules move between the phospholid molecules
- Osmotic pressure can work against hydrostatic pressure (physical pressure)
Examples of Osmosis - H2O absorbed by large intestine and in kidneys
3) Facilitated Transport:
- movement of certain molecules that are not normally able to pass through the lipid membrane. Examples: Sugars, amino acids, etc.
- move towards the concentration gradient
- from greater to lesser concentration
- same as diffusion
- moved by carrier protiens in the cell membrane
- no energy is needed.
4) Active Transport:
- movement of certain molecules that are against the concentration gradient
- from lesser to greater concentration
- like "cell pumping"
- requires energy and carrier proteins in the cell membrane
ex: Na+ and K+ in cells
5) Endocytosis: ("Endo" means "in")
- the taking in of molecules or particles by invagination of the cell membrane forming a vesicle. *Uses energy*
(i) Phagocytosis:
- large particles, visible with light microscope
- eg. white blood cells, amoeba
(ii) Pinocytosis:
- molecules
- seen with electron microscope
- intestine cells
- "Intestine sipping"
6) Exocytosis: ("Exo" means "out")
- reverse of endocytosis
- vacuole / vesicle fuses with the cell membrane and "dumps" contents to the outside.
ex: Waste from Amoeba
Cell products from Golgi Apparatus
G6. ISOTONIC, HYPERTONIC, HYPOTONIC SOLUTIONS:
a) Isotonic Solution:
- the solution concentration is equal on both sides of the membrane .
- therefore, there is no net concentration difference across the cell membrane
- no net diffusion or osmosis occurs.
b) Hypertonic:
- The solution outside the cell is more concentrated than inside
- alcohols (can disolve in phospholipids)
- gases (O2, CO2)
- water **This is called osmosis
2) Osmosis:
defined as:
- The net movement of water molecules from the area of greater concentration of water to the area of lesser concentration of water until it is evenly distributed
- must be across a selectively permeable membrane
- Water passes through the membrane, solutes (sugars, proteins, larger molecules) cannot.Water molecules move between the phospholid molecules
- Osmotic pressure can work against hydrostatic pressure (physical pressure)
Examples of Osmosis - H2O absorbed by large intestine and in kidneys
3) Facilitated Transport:
- movement of certain molecules that are not normally able to pass through the lipid membrane. Examples: Sugars, amino acids, etc.
- move towards the concentration gradient
- from greater to lesser concentration
- same as diffusion
- moved by carrier protiens in the cell membrane
- no energy is needed.
4) Active Transport:
- movement of certain molecules that are against the concentration gradient
- from lesser to greater concentration
- like "cell pumping"
- requires energy and carrier proteins in the cell membrane
ex: Na+ and K+ in cells
5) Endocytosis: ("Endo" means "in")
- the taking in of molecules or particles by invagination of the cell membrane forming a vesicle. *Uses energy*
(i) Phagocytosis:
- large particles, visible with light microscope
- eg. white blood cells, amoeba
(ii) Pinocytosis:
- molecules
- seen with electron microscope
- intestine cells
- "Intestine sipping"
6) Exocytosis: ("Exo" means "out")
- reverse of endocytosis
- vacuole / vesicle fuses with the cell membrane and "dumps" contents to the outside.
ex: Waste from Amoeba
Cell products from Golgi Apparatus
G6. ISOTONIC, HYPERTONIC, HYPOTONIC SOLUTIONS:
a) Isotonic Solution:
- the solution concentration is equal on both sides of the membrane .
- therefore, there is no net concentration difference across the cell membrane
- no net diffusion or osmosis occurs.
b) Hypertonic:
- The solution outside the cell is more concentrated than inside
- therefore, the water will move out of the cell (osmosis) because the water is more concentrated inside the cell than outside.
In a plant cell this process pulls the cell membrane away from the cell wall, the cell looses its rigidity - Plasmolysis
c) Hypo tonic:
-Concentration inside the cell is more concentrated than outside.
- Water will move into the cell
In a plant cell this process pulls the cell membrane away from the cell wall, the cell looses its rigidity - Plasmolysis
c) Hypo tonic:
-Concentration inside the cell is more concentrated than outside.
- Water will move into the cell
This is known as Turgor Pressure and gives plant cells their rigidity.
G8. SURFACE AREA WITH RESPECT TO CELL SIZE
- Use Suface Area to Volume ratio
- This is why cells are small
- If the volume of the cell increases, the amount of surface area does not increase in the same proportion.
- larger cells have much more volume for not as much increase in the amount of surface area.
- Cells overcome this by changing their shape
G8. SURFACE AREA WITH RESPECT TO CELL SIZE
- Use Suface Area to Volume ratio
- This is why cells are small
- If the volume of the cell increases, the amount of surface area does not increase in the same proportion.
- larger cells have much more volume for not as much increase in the amount of surface area.
- Cells overcome this by changing their shape
Cell Y has the most surface area, all 4 cells have the same volume
- The size of surface area is important for the amount of material entering and leaving the cell
- The cell cannot get very large, because not enough material can diffuse through the membrane, to keep it alive.
- The size of surface area is important for the amount of material entering and leaving the cell
- The cell cannot get very large, because not enough material can diffuse through the membrane, to keep it alive.