Tuesday, September 06, 2005
BIOLOGY - Movement of Material Through a Cell Membrane
There are 4 types of movement, namely diffusion, osmosis, active transport and facilitated diffusion.
Diffusion is the process where molecules of a substance move from areas of high concentration to areas of low concentration (until there is equilibrium). For example, the movement of oxygen from lungs to bloodstream and absorption of nutrients from small intestine into bloodstream etc. When there is no net movement, equilibrium is achieved.
Factors affecting the rate of diffusion:
1. Amount of substances on either side (i.e. the concentration)
2. Permeability of membrane
3. Temperature (movement of particles, increased temperature usually increases the speed of the particles, according to the kinetic theory of collision)
4. Distance to be travelled
5. Size of the particles
OSMOSIS is the process by which a passage of water (solvent) from a dilute solution (more water molecules) “moves” to a more concentrated solution (less water molecules) across a selectively permeable membrane. For example: diffusion of water molecules through a selectively permeable membrane (partially membrane)
OSMOTIC PRESSURE: Pressure exerted on 1 side of the membrane is more, water molecules (solvent) passes in that direction
Water potential: It describes the movement of water molecules and is a measure of the tendency for water to move from one place to another.
Three types of solutions:
1) Hypotonic (dilute): HIGH water potential
2) Isotonic
3) Hypertonic: LOW water potential
Plasmolysis:
It is the shrinkage of the cytoplasm and cell membrane away from the cell wall.
A plant cell in hypotonic solution:
- Cell size volume decreases
- Vacuole size decreases
- Plasmolysis occurs
ACTIVE TRANSPORT
à It is the process by which molecules of a substance move from areas of lower concentration of that substance to areas of higher concentration
à Against a concentration gradient
à For example: Absorption of mineral salts by the root hair cells, absorption of glucose and amino acids by cells in the small intestine of humans
FACILITATED DIFFUSION
à It is the movement of particles across a membrane with the help of a molecule in the membrane (globular protein in bilayer of cell membrane).
à The energy comes from the kinetic energy of the molecules involved.
à For example, the movement of ADP into mitochrondria
à MOVEMENT BY BULK via movements of vesicles
Entocytosis:
- Substances are being imported into cells via vesicles
- Phagocytosis = cell eating
- Pinocytosis = bulk transportation of liquid (when taking in of nutrients)
Exocytosis:
- Substances being exported out of cells
Surface Area: Volume Ratio
- Ratio of SA:Vol. ratio in a small organism is greater than in a large organism
- Smaller organisms have the advantage of a relatively large absorbing surface
- Larger organisms have a low SA:Vol. ratio, their skin not very permeable to gases
- Thus large organisms need special systems (e.g. circulatory systems) to help them transport the substances and special absorbing substances such as lungs or gills to increase the surface area for absorption
- The ratio decreases with increasing size of the organism
There's a comparison table, but I don't know how to put it up here. Why not do it YOURSELF? Take it as revision. (: It should be a 5 x 5 table. Compare conc. gradient, type of particles, cell membrane and energy of the 4 different movements in your table. (:
-- HH! ((:
Diffusion is the process where molecules of a substance move from areas of high concentration to areas of low concentration (until there is equilibrium). For example, the movement of oxygen from lungs to bloodstream and absorption of nutrients from small intestine into bloodstream etc. When there is no net movement, equilibrium is achieved.
Factors affecting the rate of diffusion:
1. Amount of substances on either side (i.e. the concentration)
2. Permeability of membrane
3. Temperature (movement of particles, increased temperature usually increases the speed of the particles, according to the kinetic theory of collision)
4. Distance to be travelled
5. Size of the particles
OSMOSIS is the process by which a passage of water (solvent) from a dilute solution (more water molecules) “moves” to a more concentrated solution (less water molecules) across a selectively permeable membrane. For example: diffusion of water molecules through a selectively permeable membrane (partially membrane)
OSMOTIC PRESSURE: Pressure exerted on 1 side of the membrane is more, water molecules (solvent) passes in that direction
Water potential: It describes the movement of water molecules and is a measure of the tendency for water to move from one place to another.
Three types of solutions:
1) Hypotonic (dilute): HIGH water potential
2) Isotonic
3) Hypertonic: LOW water potential
Plasmolysis:
It is the shrinkage of the cytoplasm and cell membrane away from the cell wall.
A plant cell in hypotonic solution:
- Cell size volume decreases
- Vacuole size decreases
- Plasmolysis occurs
ACTIVE TRANSPORT
à It is the process by which molecules of a substance move from areas of lower concentration of that substance to areas of higher concentration
à Against a concentration gradient
à For example: Absorption of mineral salts by the root hair cells, absorption of glucose and amino acids by cells in the small intestine of humans
FACILITATED DIFFUSION
à It is the movement of particles across a membrane with the help of a molecule in the membrane (globular protein in bilayer of cell membrane).
à The energy comes from the kinetic energy of the molecules involved.
à For example, the movement of ADP into mitochrondria
à MOVEMENT BY BULK via movements of vesicles
Entocytosis:
- Substances are being imported into cells via vesicles
- Phagocytosis = cell eating
- Pinocytosis = bulk transportation of liquid (when taking in of nutrients)
Exocytosis:
- Substances being exported out of cells
Surface Area: Volume Ratio
- Ratio of SA:Vol. ratio in a small organism is greater than in a large organism
- Smaller organisms have the advantage of a relatively large absorbing surface
- Larger organisms have a low SA:Vol. ratio, their skin not very permeable to gases
- Thus large organisms need special systems (e.g. circulatory systems) to help them transport the substances and special absorbing substances such as lungs or gills to increase the surface area for absorption
- The ratio decreases with increasing size of the organism
There's a comparison table, but I don't know how to put it up here. Why not do it YOURSELF? Take it as revision. (: It should be a 5 x 5 table. Compare conc. gradient, type of particles, cell membrane and energy of the 4 different movements in your table. (:
-- HH! ((:
# we mugged! @ 7:45 PM 
