Osmosis and Particles Diffusion
Diffusion, Osmosis, Active Transport
There are two ways in which substances can enter or leave a cell: 1) Passive
a) Simple Diffusion
b) Facilitated Diffusion
c) Osmosis (water only)
2) Active
a) Molecules
b) Particles
Diffusion
Diffusion is the net passive movement of particles (atoms, ions or molecules) from a region in which they are in higher concentration to regions of lower concentration. It continues until the concentration of substances is uniform throughout.
Some major examples of diffusion in biology:
• Gas exchange at the alveoli — oxygen from air to blood, carbon dioxide from blood to air.
• Gas exchange for photosynthesis — carbon dioxide from air to leaf, oxygen from leaf to air.
• Gas exchange for respiration — oxygen from blood to tissue cells, carbon dioxide in opposite direction.
• Transfer of transmitter substance — acetylcholine from presynaptic to postsynaptic membrane at a synapse.
• Osmosis — diffusion of water through a semipermeable membrane.
High Diffusion Rate: short distance, large surface area, big concentration difference (Fick’s Law).
High temperatures increase diffusion; large molecules slow diffusion.
Facilitated Diffusion
This is the movement of specific molecules down a concentration gradient, passing through the membrane via a specific carrier protein. Thus, rather like enzymes, each carrier has its own shape and only allows one molecule (or one group of closely related molecules) to pass through.
Selection is by size; shape; charge.
Common molecules entering/leaving cells this way include glucose and amino-acids.
It is passive and requires no energy from the cell.
If the molecule is changed on entering the cell (glucose +
ATP → glucose phosphate + ADP), then the concentration gradient of glucose will be kept high, and there will a steady one-way traffic.
Osmosis
Osmosis is a special example of diffusion. It is the diffusion of water through a partially permeable membrane from a more dilute solution to a more concentrated
There are two ways in which substances can enter or leave a cell: 1) Passive
a) Simple Diffusion
b) Facilitated Diffusion
c) Osmosis (water only)
2) Active
a) Molecules
b) Particles
Diffusion
Diffusion is the net passive movement of particles (atoms, ions or molecules) from a region in which they are in higher concentration to regions of lower concentration. It continues until the concentration of substances is uniform throughout.
Some major examples of diffusion in biology:
• Gas exchange at the alveoli — oxygen from air to blood, carbon dioxide from blood to air.
• Gas exchange for photosynthesis — carbon dioxide from air to leaf, oxygen from leaf to air.
• Gas exchange for respiration — oxygen from blood to tissue cells, carbon dioxide in opposite direction.
• Transfer of transmitter substance — acetylcholine from presynaptic to postsynaptic membrane at a synapse.
• Osmosis — diffusion of water through a semipermeable membrane.
High Diffusion Rate: short distance, large surface area, big concentration difference (Fick’s Law).
High temperatures increase diffusion; large molecules slow diffusion.
Facilitated Diffusion
This is the movement of specific molecules down a concentration gradient, passing through the membrane via a specific carrier protein. Thus, rather like enzymes, each carrier has its own shape and only allows one molecule (or one group of closely related molecules) to pass through.
Selection is by size; shape; charge.
Common molecules entering/leaving cells this way include glucose and amino-acids.
It is passive and requires no energy from the cell.
If the molecule is changed on entering the cell (glucose +
ATP → glucose phosphate + ADP), then the concentration gradient of glucose will be kept high, and there will a steady one-way traffic.
Osmosis
Osmosis is a special example of diffusion. It is the diffusion of water through a partially permeable membrane from a more dilute solution to a more concentrated