What type of transport is diffusion and why?
Passive because the energy needed for diffusion comes from the natural, inbuilt source of the particles, rather than external source e.g. ATP.
What are the 3 factors that you need to know to understand the concept of passive transport?
1) All particles are in constant motion due to the kinetic energy that they have.
2) The motion is random.
3) Particles are constantly bouncing off one another.
Due to those factors, particles that are concentrated together in a closed vessel with distributing themselves evenly throughout the vessel due to diffusion.
Define diffusion.
The net movement of molecules or ions from a region where they are highly concentrated to one where their concentration is lower until evenly distributed.
- Diffusion only happens between different concentrations of the same substance e.g. between O2 or CO2 but never between O2 and CO2.
Only what sort of molecules can pass through plasma membranes?
- Only small, non-polar molecules e.g. Oxygen can diffuse through easily.
- Charged ions and polar molecules can’t diffuse easily because of the hydrophobic nature of the fatty acid tail of the phospholipids in the membrane.
How can charged ions and polar molecules diffuse across the membrane?
Through facilitated diffusion by transmembrane channels and carriers that span the membrane.
Is facilitated diffusion a passive or active process and why?
Passive because it relies only on the inbuilt motion (kinetic energy) of the diffusing molecules.
How does facilitated diffusion differ from normal diffusion?
Facilitated diffusion occurs down a concentration gradient like normal diffusion but it occurs at specific points on the plasma membrane and with specific proteins.
What are the 2 types of proteins that are involved in facilitated diffusion?
1) Protein channels
2) Carrier proteins
What are protein channels?
- It forms water-filled hydrophilic channels across the membrane.
- Allow specific WATER-SOLUBLE ions to pass through.
- Channels are selective, each opening in the presence of a specific ion.
- If a particular ion is not present, the channel will remain closed.
- This way, there is control over the entry and exit of ions.
- The ion bind with the protein causing it to change shape in a way that closes one side of the membrane and opens on the other.
What are carrier proteins?
- An alternative form of facilitated diffusion.
- It spans across the whole plasma membrane.
- When specific molecules e.g. glucose is at present, it causes the CP to change shape.
- No external energy is needed, it moved from high concentration to low concentration by using only kinetic energy of the molecules themselves.
