Transport across membranes Flashcards
What kind of transport is simple diffusion known as?
Simple
Why is simple diffusion known as passive transport?
The energy for the movement comes from the natural, inbuilt motion of particles, rather than other sources such as ATP
Define some necessary details of particles
- All particles are constantly in motion due to the kinetic energy they posess
- This motion is random
- Particles are constantly bouncing off one another as well as other objects
What will particles that are concentrated together in a closed vessel do?
Distribute themselves evenly throughout the vessel as a result of diffusion
What is diffusion?
The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed
Which molecules can easily pass through the cell-surface membrane?
Small, non-polar molecules e.g. water and carbon dioxide
Why do charged ions and polar molecules not diffuse easily across a cell-surface-membrane?
Due to the hydrophobic nature of the fatty acid tails
How is the movement of charged ions and polar molecules made easier?
Through facilitated diffusion. The movement is made easier by transmembrane channels and carriers that span the membrane
What kind of process is facilitated diffusion?
Passive
It relies only on the inbuilt motion of the diffusing molecules. No external input of ATP from respiration
Where does facilitated diffusion occur?
It occurs down a concentration gradient but it occurs at specific points on the plasma membrane where there are special protein molecules
Which types of proteins are involved in facilitated diffusion?
Protein channels and carrier proteins
How do protein channels help in facilitated diffusion?
These proteins form water-filled hydrophilic channels across the membrane
What do protein channels allow to diffuse across?
Specific water-soluble ions
The channels are selective, each opening in the presence of a specific ion. If the particular ion is not present, the channel remains closed
What do protein channels allow for in cell-surface membranes?
They allow for control over the entry and exit of ions. The ions bind with the proteins causing it to change shape in a way that closes it to one side of the membrane and opens it to the other
What is an alternative way, aside from protein channels, for facilitated diffusion?
Another way involves carrier proteins that span the plasma membrane
How do carrier proteins carry out facilitated diffusion?
- When a molecule such as glucose that is specific to the protein is present, it binds with the protein
- This causes it to change shape so that the molecule is released to the inside of the membrane
- No external energy is needed
- The molecules move from a region where they are highly concentrated to one of lower concentration, using only the kinetic energy of the molecules themselves
How can cells be adapted for rapid transport across their internal or external membranes?
By an increase in surface area, or by an increase in the number of protein channels and carrier molecules in their membranes
What is osmosis?
The passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a selectively permeable membrane
What does selectively permeable mean?
Permeable to water molecules and a few other small molecules, but not larger molecules (cell - surface membranes and other plasma membranes are selectively permeable)
