Cell Transport Flashcards
What is diffusion?
The net movement of molecules or ions from a regions of high concentration to a region of low concentration
What type of process is diffusion
Passive process
How can the rate of diffusion be increased ?
- by increasing the SA
- increasing the gradient
- shorter diffusion pathway
- smaller molecules
- increasing temperature
What else increases the rate of facilitated diffusion and active transport
The number of Chanel/carrier proteins
What is Fricks law?
Rate of diffusion is proportional to:
SA x difference in concentration/ thickness of membrane
For maximum rate of diffusion..?
- SA and difference in concentration must be as big as possible
- thickness must be as thin as possible
The membrane must be…
What molecules diffuse more easily?
- permeable in order for diffusion to occur
- small lipid soluble molecules
What is simple diffusion
Oxygen and carbon dioxide are small and lipid soluble molecules so can diffuse easily through the phospholipid bilayer
what is facillitated diffusion?
what type of process is this?
Large lipid insoluble and water-soluble substances are too big e.g glucose and amino acids and do not readily pass through the phospholipid bilayer hence have to move through a process called facilitated diffusion. This is a passive movement of molecules down a concentration gradient.
explain how facillitated diffusion works?
Facilitated diffusion involves a specific carrier protein which is specific to a certain substance
For example if the carrier protein was specific to glucose. The glucose molecule would be complimentary to the binding site of the carrier protein
When glucose binds to the carrier protein the binding site will change shape
Glucose will be transported across the cell membrane onto the other side of the cell
The carrier protein will return to its original shape
why is facilitated diffusion down a channel protein different?
this is because the chanel protein decides what substances to let through
what is active transport?
the movement of molecules or ions from a region of lower concentration to a region of higher concentration using ATP and carrier proteins
explain the process of active transport
The specific molecule binds to the complimentary binding site on the carrier protein
Atp is hydrolysed nto adp and pi
The phosphate grouo released attaches directly onto the carrier protein causing it to change shape transporting the solute through the cell against the concentration gradient
Once the molecule has been released the phosphate group detaches it slef which causes the carrier protein to return to its original position / shape
how can we increase the rate of transport across membranes?
- more microvilli
- more carrier/channel proteins
explain how sodium and glucose are co-transported through epithelial cells?
Sodium ions are actively transported out of the small intestines epithelial cells and into the blood by the sodium-potassium pump (channel protein)
This creates a concentration gradient – there is a high Na+ concentration in the small intestines’ lumen than inside the cell
This causes sodium ions to diffuse from the small intestines’ lumen down the concentration gradient along with glucose which moves against it’s concentration gradient via a sodium-glucose co-transporter protein
So there is also a high concentration of glucose in the lumen and cells
Glucose then diffuses out of the cell and into the blood by facilitated diffusion through a carrier protein
