Transports across membrane Flashcards
1
Q
What is diffusion?
A
- Net movement of molecules from a region of high concentration to low.
- Molecules reach an concentration equilibrium, where they are evenly spread out. No net movement.
- passive process, have natural kinetic energy
2
Q
What substances can be transported via diffusion?
A
- Oxygen, non polar and small so diffuses quickly
- Carbon dioxide, polar but small so diffuses quickly
- Water, polar but small so diffuses quickly
3
Q
What factors affect the rate of diffusion?
A
- temperature
- steep concentration gradient
- thickness of the membrane
- large surface area to volume ratio (SA:V)
4
Q
How does temperature affect the rate of diffusion?
A
- Increase the amount of thermal energy, then particles have more energy to transfer into kinetic energy
- Use kinetic energy to move faster and more randomly
- Faster they move, quicker they will move down the concentration gradient
5
Q
How does a steep concentration gradient affect the rate of diffusion?
A
- Greater the difference between concentration in the two regions, the faster particles will move ‘down’ the concentration gradient to the area of lower concentration
6
Q
How does the thickness of the membrane affect the rate of diffusion?
A
- Exchange surfaces are thin and usually one cell thick
- plasma membrane is thin - approximately 7.5nm in width
- Surfaces also tend to be moist which allows gases to dissolve in the fluid first making diffusion easier
7
Q
How does large SA:V ratio affect the rate of diffusion?
A
- All exchange surfaces consist of many, microscopic structures which collectively achieve a much larger surface area than 1 large structure
8
Q
What substances does the phospholipid bilayer form a barrier to?
A
- large molecules
- water soluble substances
- charged molecules
9
Q
What is facilitated diffusion?
A
- When the molecules pass through protein carriers or channels instead of passing between the phospholipids
- moves from high to low concentration
- more protein channels, mean higher rates of diffusion
10
Q
What substances can be transported via facilitated diffusion?
A
- large polar molecules like glucose and amino acids
- charged molecules like Na+ or Cl-
11
Q
How is the placenta adapted for diffusion?
A
- large SA:V ratio
- thin shape to increase surface area and decrease diffusion distance
- located towards centre of the body to maintain warm temperature
- blood is always flowing through the placenta to maintain gradient of high oxygen to low oxygen
12
Q
What is active transport?
A
- movement of molecules from a low to high concentration
- Energy (ATP) is required to move substances against concentration gradient
- Use protein carriers in the membrane
- act as a pump
- selective process: specific substances transported by specific carrier proteins
13
Q
What is the general process of active transport?
A
- molecule or ion to be transported binds to receptors in channel of carrier protein on outside of the cell
- on inside of the cell ATP binds to carrier protein and is hydrolysed into ADP and phosphate
- the protein changes shape, opening up to the inside of the cell
- molecule or ion released into inside of the cell
- phosphate molecule released from carrier protein and recombines with ADP to form ATP
- carrier protein returns to original shape
14
Q
What can be transported by active transport?
A
- glucose, could be in short supply
- amino acids
15
Q
What is bulk transport?
A
- another form of active transport
- large molecules like enzymes, hormones and whole cells like bacteria are too large to move through channel or carrier proteins
- moved into and out of cell by bulk transport
