Diffusion Flashcards
Define diffusion
Diffusion is the net movement of particles (molecules or ions) down a concentration gradient.
What do you need to remeber about diffusion?
- It’s the net movement
- It’s a passive process - no energy is needed for it to happen.
- simple diffusion is where molecules diffuse directly through a cell membrane.
What is facilitated diffusion?
Facilitated diffusion is the transport of substances across a membrane from an area of higher concentration to an area of lower concerntration, via channel and carrier proteins.
It is a passive process.
What molecules do carrier proteins help transport /diffuse?
Carrier proteins move large molecules across membranes, down their concentration gradient. Different carrier proteins facilitate the diffusion of different molecules.
1) First, a large molecule attaches to a carrier protein in the membrane.
2) Then, the protein changes shape.
3) This releases the molecule on the opposite side of the membrane.
What type of molecules do channel proteins help transport?
Channel proteins form pores in the membrane for charged particles to diffuse through (down their concentration gradient). Different channel proteins facilitate the diffusion of different charged particles.
Give two types of particle that are able to move freely through cell membranes via simple diffusion. Explain your answer.
Small and non-polar particles diffuse easily through cell membranes. Small particles pass through spaces between the phospholipids and non-polar particles are soluble in lipids, so can dissolve in the phospholipid bilayer.
What does this graph show?
The graph shows how the rate of uptake of two solutes changed with an increase in the extracellular concentration of the solutes.
Which solute is more likely to be transported ross the cell membrane via facilitated diffusion? Explain your answer.
Solute X. Solute X is likely to be transported across cell membranes by carrier or channel proteins (facilitated
diffusion) because the rate of uptake levels off. This suggests that many of the carrier or channel proteins are
already in use, so further increases in the extracellular concentration have little effect on the rate of uptake.
The smooth endoplasmic reticulum (SER) has a folded structure. What effect is this likely to have on diffusion of substances into and out of the SER? Why might this be beneficial to the SER’s function?
The folded structure gives the SER a larger surface area. This means that more particles can be exchanged in the same amount of time, increasing the rate of diffusion into and out of the SER. This could allow the SER to obtain the materials it needs to synthesise and process lipids at a faster rate, and to release lipids into the cell at a faster rate.
What is cystinuria?
The amino acid cysteine is reabsorbed from the kidneys into the blood before it enters the urine. Cystinuria is a condition in which carrier proteins in kidney epithelial cells do not function properly.
Suggest and explain how cystinuria leads to an increase in the cysteine concentration of the urine.
7) Amino acids are large molecules, so they diffuse directly through membranes very slowly. This means they rely on carrier proteins for transport. If the carrier proteins don’t function correctly, the rate of cysteine diffusion from the kidneys into the blood will reduce and the concentration of cysteine in the urine will increase.
Why does the rate of diffusion decrease over time?
As diffusion takes place the difference in conc. between the two sides decreases until it reaches equilibrium (the conc. on both sides is equal). This means diffusion slows down over time.
What does the rate of diffusion depend on?
- The conc gradient - higher = faster rate of diffusion.
- the thickness of the exchange surface thinner = shorter diffusion distance particles have to travel = faster rate of diffusion.
- The surface area - larger = more particles can be can be exchanged in the same amount of time = faster rate.
