Diffusion

Question 1

What is diffusion

Answer 1

The net/passive movement of particles from an area of higher concentration to an area of lower concentration.

Question 2

What is a channel protein

Answer 2

Channel proteins are proteins within a cell membrane that
form pores.

Question 3

Explain how increasing the number of carrier and channel proteins in a membrane would affect the rate of facilitated diffusion.

Answer 3

It would increase the rate of facilitated diffusion as it would allow more particles to be transported across the membrane at the same time.
More proteins= more particles transported across membrane at same time

Question 4

Simple diffusion and facilitated diffusion both move particles down their concentration gradient across a cell membrane. Suggest how you could determine whether a particular particle is being transported by simple or facilitated diffusion in an experimental setting. Explain answer

Answer 4

You could increase the concentration gradient of the particle and monitor the rate of diffusion.
Facilitated diffusion requires proteins to transport particles across the cell membrane. There are a fixed number of proteins in the membrane. Once all the proteins are in use, increasing the concentration gradient won’t increase the rate of facilitated diffusion any further, whereas increasing the concentration gradient will continue to increase the rate of simple diffusion.

Question 5

The photograph on the right shows ink diffusing through a beaker of water.
Explain what is happening to the ink molecules.
Picture shows ink mixing with water

Answer 5

Diffusion of ink

The ink molecules are moving from an area of higher concentration (the original drop of ink) to an area of lower concentration (the surrounding water).

Question 6

Explain why the levels of rate of intake of epithelial cells levels of, as concentration increases 3 marks

Answer 6

The movement is through carrier proteins / facilitated diffusion

Rate of uptake is is directly proportional to each other.

As the conc increases levels of equilibrium have been reached so channel / carrier proteins is reached saturation point and have all been used up so conc can’t increase.

Question 7

What does a curved line graph mean compared to a straight line graph?

Answer 7

Curved - facilitated diffusion

Straight - simple

Question 8

Water and inorganic ions have important biological functions within cells

Compare and contrast the processes by which water and inorganic ions enter cells

3 marks

This isn’t exactly related to diffusion, just don’t know which section to put it in

Answer 8

Comparison: both move down concentration gradient;

2. Comparison: both move through (protein) channels in membrane;
   Accept aquaporins (for water) and ion channels
3. Contrast: ions can move against a concentration gradient by active transport

Question 9

What should you say instead of saying it doesn’t use energy

Answer 9

Say it’s passive

(Doesn’t use ATP)

Question 10

Describe how gas exchange occurs in single-celled organisms and explain why this method cannot be used by large, multicellular organisms.

3 marks

Answer 10

1. Diffusion (across the cell surface membrane;)
2. Large organisms have smaller sa: vol ratio
   OR
   Single-celled organisms have a large(r) sa: vol ratio;
3. Diffusion pathway would be too long
   OR
   (Rate of) Diffusion too slow;