Crossing membranes - passive processes (diffusion)

HideShow resource information
  • Created by: Steff06
  • Created on: 04-04-16 16:09
What is diffusion?
The movement of molecules from a region of higher concentration to a region of lower concentration down a concentration gradient.
1 of 19
Why is diffusion described as a passive process?
Diffusion only depends on kinetic energy.
2 of 19
How are molecules distributed in diffusion?
Molecules are distributed evenly. When even, molecules continue to move around in a state of equilibrium.
3 of 19
What do living organisms not want to be reached and how do they avoid it?
Do not want equilibrium to be reached. E.g. CO2 in photosynthesis maintained at conc gradient.
4 of 19
What factors affect the rate of diffusion?
Temperature, size, surface area, stirring/moving, conc gradient, distance/thickness.
5 of 19
How does temperature affect the rate of diffusion?
Increase in temperature, increases kinetic energy and rate of movement/diffusion.
6 of 19
How does concentration gradient rate of diffusion?
More molecules on one side of the membrane increases rate of diffusion.
7 of 19
How does stirring/moving affect rate of diffusion?
Stirring a liquid/movement increases movement and therefore rate of diffusion.
8 of 19
How does the size of the molecule affect the rate of diffusion?
Smaller molecules will diffuse faster than larger molecules.
9 of 19
How does surface area affect the rate of diffusion?
Greater SA means diffusion will be faster. Cells are adapted to increase SA e.g. red blood cells are biconcave and alveoli increase SA in the lungs.
10 of 19
How does distance/the thickness affect the rate of diffusion?
Thicker/further distance means diffusion will be slower.
11 of 19
Describe lipid-based molecules diffusion
Lipid-based molecules can pass through the bilayer, diffusing down a concentration gradient. Steroid hormones are lipid-based and so diffuse through membranes.
12 of 19
Describe how small molecules/ions diffuse
CO2 and O2 are small enough to pass through the bilayer. Water molecules are very small so can diffuse through membrane even though they are polar (charged).
13 of 19
How do large/charged molecules get across the membrane?
Small charged molecules such as sodium and glucose cannot pass through the lipid bilayer. Channel/carrier proteins allow these substances across the membrane. Diffusion of these molecules is called facilitated diffusion.
14 of 19
Describe the role of channel proteins in diffusion
Form pores in the membrane shaped to only allow 1 type of ion through. Gated so can be open or closed.
15 of 19
What is the role of carrier proteins in diffusion?
Shaped so a specific molecule e.g. glucose can fit into them at the membrane surface. When the specific molecule fits, the protein changes shape to allow the molecule through to the other side.
16 of 19
What carries out simple diffusion?
Gases e.g. CO2 and O2, lipid-based such as steroid hormones.
17 of 19
What uses facilitated diffusion with channel proteins?
E.g. sodium and calcium ions.
18 of 19
What uses facilitated diffusion with carrier proteins?
Larger molecules like glucose and amino acids.
19 of 19

Other cards in this set

Card 2

Front

Why is diffusion described as a passive process?

Back

Diffusion only depends on kinetic energy.

Card 3

Front

How are molecules distributed in diffusion?

Back

Preview of the front of card 3

Card 4

Front

What do living organisms not want to be reached and how do they avoid it?

Back

Preview of the front of card 4

Card 5

Front

What factors affect the rate of diffusion?

Back

Preview of the front of card 5
View more cards

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Cellular processes and structure resources »