Diffusion across membranes 2.5.2

Question 1

State the 5 types of movement across a cell membrane

Answer 1

• Diffusion
• Osmosis
• Active transport
• Endocytosis
• Exocytosis

Question 1

Name the 6 substances that need to move across membranes

Answer 1

• Oxygen
• Glucose
• Carbon dioxide
• Enzymes
• Hormones
• Signalling molecules

Question 2

Define diffusion

Answer 2

The movement of molecules from an area of high concentration to an area of low concentration, down a concentration gradient.

Question 3

Is diffusion passive or active?

Answer 3

Passive, as it uses only the kinetic energy on the molecule.

Question 4

Define a concentration gradient

Answer 4

The concentration difference between regions of high concentration and low concentration.

Question 5

What does a steeper concentration gradient result in?

Answer 5

Faster rate of diffusion

Question 6

Define equilibrium

Answer 6

When molecules have moved down their concentration gradient and remain evenly dispersed, so there is no net diffusion.

Question 7

State the substances that can pass through the lipid bilayer of the membrane

Answer 7

H20, O2, and CO2

Question 8

What is simple diffusion?

Answer 8

When small non-polar molecules in a high concentration on one side of the membrane can easily pass through the lipid bilayer.

Question 9

What is an aquaporin?

Answer 9

A specific water channel protein that allow water to cross the membrane without the challenge of moving through the lipid environment.

Question 10

State 5 factors affecting the rate of diffusion

Answer 10

• Temperature
• Diffusion distance
• Surface area
• Size of molecules
• Concentration gradient

Question 11

Define facilitated diffusion

Answer 11

The movement of molecules from an area of high concentration to an area of low concentration, across a partially permeable membrane - via protein channels or carriers

Question 12

Is facilitated diffusion passive or active?

Answer 12

Passive as it is down the concentration gradient.

Question 13

How do carrier proteins transport substances across a membrane?

Answer 13

They have a binding site for a specific solute, and constantly flip between two states so that the site is alternately open to opposite sides of the membrane.
(The substance will bind on the side where it is at a high concentration and be released where it is at a low concentration.)

Question 14

Give an example of a cell with different carrier proteins

Answer 14

Epithelial cells in the airway have chloride ion channels, as these are crucial in the regulation of mucus.