Diffusion

Question 1

Describe the difference between Passive and Active transport

Answer 1

Passive transport doesn’t require additional energy from ATP, whereas active transport does

Question 2

Is diffusion active or passive transport

Answer 2

passive

Question 3

Define diffusion

Answer 3

Diffusion is the passive net movement of particles from an area of a higher concentration, to an area of a lower concentration, until they’re evenly distributed

Question 4

What does it mean when particles have reached equilibrium

Answer 4

• Particles have become equally distributed
• The concentration of particles is approximately equal
• There is no net movement

Question 5

What is movement down the concentration gradient

Answer 5

From a higher to a lower concentration

Question 6

Why is saying that diffusion requires no energy inaccurate

Answer 6

With no energy, the particles will not move

Question 7

When is the rate of diffusion the highest

Answer 7

When there is the biggest difference in the concentration

Question 8

How do you increase the rate of simple diffusion

Answer 8

• Increase the concentration gradient
• Increase the SA of the membrane
• Decrease the thickness of the membrane
• Increase the temperature
• Decrease the size of the particles
• Change the state of matter to a gas

Question 9

As you climb higher, mountain climbers often become more fatigued

Explain why, using your knowledge of diffusion and the role of oxygen

Answer 9

• As you climb higher, the concentration of oxygen in the atmosphere decreases
• This results in a lower concentration gradient between the cells and the blood
• Therefore the rate of diffusion decreases
• The higher you climb, the colder the air temperature is
• Therefore body temperature will decrease, so particles will have less kinetic energy, reducing the rate of diffusion
• Less oxygen diffuses into cells, so less aerobic respiration occurs, producing less ATP

Question 10

State Fick’s law

Answer 10

The rate of diffusion is proportional to both the surface area and concentration difference, and is inversely proportional to the thickness of the membrane

Question 11

In what process do non-lipid soluble molecules diffuse across the phospholipid bilayer

Answer 11

Facilitated diffusion

Question 12

Describe what is meant by facilitated diffusion

Answer 12

Some molecules that cannot pass through the phospholipid bilayer, diffuse across the cell membrane via a transport protein

Question 13

Describe the function of channel proteins

Answer 13

These proteins open and close to allow substances through the membrsne

Question 14

Describe the function of carrier proteins

Answer 14

These proteins change shape to move substances across the membrane

Question 15

Describe how to increase the rate of facilitated diffusion

Answer 15

• Increase the concentration gradient
• Increase the SA of the membrane
• Decrease the thickness of the membrane
• Increase the number of carrier/channel proteins

Question 16

Describe what happens to the rate of facilitated diffusion as external concentration increases, and internal concentration remains 0.

Answer 16

• Increases->the rate of diffusion is proportional to the concentration gradient
• Plateaus-> the number of carrier proteins becomes a limiting factor

Question 17

Why doesn’t the simple diffusion graph plateau

Answer 17

The particles move directly across the phospholipid bilayer and so the rate of diffusion remains directly proportional to the concentration of

Question 18

Describe how substances move across cell-surface membranes by facilitated diffusion.

Answer 18

• Carrier / channel protein;
• (Protein) specific / complementary to substance;
• Substance moves down concentration gradient;

Question 19

As external concentration of a substance increases, the rate of uptake into the cell initially increases before reaching a plateau.
Explain how this suggests the substance is entering the cell through facilitated diffusion and not by simple diffusion

Answer 19

As a plateau is reached, the channel proteins would be saturated and so rate of diffusion cannot increase any further. If it were occurring by simple diffusion, the relationship between rate and extracellular concentration would be linear.