Transport across cell membranes

Question 1

What is diffusion?

Answer 1

The net movement of particles from an area of higher concentration to an area of low concentration
- Diffusion is a passive process

Question 2

What is meant by facilitated diffusion?

Answer 2

Large or charged particles diffuse through carrier proteins or channel proteins - speeding up the process
- Higher to a lower concentration gradient and a passive process

Question 3

How do carrier proteins enable large molecules to move across the membrane?

Answer 3

• Large molecule attaches to a carrier protein in the membrane
• Protein changes shape
• Releases the molecule on the opposite side of the membrane

Question 4

How do channel proteins enable large molecules to move across the membrane?

Answer 4

• Channel proteins form pores in the membrane for charged particles to diffuse through
• Different channels (sodium channel) facilitate the diffusion of different charged particles

Question 5

What 3 factors affect the rate of simple diffusion?

Answer 5

• The concentration gradient, higher it is the faster the rate of diffusion
• The thickness of the exchange surface, thinner the exchange surface the shorter the diffusion distance
• The surface area, larger the surface area the faster the rate of diffusion

Question 6

What 2 factors affect the rate of facilitated diffusion?

Answer 6

• Concentration gradient, higher the concentration gradient faster the rate of facilitated diffusion
• Number of channel/carrier proteins, faster the rate of facilitated diffusion

Question 7

What is osmosis?

Answer 7

Diffusion of water molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential

Question 8

What 3 factors affect the rate of osmosis?

Answer 8

• The water potential gradient, higher water potential gradient faster the rate of osmosis
• Thickness of the exchange surface, thinner surface faster rate of osmosis
• Surface area, larger surface area faster rate of osmosis

Question 9

What is active transport?

Answer 9

Moves solutes from a low to a high concentration, requiring ATP

Question 10

What is meant by co-transporters?

Answer 10

A type of carrier protein

• Bind two molecules at a time
• Concentration gradient of one molecules is used yo move the other molecule against its own concentration gradient
• E.g. sodium ions and glucose

Question 11

What 3 factors affect the rate of active transport?

Answer 11

• Speed of individual carrier proteins
• Number of carrier proteins present
• The rate of respiration/availability of ATP