Transport Across Cell Membranes

Question 1

Diffusion

Answer 1

Net movement of particles/molecules/ions from an area of high concentration to an area of low concentration, Down a concentration gradient

Question 2

Factors that affect diffusion

Answer 2

• The conc gradient-the higher the conc the faster rate of diffusion
• Thickness of exchange surface- the thinner the faster rate of diffusion
• Surface area-larger SA means faster rate of diffusion

Question 3

Facilitated diffusion

Answer 3

When larger molecules cannot pass through phospholipid bilayer, so the molecules diffuse through carrier channels/protein carriers.

Question 4

Role of Carrier proteins

Answer 4

• A larger molecule attaches itself to a carrier protein
• The carrier protein changes shape as they mind to molecule
• The carrier protein carry the molecule into opposite sides of the membrane.

Question 5

Role of channel proteins

Answer 5

• Channel proteins form pores in the membrane for charge particles to diffuse through.
• They have a water filled centre which means only water soluble ions/molecules can pass through

Question 6

Factors that affects facilitated diffusion

Answer 6

• The conc gradient-the higher the gradient the faster the rate
• Number of channel or carrier proteins- when all proteins are in use facilitated diffusion can’t happen

Question 7

Osmosis

Answer 7

The random movement of water molecules from an area of higher water potential to a lower one.

Question 8

Factors which affect osmosis

Answer 8

• The water potential gradient-the higher the gradient the faster rate of osmosis
• The thickness of exchange surface
• The surface area

Question 9

Active transport

Answer 9

the movement of ions or molecules across a cell membrane from a region of lower concentration to region of higher concentration, assisted by enzymes and requiring energy(ATP)

Question 10

Co-transport

Answer 10

The transfer of substances across the cell surface membrane by a protein and an energy source

Question 11

Co-transport proteins

Answer 11

They are carrier proteins which only transport glucose in presence of sodium ions.this also involves facilitated diffusion