Transport Across Membranes

Question 1

What are non-polar molecules?

Answer 1

Not charged, occurs in simple diffusion. Co2 and O2.

Question 2

What are polar molecules?

Answer 2

Charged and occur in FD and AT. Glucose and amino acids.

Question 3

Explain simple diffusion

Answer 3

• High to low concentration
• Passive
• Rate of diffusion= SA x concentration difference
• Thickness of exchange surfaces
• Rate is increased by higher concentration gradient, large SA, high temperature and short diffusion distance.

Question 4

Explain facilitated diffusion

Answer 4

• Transport of polar molecules
• Uses channel and carrier proteins
• Passive process, doesn’t require energy
• NOT inhibited by respiratory inhibitors such as cyanide.

Question 5

Explain active transport

Answer 5

• Net movement of molecules/ions through a partially permeable membrane
• Against a concentration gradient
• Use of carrier proteins which possess a specific structure complimentary to polar molecules
• Requires ATP

Question 6

Explain osmosis

Answer 6

• Net movement of water molecules from a dilute solution to a concentrated solution
• For [solute]=osmosis is from a low to a high concentration of solute molecules.
• For [water]= osmosis is from a high to low concentration

Question 7

Explain water potential

Answer 7

• Potential volume of water to leave a solution by osmosis
• The greater the [water], the higher the water potential.
• Higher to a lower water potential.
• Distilled (pure) water has highest wp. 0
• Always negative

Question 8

Explain osmosis and cell turgor

Answer 8

• As water enters the cell, the vacuole becomes bigger and exerts and outward pressure towards the cell wall with the cytoplasm and cell membrane.
• Essential is it provides support
• In distilled water (high water potential) the cell becomes turgid, water moves into cell
• In concentrated salt solution, cell becomes plasmolysed as water potential is low outside the cell, so water moves out.

Question 9

Explain osmosis in red blood cells

Answer 9

• Doesn’t occur in isotonic solution (equal wp)
• If low [solute] (higher wp) osmosis occurs. The cell will swell and may burst when the pressure causes the membrane to rupture.
• If the cell is placed in high [solute] (lower wp) osmosis occurs and the cell will shrink as water moves out of it

Question 10

What is the calculation for mass change?

Answer 10

Final mass - initial mass / initial mass X 100