Cells- Transport

Question 1

How to maximise diffusion?

Answer 1

1. ↑ sa:vol
2. maintain steep conc gradient
3. thin- ↓ diffusion distance

Question 2

Fick’s law

Answer 2

Rate of diffusion ∝ s.a. x conc. diff. / length of diffusion path

Question 3

Can hydrophobic, non-polar substances pass through the phospholipid bilayer?

Answer 3

• passes easily through membrane
• ∵ dissolves readily in lipids

Question 4

Briefly describe the roles of channel proteins

Answer 4

• x bind w/ solute –>open to let them through
• specific- only some types
• faster movement than carrier proteins
• gate- controls permeability
  – eg. sodium gates- Na+ in & out of nerve cells

Question 5

Briefly describe the roles of carrier proteins

Answer 5

• globular proteins on either side of membrane
• large molecules- eg. glucose
  — Permease- flip ∴ glucose transported in both directions

Question 6

What is water potential?

Answer 6

Pressure exerted by moving water molecules
- unit: kPa
– pure water = 0kPa (solutions = <0, -ve ψ)

Question 7

What happens when an animal cell is placed in a hypotonic solution?

Answer 7

• solution ↑ψ than cytoplasm
• water moves in
• lysis (burst)

Question 8

What happens to an animal cell when it is placed in an isotonic solution?

Answer 8

• = ψ
• x net movement of water

Question 9

What happens to an animal cell when it is placed in a hypertonic solution?

Answer 9

• solution ↓ψ than cytoplasm
• water moves out
• cell shrivels up

Question 10

State when plant cell in dilute solution

Answer 10

Turgid- protoplast pushed against cell wall

Question 11

What happens to a plant cell when it is placed in a concentrated solution?

Answer 11

• protoplast pulls away from cell wall
• plasmolysed (plasmolysis)

Question 12

Describe the process of active transport

Answer 12

• movement of particles against conc. gradient
• requires energy in form of ATP
• released during cellular resp.
• carrier proteins
• specific substances

Question 13

Condition of cell when placed in a solution with equal water potential

Answer 13

Incipient plasmolysis- protoplast beginning to pull away from cell wall

Question 14

What is the protoplast?

Answer 14

Consists of:
- outer cell-surface mem
- nucleus
- cytoplasm
- inner vacuole mem

Question 15

Describe why plant cells are turgid in pure water.

Answer 15

• water enters by osmosis
• cell wall- limited expansion
• pressure builds up
• resists entry of further water

Question 16

Explain why it is important that the reabsorption of glucose from urine to blood occurs by active transport rather than diffusion.

Answer 16

• diffusion- only reabsorb 50% max
• other 50% lost
• a.t. reabsorbs all- x lost