2.6,7,9: Selective Permeability

Question 1

What is selective permeability?

Answer 1

Some substances can cross the membrane more easily than others

Question 2

What molecules have easy passage across the membrane? (3)

Answer 2

• Small, nonpolar, hydrophobic molecules
  Examples
• hydrocarbons (such as lipids b/c of HC backbone)
• CO2, O2, N2

Question 3

Why are small, nonpolar, hydrophobic molecules easily able to pass across the membrane?

Answer 3

Fatty acid tails are nonpolar and interact nicely with other nonpolar molecules

Question 4

What molecules have difficult passage or protein assisted passage through the cell membrane? (4)

Answer 4

• hydrophilic
• polar molecules
  -large molecules
  -ions
  Ex. Sugars, waters

Question 5

What are the two main types of transport across a membrane?

Answer 5

Passive and active transport

Question 6

What is passive transport?

Answer 6

• transport of a molecule that does not require energy from the cell because a solute is moving with its concentration or electrochemical gradient

Question 7

What is passive transport involved in? (4)

Answer 7

• involved in the import of material and export of waste
  Examples
  Diffusion, osmosis, facilitated diffusion

Question 8

What is diffusion?

Answer 8

• Spontaneous process resulting from the constant motion of molecules

Question 9

What happens in the diffusion? (4)

Answer 9

• substances move from a high to a low concentration
• move down the concentration gradient
• molecules diffuse directly across the membrane
• different rate of diffusion for different molecules

Question 10

What is osmosis?

Answer 10

The diffusion of water down its concentration gradient across a selectively permeable membrane

Question 11

What can osmosis also be thought of?

Answer 11

The diffusion of water from areas of low solute concentration to areas of high solute concentration

Question 12

What is facilitated diffusion? (2)

Answer 12

• diffusion of molecules through the membrane via transport proteins
• increase the rate of diffusion for small ions, water, carbs (ALL POLAR)

Question 13

What are the two categories of transport proteins, and what can it facilitate movement for?

Answer 13

• Channel and carrier

- each transport protein is specific for substances it can facilitate movement for

Question 14

Why is facilitated diffusion passive and not active transport?

Answer 14

• The substances the proteins are helping to move are moving DOWN the concentration gradient and no energy is required

Question 15

What are channel proteins?

Answer 15

• provide a channel for molecules and ions to pass
• hydrophobic channel
• hence only a low passage when there is a stimulus

Question 16

What are aquaporins?

Answer 16

• specific channel protein for water

Question 17

What are carrier proteins?

Answer 17

Undergo conformational change is for substances to pass

Question 18

What is the difference between osmosis and facilitated diffusion? Generally what is a misconception

Answer 18

Osmosis is a term! facilitated diffusion is the process

Btw polar molecules need facilitated diffusion