Diffusion and Fd

Question 1

What is diffusion ? and key points

Answer 1

net movement of molecules/ions from an area of high conc to an area of low conc continuing until equilibrium is reached.

key points
Movement occurs down the concentration gradient (not along).

Although the overall direction is from high to low concentration, individual particle movement is random.

No membrane is needed for diffusion to occur—it can happen in air or liquid.

Question 2

What type of process is diffusion ?

Answer 2

passive process - not require energy

Question 3

What can pass through the membrane ?
and what cannot diffuse easily ?

Answer 3

small uncharged molecules ( small

Non-polar

Lipid-soluble molecules (e.g. oxygen, carbon dioxide, steroid hormones)

cannot
Charged ions (e.g. Na⁺, Cl⁻)

Large molecules (e.g. glucose)

Water-soluble or polar molecules

Question 4

factors affecting diffusion

Answer 4

• SA of membrane - larger SA -faster diffusion rate
  e.g. microvilli and folded membrane in stomach increase SA for absorption
• temperature
• size of particles
  Size of the Molecule: Smaller molecules tend to diffuse faster than larger ones.
• diffusion medium
  solid = slowest
  liquid = fastest
  gas = fastest

higher temp = particles have more kinetic energy -> leads to faster movement and faster diffusion

Question 5

factors affecting diffusion

Answer 5

Concentration Gradient: The greater the difference in concentration between two areas, the faster the rate of diffusion.

Thinner membranes = shorter distance for molecules to travel.

Results in a faster rate of diffusion.

Question 6

Define facilitated diffusion

Answer 6

net movement of molecule from high conc to low conc through the membrane and though a integral protein molecule
( passive process )

Question 7

What is facilitated diffusion ?

Answer 7

Facilitated diffusion helps large, polar, or charged molecules pass through the membrane with the help of proteins.

Still passive – no energy required

Still down a concentration gradient

Question 8

Types of Transport Proteins

Answer 8

Channel Proteins
Form pores or tunnels in the membrane.

Allow specific charged particles to pass (e.g. Na⁺, Cl⁻).

Some are always open; others are gated:

Ligand-gated (opened by molecule binding)

Voltage-gated (opened by changes in membrane potential)

Pressure-gated

Question 9

Types of Transport Proteins

Answer 9

Example:
Aquaporins – channel proteins that allow water to pass more efficiently across the membrane.
Carrier Proteins
Bind to a specific molecule.

Undergo a shape change to transport the molecule across the membrane.

Used for large molecules (e.g. glucose, amino acids).

Slower than channel proteins due to shape change.

Question 10

pure water has the ——– water potential of ————.
Adding solute to the solvent —————- the water potential of the solution

Answer 10

highest , 0 KPA
increases

Question 11

Types of Transport Proteins

Answer 11

Example:
Aquaporins – channel proteins that allow water to pass more efficiently across the membrane.
Carrier Proteins
Bind to a specific molecule.

Undergo a shape change to transport the molecule across the membrane.

Used for large molecules (e.g. glucose, amino acids).

Slower than channel proteins due to shape change.

Question 12

If two aqueous solutions are separated by a partially permeable membrane, water molecules will move from the solution with the ——- water potential to the ..

Answer 12

highest, solution with the lowest water potential

Question 13

osmosis will cease when

Answer 13

water potential on both sides of the membrane becomes equal

Question 14

Factors Affecting Facilitated Diffusion

✅ Factors That Increase Rate:

Answer 14

Steep concentration gradient

Increased number of channel/carrier proteins

Question 15

Limiting Factors:

Answer 15

Protein saturation: Once all proteins are in use, increasing concentration further has no effect.

Protein availability: More transport proteins = faster rate (up to saturation).

Question 16

Graph Explanation:

Answer 16

Facilitated diffusion starts faster than simple diffusion.

Eventually, it plateaus ( no change) due to all proteins being occupied.

This point is called the saturation point or limiting factor.