Diffusion & Facilitated Diffusion

Question 1

What is passive transport?

Answer 1

the diffusion of a substance across a biological membrane and does not require energy (down a concentration gradient)

Question 2

What are the 5 different passive transport processes?

Answer 2

1. diffusion
2. osmosis
3. plasmolysis
4. facilitated diffusion
5. countercurrent exchange

Question 3

How can the rates of passive transport increase?

Answer 3

• higher concentration gradients
• higher temperatures
• smaller particle size

Question 4

What is a concentration gradient?

Answer 4

The region along which the density of a substance increases or decreases, and doesn’t require any work to happen. Each substance diffuses independently down its own concentration gradient and isn’t affected by other substances’ concentration gradients.

Question 5

What is diffusion?

Answer 5

The net movement of substances from an area of higher concentration to an area of lower concentration. It results from random movement of molecules, but the diffusion of a population may be directional.

Question 6

Is diffusion spontaneous or nonspontaneous?

Answer 6

spontaneous, because it doesn’t require any energy

Question 7

What is the difference between diffusion and osmosis?

Answer 7

osmosis is a type of diffusion where water diffuses across a semi-permeable membrane

Question 8

What is facilitated diffusion?

Answer 8

the diffusion of solutes or water through channel proteins or carrier proteins in the plasma membrane (the lipid bilayer does not allow polar molecules and ions to go through)

Question 9

Why is facilitated diffusion considered passive transport?

Answer 9

Because the solute is moving down its concentration gradient, a process requiring no energy. (Also, it speeds the transport of a solute by providing passage through the membrane without altering the direction of transport.)

Question 10

What are transport proteins?

Answer 10

a transmembrane protein that helps a specific substance to cross the membrane

Question 11

What are the two types of transport proteins?

Answer 11

1. channel: provides a hydrophilic tunnel to allow specific molecules to pass the membrane
2. carrier: binds to molecule and changes shape as it moves a solute across the membrane

Both proteins can transport the solute in either direction, but the net movement is down the concentration gradient of the solute.

Question 12

What are the channel proteins that transport ions called?

Answer 12

ion channels, which function as gated channels that open or close in response to a chemical or electrical stimulus (some ions include: Na⁺, K⁺, Ca²⁺, or Cl^-)

Question 13

What specialized type of channel protein facilitates the movement of water across the plasma membrane?

Answer 13

aquaporins

Question 14

What do carrier proteins facilitate the movement of?

Answer 14

the movement of ions AND some larger organic molecules, such as amino acids and glucose

Question 15

What happens when the concentration gradient is greater?

Answer 15

The initial rate of diffusion is faster. However, equilibrium is reached sooner when the concentration gradient is smaller due to the fewer number of solutes necessary to establish equilibrium.

Question 16

What happens when the temperature of solutions are greater?

Answer 16

The rate of diffusion is faster. Molecules at higher temperatures have more kinetic energy and move faster.

Question 17

What happens when the solute weight is greater?

Answer 17

The rate of diffusion is slower. All molecules at the same temperature have the same average kinetic energy. But remember: kinetic energy = 1/2 x mass x velocity². Thus, lighter molecules move faster.

Question 18

Do small, noncharged particles, primarily gases (like carbon dioxide and oxygen), need facilitated diffusion?

Answer 18

no, they can diffuse through the plasma membrane without any help