3.2.3.2 - Simple and Facilitated Diffusion

Question 1

Diffusion is an example of

Answer 1

passive transport - energy comes from natural, inbuilt motion of particles

Question 2

In diffusion the motion of the particles is described as

Answer 2

random motion

Question 3

In diffusion the direction of particle movement is

Answer 3

from an area of high concentration to an area of lower concentration - until equilibrium is reached

Question 4

Molecules which can diffuse through the phospholipid bilayer include

Answer 4

non-polar, small molecules e.g. oxygen and carbon dioxide

Question 5

Facilitated diffusion and diffusion differ because

Answer 5

facilitated diffusion requires a special protein molecules e.g. carrier or channel protein

Question 6

Facilitated and diffusion are similar because

Answer 6

they are both passive and molecules move with their concentration gradient (high to low)

Question 7

Molecules which do not diffuse easily across the phospholipid bilayer are

Answer 7

large, charged ions and polar molecules e.g. glucose

Question 8

What prevents large, charged and polar molecules diffusing across the plasma membrane

Answer 8

the hydrophobic fatty acids tails of the phospholipid bilayer

Question 9

Name the two types of protein molecules involved in facilitated diffusion

Answer 9

carrier and channel proteins

Question 10

Carrier proteins transport

Answer 10

molecules like glucose

Question 11

How do carrier proteins transport molecules like glucose?

Answer 11

glucose binds to the carrier specifically, carrier changes shape, releasing it onto the other side of the membrane

Question 12

Channel proteins transport…

Answer 12

water soluble ions

Question 13

How do channel proteins transport molecules like water soluble ions?

Answer 13

ion binds causing a change in the shape of the channel allowing the ion to enter the cell

Question 14

State 3 factors that affect the rate of diffusion

Answer 14

surface area, concentration gradient and thickness of exchange surface

Question 15

For maximum diffusion what adaptations does the exchange surface need

Answer 15

large surface area
Large concentration gradient
Thin - short diffusion distance

Question 16

Name 2 exchange surfaces in living organisms (humans)

Answer 16

alveoli and villi

Question 17

Where does diffusion take place in living organisms

Answer 17

1. alveoli - exchanging oxygen and carbon dioxide
2. Villi - exchange soluble molecules into the blood
3. Leaf (stomata) - carbon dioxide and oxygen
4. Roots - water

Question 18

How would diffusion be affected if the alveoli surface area is doubled

Answer 18

doubles

Question 19

How would diffusion be affected if the surface area is halved but the oxygen concentration gradient is doubled

Answer 19

no change

Question 20

How would diffusion be affected if the oxygen concentration is halved and the total thickness of the exchange surface is doubled

Answer 20

decreases 4 fold/quarter

Question 21

what is a protein channel filled with?

Answer 21

water

Question 22

What do carrier proteins and channel proteins have in order to transport molecules across the membrane?

Answer 22

binding sites

Question 23

How do substances move across the cell surface membrane by facilitated diffusion

Answer 23

1. Carrier/channel protein;
2. (Protein) specific/complementary to substance;
3. Substance moves down concentration gradient;

Question 24

many different substances enter and leave a cell by crossing its cell surface membrane. describe how substances can cross a cell surface membrane?

Answer 24

• small, non-polar mol pass via phospholipid bilayer
• large, polar mol go through proteins
• simple diffusion - from high conc to low conc - down conc gradient
• water moves by osmosis - from high wp to low wp
• active transport - from low conc to high conc - against conc gradient
• active transport uses carrier proteins / protein channels
• active transport needs ATP