Cell Transport

Question 1

what is simple diffusion

Answer 1

net movement of molecules or ions from a region of high concentration to low concentration through a partially permeable membrane

Question 2

what is facilitated diffusion

Answer 2

movement of molecules and ions facilitated by transmembrane proteins and channels

Question 3

limitations of simple diffusion

Answer 3

only small and non polar molecules can use this

Question 4

Why can’t polar molecules use simple diffusion

Answer 4

polar molecules have difficulty passing through the non polar hydrophobic tails in the phospholipids due to the nature of them

Question 5

Why can’t polar molecules use simple diffusion

Answer 5

polar molecules have difficulty passing through the non polar hydrophobic tails in the phospholipids due to the nature of the tails

Question 6

during facilitated diffusion, these proteins are used

Answer 6

1. protein channels
2. carrier proteins

Question 7

what are protein channels?

Answer 7

1. They are water-filled pores
2. They allow water-soluble ions to pass through the cell membrane
3. They bind to specific ions
4. One side of the protein closes and the other opens

Question 8

what are carrier proteins

Answer 8

they allow the diffusion of:
1. glucose
2. Amino acids
3. nucleotides

Question 9

what is osmosis

Answer 9

osmosis is the net movement of water molecules from a region of high water potential to low water potential through a partially permeable membrane

Question 10

what is water potential

Answer 10

water potential is the tendency for water to move out a solution

Question 11

what does turgid mean

Answer 11

turgid is when a plant cell is fully inflated with water, and has become rigid and firm

Question 12

meaning of plasmolysis

Answer 12

when the water potential in the plant cell is higher than the surrounding environment, water leaves the cell via osmosis, this causes the cell to shrink which can lead to plasmolysis

Question 13

The meaning of a hypertonic solution

Answer 13

The water potential of the cell is higher than the solution, this means osmosis moves out of the cell via osmosis, the shrinks and becomes shrivelled

Question 14

The meaning of an isotonic solution

Answer 14

The water potential inside the cell is the same as the water potential of the solution, therefore no osmosis takes place and the cell remains normal

Question 15

The meaning of a hypotonic solution

Answer 15

The water potential is lower than the water potential of the solution therefore water moves into the cell via osmosis, this causes the cell to expand which can lead to the cell bursting aka lysis

Question 16

What is active transport

Answer 16

Active transport is the net movement of molecules or ions from a low concentration to a high concentration against the concentration gradient that requires energy from respiration

Question 17

What else does active transport require

Answer 17

Active transport requires carrier proteins

Question 18

Why is energy required for active transport

Answer 18

the energy is required to make the carrier proteins change shape, this allows the carrier proteins to transfer molecules or ions across the the cell membrane

Question 19

How is the energy produced from respiration

Answer 19

Respiration produces ATP. ATP is hydrolysed to form adenine diphosphate and energy is released from this

Question 20

How do carrier proteins work

Answer 20

1. They bind to the complementary molecule
2. This causes a conformational change, this releases molecule on the other side

Question 21

Factors affecting simple diffusion

Answer 21

1. The concentration gradient
2. The thickness of the exchange surface
3. The surface area

Question 22

How does the concentration gradient affect simple diffusion

Answer 22

1. The higher it is, the faster the rate of diffusion
2. As diffusion takes place, the difference in concentration between the 2 sides will decrease until it reaches an equilibrium
3. This means that diffusion will slow down

Question 23

How does the thickness of the surface affect simple diffusion

Answer 23

1. The thinner the surface, the quicker diffusion takes place
2. This is because there is a smaller distance for the particles to travel

Question 24

How does the surface area affect the rate of diffusion

Answer 24

the larger the surface area, the faster rate of diffusion

Question 25

Factors affecting the rate of facilitated diffusion

Answer 25

1. Concentration gradient
2. the number of carrier proteins or protein channels

Question 26

How does the concentration gradient affect the rate of facilitated diffusion

Answer 26

1. The higher it is, the faster the rate of diffusion
2. As diffusion takes place, the difference in concentration between the 2 sides will decrease until it reaches an equilibrium
3. This means that diffusion will slow down

Question 27

How does the number of carrier proteins or protein channels affect the rate of facilitated diffusion

Answer 27

1. Once all the carrier proteins and the protein channels have been used up, facilitated diffusion cant go any quicker
2. therefore more carrier proteins and protein channels means faster rate of facilitated diffusion

Question 28

What is co-transport

Answer 28

Co-transport is the coupled movement of substances across a cell membrane via a carrier protein

Question 29

example of co-transport

Answer 29

A well known example can be found on the cell surface membrane of the epithelial cells lining the ileum

Question 30

How does this example work

Answer 30

1. sodium ions and glucose molecules are transported into the epithelial cells via facilitated diffusion
2. The facilitated diffusion can only continue if the concentration gradient is maintained
3. The active transport of sodium ions out of the cell into the blood helps maintain this gradient
4. The glucose molecules exit the epithelial cell and enter the blood via facilitated diffusuion