Transport Across Cell Membranes

Question 1

Why is the cell membrane described as fluid?

Answer 1

Phospholipids form a bilayer in which the phospholipid molecules are constantly moving

Question 2

Why is the cell membrane described as mosaic?

Answer 2

There are proteins of different sizes and shapes embedded in the phospholipid bilayer

Question 3

What is the phospholipid bilayer made up out of?

Answer 3

Phospholipids with hydrophilic heads outwards and hydrophobic tails inwards

Question 4

What are the two types of proteins found in the phospholipid bilayer?

Answer 4

Carrier and channel

Question 5

What are glycoproteins?

Answer 5

Proteins attached to a carbohydrate

Question 6

What are glycolipids?

Answer 6

Lipids attached to a carbohydrate

Question 7

What is the function of cholesterol in the phospholipid bilayer?

Answer 7

Adds stability

Question 8

What substances cannot pass through the bilayer?

Answer 8

Water-soluble

Question 9

What are the 2 main types of cell membrane?

Answer 9

• cell-surface membrane
• membrane around organelles

Question 10

What is the function of cell-surface membranes?

Answer 10

Act as a barrier between the cell and its environment, controlling which substances enter and leave the cell

Question 11

What is the function of membranes around organelles?

Answer 11

Act as a barrier between the organelle and the cytoplasm, dividing the cell into different compartments

Question 12

What is diffusion?

Answer 12

The net movement of particles from an area of higher concentration to an area of lower concentration

Question 13

What is a passive process?

Answer 13

Doesn’t require energy

Question 14

What are the two types of diffusion?

Answer 14

• simple diffusion
• facilitated diffusion

Question 15

What is simple diffusion?

Answer 15

Molecules can diffuse directly across cell membranes

Question 16

Which two molecules diffuse into cells via simple diffusion?

Answer 16

Oxygen and carbon dioxide

Question 17

Give 2 reasons why oxygen and carbon dioxide can diffuse into cells via simple diffusion

Answer 17

• small (can pass through the spaces between phospholipids)
• non-polar (can dissolve in the hydrophobic core of the cell membrane)

Question 18

What is facilitated diffusion?

Answer 18

Large and polar molecules can cross cell membranes via carrier and channel proteins

Question 19

How does a carrier protein work in facilitated diffusion?

Answer 19

1. Large molecule attaches to a carrier protein
2. Causes the carrier protein to change shape
3. Releases the molecule in the opposite side of the membrane

Question 20

How do channel proteins work?

Answer 20

Form pores in the cell membrane, which ions can travel through

Question 21

What are the 5 factors affecting the rate of diffusion?

Answer 21

• temperature
• concentration gradient
• thickness of membrane
• surface area
• number of carrier or channel proteins

Question 22

What is osmosis?

Answer 22

The diffusion of water molecules from an area of higher water potential to an area of lower water potential across a partially permeable membrane

Question 23

What is a hypotonic solution?

Answer 23

Has a higher water potential than the cell

Question 24

What is the direction of water movement between hypotonic solutions and animal cells?

Answer 24

Moves into the cell from the solution

Question 25

What happens to the animal cell in hypotonic solutions?

Answer 25

Swells and bursts

Question 26

What is an isotonic solution?

Answer 26

Has the same water potential as the cell

Question 27

What is the direction of water movement between isotonic solutions and animal cells?

Answer 27

No net movement

Question 28

What happens to the animal cell in isotonic solutions?

Answer 28

Stays the same size

Question 29

What is a hypertonic solution?

Answer 29

Has a lower water potential than the cell

Question 30

What is the direction of water movement between the hypertonic solution and an animal cell?

Answer 30

Water molecules move out of the cell

Question 31

What happens to the animal cell in hypertonic solutions?

Answer 31

Shrinks

Question 32

What happens to a plant cell in hypotonic solutions?

Answer 32

Swells and becomes turgid

Question 33

What happens to plant cells in isotonic solutions?

Answer 33

Stays the same size

Question 34

What happens to plant cells in hypertonic solutions?

Answer 34

Shrinks and becomes plasmolysed

Question 35

What are the 4 key factors that affect the rate of osmosis?

Answer 35

1. Temperature 2. Water potential gradient 3. Thickness of membrane 4. Surface area

Question 36

What is active transport?

Answer 36

The movement of particles from an area of lower concentration to an area of higher concentration, requiring energy from respiration in the form of ATP

Question 37

What is an active process?

Answer 37

Energy is need to move particles against a concentration gradient

Question 38

How do carrier proteins work during active transport?

Answer 38

1. The molecule or ion binds to the carrier protein 2. ATP binds to the carrier protein 3. Hydrolysis of ATP to ADP and Pi causes carrier protein to change shape, releasing the molecule or ion on the opposite side of the membrane 4. Pi is released from the carrier protein, causing the carrier protein to return to its original shape

Question 39

What are the 4 factors affecting the rate of active transport?

Answer 39

1. Temperature 2. Thickness of membrane 3. Number of carrier proteins 4. Rate of respiration

Question 40

What is co-transport?

Answer 40

Using the concentration gradient of one molecule to move the other molecule against its own concentration gradient

Question 41

What are the 3 different proteins the co-transport of glucose involves?

Answer 41

- sodium-potassium pumps (actively transport sodium and potassium ions) - sodium-glucose co-transporter proteins (use FD to transport sodium ions and glucose molecules) - glucose protein channels (use FD to transport glucose molecules)

Question 42

What is the first stage of co-transport of sodium and glucose?

Answer 42

- Na+ is actively transported out of epithelial cells into the blood by the sodium-potassium pump - this pump transports three Na+ out for every two K+ in - creates a concentration gradient as there is now a higher concentration of Na+ in the lumen than in the epithelial cells

Question 43

What is the second stage of co-transport of sodium and glucose?

Answer 43

- Na+ diffuses from a high conc in the lumen to a low conc in the epithelial cells - transported via sodium-glucose co-transporter proteins, which also carry glucose molecules - causes the conc of glucose inside the epithelial cells to increase

Question 44

What is the third stage of co-transport of sodium and glucose?

Answer 44

- now a higher glucose conc in the epithelial cells than in the blood - so, glucose diffuses out of epithelial cells and into the blood via facilitated diffusion