2.2 (4) - Transport Across Cell Membranes

Question 1

What are some functions of cell membranes?

Answer 1

• Partially-permeable barrier, regulating entry/exit of particles
• Has binding sites
• Confers antigenic properties to the cell
• Site of certain reactions
• Compartmentalises different cell reactions in organelles

Question 2

What are the 5 main parts of a phospholipid?

Answer 2

• Phosphate group
• Phosphoester bond
• Glycerol
• Ester bond
• Fatty acids

Question 3

What is the fluid mosaic model? Why is it called that?

Answer 3

• The phospholipid bilayer has proteins embedded in it (mosaic)
• The phospholipids can move freely through the bilayer (fluid)

Question 4

Describe cholesterol

Answer 4

• Fatty substance
• Hydrophobic, so pulls the phospholipid tails together
• Adds strength and some rigidity to the membrane (particularly at high temperatures)
• Reduces the movement of other molecules in the membrane

Question 5

Describe glycolipids

Answer 5

• Carbohydrate bound to a lipid
• Lipid portion embedded in phospholipid bilayer, carbohydrate protein extends outside the cell
• Acts as recognition and binding sites

Question 6

What are the two types of membrane proteins?

Answer 6

• Intrinsic proteins

- Extrinsic proteins

Question 7

What is an intrinsic protein?

Answer 7

Spans the membrane and acts as channel and carrier proteins (made from protein only)

Question 8

What is an extrinsic protein?

Answer 8

• On the surface of the membrane (internal or external) and acts as receptors or enzymes
• May have glycolipids bound to them

Question 9

What is diffusion?

Answer 9

The net movement of molecules/ions from a region where they are more highly concentrated to one where their concentration is lower, until evenly distributed

Question 10

Describe facilitated diffusion

Answer 10

• Passive process
• Relies on the KE of diffusing molecules, in order to work
• Through transmembrane channels and carriers (MUST happen at these points)
• Occurs down the concentration gradient

Question 11

Describe channel proteins

Answer 11

• Water-filled hydrophilic channels, to allow a stream in and out of the cell
• Allows specific water-soluble ions to pass through
• Selective in what passes through
• Channels remain closed unless specific ions are present

Question 12

Describe carrier proteins

Answer 12

• Molecule has to be specific to protein
• It binds to the protein, which causes it to change shape and is then released
• Only uses the KE of the molecules to work

Question 13

What is osmosis?

Answer 13

The passage of water from a region where is has a higher water potential to a region where it has a lower water potential through a selectively-permeable membrane

It can be quantified using water potential

Question 14

Describe water potential

Answer 14

• WP always moves down the concentration gradient
• Addition of solutes reduces the WP (-ve value)
• WP is measured in units of pressure

Question 15

What is the water potential of pure water?

Answer 15

0Ѱ

Question 16

In a hypertonic solution, does water move into or out of the cell?

Answer 16

Out, making the cell plasmolysed

Question 17

In a isotonic solution, does water move in or out of the cell?

Answer 17

Equal balance of water inside and outside the cell, making the cell flaccid

Question 18

In a hypotonic solution, does water move in or out of the cell?

Answer 18

In, making the cell turgid

Question 19

What is active transport?

Answer 19

The movement of molecules/ions into or out of a cell from a region of lower to higher concentration, using ATP and carrier proteins

Question 20

What is an example of active transport in the body?

Answer 20

The sodium-potassium pump, found in all animal cell membranes

Question 21

Describe the Na-P pump

Answer 21

It continually uses ATP to actively pump sodium out of the cell and potassium into the cell, creating concentration gradients across the cell membrane

Question 22

What is co-transport?

Answer 22

• Carrier proteins can sometimes transport 2 types of particle at once
• But, both must be present for co-transport to take place
• Often, it’s both active and passive, because 1 particle is moved with the concentration gradient and the other is moved against it
• Substances can be moves in the same (symport) direction or the opposite (antiport) direction