Chapter 4- Transport across cell membranes

Question 1

What two things does a phospholipid contain to form a phospholipid bilayer

Answer 1

-hydrophilic head - points to the outside of the cell surface membrane as they are attracted to water
- hydrophobic tail - point into the cell membrane as they are repelled from water

Question 2

Roles of phospholipids in the membrane

Answer 2

1. allow lipid soluble substances to enter and leave the cell
2. prevent water soluble substances entering and leaving the cell
3. make the membrane flexible and self sealing

Question 3

Function of
1. protein channels
2. carrier proteins

Answer 3

1. form water-filled tubes to allow water soluble ions to diffuse across
2. bind to ions or molecules like glucose then change shape to move the molecules across the membrane

Question 4

Functions of proteins in the membrane

Answer 4

• provide structural support
• act as channels transporting water soluble substances across the membrane
• allow active transport across the membrane through carrier proteins
• form cell-surface receptors for identifying cells
• help cells adhere together
• act as receptors like hormones

Question 5

why is the fluid mosaic model given its name

Answer 5

fluid- because the individual phospholipid molecules can move relative to one another which gives the membrane flexibility

mosaic- because the proteins are embedded in the phospholipid bilayer vary in shape, size and pattern

Question 6

what does passive mean in the case of simple diffusion

Answer 6

energy comes from the natural, inbuilt motion of particles rather than from external sources such as ATP

Question 7

Definition of simple diffusion

Answer 7

the net movement of molecules or ions from a state of higher concentration to a state of lower concentration down a concentration gradient

Question 8

What are the types of protein used in facilitated diffusion

Answer 8

protein channels
Carrier proteins

Question 9

How do protein channels help with facilitated diffusion

Answer 9

• form water-filled hydrophilic channels across the membrane
• these allow specific water-soluble ions to pass through
• the channels are selective in this way can control the entry and exit of ions

Question 10

How do carrier proteins help with facilitated diffusion

Answer 10

• span across the entire membrane
• when a molecule that is specific to the protein is present, it binds with the protein
• this makes it change shape to which the molecule gets released to the inside of the membrane
• there is no external energy to move from the higher to lower concentration they only use their own kinetic energy

Question 11

Define osmosis

Answer 11

the movement of water from a region of higher concentration to a region of lower concentration through a selectively permeable membrane

Question 12

What does it mean by cell surface membranes to be selectively permeable

Answer 12

they allow water molecules and small molecules to pass through but they don’t allow large molecules to pass

Question 13

1. what is a solute
2. how does a solute make a solution

Answer 13

1. a solute is any substance dissolved in a solvent
2. the solute added to a solvent together make a solution

Question 14

What is water pressure measured in

Answer 14

units of pressure, usually kilopascals (KPa)

Question 15

What would happen to a cell if the water potential of external solution compared to cell solution was:
1. higher (less negative)
2. equal
3. lower (more negative)

Answer 15

1. the cell will swell and burst because water enters into the cell
2. no change because no water enters or leaves the cell
3. the cell will shrink because water will leave the cell

Question 16

Definition of active transport

Answer 16

the movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration against a concentration gradient using ATP and carrier proteins

Question 17

How can the rate of movement across membrane be increased

Answer 17

• microvilli- provide more surface area for the insertion of carrier proteins
• to increase the number of protein channels or carrier proteins in any given area of the membrane

Question 18

Describe co transport

Answer 18

when glucose or AA’s are drawn into the small intestine cells along with sodium ions that have been actively transported out by the sodium- potassium pump

Question 19

Describe the process of the sodium potassium pump

Answer 19

1. sodium ions are transported out of the epithelial cell by the sodium potassium pump
2. this maintains a higher conc. of sodium ions in the lumen of the intestine than inside the epithelial cell
3. as sodium ions diffuse through a second carrier protein, they carry either AA molecules or glucose molecules into the cell with them
4. the glucose/AA’s pass into the blood plasma by facilitated diffusion using another type of carrier