Transport across membranes

Question 1

Phospholipids

Answer 1

Made up of phosphate head and fatty acid tail

Question 2

Cholesterol

Answer 2

provide strength and are hydrophobic so help prevent water loss by limiting the movement of phosoplipids and fatty acids

Question 3

2 types of proteins

Answer 3

carrier and channel

Question 4

Why is it called a fluid- mosaic model

Answer 4

phospholipids can move in membranes, and it’s made from different molecules

Question 5

hydrophobic

Answer 5

water hating

Question 6

hydrophillic

Answer 6

water loving

Question 7

glycoprotein

Answer 7

Protein in the membrane with a carbohydrate chain attached that act as mechanical support and cell receptors

Question 8

glycolipid

Answer 8

carbohydrate covalently bonded to a lipid which acts as a cell surface receptor for specific chemicals

Question 9

What do channel proteins allow through the membrane?

Answer 9

water soluble Ions

Question 10

What do carrier proteins allow through the membrane?

Answer 10

Larger molecules/ ions

Question 11

How do phospholipids arrange themselves in a membrane

Answer 11

In a bilayer

Question 12

Diffusion

Answer 12

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

Question 13

Extracellular

Answer 13

outside the cell

Question 14

What cells can move through the bilayer ?

Answer 14

small, uncharged, lipid soluble molecules

Question 15

Facilitated diffusion

Answer 15

Diffusion involving the presence of protein carrier and channel molecules to allow the passive movement of charged and larger molecules across plasma membranes

Question 16

Channel proteins

Answer 16

water filled hydrophilic channels across the membrane which only open to allow specific ions across.

Question 17

Carrier proteins

Answer 17

when a specific molecule eg glucose binds and conformational change occurs which releases the molecule to the other side of the membrane

Question 18

water potential

Answer 18

the tendency for water molecules to move (kilopascals)

Question 19

Osmosis

Answer 19

Passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a selectively permeable membrane

Question 20

Equilibrium

Answer 20

Osmosis stops when both sides of the membrane have equal water potential

Question 21

What sort of process is diffusion and osmosis

Answer 21

Passive

Question 22

hypotonic

Answer 22

When the water potential is higher, and the net movement of molecules enters the cell causing it to swell and burst

Question 23

isotonic

Answer 23

When the water potential is equal and the net movement of molecules neither enters nor exits the cell so there is no change.

Question 24

hypertonic

Answer 24

the water potential is lower so the net movement of molecules leaves the cell so the cell shrivels

Question 25

Active transport

Answer 25

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

Question 26

explain how an ion is transported into a cell by active transport

Answer 26

• The ion binds to a complimentary receptor in the carrier protein
• Inside the cell ATP binds to protein
• The ATP splits into ADP and a phosphate molecule
• This results in the carrier protein changing shape and opening to allow the ion to be released.
• The phosphate is released from the protein causing the protein to revert to it original shape

Question 27

Explain how co-transport occurs using absorption of sodium ions and glucose by cells lining the mammalian ileum as an example

Answer 27

Sodium ions actively transported out of epithelial cells by sodium potassium pump (carrier protein) into the blood
This maintains a higher concentration of sodium ions in the lumen of the illeum compared with the inside of the epithelial cells
Sodium ions diffuse into the epithelial cell through a co-transport protein (carrier protein)
The movement of sodium ions carries glucose/amino acids throught the same protein into the epithelial cell
Glucose/amino acids move into the blood by facilitated diffusion (through another carrier protein)

Question 28

Factors affecting the rate of diffusion

Answer 28

• concentration gradient
• particle charge/ size
• temperature
• surface area
• distance
• channels and carrier proteins

Question 29

What is the function of phospholipids in the phospholipid bilayer

Answer 29

• allow lipid-soluble substances to enter and leave the cell
  -prevent water-soluble substances entering and leaving the cell
  -make the membrane flexible and self-sealing

Question 30

Why do most molecules not freely diffuse across the cell surface membrane

Answer 30

-not soluble in lipids
-too large
-of the same charge as the protein channels
-polar

Question 31

What does the addition of solute do to pure water

Answer 31

lower the water potential

Question 32

How does water potential affect water movement

Answer 32

-The more solute that is added the lower its water potential
-Water will move by osmosis from a region of higher (less negative) water potential to one of lower water potential (more negative)

Question 33

What is the water potential of pure water

Answer 33

0