4: Transport across cell membranes

Question 1

Parts of the cell surface membrane

Answer 1

• phospholipids
• proteins
• cholesterol
• glycolipids
• glycoproteins

Question 2

Phospholipids

Answer 2

form a bilayer
- hydrophilic heads point outwards of the membrane, hydrophobic tails point inwards to the centre of cell membrane
- it ALLOWS LIPID SOLUBLE substances to enter and leave
- PREVENTS WATER SOLUBLE substances from enter or leave
- flexible and self sealing

Question 3

Proteins

Answer 3

• some are embedded in the surface of phospholipid bilayer, never through it. offer support or cell receptors for hormones
• some go through the bilayer: CHANNEL PROTEINS - water filled tubes allowed water soluble ions. and CARRIER PROTEINS: bind to ions or molecules and change the shape so can move across membrane

Question 4

Cholesterol

Answer 4

• occur within the bilayer
• they add strength and are very hydrophobic so prevent loss of water
• pull together the fatty acids tails to limit movement

Question 5

Glycolipids

Answer 5

carbohydrate covalently bonded with a lipid. it extends from bilayer into the watery outside where it acts as a receptor.

Question 6

Glycoproteins

Answer 6

carbohydrate chains attach to extrinsic proteins on the outer surface of membrane

Question 7

Fluid mosaic model

Answer 7

• fluid; membrane is flexible and changing shape bc the phospholipid molecules can move relative to one another
• mosaic; the proteins embedded are all diff shapes, sizes and patterns

Question 8

Simple diffusion

Answer 8

net movement of molecules from an area of high concentration to an area of low, until equilibrium is reached (energy needed is only kinetic)
- to diffuse across membrane they need to be lipid soluble and small

Question 9

Facilitated diffusion

Answer 9

proteins are used as transport molecules (carrier proteins and protein channels), movement of ion and polar molecules.

Question 10

Osmosis

Answer 10

movement of water from an area of high water potential to an area of low water potential across a partially permeable membrane (the more solutes dissolved in water ie high cooncentration the more negative the water potential is)

Question 11

definitions if an isotonic, hypertonic and hypotonic solution

Answer 11

• isontonic; the water potential in the cell is the same as the solution the cells in
• hypertonic; the water potential in solution is more negative than the cell (cell shrivels up)
• hypotonic; the water potential is more negative in the cell than the solution (cell can burst)

Question 12

Active transport

Answer 12

movement of molecules and ions from an area of low concentration to an area of high using ATP and carrier proteins. - - carrier protein acts as a pump, certain molecules bind to it (complementary shape). the atp binds to the protein and is hydrolysed into adp + Pi which causes the protein to change shape. the Pi is then released after the molecule which causes the protein to change back shape
- SODIUM POTASSIUM PUMP,sodium removed out from cell, potassium in, creates nerve impluses

Question 13

what lines the ileum

Answer 13

epithelial cells that have microvilli and carrier proteins and protein channels

Question 14

The role of diffusion in absorption

Answer 14

greater conc of glucose and amino acids within the ileum than in blood, so diffuses into blood down a conc grad. bloods continously circulated so theres always glucose being used by cells in respiration so the conc grad is maintained

Question 15

Role of active transport in absorption

Answer 15

• so all the glucose and amino acids are dissolved into the blood
• through CO-TRANSPORT, sodium ions attach the glucose/amino acid so they can enter into the blood with the sodium potassium pump through active transport

Question 16

Co transport of glucose and sodium ions in the ileum

Answer 16

1. sodium ions actively transported out the epithelial cells into the blood (atp attaches, the hydrolyses etc)
2. this reduces conc of sodium in epithelial cell
3. so diff sodium ions can diffuse down a conc grad from the lumen to the epithelial cell, this is with co-transport of either glucose or amino acids (against their conc grad)
4. glucose then moves into blood down conc grad by facilitated diffusion