Biological membranes

Question 1

what is the role of a plasma membrane

Answer 1

partially permeable so controls what enters and leaves , allow recognition by other cells (immune system) and cell signalling

Question 2

what is the role of membranes within the cell

Answer 2

act as a barrier between organelle and cytoplasm, can form vesicles, site of chemical reactions, partially permeable so can control what enters and leaves organelle,

Question 3

draw the fluid mosaic model

Question 4

what is the role of phospholipids in the membrane

Answer 4

have hydrophilic heads which face outwards and hydrophobic tails which face inwards, centre of membrane is then hydrophobic so water soluble substances cannot pass through, fat soluble substances dissolve in bilayer so can pass directly through the membrane

Question 5

what is the role of cholesterol in the membrane

Answer 5

gives membrane stability, fit between phospholipids and at high temps bind to hydrophobic tails to pack them more closely together so membrane is less fluid and more rigid, also has hydrophobic regions so creates further barrier to polar substances

Question 6

what is the role of proteins in the membrane

Answer 6

control what enters and leaves the cell, some form channels which allow small, charged particles through, carrier proteins however transport larger molecules by active transport and facilitated diffusion

Question 7

what is the role of glycolipids and glycoproteins in the membrane

Answer 7

stabilise the membrane by forming hydrogen bonds with surrounding water molecules, act as receptors for messenger molecules in cell signalling, also antigens involved in self-recognition and the immune response

Question 8

how do solvents affect membrane solubility

Answer 8

solvents like ethanol dissolve lipids in the membrane so the membrane loses structure
increasing the conc of the solvent will also increase membrane permeability

Question 9

how do temperatures below 0oc affect membrane permeability

Answer 9

not a lot of energy so phospholipids cant move
packed closely and membrane is rigid
channel and carrier proteins denature, increasing permeability
ice crystals form and pierces membrane

Question 10

how do temperatures above 45oc affect membrane permeability

Answer 10

bilayer starts to melt, channel and carrier proteins denature and water inside cell expands putting pressure on the membrane

Question 11

define the term diffusion and what type of process is it

Answer 11

movement of particles from an area of high conc to an area of low conc. passive

Question 12

what factors affect the rate of diffusion

Answer 12

conc. gradient
thickness of exchange surfaces
the surface area
the temperature

Question 13

define the term osmosis

Answer 13

the movement of water molecules down the water potential gradient from an area of high water potential to an area of low water potential

Question 14

what water potential does pure water have

Answer 14

zero

Question 15

if two solutions have the same water potential what is the solution known as

Answer 15

isotonic

Question 16

if a cell is placed in a solution that has a higher water potential what is the solution known as and what will happen

Answer 16

hypotonic, water will move into the cell where there is a lower water potential which could cause the cell to burst

Question 17

if a cell is placed in a solution that has a lower water potential what is the solution called and what will happen

Answer 17

hypertonic, water will move out of the cell and the cell will shrink

Question 18

define facilitated diffusion

Answer 18

particles moving down a concentration gradient using carrier or channel proteins

Question 19

how do carrier proteins work

Answer 19

large molecule attaches to the carrier protein, the proteins then changes shape, this releases molecule on the other side of the membrane

Question 20

how do channel proteins work

Answer 20

form pores in the membrane for smaller ions and polar molecules

Question 21

what is active transport

Answer 21

uses energy to move molecules rom an area of low conc. to high conc. and involves carrier proteins

Question 22

what is endocytosis

Answer 22

when a cell surrounds a molecule with its plasma membrane which is too big to pass through via carrier proteins and the membrane then pinches off to form a vesicle inside the cell, uses ATP

Question 23

what is exocytosis

Answer 23

vesicles form containing substances that need to be transported out of the cell, vesicles pinch off from the golgi apparatus and move towards the plasma membrane, vesicles fuse with plasma mebrane and release their contents outside of the cell, uses ATP as energy source