3.2.2 transport across the membrane

Question 1

describe the structure of the phospholipid bilayer

Answer 1

phospholipd: allow lipid soluble substances to pass through
proteins: act as receptors and channels
cholesterol: reduces fluidity
glycolipids and glycoproteins: act as recognition sites

Question 2

why do plasma membranes have a fluid mosaic structure

Answer 2

fluid due to the phospholipids constantly moving
mosaic as the proteins are scattered through the membranes

Question 3

what is the effect of cholesterol on the cell surface membrane

Answer 3

they bind to the hydrophobic fatty acid tails causing them to pack together, restricting movement of other molecules, making the membrane more rigid

Question 4

3 functions of glycolipids

Answer 4

1. recognition
2. stability
3. help cells attach to eachother

Question 5

3 functions of glycoproteins

Answer 5

1. recognition
2. help cells attach to each other
3. help cells recognise each other

Question 6

what is the function of the membrane within the cell

Answer 6

the membrane divides the cells making cell function more efficient. it is partially permeable to control movement inside and outside of the cells.
site of chemical reactions e.g. respiration

Question 7

definition of diffusion

Answer 7

movement of molecules from an area of high concentration to an area of low concentration down a concentration gradient (passive process)

Question 8

definition of osmosis

Answer 8

movement of water molecules from an are of high water potential to an area of low water potential across a partially permeable membrane, down a concentration gradient (passive process)

Question 9

definition of active transport

Answer 9

movement of molecules from an area of low concentration to an area of high concentration against a concentration gradient using energy and carrier proteins (active process)

Question 10

5 factors which affect the rate of diffusion

Answer 10

1. concentration gradient
2. diffusion distance
3. surface area
4. temperature
5. size of molecules

Question 11

what is the difference between simple and facilitated diffusion

Answer 11

simple: diffusion straight across the membrane with out proteins
facilitated: diffusion across the membrane using channel and carrier proteins

Question 12

how does temp effect rate of diffusion

Answer 12

increasing temp increases rate of diffusion
molecules have more kinetic energy so will move faster

Question 13

describe the process of active transport

Answer 13

a molecule attaches to a carrier protein
the carrier protein changes shape
molecule moves across the membrane against the conc gradient
movement happens due to the hydrolysis of ATP to ADP + Pi

Question 14

3 factors which affect the rate of osmosis

Answer 14

1. water potential gradient
2. diffusion distance
3. surface area

Question 15

describe water potential

Answer 15

how pure a solution is in regards to water. water has the highest potential of 0, the more solute the lower the number

Question 16

what happens when a cell is hypertonic

Answer 16

1. low water potential
   2.net movement of water out
   3.causes cell the shrivel up and causes a plant cell to be plasmolysed

Question 17

what happens when a cell is isotonic

Answer 17

1. equal water potential
2. no net movement of water
3. no change to cells

Question 18

what happens when a cell is hypotonic

Answer 18

1. high water potential
2. net movement of water in
3. causes cell to burst (cytolysis) and plant cell to become turgid

Question 19

describe co transport of glucose

Answer 19

1. Na+ moves out epithelial cel via active transport and K+ moves using a Na/K pump
   2.this forms a low concentration gradient of Na+ ions inside the epithelial cells
2. Na+ moves into the epithelial cell from the top via facilitated diffusion via a co transporter, glucose also moves in but via active transport
3. glucose moves out the epithelial cell via facilitated diffusion into the capillary