11.2 light-dependent reaction

Question 1

Four stages of ldr

Answer 1

1. photoionisation
2. chemiosmosis
   3.production of atp and reduction NADP
3. photolysis

Question 2

photoionisation

Answer 2

chlorophyll molecule absorbs light energy

energy raises energy level of pair of electrons

electrons leave chlorophyll molecule

chlorphyll molecule becomes ionsied(oxidised)

electron carrier has been reduced

electrons are passed along number of electron carries in oxidation-reduction reactions- forming a transfer chain located in the membranes of the thylaoids

Question 3

Chemiosmotic theory

Answer 3

each thylakoid is in enclosed chamber where protons H+ are pumped from stroma using protein carries in thylakoid membranes(proton pumps)

energy comes from electrons when water molecules are split by light(photolysis)

photolysis of water also produces protons which increase conc inside thylakoid

creates and maintains conc gradient of protons across thylakoid membrane(high in thylakoid, low in stroma)

protons can only cross thylakoid membrane through ATP synthase channel proteins(rest of membrane is impermeable).

channels form small granule on membrane surface- stalked granules

As protons pass through ATP synthase channels they cause changes to structure of enzyme which catalyses ADP + Pi -> ATP

Question 4

photolysis of water equation

Answer 4

2H2O -> 4H+ + 4e- + O2

Question 5

need of photolysis of water explanation

Answer 5

when light hits chlorophyll, the loss of electrons is replaced by water molecules that are split using light energy

Question 6

proton products of photolysis

Answer 6

protons pass out of thylakoid space through ATP synthase channels

taken up by electron carrier NADP, so it becomes reduced

reduced NADP is main product of ldr and goes into lir with electrons, used as chemical energy

Question 7

oxygen product of photolysis

Answer 7

used in respiration

diffuses out of leaf as waste product

Question 8

adaptations of chloroplasts

Answer 8

1. thylakoid membrane has large SA for attachment of chlorophyll, electron carriers and enzymes for ldr
2. network of proteins in grana hold chlorophyll in very precise manner that allows max absorption of light
3. granal membranes have ATP synthase channels which catalyse prodycts of ATP and are selectively permeable which allows proton gradient
4. chloroplasts contain DNA and ribosomes so can quickly and easily manufacture proteins involved in ldr