5.1 Photosynthesis - Light Dependent Reaction

Question 1

what are photosystems?

Answer 1

functional units for photosynthesis, defined by a particular pigment, whose work is the absorption and transfer of light energy which implies the transfer of electrons

Question 2

describe redox in terms of electrons

Answer 2

oxidation = loss of electrons, reduction = gain of electrons

Question 3

describe redox in terms of hydrogen

Answer 3

oxidation = loss of hydrogen, reduction = gain of hydrogen

Question 4

describe redox in terms of oxygen

Answer 4

oxidation = gain of oxygen, reduction = loss of oxygen

Question 5

describe redox in terms of energy

Answer 5

oxidation = energy given out, reduction = energy taken in

Question 6

where does the light dependent reaction occur?

Answer 6

in the thykaloid membranes of a granum in a chloroplast

Question 7

what are the products of the light dependent reaction?

Answer 7

reduced NADP (NADPH,) ATP and oxygen

Question 8

name the 6 main processes involved in the light dependent reaction

Answer 8

1) photoionisation
2) photolysis
3) electron transport chain
4) reduction of NADP to NADPH
5) proton pumps
6) chemiosmosis and synthesis of ATP (photophosphorylation)

Question 9

describe the process of photoionisation

Answer 9

chlorophyll molecules absorb light energy, which excites electrons to a state where they are lost from the molecule altogether.
the chlorophyll molecule that loses e- is oxidised and the electron carrier which gains e- is reduced.

Question 10

describe the process of photolysis and state what each of the products is used for

Answer 10

light energy splits water molecules into hydrogen, oxygen and electrons.
the electrons produced replace those lost through the transport chain.
the protons produced are used to reduce NADP into NADPH.
the oxygen produced is either used in respiration or diffuses out of the plant as a waste product

Question 11

describe the process of the electron transport chain

Answer 11

electron carrier proteins receive electrons from photolysis of chlorophyll molecules.
the electrons are passes down the transfer chain in a series of redox reactions.
energy PSII > C > PSI > FD, so electrons lose energy at each step.
this energy is used to combine ADP to Pi to form ATP during photophosphorylation

Question 12

describe the process of the reduction of NADP to NADPH

Answer 12

the NADP co-enzyme is reduced to NADPH as it accepts an electron from the transfer chain and a proton from the stroma produced during photolysis

Question 13

describe the process of proton pumps

Answer 13

protons are pumped from the stroma into the thylakoid lumen using a proton pump.
this is an active process and the energy to do so comes from the splitting of water molecules during photolysis

Question 14

how is the concentration gradient created and maintained for chemiosmosis?

Answer 14

H+ pumped from the stroma and into the thylakoid membrane.
Photolysis also produces H+ which further increases the concentration

Question 15

define chemiosmosis

Answer 15

the movement of ions (e.g. H+) across a semipermeable membrane, down their electrochemical gradient.

Question 16

describe the process of chemiosmosis and synthesis of ATP (phosphorylation)

Answer 16

concentration gradient created by proton pumps and photolysis product
the rest of the thylakoid membrane is impermeable so the H+ ions pass through ATP synthase channels and cause change to the structure of the enzyme
this catalyses the reaction of ADP and an inorganic phosphate, Pi to form ATP (photosphorylation)

Question 17

give the word and symbol equations for photolysis

Answer 17

water –> hydrogen + electrons + oxygen
2H₂O –> 4H+ + 4e- + O₂

Question 18

give the equation for photophosphorylation

Answer 18

ADP + Pᵢ –> ATP

Question 19

give the equation for the production of NADPH

Answer 19

2NADP+ + 4e- + 4H+ 2 NADPH + 2 H+

Question 20

how are chloroplasts adapted to the light dependent reaction? (4 points)

Answer 20

1) thylakoid membranes provide large surface area for the attachment of chlorophyll, electron carriers and necessary enzymes
2) network of proteins in grana hold chlorophyll in a very precise manner to allow for maximum absorption of sunlight
3) granal membranes have ATP synthase channels to catalyse the production of ATP. they are also selectively permeable to allow the establishment of a concentration gradient
4) prescence of DNA and ribosomes in order to quickly manufacture the necessary proteins involved in the LDR