Topic 8.3: Photosynthesis

Question 1

Site of light dependent reactions

Answer 1

Intermembrane space of thylakoids

Question 2

Function of light dependent reactions

Answer 2

Convert light energy from the Sun into chemical energy (ATP + NADPH)

Question 3

Overall process of light dependent reactions

Answer 3

a) Excitation of Photosystems by light
b) Production of ATP via ETC
c) Reduction of NADP+ and the Photolysis of Water

Question 4

Excitation of Photosystems by light

Answer 4

a) Photosystem II absorbs light energy
b) Delocalized electrons within the pigments become excited
c) Excited e- are transferred to carrier molecules within the thylakoid membrane

Question 5

Production of ATP via an Electron Transport Chain

Answer 5

a) Excited electrons from Photosystem II are transferred to an ETC within the thylakoid membrane
b) As the e- are passed through the chain, they lose energy to translocate H+ ions into the thylakoid
c) This builds up of protons within the thylakoid creates an electrochemical gradient
d) H+ ions return to the stroma along the H+ gradient via ATP synthase
e) Photophosphorylation
f) The newly de-energized electrons from Photosystem II are taken up by Photosystem I

Question 6

Reduction of NADP+ and the Photolysis of Water

Answer 6

a) Excited e- from Photosystem I are transferred to reduce NADP+ into NADPH
b) e- lost from Photosystem I are replaced by de-energized electrons from Photosystem II
c) H2O is split by light energy into H+ ions (used in chemiosmosis) and O2 (released as a by-product)
d) e- lost from Photosystem II are replaced by electrons released from H2O via photolysis

Question 7

Types of photophosphorylation

Answer 7

a) Cyclic

b) Non-cyclic

Question 8

Cyclic phosphorylation (Steady supply of ATP)

Answer 8

a) Only chlorophyll in PS I are photoactivated
b) e- move through ETC before returning to their original location
c) ETC produces ATP
a) NADPH is not synthesized

Question 9

Non-cyclic phosphorylation (Synthesis of organic molecules)

Answer 9

a) Chlorophyll in PS I and II are photoactivated
b) Electrons from PS I reduce NADP to produce NADPH
c) Electrons from PS II move through ETC before replacing those from PS I
d) ETC produces ATP
e) Electrons lost from PS II are replaced by water (Photolysis)

Question 10

Site of light independent reactions

Answer 10

Stroma

Question 11

Function of light independent reactions

Answer 11

Use the chemical energy to synthesize organic compounds (Glucose)

Question 12

Overall process of light independent reactions

Answer 12

a) Carbon fixation
b) Reduction of GP
c) Regeneartion of RuBP

Question 13

Carbon fixation

Answer 13

a) Rubisco catalyzes the attachment of a CO2 of ribulose bisphosphate
b) Unstable 6C compound breaks down into two glycerate-3-phosphates

Question 14

Reduction of GP

Answer 14

a) GP is phosphorylated by ATP and reduced by NADPH

b) This converts each GP molecule into a triose phosphate

Question 15

Regeneration of RuBP

Answer 15

a) One molecule of the six of TP is used to produce half a sugar
b) Remaining TP molecules are used to regenerate stocks of RuBP
c) ATP is required for the regeneration of RuBP

Question 16

Aim of lollipop experiment

Answer 16

Elucidate the carbon compounds involved in the light independent reactions

Question 17

Process of lollipop experiment

Answer 17

a) Radioactive carbon-14 is added to a ‘lollipop’ apparatus containing green algae
b) Light is shone on the apparatus to induce photosynthesis
c) Algae is killed by running it into a solution of heated alcohol
d) Dead algal samples are analyzed using 2D chromatography to separate out different carbon compounds
e) Radioactive carbon compounds on the chromatograph were identified using autoradiography
f) By comparing different periods of light exposure, the order by which carbon compounds are generated was determined

Question 18

Function of chloroplast

Answer 18

Convert light energy into chemical energy (ATP / Organic compounds)

Question 19

Structure of chloroplast

Answer 19

a) Double membrane
b) Stroma
c) Thylakoids
d) Grana
e) Lamella
f) Starch granules

Question 20

Double membrane

Answer 20

Evidence for endosymbiosis

Question 21

Stroma

Answer 21

Has appropriate enzymes and a suitable pH for the Calvin cycle

Question 22

Thylakoids

Answer 22

a) Have ETC and ATP synthase for phosphorylation

b) Have a small internal volume to maximize H+ gradient

Question 23

Grana

Answer 23

Arranged into stacks to increase SA:Vol ratio

Question 24

Lamella

Answer 24

Connects and separates thylakoid stacks

Question 25

Similarities between Photosynthesis and Cell Respiration

Answer 25

a) ATP production

b) ETC / Chemiosmosis

Question 26

Differences between photosynthesis and cell respiration (

Answer 26

a) Water is broken down to oxygen to release electrons for ETC
a) Electrons from ETC are taken up by oxygen to form water
b) Electrons are taken up by electron carriers
b) Hydrogen carriers release electrons for ETC
c) Uses Calvin cycle to synthesize glucose
c) Uses Kelvin cycle to break down glucose