Match structure and function
Double membrane chloroplast envelope
Thylakoids have large surface area
ATP synthase molecules in thylakoid membrane
Stroma contains enzymes, sugars and organic acids
As much light as possible can be absorbed
Needed for the light-independent reaction to take place
Reactants kept close to reaction sites
Produce ATP in the light-dependent reaction
Learning Objectives
• Outline how the products of the LDS are used in the LIS
• Explain the role of carbon dioxide in the LIS• State what TP is used to make• State that TP is recycled to make RuBP
Photosynthesis
Photophosphorylation:
‘The making of ATP energy using the energy from light’
May involve cyclic or non-cyclic phosphorylation
Cyclic – PSI – intergranal lamellaeNon – cyclic PSI & PSII – granal lamellae
Non-cyclic
• Light excites electrons of Mg in PSII & PSI• Electrons passed along electron carriers
• Energy released drives H+ proton pumps• H+ accumulates in thylakoid space – gradient forms• H+ flow down gradient through ATP synthase
• ATP used in light independent stage• Photolysis of H20 and generation of NADPH
Cyclic
• Only uses PSI• Excited electrons are passed back to Mg in PSI
• No photolysis or generation of NADPH• Small amounts of ATP made
Used in light independent or to open stomata
1.3.4 Light independent stage
• Occurs in the stroma – also called the Calvin Cycle
• Uses ATP made in the light dependent stage
• CO2 becomes fixed into complex organic compounds
• C & O used for structure and energy store
Three phases
1. CarboxylationCarbon dioxide fixation with ribulose bisphosphate (RuBP)
2. ReductionReduction of glycerate 3-phosphate (GP) to glyceraldehyde 3-phosphate (GALP)
3. RegenerationRe-formation of the CO2
acceptor molecules
Rubisco
Regeneration of RuBP
TP
RUBISCO
1.3.4 Light Independent
• CO2 diffuses into the stroma• Combines with a 5C acceptor RuBP – uses enzyme
• RuBP has become carboxylated – carboxyl group• Produces 2 x 3C molecule – glycerate 3-phosphate
• GP is reduced & phosphorylated to TP• TP recycled by phosphorylation to RuBP
1.3.4 Light Independent stage
Products of the Calvin Cycle
•GP used to make amino acids & fatty acids•TP combines to form 6C glucose•Some glucose isomerised to Fructose•Fructose & glucose combine = disaccharide•Some sugars polymerised – cellulose•TP converted to glycerol – makes lipids
The light-independent reaction
Triose phosphates (TPs) are used to form glucose.
1C (x6) Hexose (6C)3C (TP)+ 6C3C (TP)
5C Regenerate RuBP
•`6 cycles are required to form 1 molecule of glucose
• RuBP is then joined with carbon dioxide to re-start the cycle.
ATP
1C (6 cycles) Hexose
5C RuBP) + 1C (CO2) 6C 2 x 3C (TP) 6C
5C Regenerate RuBP
The Maths• 2 molecules of GALP are made each turn• 5 out of 6 molecules of GALP are used to
regenerate RuBP• 2 molecules of GALP are needed to make a
hexose sugar• How many turns are needed to make 1
molecule of hexose sugar?• How many molecules of ATP and reduced
NADP are needed?
Products of the Calvin cycleProducts of the light-independent reaction that pass back into the light-dependent reaction:
Products of the light-independent reaction that are used in other processes:
NADP
ADP
triose phosphate – used to build complex carbohydrates, amino acids and lipids.
inorganic phosphate
How much can you remember?
Summary of photosynthesis
light- dependent reactions
light- independent reactions
light
carbohydrates, other complex molecules
Photosynthesis: true or false?
Outline how light energy is converted to chemical energy (ATP and reduced NADP) in the light-dependent stage (reference should be made to cyclic and non-cyclic photophosphorylation) Explain the role of water in the light-dependent stage. Outline how the products of the light-dependent stage are used in the light-independent stage (Calvin cycle) to produce triose phosphate (TP) (reference should be made to ribulose bisphosphate (RuBP), ribulose bisphosphate carboxylase (rubisco) and glycerate 3-phosphate (GP)). Explain the role of carbon dioxide in the light-independent stage (Calvin cycle).
• The carbon fixation stage occurs in the stroma and results in the production of glucose.
• It is a result of an enzyme controlled sequence of reactions requiring ATP and hydrogens (from reduced NADP) from the light stage, and carbon dioxide (“fixed” from the air).
• It involves the reduction of carbon dioxide, that is the addition of hydrogen (from reduced NADP), to form carbohydrate.
• CO2 is accepted by the 5C compound ribulose 1,5-biphosphate (RuBP) to form an unstable 6C compound.
• The 6C compound formed immediately splits into two molecules of a 3C compound called glycerate 3-phosphate (GP).
• ATP and reduced NADP is used to convert the two GP molecules into two molecules of triose phosphate (TP), a 3 carbon compound.
• TP’s are used in the formation of carbohydrate (glucose) and to regenerate RuBP
• ATP is required to regenerate RuBP
Carbon Fixation – Light Independent Stage (Calvin Cycle)
Examination Questions – Model Answers
ATPReduced NADP / NADPH / NADPH2 / NADPH + H+
Regenerates / produces, ribulose bisphosphate / RuBPSo cycle can continue / for (further) CO2 fixation / to combine with CO2
Formation of , sugar / glucose / hexose / sucrose / starch / celluloseFormation of fat / triglyceride / lipid fatty acids / glycerol / amino acids / protein / nucleic acids / nucleotidesMost triose phosphate used to produce RuBP and the rest for production of hexose
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Oxygen used and CO2 produced / excretedLight energy requiredUses RubiscoInvolves calvin cycle
Reduces rate of photosynthesis / increases rate of photorespirationLess Rubisco available for CO2 / more oxygen competing with CO2 for RubiscoMore O2 binding to RubiscoO2 outcompetes CO2 for RubiscoLess CO2 fixation / for Calvin cycleCO2 given offLess GP / TP, producedLess RuBP, regenerated
O2, not a substrate for / cannot bind to / will not compete for.PEP carboxylasePEP carboxylase, is only specific to CO2
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(i) A(ii)D(iii)A
Flattened membrane bound sacsTermed thylakoidsArranged as stacks / granaContain pigment / chlorophyll arranged in photosystems / quantosomes, in membrane
(62.4 / 162) x 100 Answer 38.5 %
Different lighting has little effectVariation in percentage less than 3Probably not significantYield is less for low pressure sodium lampsThe best yield is metal halide
Crops can be grown out of season /all year roundPlants photosynthesize 24 hours a dayLess physical damage from weather /animalsPest control easierOther factors can be controlled – e.g. Temperature, CO2, water supply, humidity