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