Light-independent reactionLight-independent reaction

To be able to explain that:To be able to explain that:

• Energy from the light-independent Energy from the light-independent reaction is used to fix carbon dioxide.reaction is used to fix carbon dioxide.

1.1. Write a balanced equation for photosynthesisWrite a balanced equation for photosynthesis

2.2. Give reasons why photosynthesis is important.Give reasons why photosynthesis is important.

3.3. In which cycle does photosynthesis feature?In which cycle does photosynthesis feature?

4.4. What is the waste product of photosynthesis?What is the waste product of photosynthesis?

5.5. What is the splitting of water called? What is the splitting of water called?

6.6. What is made during the light dependent reaction?What is made during the light dependent reaction?

6CO6CO22 + 6H + 6H22O O 6O 6O22 + C + C66HH1212OO66

Makes food, oxygenMakes food, oxygen

carboncarbon

oxygenoxygen

photolysisphotolysis

ATP, NADPH, oxygenATP, NADPH, oxygen

The Light-Independent Reactions

• The light-independent, or carbon-fixing The light-independent, or carbon-fixing reactions, of photosynthesis take place in the reactions, of photosynthesis take place in the stroma of the chloroplastsstroma of the chloroplasts

• COCO22 readily diffuses into the chloroplast where it readily diffuses into the chloroplast where it

is built up into sugars in another cyclic process is built up into sugars in another cyclic process called the Calvin cycltcalled the Calvin cyclt

GlossaryGlossary

• Ribulose Ribulose biphosphate (RuBP)biphosphate (RuBP)

• glycerate 3-glycerate 3-phosphate (GP)phosphate (GP)

• ribulose ribulose bisphosphate bisphosphate carboxylasecarboxylase

• 5 carbon sugar5 carbon sugar

• A 3 carbon A 3 carbon compound (an acid)compound (an acid)

• An enzyme also An enzyme also known as RuBISCOknown as RuBISCO

• The fixation of Carbon Dioxide is light The fixation of Carbon Dioxide is light independent.independent.

• Carbon Dioxide combines with RuBPCarbon Dioxide combines with RuBP

COCO22 RuBPRuBP

= 2 x glycerate 3 phosphate= 2 x glycerate 3 phosphate

•CO2 is covalently bonded to CO2 is covalently bonded to RuBP catalysed by the enzyme RuBP catalysed by the enzyme RuBISCORuBISCO

•The product is two molecules The product is two molecules of glycerate 3 phosphateof glycerate 3 phosphate

•This process is called fixationThis process is called fixation

• Energy and HEnergy and H++ ions are required to turn the ions are required to turn the Glycerate 3 phosphate into the 3 carbon Glycerate 3 phosphate into the 3 carbon sugar triose phosphatesugar triose phosphate

• Energy is provided by ATP and the HEnergy is provided by ATP and the H++ ion is ion is provided by the NADPH from the light provided by the NADPH from the light dependant reaction dependant reaction

COCO22 RuBPRuBP

= 2 x glycerate 3 phosphate= 2 x glycerate 3 phosphate

2ATP2ATP

2ADP + P2ADP + Pii

2NADPH2NADPH2NADP2NADP

2 x Triose Phosphate2 x Triose Phosphate

• Two triose phosphate molecules join together to form Two triose phosphate molecules join together to form one hexose sugar e.g. glucoseone hexose sugar e.g. glucose

• Glucose may be immediately respired, stored as starch or Glucose may be immediately respired, stored as starch or converted into other productsconverted into other products

• The bulk of triose phosphate is converted into more The bulk of triose phosphate is converted into more RuBP to enable the fixation of Carbon to continueRuBP to enable the fixation of Carbon to continue

• This uses the rest of the ATP produced in the light This uses the rest of the ATP produced in the light dependant reactiondependant reaction

COCO22 RuBPRuBP

= 2 x glycerate 3 phosphate= 2 x glycerate 3 phosphate

2ATP2ATP

2ADP + P2ADP + Pii

2NADPH2NADPH2NADP2NADP

2 x Triose Phosphate2 x Triose Phosphate

Hexose sugarHexose sugar

ATPATP

ADP + PADP + Pii

• Plants can’t ingest proteins Plants can’t ingest proteins and fatsand fats

• Calvin cycle is the starting Calvin cycle is the starting point for all the substances a point for all the substances a plant needsplant needs

Product Product synthesissynthesis

Hexose sugarHexose sugarEg Glucose, Eg Glucose,

FructoseFructose

Glycerol fromGlycerol fromTriose phosphateTriose phosphate

Fatty acids Fatty acids from glycerate from glycerate

3 phosphate3 phosphate

Amino acids Amino acids synthesised synthesised

from glycerate from glycerate 3 phosphate3 phosphate

Starch, Starch, Cellulose,Cellulose,

OtherOtherCarbohydrates Carbohydrates

LipidsLipids ProteinsProteins

• 5 out of every 6 5 out of every 6 molecules of triose molecules of triose phosphate are used to phosphate are used to regenerate RuBPregenerate RuBP

Calvin cycle in summary• COCO2 2 combines with combines with ribulose bisphosphate ribulose bisphosphate

• Glycerate phosphateGlycerate phosphate is made is made • Glycerate phosphateGlycerate phosphate is converted into triose is converted into triose

phosphatephosphate• Triose phosphate is converted into glucose Triose phosphate is converted into glucose • RuBP is regeneratedRuBP is regenerated

QuestionsQuestions1.1. Which compound is carboxylated? Which compound is carboxylated? 2.2. How is carbon dioxide fixed? How is carbon dioxide fixed? 3.3. What does GP stand for? What does GP stand for? 4.4. Which compound is regenerated? Which compound is regenerated? 5.5. What is ATP required for?What is ATP required for? 6.6. What is NADPH required for?What is NADPH required for? 7.7. What reaction converts GP into triose What reaction converts GP into triose

phosphate? phosphate? 8.8. What kind of sugar is RuBP? What kind of sugar is RuBP? 9.9. Which enzyme is important in the Which enzyme is important in the

Calvin Cycle? Calvin Cycle? 10.10. How many carbon atoms in GP? How many carbon atoms in GP? 11.11. Where does the Calvin Cycle happen? Where does the Calvin Cycle happen?

• RuBPRuBP

• Joined to RuBPJoined to RuBP• Glycerate-3-phosphateGlycerate-3-phosphate• RuBP RuBP

• Energy for reduction and Energy for reduction and regeneration of RuBPregeneration of RuBP

• Source of hydrogen for reductionSource of hydrogen for reduction

• reduction reduction

• pentose pentose

• RubiscoRubisco

• 33• stromastroma