Process of Photosynthesis

Photosynthesis Equation  Photosynthesis is the process of capturing light energy and converting it into chemical energy, (usually in the form of carbohydrates)  6 CO H 2 O + Light  C 6 H 12 O 6 + 6O 2

Photosynthesis is broken down into two reactions.  Light Dependent Reaction - energy from light makes the reaction happen  Light Independent Reaction (Calvin Cycle; Dark Reaction) Doesn’t need direct light energy, but it does need the high-energy products from the Light Rx. ATP and NADPH

Light Dependent Reactions- In the Chloroplast 1.Light energy is absorbed by _________ in the thylakoid membranes of the chloroplast (pigments are located in Photosystem I & II) pigments

2.In Photosystem II the electrons become ________________or “excited”. energized

3.The excited electrons are passed down a series of molecules called the ____________________ _________. Electron Transport Chain

4.To replace the electrons that are lost, some are stolen from water. This breaks the water molecule apart like this: 2H 2 O  4H + + O 2

5.As electrons move down the chain, their energy is used to make ______ (a high- energy molecule) ATP

6.The electrons now go to Photosystem I. Light energizes new electrons in PI and they combine with NADP+ to make ________ (another high-energy molecule). NADPH

LIGHT RX s.swf

The final products of the light reaction At the end of the light reaction we have made: 1.ATP 2.NADPH 3.O 2

Reactants used during the light reaction: 1.Water 2.Also used sunlight

Light independent reaction ( Calvin Cycle) A. Needs: CO 2, ATP, NADPH B. Where do they come from?  Light Reaction- ATP NADPH  Air-CO2 C. Where do they go?  Calvin Cycle  Location stroma  Enzymes are found in the stroma

Calvin cycle (dark reaction):  doesn’t need light - Uses the ATP and NADPH “charged” by the light reactions to link CO 2 together to build C 6 H 12 O 6 - Uses the ATP and NADPH “charged” by the light reactions to link CO 2 together to build C 6 H 12 O 6 Reactant: 6CO 2 Product: C 6 H 12 O 6

What happens to the glucose? 1.Move to the mitochondria to be converted into ATP through Cell respiration 2. Go through dehydration synthesis to build a big starch chain and be stored for future use

Chloroplast Photosynthesis: An Overview Light O2O2 Sugars CO 2 Light- Dependent Reactions Calvin Cycle NADPH ATP ADP + P NADP + H2OH2O

Factors affecting Photosynthesis:  Light Intensity: the rate of photosynthesis _________as light intensity_________, then levels off  CO 2 levels: the rate of photosynthesis _________ as CO 2 _________, then levels off increases increases increases increases

What causes the rate to level off in each case?  With more light, the plant is limited by the amount of CO 2 available.  Don’t forget that the wavelength of light matters!!!  With more CO 2, the plant is limited by the amount light energy available.

 Temperature: increasing the temperature, _________the rate of photosynthesis, then the rate peaks and ____________. increases decreases

Why does the rate decrease after a certain temperature?  The enzymes and other molecules controlling the reaction start to break down after that temperature.

Alternative Pathways  Some plants that live in ____, ____ environments have modified internal structures and use alternative carbon fixation pathways.  Better at preventing _________. hot dry water loss

Leaf structure

Stoma (stomata pl.)

 How does a plant stop water loss?  Close the stomata.  But what problem does that cause?  Run out of CO 2 and too much O 2 builds up.

C4 pathway  The C4 pathway uses a special ____-carbon compound to “fix” carbon into glucose.  This is more efficient when the level of CO 2 is low. four

Examples: corn, crab grass, sugar cane

CAM pathways  ________ stomata at night to store CO 2.  Close stomata in the day, which prevents water loss. Opens

Examples: pineapple, cacti

Exceptions to the Rules:  Autotrophic Bacteria:  Example: Cyanobacteria (“Blue” bacteria)

Exceptions to the Rules:  Autotrophic Protists:  Example: Algae and Euglena

Exceptions to the Rules:  Heterotrophic plants: some plants get food from other organisms  Mistletoe: makes food AND takes sap (high in sugar) from other trees

Exceptions to the Rules: Venus Flytrap: traps and digests insects as a food source

Photosynthesis Summary Light Reaction Calvin Cycle Location Reactants Products

Photosynthesis Summary Light Reaction Calvin Cycle LocationThylakoid Reactants Products

Photosynthesis Summary Light Reaction Calvin Cycle LocationThylakoidStroma Reactants Products

Photosynthesis Summary Light Reaction Calvin Cycle LocationThylakoidStroma Reactants Light, H 2 O Products

Photosynthesis Summary Light Reaction Calvin Cycle LocationThylakoidStroma Reactants Light, H 2 O CO 2, ATP, NADPH Products

Photosynthesis Summary Light Reaction Calvin Cycle LocationThylakoidStroma Reactants Light, H 2 O CO 2, ATP, NADPH Products ATP, NADPH, O 2

Photosynthesis Summary Light Reaction Calvin Cycle LocationThylakoidStroma Reactants Light, H 2 O CO 2, ATP, NADPH Products ATP, NADPH, O 2 Glucose

Chloroplast Photosynthesis: An Overview Light O2O2 Sugars CO 2 Light- Dependent Reactions Calvin Cycle NADPH ATP ADP + P NADP + H2OH2O

Photosynthesis includes of take place in takes place in uses to produce use Light- dependent reactions Calvin cycle Thylakoid membranes StromaNADPH ATP Energy from sunlight ATPNADPHO2 Chloroplasts High-energy sugars Concept Map