PhotosynthesisPhotosynthesis

The Light and Dark ReactionsThe Light and Dark Reactions(Chapter 10)(Chapter 10)

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Early QuestionsEarly Questions QuestionQuestion: How can a plant grow from a seedling of a few grams to a : How can a plant grow from a seedling of a few grams to a

tree of a several tons?tree of a several tons? Jan van Helmont conducts an experiment to find out (1600’s)Jan van Helmont conducts an experiment to find out (1600’s)

Measures the mass of a seedMeasures the mass of a seed Measures the mass of a pot of soilMeasures the mass of a pot of soil Lets it grow for five years and measures the mass of the tree: Lets it grow for five years and measures the mass of the tree:

now at 75 kilogramsnow at 75 kilograms Soil did not change in massSoil did not change in mass He assumes that the change in mass is due to the water.He assumes that the change in mass is due to the water.

C.B. van Niel, StanfordC.B. van Niel, Stanford OO22 from H from H220 or C00 or C022??

Melvin CalvinMelvin Calvin

What is Photosynthesis?What is Photosynthesis? Definition of Definition of

PhotosynthesisPhotosynthesis In the green plants, the In the green plants, the

conversion of light conversion of light energy from the sun energy from the sun into chemical energy into chemical energy stored in the bonds stored in the bonds within carbohydrates-within carbohydrates-sugars and starches sugars and starches

In other words: Plants In other words: Plants use sunlight to make use sunlight to make sugarsugar

30 to 40 chloroplasts 30 to 40 chloroplasts per cellper cell

The Requirements of PhotosynthesisThe Requirements of Photosynthesis Carbon Dioxide + Water Carbon Dioxide + Water

Glucose + OxygenGlucose + Oxygen 6CO6CO22 + 6H + 6H22O + LightO + Light C C66HH1212OO66+ 6O+ 6O22

SunlightSunlight is also required is also required Autotrophs-use sunlight to make foodAutotrophs-use sunlight to make food Heterotrophs-obtain energy from Heterotrophs-obtain energy from

food they eatfood they eat PigmentsPigments are also required are also required

White light from the sun is actually a White light from the sun is actually a mixture of different color, or mixture of different color, or wavelengths of lightwavelengths of light

Chlorophyll is very good at absorbing Chlorophyll is very good at absorbing red and blue light (high and low ends red and blue light (high and low ends of the spectrum).of the spectrum).

Light SpectrumLight Spectrum

Other Requirements of PhotosynthesisOther Requirements of Photosynthesis Energy-Storing CompoundsEnergy-Storing Compounds are also neededare also needed

ATP (Adenosine triphosphate)ATP (Adenosine triphosphate) The most important energy-storing compoundThe most important energy-storing compound Used by every living cellUsed by every living cell Made of the following:Made of the following:

A nucleotide called A nucleotide called AdenineAdenine A sugar with 5 carbons in it’s ring called A sugar with 5 carbons in it’s ring called RiboseRibose Three phosphate groupsThree phosphate groups AMP + P = ADP + P = ATPAMP + P = ADP + P = ATP

Cellular uses of ATPCellular uses of ATP Muscle contractionMuscle contraction Protein synthesisProtein synthesis Active transportActive transport The second part of photosynthesisThe second part of photosynthesis

NADP + (nicotinamide adenine dinucleotide phosphate)NADP + (nicotinamide adenine dinucleotide phosphate) High energy electron carrier/acceptorHigh energy electron carrier/acceptor

ATPATP

The Light Reactions of Photosynthesis The Light Reactions of Photosynthesis (Stage 1 of 2) (Stage 1 of 2)

The production of NADPH and ATP require sunlightThe production of NADPH and ATP require sunlight The Light Reactions of Photosynthesis are the The Light Reactions of Photosynthesis are the

reactions that involve capturing the light energy and reactions that involve capturing the light energy and creating “energy storing compounds”.creating “energy storing compounds”.

NADPH and ATP are not very stable and thus, don’t NADPH and ATP are not very stable and thus, don’t hold the energy very long hold the energy very long

Mechanisms of the Light ReactionsMechanisms of the Light Reactions:: Take place in the photosynthetic membranes that Take place in the photosynthetic membranes that

contain chlorophyllcontain chlorophyll These reactions can be divided into four main These reactions can be divided into four main

parts:parts:

Light Reactions of Photosynthesis Light Reactions of Photosynthesis (Stage 1 of 2)(Stage 1 of 2)

Light AbsorptionLight Absorption Clusters of pigment molecules or Photosystems capture the light Clusters of pigment molecules or Photosystems capture the light

energy of the sun.energy of the sun. There are two There are two photosystemsphotosystems: Photosystem I and Photosystem II: Photosystem I and Photosystem II

Each photosystem contains hundreds of chlorophyll molecules and Each photosystem contains hundreds of chlorophyll molecules and accessory pigmentsaccessory pigments

The accessory pigments are there to absorb the wavelengths in The accessory pigments are there to absorb the wavelengths in the spectrum that chlorophyll is not good at absorbing, thus, the spectrum that chlorophyll is not good at absorbing, thus, making it more efficient at capturing light energy.making it more efficient at capturing light energy.

Energy from the sun excites molecules in the photosystems Energy from the sun excites molecules in the photosystems enough that an electron “e-“ is torn away from its molecule, thus enough that an electron “e-“ is torn away from its molecule, thus making it very energy rich.making it very energy rich.

This electron is then passed along to the other pigment molecule This electron is then passed along to the other pigment molecule until it reaches a special chlorophyll molecule that can actually until it reaches a special chlorophyll molecule that can actually process that energy.process that energy.

Light Reactions of Photosynthesis Light Reactions of Photosynthesis (Stage 1 of 2)(Stage 1 of 2)

Electron TransportElectron Transport The special molecule passes that electron off to special The special molecule passes that electron off to special

electron carriers in the photosynthetic membrane, called electron carriers in the photosynthetic membrane, called electron transport and the actual electron carriers, are the electron transport and the actual electron carriers, are the electron transport chain.electron transport chain.

At the end of this chain, high energy electrons are passed to At the end of this chain, high energy electrons are passed to NADP+, where the plus signifies an atom without an NADP+, where the plus signifies an atom without an electron, thus, an atom very eager to pick up a new electron, thus, an atom very eager to pick up a new electron.electron.

The high energy electron bonds to the NADP+ to form The high energy electron bonds to the NADP+ to form NADPH NADPH

Light Reactions of Photosynthesis Light Reactions of Photosynthesis (Stage 1 of 2)(Stage 1 of 2)

Oxygen ProductionOxygen Production Light continues to strip electrons away from the Light continues to strip electrons away from the

chlorophyllchlorophyll These electrons are replaced by the breaking apart These electrons are replaced by the breaking apart

of 2 molecules of Hof 2 molecules of H22OO 4 electrons are taken away from the 2 molecules of 4 electrons are taken away from the 2 molecules of

water leaving you with 4 H+ ions and Owater leaving you with 4 H+ ions and O22 or or

oxygen gas oxygen gas

Light Reactions of Photosynthesis Light Reactions of Photosynthesis (Stage 1 of 2)(Stage 1 of 2)

ATP FormationATP Formation All the remaining H+ ions start to pool on the All the remaining H+ ions start to pool on the

inside of the photosynthetic membrane.inside of the photosynthetic membrane. This pooling causes a distinct difference in charge This pooling causes a distinct difference in charge

between the inside and outside of the membrane.between the inside and outside of the membrane. This difference in charge creates enough energy to This difference in charge creates enough energy to

help ATP synthetase (the enzyme that makes ATP help ATP synthetase (the enzyme that makes ATP from ADP and P) bond an extra phosphate to ADP from ADP and P) bond an extra phosphate to ADP in order to form ATP.in order to form ATP.

Summary of The Light ReactionsSummary of The Light Reactions Use: Use:

Water, Water, ADP ADP NADP+ NADP+

ProduceProduce OO22 ATP ATP NADPHNADPH

The Dark Reactions of Photosynthesis: The Dark Reactions of Photosynthesis: The Calvin Cycle or Light Independent The Calvin Cycle or Light Independent

ReactionsReactions (Stage 2 of 2) (Stage 2 of 2) The reactions of photosynthesis that do not The reactions of photosynthesis that do not requirerequire

sunlight but they do sunlight but they do take placetake place in light. in light. This stage deals with the use of NADPH and ATP in This stage deals with the use of NADPH and ATP in

the formation of glucose.the formation of glucose. Glucose is far more stable than NADPH and ATP.Glucose is far more stable than NADPH and ATP. Glucose (a single molecule) can hold approximately Glucose (a single molecule) can hold approximately

100 times more energy than a phosphate group in 100 times more energy than a phosphate group in ATP does.ATP does.

The Dark Reactions of Photosynthesis The Dark Reactions of Photosynthesis (Stage 2 of 2)(Stage 2 of 2)

Mechanisms of the Dark ReactionsMechanisms of the Dark Reactions (also known as the Calvin Cycle): (also known as the Calvin Cycle): COCO22, or carbon dioxide is used in the Dark Reactions to form , or carbon dioxide is used in the Dark Reactions to form

complex organic moleculescomplex organic molecules 3 Reactions take place3 Reactions take place

1st Reaction1st Reaction: A five carbon sugar C5 combines with CO2 to : A five carbon sugar C5 combines with CO2 to form two 3-Carbon sugars (2C3)form two 3-Carbon sugars (2C3)

2nd and 3rd Reactions:2nd and 3rd Reactions: The energy stored in ATP and NADPH The energy stored in ATP and NADPH are used to convert the 3-carbon sugars into what is called are used to convert the 3-carbon sugars into what is called PGAL or phosoglyceraldehyde. This is the building block for PGAL or phosoglyceraldehyde. This is the building block for glucoseglucose

Other intermediate compounds formed during the Calvin Cycle are Other intermediate compounds formed during the Calvin Cycle are used for:used for: Form sugars other than glucoseForm sugars other than glucose Used to form amino acidsUsed to form amino acids Some converted to lipidsSome converted to lipids

Glycolysis, Respiration Glycolysis, Respiration and Fermentationand Fermentation

GlycolysisGlycolysis

Breaking Down GlucoseBreaking Down Glucose Glucose is a 6 carbon sugar (think hexagon!)Glucose is a 6 carbon sugar (think hexagon!) If glucose completely breaks down in the presence If glucose completely breaks down in the presence

of oxygenof oxygen CO CO22 and H and H22O are produced:O are produced: CC66HH1212OO66 + 6O + 6O22 6CO 6CO22 + 6H + 6H22OO

This reaction gives off 3811 calories per gram of This reaction gives off 3811 calories per gram of glucose (3.8 Kcal)glucose (3.8 Kcal)

Glycolysis takes place in the cytoplasm of the cellGlycolysis takes place in the cytoplasm of the cell

Mechanics of Glycolysis:Mechanics of Glycolysis:

Glucose undergoes chemical reactions Glucose undergoes chemical reactions Split into Split into two 3-carbon PGAL molecules (2 ATP used in the two 3-carbon PGAL molecules (2 ATP used in the process)process)

2 PGAL molecules undergo chemical reactions 2 PGAL molecules undergo chemical reactions transform them into 2 molecule of pyruvic acid, a 3 transform them into 2 molecule of pyruvic acid, a 3 carbon compoundcarbon compound The energy is used to makeThe energy is used to make

4 molecules of ADP4 molecules of ADP 2 molecules of NADH (Similar to NADPH-electron storage)2 molecules of NADH (Similar to NADPH-electron storage)

There are 4 ATP synthesized overall, but two are There are 4 ATP synthesized overall, but two are used initially used initially NET GAIN of 2 ATPNET GAIN of 2 ATP

Respiration Respiration

The breaking down of food molecules into energy The breaking down of food molecules into energy Only takes place if oxygen is available (thus called an Only takes place if oxygen is available (thus called an

aerobic process)aerobic process) Takes place in the mitochondria of cellsTakes place in the mitochondria of cells

1st reactions take place inside the enclosed inner 1st reactions take place inside the enclosed inner membranemembrane

2nd reactions take place in the actual membrane2nd reactions take place in the actual membrane Utilizes the pyruvic acid generated in Glycolysis in Utilizes the pyruvic acid generated in Glycolysis in

order to make 34 additional ATPorder to make 34 additional ATP Consists of 2 sets of reactions:Consists of 2 sets of reactions:

The Krebs CycleThe Krebs Cycle (a.k.a.- the citric acid (a.k.a.- the citric acid cycle)cycle)

There is no definitive end There is no definitive end These processes are These processes are cyclicalcyclical

Mechanics of Krebs Cycle:Mechanics of Krebs Cycle: Pyruvic acid is broken down into COPyruvic acid is broken down into CO22 and a 2-carbon and a 2-carbon

acetyl group (briefly bound to coenzyme A)acetyl group (briefly bound to coenzyme A) Acetyl-coenzyme A complex passes the 2 carbons of the Acetyl-coenzyme A complex passes the 2 carbons of the

acetyl group in to the Krebs cycle where they join w/a 4-acetyl group in to the Krebs cycle where they join w/a 4-carbon compound to produce citric acid, a 6-carbon carbon compound to produce citric acid, a 6-carbon compoundcompound

9 reactions and 9 intermediates are found in the Krebs 9 reactions and 9 intermediates are found in the Krebs cyclecycle

COCO22 released at 2 places (the carbon comes from glucose) released at 2 places (the carbon comes from glucose) High energy electrons are accepted at 4 placesHigh energy electrons are accepted at 4 places

The Krebs CycleThe Krebs Cycle (a.k.a.- the citric acid (a.k.a.- the citric acid cycle)cycle)

Summary of Events:Summary of Events: 2 carbon atoms added (from the breakdown of 2 carbon atoms added (from the breakdown of

pyruvic acid)pyruvic acid) 2 carbon atoms removed (in two molecules of CO22 carbon atoms removed (in two molecules of CO2 3 molecule of NAD+ converted to NADH3 molecule of NAD+ converted to NADH 1 molecule of FAD converted to FADH21 molecule of FAD converted to FADH2 1 molecule of GDP converted to GTP1 molecule of GDP converted to GTP

Electron transport in the mitochondriaElectron transport in the mitochondria

NADH and FADH2 are passed through NADH and FADH2 are passed through transport enzymes (inner membrane)transport enzymes (inner membrane)

End of the chain:End of the chain: Enzyme combines high energy electrons, hydrogen Enzyme combines high energy electrons, hydrogen

ions (H+) and oxygen to form Hions (H+) and oxygen to form H22O, or waterO, or water Oxygen is the final electron acceptor in this Oxygen is the final electron acceptor in this

processprocess

ATP formationATP formation

Similar to chloroplastSimilar to chloroplast Difference in charge generates the combining of ADP and P Difference in charge generates the combining of ADP and P

into ADPinto ADP Energy Totals for Glucose BreakdownEnergy Totals for Glucose Breakdown

ATP FormationATP Formation 6 ATP formed during Glycolysis6 ATP formed during Glycolysis 30 ATP formed during Respiration30 ATP formed during Respiration

36 ATP represents 37% of total energy from glucose36 ATP represents 37% of total energy from glucose More efficient than an automobileMore efficient than an automobile

Obtaining Energy from foodObtaining Energy from food

Lipids and Proteins can also be used as fuel Lipids and Proteins can also be used as fuel sourcessources

They can be broken down into molecules that They can be broken down into molecules that enter Glycolysis or respiration at different enter Glycolysis or respiration at different pointspoints

Not as efficient at producing energy.Not as efficient at producing energy. Energy in BalanceEnergy in Balance

Photosynthesis makes that glucose, Glycolysis and Photosynthesis makes that glucose, Glycolysis and Respiration break it downRespiration break it down

FermentationFermentation Production of ATP in the absence of oxygen (anaerobic)Production of ATP in the absence of oxygen (anaerobic) Needs to convert NADH back to NAD+Needs to convert NADH back to NAD+ Two types of FermentationTwo types of Fermentation

Lactic Acid FermentationLactic Acid Fermentation Pyruvic acid accumulates Pyruvic acid accumulates Glycolysis turns this into lactic acid Glycolysis turns this into lactic acid Regenerates NAD+ so Glycolysis can continueRegenerates NAD+ so Glycolysis can continue

Pyruvic acid + NADH Pyruvic acid + NADH lactic acid + NAD+ lactic acid + NAD+ This is seen in activities that fatigue the muscles faster than oxygen can get This is seen in activities that fatigue the muscles faster than oxygen can get

to them to in order to produce all the ATP necessaryto them to in order to produce all the ATP necessary Alcoholic FermentationAlcoholic Fermentation

Pyruvic acid (3-carbon compound) is broken down into a 2-carbon Pyruvic acid (3-carbon compound) is broken down into a 2-carbon compound and COcompound and CO22

Alcohol is a byproductAlcohol is a byproduct Pyruvic acid + NADH Pyruvic acid + NADH alcohol + CO alcohol + CO22 + NAD+ + NAD+

Glycolysis 1Glycolysis 1

Glycolysis 2Glycolysis 2

Carotene

Xanthophyll

Chlorophyll a

Chlorophyll b