Ch. 10 part 1Ch. 10 part 1

The light reactionThe light reaction

I. Autotrophs- I. Autotrophs- Organisms that make their own food (convert light Organisms that make their own food (convert light energy to chemical energy)energy to chemical energy)

A. Plants require only A. Plants require only CO2CO2, H2O and minerals., H2O and minerals.

B. Known also as B. Known also as PhotoautotrophPhotoautotroph..

1. Photoautotroph- 1. Photoautotroph- Convert light energyConvert light energy

2. Chemoautotroph-2. Chemoautotroph-Obtain energy from inorganic substancesObtain energy from inorganic substances

3. Heterotrophs- 3. Heterotrophs- must eat other organisms to obtain energymust eat other organisms to obtain energy

II. ChloroplastsII. Chloroplasts

A. Chlorophyll – A. Chlorophyll – A green pigment found in photosynthetic A green pigment found in photosynthetic organisms, that captures lightorganisms, that captures light..

B. Found in B. Found in chloroplasts and photosynthetic bacteriachloroplasts and photosynthetic bacteria

C. Pores in leaf were gases pass through are called C. Pores in leaf were gases pass through are called stomatastomata..

D. Intermembrane space- separation between the two D. Intermembrane space- separation between the two membranesmembranes of the chloroplast. of the chloroplast.

E. Thylakoid space- thylakoids are disks inside the E. Thylakoid space- thylakoids are disks inside the chloroplastschloroplasts, , where where chlorophyllchlorophyll is found. Grana are a stack of these is found. Grana are a stack of these thylakoidsthylakoids

F. Stroma – Conversion of Carbon F. Stroma – Conversion of Carbon dioxidedioxide happens here. It is happens here. It is the fluid (cytoplasm) of the the fluid (cytoplasm) of the chloroplastchloroplast..

III.Pathways of PhotosynthesisIII.Pathways of Photosynthesis

A. Chloroplasts A. Chloroplasts splitssplits water water

66CO2 + CO2 + 1212H2O + LIGHT ENERGY -> C6H12O6 + H2O + LIGHT ENERGY -> C6H12O6 + 66O2 + O2 + 66H2OH2O

The net equation is?The net equation is?

6CO2 + 6H2O + LIGHT ENERGY -> C6H12O6 + 6O26CO2 + 6H2O + LIGHT ENERGY -> C6H12O6 + 6O2

The simplest form of the equation is?The simplest form of the equation is?

CO2 + H2O -> CH2O + O2CO2 + H2O -> CH2O + O2

B. The splitting of waterB. The splitting of water

1. The electrons associated with hydrogen have more 1. The electrons associated with hydrogen have more potentialpotential energy in organic molecules than in energy in organic molecules than in waterwater..

2. Energy can then be stored in 2. Energy can then be stored in glucoseglucose..

C. Redox processC. Redox process

1. Photosynthesis is 1. Photosynthesis is anabolicanabolic; energy is required to reduce ; energy is required to reduce carbon carbon dioxidedioxide

2. Light is the 2. Light is the energyenergy source. source.

3. When water is split the 3. When water is split the electronselectrons are transferred to are transferred to carbon dioxidecarbon dioxide making sugar.making sugar.

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

B. The light reactionB. The light reaction

1. Light reaction – Conversion of light to 1. Light reaction – Conversion of light to chemicalchemical energy of energy of ATP and ATP and NADPHNADPH..

2. Occurs in the 2. Occurs in the thylakoidthylakoid membranes of the chloroplast. membranes of the chloroplast.

3. Reduce 3. Reduce carboncarbon dioxidedioxide to sugar to sugar

a. Hydrogens are added to ita. Hydrogens are added to it

4. O2 released as waste from 4. O2 released as waste from water being splitwater being split..

5. ATP generated.5. ATP generated.

. How it happens. How it happens

a. Photons of a. Photons of lightlight boost the pigment molecule’s electron to a boost the pigment molecule’s electron to a higherhigher orbital orbital

b. Electrons fall back giving off b. Electrons fall back giving off energyenergy..

c. Photosystems- pigments are arranged within thylakoid c. Photosystems- pigments are arranged within thylakoid membranemembrane

1. Antenna complex – Absorb 1. Antenna complex – Absorb photonphoton and pass energy to other and pass energy to other pigmentpigment molecule. molecule.

2. Reaction center- Chlorophyll a transfers 2. Reaction center- Chlorophyll a transfers excitedexcited electron. electron.

3. Primary electron acceptor- traps excited 3. Primary electron acceptor- traps excited electronelectron, powering the , powering the synthesis of synthesis of ATPATP and NADPH. and NADPH.

4. Photosystem 1 – P7004. Photosystem 1 – P700

5. Photosystem 2 _ P6805. Photosystem 2 _ P680

6. Noncyclic – involves both 6. Noncyclic – involves both photosystemsphotosystems, electrons are passed , electrons are passed from from waterwater to NADP+. ATP, NADPH to NADP+. ATP, NADPH and and oxygenoxygen are produced. are produced.

. . An electron transport chain is used where each link in An electron transport chain is used where each link in the chain passes an electron to the next link until it reaches the the chain passes an electron to the next link until it reaches the next photosystem.next photosystem.

c. NADP+ is the last link in the chain and becomes reduced.c. NADP+ is the last link in the chain and becomes reduced.

d. Chemiosmosis produces d. Chemiosmosis produces ATPATP; see 10.14, Basically an ; see 10.14, Basically an electrochemical gradient has been created. While the electrons electrochemical gradient has been created. While the electrons have been passed along H+ have been pumped across the have been passed along H+ have been pumped across the membrane, building up in the membrane, building up in the thylakoidthylakoid space. These H+ want to space. These H+ want to come back into the come back into the stromastroma. They are ions so they cannot pass . They are ions so they cannot pass without help. without help. FacilatedFacilated diffusiondiffusion is used to bring them back. The is used to bring them back. The protein involved is protein involved is ATPATP synthase. All the H+ coming back synthase. All the H+ coming back generates generates energyenergy allowing for ATP to be made. allowing for ATP to be made.

I. Calvin CycleI. Calvin Cycle

A. Carbon Fixation- the conversion of COA. Carbon Fixation- the conversion of CO2 2 to an organic to an organic compound.compound.

1. This happens to 3 1. This happens to 3 COCO22 to form one 3 carbon sugar to form one 3 carbon sugar ((G3PG3P) in the Calvin Cycle) in the Calvin Cycle

2. 2. RubiscoRubisco (the most plentiful enzyme in the world) (the most plentiful enzyme in the world) attaches the COattaches the CO2 2 to a 5C sugar called RuBP to a 5C sugar called RuBP (this happens 3 at a time)(this happens 3 at a time)

3. RuBP is like the cart on a roller coaster- 3. RuBP is like the cart on a roller coaster- COCO22

comes on for a ride and gets off forming G3P ( 1for every 3 COcomes on for a ride and gets off forming G3P ( 1for every 3 CO2 2 ), ), leaving the leaving the RuBPRuBP to go back to pick up a new CO to go back to pick up a new CO2.2.

4. So it takes a total of 4. So it takes a total of 22 turns of the cycle to get turns of the cycle to get 22 G3P, the equivalent of a glucose molecule.G3P, the equivalent of a glucose molecule.

B. Reduction- this is a reduction of B. Reduction- this is a reduction of COCO22 to sugarto sugar

1. ATP is used to make the reactions spontaneous- in 1. ATP is used to make the reactions spontaneous- in other words the phosphates are moved on and off the intermediate sugars other words the phosphates are moved on and off the intermediate sugars to make the ultimate conversion to G3P- It is a to make the ultimate conversion to G3P- It is a coupling coupling of the ATP reaction of the ATP reaction to the formation of to the formation of G3PG3P..

2. NADPH gives the 2. NADPH gives the hydrogenshydrogens over to the sugar as well- over to the sugar as well- those are the original hydrogens from those are the original hydrogens from waterwater. What happened to the water in . What happened to the water in the light reaction?the light reaction?

C. Photorespiration- Its not respiration, what is it?C. Photorespiration- Its not respiration, what is it?

1. C3 plants- a C3 plant does photosynthesis as just discribed- its called 1. C3 plants- a C3 plant does photosynthesis as just discribed- its called C3 C3 because because a 3C sugar is madea 3C sugar is made

a. On hot days the plant a. On hot days the plant closescloses its stomata ( its stomata (porespores), trapping ), trapping oxygen and oxygen and water in and COwater in and CO22 outout..

b. oxygen b. oxygen competitivelycompetitively inhibits Rubisco, binding it when inhibits Rubisco, binding it when there is low there is low COCO22. . This is not This is not a good thing,a good thing,it wastes O2 and generates no it wastes O2 and generates no ATP.ATP.

2. C4 plants- they still do photosynthesis the same way but there is a 2. C4 plants- they still do photosynthesis the same way but there is a step step added to the process. added to the process.

a. These plants storea. These plants store COCO22 in cells called in cells called mesophyllmesophyll, in the , in the form of a form of a 44 carbon sugar (Malate).carbon sugar (Malate).

b. The enzyme b. The enzyme PEPPEP carboxylase does this in the carboxylase does this in the mesophyllmesophyll cellscells

c. This allows plants to keep the levels of COc. This allows plants to keep the levels of CO22 highhigh at all at all times and times and minimize minimize photorespirationphotorespiration. Calvin cycle takes place in the . Calvin cycle takes place in the bundle sheathbundle sheath cell of these cell of these plantsplants

3. CAM plants- work on the same principles as C43. CAM plants- work on the same principles as C4

a. The stomates are closed during the a. The stomates are closed during the day day and and open during the open during the nightnight..

b. At night organic acids are made, in the day b. At night organic acids are made, in the day they are converted back to they are converted back to COCO22 and put into the Calvin and put into the Calvin

cyclecycle