Chapter 7 Photosynthesis

Chapter 7 Photosynthesis
CO 7 Chapter 7 Photosynthesis CO 7 Name a plant you have seen recently.

obtains organic food without eating other organisms
Nutrition Patterns Autotrophs (producers) Photosynthesis:plants, algae and some prokaryotes Chemosynthesis - rare - some bacteria obtains organic food without eating other organisms Heterotrophs (consumers/decomposers) -obtains organic food by eating other organisms or their by-products

Oxidation: partial or complete loss of electrons -exergonic (release energy)
Reduction: partial or complete gain of electrons -endergonic (absorb energy)

6H2O + 6CO2 C6H12O6 + 6O2 light oxygen Water + in the chloroplast
A. Photosynthetic Reaction 1. In 1930 C. B. van Niel showed that O2 given off by photosynthesis comes from water and not from CO2. 2. The net equation reads: light 6H2O + 6CO C6H12O6 + 6O2 Pg 119a Carbon dioxide oxygen Water + Glucose + in the chloroplast

How are they connected? Heterotrophs  Autotrophs 
making energy & organic molecules from ingesting organic molecules glucose + oxygen  carbon + water + energy dioxide C6H12O6 6O2 6CO2 6H2O ATP  + oxidation = exergonic Autotrophs Where’s the ATP? making energy & organic molecules from light energy So, in effect, photosynthesis is respiration run backwards powered by light. Cellular Respiration oxidize C6H12O6  CO2 & produce H2O fall of electrons downhill to O2 exergonic Photosynthesis reduce CO2  C6H12O6 & produce O2 boost electrons uphill by splitting H2O endergonic + water + energy  glucose + oxygen carbon dioxide 6CO2 6H2O C6H12O6 6O2 light energy  + reduction = endergonic

2. Photosynthesis transforms solar energy into chemical energy
Photosynthetic Organisms 2. Photosynthesis transforms solar energy into chemical energy Organic molecules (carbs!) built by photosynthesis provide both the building blocks and energy for cells. Figure 7.1a

Stoma: opening in the leaf to exchange gas
Figure 7.1b 3. Plants use the raw materials: carbon dioxide and water 4. Chloroplasts carry out photosynthesis Stoma: opening in the leaf to exchange gas aka: stomata Figure 7.1b

Figure 7.1c Chlorophylls and other pigments involved in absorption of solar energy reside within thylakoid membranes of chloroplasts Figure 7.1c

4. The chloroplast - Location of light reaction
Stomata: opening in leaf for gas exchange Pigment: chlorophyll Mesophyll: Plant cell photosynthetic layer: Sites of photosynthesis (Double membrane) granum (stack) Thylakoids (pancake) contains: chlorophyll molecules electron transport chain ATP synthase - Location of light reaction Stroma-fluid-filled interior (syrup) - Location of dark reaction Figure 7.2

Quick Check - FIVE OR FEWER 1. Chloroplast
2. Thylakoid 3. Photosynthesis 4. Organic Molecules involved Two words that sound alike but are not at all similar: Stroma: liquid in chloroplast Stoma: pore in leaves

7.2 Plants as Solar Energy Converters Solar Radiation - Only 42% of solar radiation that hits the earth’s atmosphere reaches surface; most is visible light.

Sunlight has all the colors
Objects only reflect some colors

A. Photosynthetic Pigments - Pigments found in chlorophyll absorb various portions of visible light; absorption spectrum. 1. Two major photosynthetic pigments are chlorophyll a and chlorophyll b. 2. Both chlorophylls absorb violet, blue, and red wavelengths best Most green is reflected back; this is why leaves appear green.

3. Carotenoids are yellow-orange pigments which absorb light in violet, blue, and green regions.
4. When chlorophyll breaks down in fall, the yellow-orange pigments in leaves show through. Figure 7.3a

Chromatography - Separation of pigments based on their size and solubility

B. Absorption and action spectrum - A spectrophotometer measures the amount of light that passes through a sample of pigments. 1) As different wavelengths are passed through, some are absorbed. 2) Graph of percent of light absorbed at each wavelength is absorption spectrum .

Absorption spectrum 3) Photosynthesis produces oxygen; production of oxygen is used to measure the rate of photosynthesis. 4) Oxygen production and, therefore, photosynthetic activity is measured for plants under each specific wavelength; plotted on a graph, this produces an action spectrum. 5) Since the action spectrum resembles absorption spectrum, this indicates that chlorophylls contribute to photosynthesis. action spectrum

Checkpoint: http://www. glencoe
What is the relationship between the absorption spectrum and the action spectrum? 2. How can we measure the rate of photosynthesis? 3. How is the wavelength of light related to the rate of photosynthesis? 4. A radish plant is grown behind using lights of different colors. Explain the chart.

QOD: write the equation for photosynthesis (from memory)
How can we measure the rate of photosynthesis? 3. How is the wavelength of light related to the rate of photosynthesis? 4. A radish plant is grown using lights of different colors. Explain the chart.

6H2O + 6CO2 C6H12O6 + 6O2 light oxygen Water + in the chloroplast
Carbon dioxide oxygen Water + Glucose + in the chloroplast

Light- dependent reactions
Inside a Chloroplast H2O CO2 Light NADP+ ADP + P Light- dependent reactions Calvin Cycle Calvin cycle Copyright Pearson Prentice Hall The process of photosynthesis includes the light-dependent reactions as well as the Calvin cycle. Chloroplast O2 Sugars C6H12O6

1. Light reactions cannot take place unless light is present
1. Light reactions cannot take place unless light is present. They are the energy-capturing reactions. b. Chlorophyll within thylakoid membranes absorbs solar energy and energizes electrons. c. Energized electrons move down the electron transport system; energy is captured and used for ATP production. d. Energized electrons are also taken up by NADP+, becoming NADPH. Pg 119b

2. Calvin Cycle Reactions
a. These reactions take place in the stroma; can occur in either the light or the dark. b. These are synthesis reactions that use NADPH and ATP to reduce CO2. -- and make a carbohydrate, sugar Figure 7.4

What you should know by now..
1. The equation for photosynthesis. Write it! 2. The structure of a chloroplast. Sketch it! 3. The two reactions of photosynthesis. **Things are about to get much more difficult**

The Light Reactions 1. PHOTOPHOSPHORYLATION = ATP production
also called CHEMIOSMOSIS, - occurs on thylakoid membrane 2. Two paths operate within the thylakoid membrane noncyclic and cyclic *straight line *in a circle 3. Both paths use ATP, but the noncyclic also produces NADPH

1. Light hits photosystem II and excites an electron, H20
2. The primary electron acceptor passes the electron down the ETC and generates ATP 3. Light is required for PSI, but not water, it generates NADPH

Light-Dependent Reactions
Inside thyloakoid The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. The light-dependent reactions take place within the thylakoid membranes of chloroplasts. Thylakoid membrane Stroma Copyright Pearson Prentice Hall

Photosystems: Light harvesting units of the thylakoid membrane
Composed mainly of protein and pigment antenna complexes Antenna pigment molecules are struck by photons Energy is passed to reaction centers (redox location) Excited e- from chlorophyll is trapped by a primary e- acceptor

Something trivial.... Photosystem I and Photosystem II are named based on when they were discovered, PSI was established first.

1. Photosynthesis begins when pigments in photosystem II absorb light, increasing their energy level. Photosystem II The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. The light-dependent reactions take place within the thylakoid membranes of chloroplasts. Copyright Pearson Prentice Hall

These high-energy electrons are passed on to the electron transport chain. Photosystem II Electron carriers High-energy electron Copyright Pearson Prentice Hall

2. Enzymes on the thylakoid membrane break water molecules into: Photosystem II 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Electron carriers High-energy electron Copyright Pearson Prentice Hall

-hydrogen ions -oxygen atoms -energized electrons Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Electron carriers High-energy electron Copyright Pearson Prentice Hall

(2)The energized electrons from water replace the high-energy electrons that chlorophyll lost to the electron transport chain. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. High-energy electron Copyright Pearson Prentice Hall

(2) As plants remove electrons from water, oxygen is left behind and is released into the air. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. The light-dependent reactions take place within the thylakoid membranes of chloroplasts. High-energy electron Copyright Pearson Prentice Hall

(2)The hydrogen ions left behind when water is broken apart are released inside the thylakoid membrane. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Pc Pq Cytochrome complex High-energy electron Copyright Pearson Prentice Hall

3. Energy from the electrons is used to transport H+ ions from the stroma into the inner thylakoid space. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Pc Pq Cytochrome complex: catalyzing the transfer of electrons from plastoquinol to plastocyanin Cytochrome complex Copyright Pearson Prentice Hall

3. High-energy electrons move through the electron transport chain from photosystem II to photosystem I. Photosystem II + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Pc Pq Cytochrome complex Photosystem I Copyright Pearson Prentice Hall

4. Pigments in photosystem I use energy from light to re-energize the electrons. + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. Cytochrome complex Photosystem I Copyright Pearson Prentice Hall

5. NADP+ then picks up these high-energy electrons, along with H+ ions, and reduces to NADPH. + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall

5. As electrons are passed from chlorophyll to NADP+, more H+ ions are pumped across the membrane. + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall

(5) Soon, the inside of the membrane fills up with positively charged hydrogen ions, which makes the outside of the membrane negatively charged. + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall

6. The difference in charges across the membrane provides the energy to make ATP + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall

(6) H+ ions cannot cross the membrane directly. ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall

(6) The cell membrane contains a protein called ATP synthase that allows H+ ions to pass through it ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall

(6) As H+ ions pass through ATP synthase, the protein rotates. ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall

(6) As it rotates, ATP synthase binds ADP and a phosphate group together to produce ATP. ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. ADP 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall

Because of this system, light-dependent electron transport produces not only high-energy electrons but ATP as well. ATP synthase + O2 2H2O The light-dependent reactions use energy from sunlight to produce ATP, NADPH, and oxygen. ADP 2 NADP+ 2 2 NADPH Copyright Pearson Prentice Hall

Photosystems of photosynthesis
2 photosystems in thylakoid membrane collections of chlorophyll molecules Photosystem II: contains chlorophyll a P680 = absorbs 680nm wavelength red light Photosystem I: contains chlorophyll b P700 = absorbs 700nm wavelength red light reaction center Photons are absorbed by clusters of pigment molecules (antenna molecules) in the thylakoid membrane. When any antenna molecule absorbs a photon, it is transmitted from molecule to molecule until it reaches a particular chlorophyll a molecule = the reaction center. At the reaction center is a primary electron acceptor which removes an excited electron from the reaction center chlorophyll a. This starts the light reactions. Don’t compete with each other, work synergistically using different wavelengths. antenna pigments

1. Light hits photosystem II and excites an electron, H20
2. The primary electron acceptor passes the electron down the ETC and generates ATP 3. Light is required for PSI, but not water, it generates NADPH

Figure 7.5 Figure 7.5

Indicate which system (PS1 or PS2 or BOTH)
____1. Splits water ____2. Produces NADPH ____3. Has an electron transport chain ____4. Requires light ____5. Utilizes a primary electron acceptor ____6. Occurs in the thylakoid ____7. Requires the input of H20 ____8. The cyclic path ____9. Uses chlorophyll ____10. Releases oxygen ____11. chlorophyll a ____12. chlorophyll b PS2 PS1 Both

ETC of Photosynthesis chlorophyll a chlorophyll b Photosystem II
Two places where light comes in. Remember photosynthesis is endergonic -- the electron transport chain is driven by light energy. Need to look at that in more detail on next slide

ETC of Photosynthesis split H2O sun sun to Calvin Cycle ATP e e H+ O
Two places where light comes in. Remember photosynthesis is endergonic -- the electron transport chain is driven by light energy. Need to look at that in more detail on next slide O to Calvin Cycle split H2O ATP

Two Pathways of Light Reactions 1. Noncyclic 2. Cyclic
Two Pathways of Light Reactions 1. Noncyclic 2. Cyclic ATP Production --> CHEMIOSMOSIS When H20 is split, two H+ remain These H+ are pumped from the stroma into the thylakoid This creates a gradient used to produce ATP from ADP ATP is the whole point of Photosystem II and will be used to power the Light Independent Reactions (Calvin Cycle) Two main subunits of PS I, PsaA and PsaB, are closely related proteins involved in the binding of P700, A0, A1, and Fx. PsaA and PsaB are both integral membrane proteins of 730 to 750 amino acids that seem to contain 11 transmembrane segments. The Fx 4Fe-4S iron-sulphur centre is bound by four cysteines; two of these cysteines are provided by the PsaA protein and the two others by PsaB. The two cysteines in both proteins are proximal and located in a loop between the ninth and tenth transmembrane segments. A leucine zipper motif seems to be present downstream of the cysteines and could contribute to dimerisation of psaA/psaB.

Noncyclic Photophosphorylation
Light reactions elevate electrons in 2 steps (PS II & PS I) PS II generates energy as ATP PS I generates reducing power as NADPH 1 photosystem is not enough. Have to lift electron in 2 stages to a higher energy level. Does work as it falls. First, produce ATP -- but producing ATP is not enough. Second, need to produce organic molecules for other uses & also need to produce a stable storage molecule for a rainy day (sugars). This is done in Calvin Cycle! ATP

Cyclic photophosphorylation
If PS I can’t pass electron to NADP…it cycles back to PS II & makes more ATP, but no NADPH coordinates light reactions to Calvin cycle Calvin cycle uses more ATP than NADPH  ATP 18 ATP + 12 NADPH  1 C6H12O6

Photophosphorylation
cyclic photophosphorylation NADP NONcyclic photophosphorylation ATP

Are you still confused? This is pretty hard to visualize, but through the magic of technology, we can watch these processes as animations McGraw Hill Animation:

Figure 7.7 Figure 7.7

Figure 7.6

Chemiosmosis is difficult to visualize. So... you get to color it!
Yay! coloring!

Thurs 10/23 Photosynthesis Lab Fri 10/24: Calvin Cycle
Schedule: Thurs 10/23 Photosynthesis Lab Fri 10/24: Calvin Cycle Tues 10/28: Photosynthesis Quiz Start Cellular respiration Thurs: 10/30 Finish Cellular Respiration Tues 11/ 4 Quiz Cellular Respiration Start Genetics Unit Ch 9 Fri 10/25: Calvin Cycle Tues 10/29: in class lab and simulation Thurs: 10/30 Halloween Tues 11/ 5 Photosynthesis Quiz Start Cellular respiration Thurs: 11/7 Finish Cellular Respiration Tues 11/ 12 Quiz Cellular Respiration Start Genetics Unit Ch 9

Relate a plants anatomy to it’s function of photosynthesis.
(how do roots, stem, leaves, stoma all help with photosynthesis) - Stoma: opening in the leave to exchange gas

The Calvin Cycle 1950s | 1961 Whoops! Wrong Calvin…

The Calvin Cycle Also called *The Light Independent Reactions
*The Dark Reactions 1. Named after Melvin Calvin, who used a radioactive isotope of carbon to trace the reactions.

2. Joseph Priestley Experiment:
He put a dome over a candle, the candle went out. He added a plant for a few days to the dome, the candle stayed lit for a while Conclusion: The plant produced a substance required for burning. Jan Ingenhousz: showed the effect observed by Priestly occurred only when the plant was exposed to light Conclusion: Light is necessary to produce oxygen a. a. b. b. b

Convert solar energy to chemical energy ATP NADPH
The Calvin Cycle is a series of reactions producing carbohydrates. carbon dioxide fixation, carbon dioxide reduction, and regeneration of RuBP. Convert solar energy to chemical energy ATP NADPH  energy  reducing power

Fixation of Carbon Dioxide
1. CO2 fixation is the attachment of CO2 to an organic compound called RuBP. 2. RuBP (ribulose bisphosphate) is a five-carbon molecule that combines with carbon dioxide.

Calvin Cycle Animation
3. The enzyme RuBP carboxylase (RuBisCo) speeds this reaction; this enzyme comprises 20–50% of the protein content of chloroplasts Mainly this is a reshuffling of carbons using ATP and NADPH as energy Calvin Cycle Animation

Fortunately.... Summary Statements:
AP Biology no longer requires the memorization of every step of the Calvin Cycle, but you should understand the beginning and the end and what it's purpose is. Summary Statements: What is the purpose of the Calvin Cycle? Where does the cell get its energy to perform these reactions? What are the main molecules involved in carbon fixation? What is the final product?

Calvin cycle 1C 5C 6C 5C 3C 3C 3C CO2 RuBP RuBisCo 3 ATP 3 ADP used
1. Carbon fixation 3. Regeneration of RuBP C 5C C RuBP RuBisCo C ribulose bisphosphate 6C starch, sucrose, cellulose & more 3 ADP 3 ATP C ribulose bisphosphate carboxylase 5C C used to make glucose C glyceraldehyde-3-P C 1.Carbon Fixation: A five-carbon sugar molecule called ribulose bisphosphate, or RuBP, is the acceptor that binds CO2 dissolved in the stroma. This process, called CO2 fixation, is catalyzed by the enzyme RuBP carboxylase, forming an unstable six-carbon molecule. This molecule quickly breaks down to give two molecules of the three-carbon 3-phosphoglycerate (3PG), also called phosphoglyceric acid (PGA). 2. Reduction: The two 3PG molecules are converted into glyceraldehyde 3-phosphate (G3P, a.k.a. phosphoglyceraldehyde, PGAL) molecules, a three-carbon sugar phosphate, by adding a high-energy phosphate group from ATP, then breaking the phosphate bond and adding hydrogen from NADH + H+. 3. Regeneration: Three turns of the cycle, using three molecules of CO2, produces six molecules of G3P. However, only one of the six molecules exits the cycle as an output, while the remaining five enter a complex process that regenerates more RuBP to continue the cycle. Two molecules of G3P, produced by a total of six turns of the cycle, combine to form one molecule of glucose. 3C PGA G3P C phosphoglycerate C C C 3C C = C C C 6 ADP 6 ATP C 2. Reduction | H C – C 6 NADP 6 NADPH 3C C

Molecules of Calvin Cycle
RuBP (ribulose bisphosphate) is a five-carbon molecule that combines with carbon dioxide= carbon fixation RuBisCo: the enzyme that fixes carbon from the air (most important enzyme in the world?) G3P: Glyceraldehyde-3-P: end product of Calvin cycle, energy rich 3 carbon sugar - 2 G3P combine to form 1 glucose

G3P: Glyceraldehyde-3-P: end product of Calvin cycle, energy rich 3 carbon sugar
This is called “C3 photosynthesis” (normal) G3P is an important intermediate G3P   glucose   carbohydrates   lipids   phospholipids, fats, waxes   amino acids   proteins   nucleic acids   DNA, RNA

G3P can be converted into other things
Figure 7.9

copy and fill out this table as best you can. Process Light? Location
QOD: photosynthesis copy and fill out this table as best you can. Process Light? Location Reactant Product (photosynthesis) 1. ETC 2. Calvin Cycle 3. Relate a plants anatomy to it’s function of photosynthesis. (how do roots, stem, leaves, stoma all help with photosynthesis)

Process Light? Location Reactant Product (photosynthesis) 1. ETC
Light dependent rxn Thylakoid membrane Light H2O ATP NADPH O2 2. Calvin Cycle Independent rxn stroma CO2 Glucose

Relate a plants anatomy to it’s function of photosynthesis.
Roots: collect water for light rxn Stem: transport water, minerals, Leaves: collect sun light, stoma: collect CO2) - Stoma: opening in the leave to exchange gas

From CO2  C6H12O6 CO2 has very little chemical energy
fully oxidized C6H12O6 contains a lot of chemical energy highly reduced (contains energy in form of e-) Synthesis = endergonic process put in a lot of energy Reduction of CO2  C6H12O6 proceeds in many small uphill steps each catalyzed by a specific enzyme using energy stored in ATP & NADPH

Photosynthesis summary
Light reactions produced ATP produced NADPH consumed H2O produced O2 as byproduct Calvin cycle consumed CO2 produced G3P (sugar) regenerated ADP regenerated NADP ADP NADP

Types of phosphorylation
Alternative Pathways C3 PLANTS: use the normal Calvin Cycle exclusively to fix carbon, the MOST Common Pathway Adaptations: Plants in hot dry environments have a problem with water loss, so they keep their stomata partly closed... this results in: CO2 deficit (Used in Calvin Cycle), and the level of O2 RISES (as Light reactions Split Water Molecules).

Some Plant Taxonomy In order for photosynthesis to occur, plants must open tiny pores on their leaves called STOMATA. Opening these pores can lead to loss of water.

The problem: Calvin cycle when O2 is high
to mitochondria ––––––– lost as CO2 without making ATP O2 5C RuBP Hey Dude, are you high on oxygen! RuBisCo 2C 3C Photorespiration: RuBisCo fixation of O2, lose carbon to CO2 without making ATP, makes photosynthesis less efficient It’s so sad to see a good enzyme, go BAD!

Figure 7.10 C4 plants and CAM plants use an alternate pathway to FIX carbon dioxide from the air. Figure 7.10

Reducing photorespiration
Alternative pathways: Separate carbon fixation from Calvin cycle C4 plants: PHYSICALLY separate carbon fixation from Calvin cycle (corn, sugar cane) different cells to fix carbon vs. where Calvin cycle occurs store carbon in 4C compounds different enzyme to capture CO2 (fix carbon) called PEP carboxylase different leaf structure CAM plants: separate carbon fixation from Calvin cycle by TIME OF DAY (cactus, pineapple) fix carbon during night perform Calvin cycle during day The key point is how carbon dioxide is grabbed out of the air -- carbon fixation -- and then handed off to the Calvin cycle. C4 plants separate the 2 steps of carbon fixation anatomically. They use 2 different cells to complete the process. CAM plants separate the 2 steps of carbon fixation temporally. They do them at 2 different times. The key problem they are trying to overcome is that Rubisco is a very inefficient enzyme in the presence of high O2. In high O2, Rubisco bonds oxygen to RuBP rather than carbon, so the plants have to keep O2 away from Rubsico. C4 & CAM should be seen as variations on *carbon fixation*, because plants had to evolve alternative systems given the limitations of their enzymes and their need to conserve water.

C4 vs CAM Summary Ex: Ex: Pineapple Sugarcane Cactus Corn Crabgrass
solves CO2 / O2 gas exchange vs. H2O loss challenge Ex: Pineapple Cactus Ex: Sugarcane Corn Crabgrass C4 plants separate 2 steps of C fixation anatomically in 2 different cells CAM plants separate 2 steps of C fixation temporally = 2 different times night vs. day C3, C4, and CAM truly refer to the alternative method of carbon fixation -- grabbing carbon out of the air -- and not the Calvin Cycle itself. They *all* use the Calvin Cycle for sugar generation, but they differ in how they turn carbon from thin air into solid stuff. In C4, CO2 is fixed into 4-carbon "storage" compounds like oxaloacetate & malate (hence C4) In CAM, CO2 is fixed into organic acids like malic acid & isocitric acid (hence Crassulacean Acid Metabolism) In C3, while CO2 is initially fixed into a 6-carbon molecule, it is unstable & quickly breaks down to 3-carbon phosphoglycerate (PGA) (hence C3) C4 & CAM should be seen as variations on *carbon fixation*, because plants had to evolve alternative systems given the limitations of their enzymes and their need to conserve water.

Photophosphorylation
cyclic photophosphorylation NADP NONcyclic photophosphorylation ATP

Quick Practice

Quick Practice grana thylakoid stroma O2

Summarize what is happening at 1, 2 ,and 3
C C C 1C CO2 C C 1. Carbon fixation 3. Regeneration of RuBP C 5C C RuBP RuBisCo C ribulose bisphosphate 6C starch, sucrose, cellulose & more 3 ADP 3 ATP C ribulose bisphosphate carboxylase 5C C used to make glucose C glyceraldehyde-3-P C 1.Carbon Fixation: A five-carbon sugar molecule called ribulose bisphosphate, or RuBP, is the acceptor that binds CO2 dissolved in the stroma. This process, called CO2 fixation, is catalyzed by the enzyme RuBP carboxylase, forming an unstable six-carbon molecule. This molecule quickly breaks down to give two molecules of the three-carbon 3-phosphoglycerate (3PG), also called phosphoglyceric acid (PGA). 2. Reduction: The two 3PG molecules are converted into glyceraldehyde 3-phosphate (G3P, a.k.a. phosphoglyceraldehyde, PGAL) molecules, a three-carbon sugar phosphate, by adding a high-energy phosphate group from ATP, then breaking the phosphate bond and adding hydrogen from NADH + H+. 3. Regeneration: Three turns of the cycle, using three molecules of CO2, produces six molecules of G3P. However, only one of the six molecules exits the cycle as an output, while the remaining five enter a complex process that regenerates more RuBP to continue the cycle. Two molecules of G3P, produced by a total of six turns of the cycle, combine to form one molecule of glucose. 3C PGA G3P C phosphoglycerate C C C 3C C = C C C 6 ADP 6 ATP C 2. Reduction | H C – C 6 NADP 6 NADPH 3C C

What Factors the Affect Photosynthesis?
1. Light Quality (color/wavelength) 2. Light intensity 3. Carbon Dioxide Availability 4. Water Availability *Using the photosynthesis simulation, design and test an experiment to test light intensity and wavelength Photosynthesis Simulation Waterweed Simulator

Pg 129b Light & H2O CO2 ADP NADP ATP Pg 129b NADPH O2 glucose

AB = ATP AC = phospholipids AD = light (energy)
A = photosystem II B = photosystem I C = H20 D = Electron Transport Chain E = ATP Synthase AB = ATP AC = phospholipids AD = light (energy)

Photosynthesis Activities
Chromatography of a spinach leaf Light intensity and color simulation: Rate of photosynthesis LAB: Elodiea observation:

Multiple Choice Chapter 6
Standardized Test Prep Multiple Choice 1. Which of the following is a reactant in the Calvin cycle? A. O2 B. CO2 C. H2O D. C6H12O6

Multiple Choice, continued
Chapter 6 Standardized Test Prep Multiple Choice, continued 1. Which of the following is a reactant in the Calvin cycle? A. O2 B. CO2 C. H2O D. C6H12O6

Chapter 6 Standardized Test Prep Multiple Choice, continued 2. Which of the following statements is correct about the carotenoid pigments? F. Accessory pigments are not involved in photosynthesis. G. Accessory pigments add color to plants but do not absorb light energy. H. Accessory pigments absorb colors of light that chlorophyll a cannot absorb. J. Accessory pigments receive electrons from the electron transport chain of photosystem I.

Chapter 6 Standardized Test Prep Multiple Choice, continued 3. Oxygen is produced at what point during photosynthesis? A. when CO2 is fixed B. when water is split C. when ATP is converted into ADP D. when 3-PGA is converted into G3P

Chapter 6 Standardized Test Prep Multiple Choice, continued The diagram below shows a portion of a chloroplast. Use the diagram to answer the question that follows. 4. Which of the following correctly identifies the structure marked X and the activities that take place there? F. stroma—Calvin cycle G. stroma—light reactions H. thylakoid—Calvin cycle J. thylakoid—light reactions

Chapter 6 Standardized Test Prep Multiple Choice, continued 5. light reactions : ATP :: Calvin cycle : A. H+ B. O2 C. G3P D. H2O

Chapter 6 Multiple Choice, continued
Standardized Test Prep Multiple Choice, continued The diagram below shows a step in the process of chemiosmosis. Use the diagram to answer the question that follows. 6. What is the substance identified as Y in the image? F. H+ G. NAD+ H. NADPH J. ADP synthase

Short Response Chapter 6
Standardized Test Prep Short Response Chloroplasts are organelles with areas that conduct different specialized activities. Where in the chloroplast do the light reactions and the Calvin cycle occur?

Short Response, continued
Chapter 6 Standardized Test Prep Short Response, continued Chloroplasts are organelles with areas that conduct different specialized activities. Where in the chloroplast do the light reactions and the Calvin cycle occur? Answer: The light reactions of photosynthesis occur along the thylakoid membrane. The Calvin cycle occurs in the stroma, surrounding the thylakoids.

Extended Response Chapter 6
Standardized Test Prep Extended Response The reactions of photosynthesis make up a biochemical pathway. Part A What are the reactants and products for both the light reactions and the Calvin cycle? Part B Explain how the biochemical pathway of photosynthesis recycles many of its own reactants, and identify the recycled reactants.

Extended Response, continued
Chapter 6 Standardized Test Prep Extended Response, continued Answer: Part A The reactants for the light reactions of photosynthesis are sunlight, water, NADP+, and ADP. The products are oxygen, ATP, and NADPH. The reactants for the Calvin cycle are ATP, NADPH, CO2, and RuBP. The products are NADP+, ADP, and organic compounds. Part B ADP/ATP, NADP+/NADPH, and electrons are recycled during photosynthesis. RuBP, which reacts with CO2 in the Calvin cycle, is regenerated at each turn of the cycle.

Review of ETC of Photosynthesis
sun 1 e PS II absorbs light Excited electron passes from chlorophyll to the primary electron acceptor Need to replace electron in chlorophyll An enzyme extracts electrons from H2O & supplies them to the chlorophyll This reaction splits H2O into 2 H+ & O- which combines with another O- to form O2 O2 released to atmosphere Chlorophyll absorbs light energy (photon) and this moves an electron to a higher energy state Electron is handed off down chain from electron acceptor to electron acceptor In process has collected H+ ions from H2O & also pumped by Plastoquinone within thylakoid sac. Flow back through ATP synthase to generate ATP. Photosystem II P680 chlorophyll a

ETC of Photosynthesis ATP Photosystem II P680 chlorophyll a H+ H+
Inhale, baby! thylakoid chloroplast H+ H+ ATP Plants SPLIT water! 1 O H 2 e O O H H+ +H e- e e fill the e– vacancy Photosystem II P680 chlorophyll a

ETC of Photosynthesis to Calvin Cycle ATP ATP
thylakoid chloroplast H+ H+ ATP e H+ 3 1 2 e H+ ATP 4 to Calvin Cycle H+ ADP + Pi energy to build carbohydrates Photosystem II P680 chlorophyll a ATP

ETC of Photosynthesis Photosystem I P700 chlorophyll b
sun fill the e– vacancy e 5 Need a 2nd photon -- shot of light energy to excite electron back up to high energy state. 2nd ETC drives reduction of NADP to NADPH. Light comes in at 2 points. Produce ATP & NADPH e e Photosystem I P700 chlorophyll b Photosystem II P680 chlorophyll a

ETC of Photosynthesis NADPH to Calvin Cycle
electron carrier e 6 e 5 sun NADPH to Calvin Cycle Need a 2nd photon -- shot of light energy to excite electron back up to high energy state. 2nd ETC drives reduction of NADP to NADPH. Light comes in at 2 points. Produce ATP & NADPH Photosystem I P700 chlorophyll b Photosystem II P680 chlorophyll a $$ in the bank… reducing power!

Chapter 7 Photosynthesis

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Chapter 7 Photosynthesis

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