Chapter 10: Photosynthesis

Introduction Photosynthesis converts __________ into _________ Why is it significant?

Building on previous vocab Autotroph Photoautotroph What could be another type of autotroph? What is the opposite of an autotroph?

Ex. Of photoautotrophs plants algae some protists some prokaryotes Is it possible to photosynthesize without a choloplast? What do you need?

Heterotrophs Consumers Obtain energy from______

Concept 10.1: Photosynthesis converts light energy to the chemical energy of food Chloroplasts have structure similar to photosynthetic bacteria What is that evidence supporting?? Structure necessary for function

Photosynthesis in plants In what organ of plants does the majority of photosynthesis take place? Green because of what pigment? Stomata Mesophyll- cells in the interior of a leaf that contain 30-40 chloroplasts each! What type of tissue do you think mesophyll is?

Fig. 10-3a Leaf cross section Vein Mesophyll Stomata CO2 O2 Chloroplast Mesophyll cell 5 µm

Parts of a chloroplast Outer membrane Inner membrane] Stroma Thylakoid Thylakoid membrane Thylakoid space Granum

Equation for photosynthesis Fig. 10-4 6 CO2 + 12 H2O + Light energy  C6H12O6 + 6 O2 + 6 H2O How did we get this? Reactants: 6 CO2 12 H2O Products: C6H12O6 6 H2O 6 O2

Photosynthesis is a redox process in which H2O is oxidized and CO2 is reduced

Two main parts of photosyn. Light reactions (light-dependent rxns) “photo” Calvin Cycle (light-independent rxn) “synthesis”

The light Reactions Water is split during the light rxns ______ is waste What happens to the other part? _______an electron acceptor that will shuttle to the ETC ________________using chemiosmosis to make ATP from _____

The Calvin Cycle CO2 incorporated into organic compounds = Carbon Fixation Requires NADPH and ATP Makes sugar Does not require ______BUT does require NADPH and ATP…

What happens where?

Concept Check 10.1 1. How do the reactant molecules of photosynthesis reach the chloroplasts in leaves? A classmate says that the Calvin cycle needs The products of the light reaction to function but the light reaction does not need the products of the Calvin cycle to function as long as it has light. Agree, disagree? Why?

10.2 The light reactions convert solar energy to the chemical energy of ATP and NADPH Light- electromagnetic radiation Light is cool:

Light words Wavelength Visible light electromagnetic spectrum

1 m (109 nm) 10–5 nm 10–3 nm 1 nm 103 nm 106 nm 103 m Micro- waves Fig. 10-6 1 m (109 nm) 10–5 nm 10–3 nm 1 nm 103 nm 106 nm 103 m Gamma rays Micro- waves Radio waves X-rays UV Infrared Visible light 380 450 500 550 600 650 700 750 nm Shorter wavelength Longer wavelength Higher energy Lower energy

Light cntd Spectrophotometer-

TECHNIQUE White light Refracting prism Chlorophyll solution Fig. 10-8 TECHNIQUE White light Refracting prism Chlorophyll solution Photoelectric tube Galvanometer 2 3 1 4 The high transmittance (low absorption) reading indicates that chlorophyll absorbs very little green light. Slit moves to pass light of selected wavelength Green light The low transmittance (high absorption) reading indicates that chlorophyll absorbs most blue light. Blue light

Light and Pigments Pigments_______light Light that is not absorbed is _______ Chlorophyll!

Pigments found in many plants Chlorophyll a- main photosynthetic pigment Chlorophyll b Cartenoids Chlorophyll b Chloro- phyll a Carotenoids

Excited Chlorophyll What happens when light hits chlorophyll? Pigment absorbs light and becomes “excited state” Excited electrons Give off florescence (light and heat)

Photosystem Photosystem= reaction-center complex + light-harvesting complexes Light-harvesting complex- pigment molecules bound in a protein.

A primary electron acceptor in the reaction center accepts an excited electron from chlorophyll a That’s the first step of the light rxn!

(INTERIOR OF THYLAKOID) Fig. 10-12 Photosystem STROMA Photon Primary electron acceptor Light-harvesting complexes Reaction-center complex e– Thylakoid membrane Pigment molecules Transfer of energy Special pair of chlorophyll a molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID)

Different Photosystems PS I has a P700 rxn center PS II has a P680 rxn center Linear Electron Flow Cyclic electron flow

Linear v. cyclic Some organisms such as purple sulfur bacteria have PS I but not PS II Cyclic electron flow is thought to have evolved ________linear electron flow Cyclic electron flow may protect cells from light-induced damage

Compare Mito and Chloro

ATP Synthase Fig. 10-17 STROMA (low H+ concentration) Cytochrome complex Photosystem II Photosystem I 4 H+ Light NADP+ reductase Light Fd 3 NADP+ + H+ Pq e– Pc NADPH e– 2 1 THYLAKOID SPACE (high H+ concentration) H2O +2 H+ 4 H+ 1/2 O2 To Calvin Cycle Thylakoid membrane ATP synthase STROMA (low H+ concentration) ADP + ATP P i H+

10.2 concept check What color light is least effective in driving photosynthesis? Explain In the light rxns, what is the initial electron donor? Where do the electrons end up?

Chemiosmosis Making ATP by shuttling electrons/protons through a membrane ETC and proton pumps Chloro. Capture _______ energy to break apart ________ Transport those electrons and protons to ultimately Photophosphorylate_____ into _______

10.3 The Calvin cycle uses ATP and NADPH to convert CO2 to sugar Uses ATP synthesized from_____ Uses electrons from the carrier______ Products?

Phases of the Calvin Cycle 1. Carbon fixation (catalyzed by rubisco) 2. Reduction 3.Regeneration of the CO2 acceptor (RuBP) *Why is step 3 necessary?*

1 turn of the Calvin Cycle Carbon enters the cycle as CO2 and leaves as a sugar named glyceraldehyde-3-phospate (G3P) For net synthesis of 1 G3P, the cycle must take place three times, fixing 3 molecules of CO2

Fig. 10-18-3 Input 3 (Entering one at a time) CO2 Phase 1: Carbon fixation Rubisco 3 P P Short-lived intermediate 3 P P 6 P Ribulose bisphosphate (RuBP) 3-Phosphoglycerate 6 ATP 6 ADP 3 ADP Calvin Cycle 6 3 P P ATP 1,3-Bisphosphoglycerate 6 NADPH Phase 3: Regeneration of the CO2 acceptor (RuBP) 6 NADP+ 6 P i 5 P G3P 6 P Glyceraldehyde-3-phosphate (G3P) Phase 2: Reduction 1 P Glucose and other organic compounds Output G3P (a sugar)

10.3 concept check Explain why a poison that inhibits an enzyme of the Calvin cycle will also inhibit the light reaction

10.4 Alternative mechanisms of carbon fixation have evolved in hot, arid climates What is the problem in those climates? What would be the typical plant solution? What problems arise b/c of that solution? **favors photorespiration**

Photorespiration In C3 plants initial fixation of CO2, via rubisco, forms a three-carbon compound In photorespiration, rubisco adds O2 instead of CO2 in the Calvin cycle consumes __ and organic fuel and releases __ without producing ATP or sugar

Why Photorespiration? rubisco first evolved at a time when the atmosphere _______________ limits damaging products of light reactions that build up in the absence of the Calvin cycle On a hot, dry day _____ of the products of the Calvin cycle could be drained

C4 plants incorporate CO2 into four-carbon compounds in mesophyll cells (instead of photoresp) PEP carboxylase needed has a higher affinity for CO2 than rubisco does; it can fix CO2 even when CO2 concentrations are low Make four-carbon compounds, export to bundle-sheath cells release CO2 to be used in the Calvin cycle

C4 cntd HUH?

Plant anatomy C4 leaf anatomy Mesophyll cell Photosynthetic Fig. 10-19a Plant anatomy C4 leaf anatomy Mesophyll cell Photosynthetic cells of C4 plant leaf Bundle- sheath cell Vein (vascular tissue) Stoma

The C4 pathway Mesophyll cell CO2 PEP carboxylase Oxaloacetate (4C) Fig. 10-19b The C4 pathway Mesophyll cell CO2 PEP carboxylase Oxaloacetate (4C) PEP (3C) ADP Malate (4C) ATP Pyruvate (3C) Bundle- sheath cell CO2 Calvin Cycle Sugar Vascular tissue

Where C4? Why is C4 beneficial? In what kinds of environments would you find C4 plants?

CAM plants Open stomata at night Close during day Opposite of other plants Succulent plants (water-storing) pineapple, cactus

CAM Crassulacean acid metabolism (CAM) Take in CO2 at night and form into organic acids Store acid in mesophyll Release CO2 from acid during day What’s so special about day time?

(a) Spatial separation of steps (b) Temporal separation of steps Fig. 10-20 Sugarcane Pineapple C4 CAM CO2 CO2 Mesophyll cell 1 CO2 incorporated into four-carbon organic acids (carbon fixation) Night Organic acid Organic acid Bundle- sheath cell CO2 CO2 Day 2 Organic acids release CO2 to Calvin cycle Calvin Cycle Calvin Cycle Sugar Sugar (a) Spatial separation of steps (b) Temporal separation of steps

Photo= impt Sugar made in the chloroplasts supplies chemical energy and carbon skeletons to synthesize the organic molecules of cells Plants store excess sugar as starch in structures such as roots, tubers, seeds, and fruits In addition to food production, photosynthesis produces the O2 in our atmosphere

10.4 Concept check Explain why photorespiration lowers photosynthetic output for plants How would you expect the relative abundance of C3 versus C4 and CAM species to change in a geographic region whose climate becomes much hotter and drier?

Things to know Describe the structure of a chloroplast Describe the relationship between an action spectrum and an absorption spectrum Trace the movement of electrons in linear electron flow Trace the movement of electrons in cyclic electron flow

TTK cntd Describe the similarities and differences between oxidative phosphorylation in mitochondria and photophosphorylation in chloroplasts Describe the role of ATP and NADPH in the Calvin cycle Describe the major consequences of photorespiration Describe two important photosynthetic adaptations that minimize photorespiration