Photosynthesis Chp 7

Carbon and Energy Sources • Photoautotrophs – Carbon source is carbon dioxide – Energy source is sunlight

• Heterotrophs – Get carbon and energy by eating autotrophs or one another

Flow Chart

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http://en.wikipedia.org

Photoautotrophs • Capture sunlight energy and use it to carry out photosynthesis – Plants – Some bacteria – Many protistans

Spirogyra and Maidenhead Fern

Question 1 • 1. what is a photoautotroph and give an example?

Answer 1 • 1. what is a photoautotroph and give an example? • An organism which uses CO2 as a carbon source, converts light energy to chemical energy to make its own food.

T.E. Englemann’s Experiment Background • Certain bacterial cells will move toward places where oxygen concentration is high • Photosynthesis produces oxygen

T.E. Englemann’s Experiment

Figure 7.1 Page 111

Question 2 • 2. Which colors do photoautotrophs absorb (to make chemical bonds)?

Answer 2 • 2. Which colors do photoautotrophs absorb (to make chemical bonds)? • Blue and red

Question 3 • 3. Why are most photoautotrophs green?

Answer 3 • 3. Why are most photoautotrophs green? • They reflect primarily green light because they absorb blues and reds.

Question 4 • 4. how did Englemann know that the plant absorbed blue and red light?

Answer 4 • 4. how did Englemann know that the plant absorbed blue and red light? • The bacteria in the culture clustered about the areas of high oxygen concentration . The oxygen indicated the light zones used in photosynthesis.

Linked Processes Photosynthesis • Energy-storing pathway • Releases oxygen • Requires carbon dioxide

Aerobic Respiration • Energy-releasing pathway • Requires oxygen • Releases carbon dioxide

Linked Processes

http://www.bios.niu.edu/sims/metabolism/metabolism13.htm

Energy Currency

ATP

Chloroplast Structure

two outer membranes

stroma inner membrane system (thylakoids connected by channels)

Figure 7.3d, Page 116

Photosynthesis Equation

LIGHT ENERGY 12H2O + 6CO2 Water Carbon Dioxide

6O2 + C2H12O6 + 6H2O Oxygen Glucose Water

In-text figure Page 115

Question 5 5. What is the cellular energy currency?

Answer 5 • 5. What is the cellular energy currency? • ATP

Where Atoms End Up

Reactants

Products

12H2O

6O2

6CO2

C6H12O6

6H2O

In-text figure Page 116

Two Stages of Photosynthesis sunlight

water uptake

carbon dioxide uptake

ATP LIGHTDEPENDENT REACTIONS

ADP + Pi NADPH

LIGHTINDEPENDENT REACTIONS

NADP+ P

oxygen release

glucose

new water

In-text figure Page 117

Question 6 6. What molecule(s) links the light reaction to the dark reaction?

Answer 6 6. What molecule(s) links the light reaction to the dark reaction? ATP and NADPH

Electromagnetic Spectrum Stopped Here 10/28 Shortest wavelength

Longest wavelength

Gamma rays X-rays UV radiation Visible light Infrared radiation Microwaves Radio waves

Visible Light • Wavelengths humans perceive as different colors • Violet (380 nm) to red (750 nm) • Longer wavelengths, lower energy

Figure 7.5a Page 118

Photons • Packets of light energy • Each type of photon has fixed amount of energy • Photons having most energy travel as shortest wavelength (blue-violet light)

Pigments • Color you see is the wavelengths not absorbed • Light-catching part of molecule often has alternating single and double bonds • These bonds contain electrons that are capable of being moved to higher energy levels by absorbing light

Variety of Pigments Chlorophylls a and b Carotenoids Anthocyanins Phycobilins

Chlorophylls

Wavelength absorption (%)

Main pigments in most photoautotrophs

chlorophyll a

chlorophyll b

Wavelength (nanometers)

Figure 7.6a Page 119

Figure 7.7 Page 120

Accessory Pigments

percent of wavelengths absorbed

Carotenoids, Phycobilins, Anthocyanins

beta-carotene phycoerythrin (a phycobilin)

wavelengths (nanometers)

Pigments in Photosynthesis • Bacteria – Pigments in plasma membranes

• Plants – Pigments and proteins organized into photosystems that are embedded in thylakoid membrane system

Question 8 • 8. IN the pigments, the color you see is the wavelengths absorbed / not absorbed?

Answer 8 • 8. IN the pigments, the color you see is the wavelengths absorbed / not absorbed?

Photo systems are embedded in the membranes within the thylakoid

Arrangement of Photosystems water-splitting complex H2O

thylakoid compartment

2H + 1/2O2 P680

P700

acceptor

acceptor

PHOTOSYSTEM II

pool of electron carriers

stroma

PHOTOSYSTEM I

Figure 7.10 Page 121

Light-Dependent Reactions • Pigments absorb light energy, give up e-, which enter electron transfer chains • Water molecules split, ATP and NADPH form, and oxygen is released • Pigments that gave up electrons get replacements

Photosystem Function: Harvester Pigments • Most pigments in photosystem are harvester pigments • When excited by light energy, these pigments transfer energy to adjacent pigment molecules • Each transfer involves energy loss

Photosystem Function: Reaction Center • Energy is reduced to level that can be captured by molecule of chlorophyll a • This molecule (P700 or P680) is the reaction center of a photosystem • Reaction center accepts energy and donates electron to acceptor molecule

Pigments in a Photosystem

reaction center Figure 7.11 Page 122

Electron Transfer Chain • Adjacent to photosystem • Acceptor molecule donates electrons from reaction center • As electrons pass along chain, energy they release is used to produce ATP

Cyclic Electron Flow • Electrons – are donated by P700 in photosystem I to acceptor molecule – flow through electron transfer chain and back to P700

• Electron flow drives ATP formation • No NADPH is formed

Cyclic Electron Flow electron acceptor

e

–

e–

electron transfer chain

Electron flow through transfer chain sets up conditions for ATP formation at other membrane sites. e–

ATP

e–

Figure 7.12 Page 122

Noncyclic Electron Flow • Two-step pathway for light absorption and electron excitation • Uses two photosystems: type I and type II • Produces ATP and NADPH • Involves photolysis - splitting of water

Machinery of Noncyclic Electron Flow

H2O photolysis

e–

second electron transfer chain

e–

PHOTOSYSTEM II

first electron NADP+ NADPH transfer chain PHOTOSYSTEM I

ATP SYNTHASE ADP + Pi

ATP

Figure 7.13a Page 123

Potential to transfer energy (volts)

Energy Changes second transfer chain e– first transfer chain e–

e–

NADPH

e– (Photosystem I) (Photosystem II)

H2O

1/2O2 + 2H+ Figure 7.13b Page 123

Photosynthesis: The Movie • The following link will take you to this movie. It is an excellent overview of the light dependant reactions. • In class, you’ll get a copy of the complete narrative. • http://vcell.ndsu.nodak.edu/animations/ph otosynthesis/movie.htm

Photosystem II: The Movie

• http://vcell.ndsu.nodak.edu/animations/photos • This movie provides an excellent explanation of Photosystem II’s structure and function. • A written transcript is available at this site.

Chemiosmotic Model of ATP Formation • Electrical and H+ concentration gradients are created between thylakoid compartment and stroma • H+ flows down gradients into stroma through ATP synthesis • Flow of ions drives formation of ATP

Chemiosmotic Model for ATP Formation Photolysis in the thylakoid compartment splits water H2O e–

H+ is shunted across membrane by some components of the first electron transfer chain

Gradients propel H+ through ATP synthases; ATP forms by phosphate-group transfer

acceptor

ATP SYNTHASE PHOTOSYSTEM II

Figure 7.15 Page 124

ADP + Pi

ATP

ATP Synthase Gradient: The Movie

http://vcell.ndsu.nodak.edu/animations/atpgradie Another excellent animation from MCBE. Note: The ATP Synthase complex in the chloroplast works the same way as it does in the mitochondria.

Light-Independent Reactions • Synthesis part of photosynthesis • Can proceed in the dark • Take place in the stroma • Calvin-Benson cycle

Calvin-Benson Cycle • Overall reactants

• Overall products

– Carbon dioxide

– Glucose

– ATP

– ADP

– NADPH

– NADP+

Reaction pathway is cyclic and RuBP (ribulose bisphosphate) is regenerated

6

CO2 (from the air) CARBON FIXATION

CalvinBenson Cycle

6

6 RuBP unstable intermediate 12 PGA

6 ADP 6

12 ATP

ATP

12 NADPH

4 Pi

12 ADP 12 Pi 12 NADP+

10 PGAL

12 PGAL

2

PGAL

Pi

Figure 7.16 Page 125

P

glucose

The C3 Pathway • In Calvin-Benson cycle, the first stable intermediate is a three-carbon PGA • Because the first intermediate has three carbons, the pathway is called the C3 pathway

Leaf Anatomy

Leaf Anatomy #2

Photorespiration in C3 Plants • On hot, dry days stomata close • Inside leaf – Oxygen levels rise – Carbon dioxide levels drop

• Rubisco attaches RuBP to oxygen instead of carbon dioxide • Only one PGAL forms instead of two

C4 Plants • Carbon dioxide is fixed twice – In mesophyll cells, carbon dioxide is fixed to form four-carbon oxaloacetate – Oxaloacetate is transferred to bundle-sheath cells – Carbon dioxide is released and fixed again in Calvin-Benson cycle

C4 Leaf Anatomy

CAM Plants • Carbon is fixed twice (in same cells) • Night – Carbon dioxide is fixed to form organic acids

• Day – Carbon dioxide is released and fixed in Calvin-Benson cycle

Cam vs. C4

Summary of Photosynthesis light

LIGHT-DEPENDENT REACTIONS

6O2

12H2O ATP

ADP + Pi

NADP+

NADPH

LIGHT-INDEPENDENT REACTIONS PGA 6CO2

RuBP

CALVINBENSON CYCLE

PGAL 6H2O

P C6H12O6 (phosphorylated glucose) end product (e.g., sucrose, starch, cellulose)

Figure 7.21 Page 129

Satellite Images Show Photosynthesis

Atlantic Ocean

Photosynthetic activity in spring Figure 7.20 Page 128

Solar­Hydrogen Energy • Photovoltaic cells use sunlight energy  to split water  • Hydrogen gas produced in this way  can be used as fuel or to generate  electricity • Clean, renewable technology

Fuel Cells

Farmed Hydrogen • Photobiological Hydrogen Production • Aquatic algae bio-engineered to produce hydrogen gas rather than sugars via photosynthesis • Place algae in a clear tube, reduce sulfur, place in sunlight, and collect the hydrogen!

Hydrogen from Algae

Chlamydomonas reinhardt