• Photoautotrophs

– Carbon source is carbon dioxide

– Energy source is sunlight

• Heterotrophs

– Get carbon and energy by eating autotrophs or one

another

Carbon and Energy Sources

Flow Chart

? http://en.wikipedia.org/wiki/Autotrophs

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 7.1Page 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

inner membrane system(thylakoids connected by channels)

stroma

Figure 7.3d, Page 116

Photosynthesis Equation

12H2O + 6CO2 6O2 + C2H12O6 + 6H2O

Water Carbon Dioxide

Oxygen Glucose Water

LIGHT ENERGY

In-text figurePage 115

Question 5

5. What is the cellular energy currency?

Answer 5

• 5. What is the cellular energy currency?

• ATP

Where Atoms End Up

Products 6O2 C6H12O6 6H2O

Reactants 12H2O 6CO2

In-text figurePage 116

Two Stages of Photosynthesis

sunlight water uptake carbon dioxide uptake

ATP

ADP + Pi

NADPH

NADP+

glucoseP

oxygen release

LIGHT-INDEPENDENT

REACTIONS

LIGHT-DEPENDENT REACTIONS

new water

In-text figurePage 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 SpectrumStopped Here 10/28

Shortest Gamma rays

wavelength X-rays

UV radiation

Visible light

Infrared radiation

Microwaves

Longest Radio waves

wavelength

Visible Light

• Wavelengths humans perceive as different colors

• Violet (380 nm) to red (750 nm)

• Longer wavelengths, lower energy

Figure 7.5aPage 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

ChlorophyllsW

avel

eng

th a

bso

rpti

on

(%

)

Wavelength (nanometers)

chlorophyll b

chlorophyll a

Main pigments in most photoautotrophs

Figure 7.6a Page 119 Figure 7.7Page 120

Accessory Pigmentsp

erce

nt

of

wav

elen

gth

s ab

sorb

ed

wavelengths (nanometers)

beta-carotenephycoerythrin (a phycobilin)

Carotenoids, Phycobilins, Anthocyanins

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 thylakoidcompartment

H2O 2H + 1/2O2

P680

acceptor

P700

acceptor

pool of electron carriers stromaPHOTOSYSTEM II

PHOTOSYSTEM I

Figure 7.10Page 121

• 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

Light-Dependent Reactions

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 7.11Page 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

electron transfer chain

e–

e–

e–

e–

ATP

Electron flow through transfer chain sets up

conditions for ATP formation at other membrane sites.

Figure 7.12Page 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

photolysis

H2O

NADP+ NADPH

e–

ATP

ATP SYNTHASE

PHOTOSYSTEM IPHOTOSYSTEM II ADP + Pi

e–

first electron transfer chain

second electron transfer chain

Figure 7.13aPage 123

Energy Changes

Figure 7.13bPage 123

Po

ten

tial

to

tra

nsf

er e

ner

gy

(vo

lts)

H2O 1/2O2 + 2H+

(Photosystem II)

(Photosystem I)

e– e–

e–e–

secondtransfer

chain

NADPHfirst

transferchain

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/photosynthesis/movie.htm

Photosystem II: The Movie

• http://vcell.ndsu.nodak.edu/animations/photosystemII/movie.htm

• 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

ADP + Pi

ATP SYNTHASE

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

ATP

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

PHOTOSYSTEM II

H2Oe–

acceptor

Photolysis in the thylakoid compartment splits water

Figure 7.15Page 124

ATP Synthase Gradient: The Movie

http://vcell.ndsu.nodak.edu/animations/atpgradient/movie.htm

Another excellent animation from MCBE.

Note: The ATP Synthase complex in the chloroplast works the same way as it does in the mitochondria.

• Synthesis part of

photosynthesis

• Can proceed in the dark

• Take place in the stroma

• Calvin-Benson cycle

Light-Independent Reactions

Calvin-Benson Cycle

• Overall reactants

– Carbon dioxide

– ATP

– NADPH

• Overall products

– Glucose

– ADP

– NADP+

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

Calvin- Benson Cycle

CARBON FIXATION

6 CO2 (from the air)

6 6RuBP

PGA

unstable intermediate

6 ADP

6

12

12ATP

ATP

NADPH

10

12PGAL

glucoseP

PGAL2

Pi

12 ADP12 Pi

12 NADP+

12

4 Pi

PGAL

Figure 7.16Page 125

• 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

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

Figure 7.21Page 129

light6O2

12H2O

CALVIN-BENSON CYCLE

C6H12O6

(phosphorylated glucose)

NADPHNADP+ATPADP + Pi

PGA PGAL

RuBP

P

6CO2

end product (e.g., sucrose, starch, cellulose)

LIGHT-DEPENDENT REACTIONS

6H2O

LIGHT-INDEPENDENT REACTIONS

Satellite Images Show Photosynthesis

 Photosynthetic activity in spring

Atlantic Ocean

Figure 7.20Page 128

Solar-Hydrogen 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 reinhardtii