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
?
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