Chapter 4
•Photosynthesis
– Photosynthesis is the process by which certain organisms use light energy• To make sugar and oxygen gas from carbon dioxide and water
• What does it need? (Input)• What does it make? (Output)
Lightenergy
PHOTOSYNTHESIS
6 CO2 6+ H2O
Carbon dioxide Water
C6H12O6 6+ O2
Glucose Oxygen gas
Trophic Roles• Autotrophs
Producers of the biosphere:– produce organic
molecules from CO2 & inorganic raw materials
• Heterotrophs consumers
Learning Target
1. Describe Oxidation & Reduction reactions
REDOX Reactions
LEO th
e Lio
n Say
s GER
REDOX Reactions
• Oxidation– When a compound loses electrons
• Reduction– When a compound gains electrons
• CO2 + H2O + energy → C6H12O6 + O2
– CO2 is reduced to form glucose
– Water is oxidized to form O2
•Photosynthesis is a redox process, as is cellular respiration– In photosynthesis
• H2O is oxidized and CO2 is reduced
Figure 7.4A, B Reduction
Oxidation
6 O2 6 H2O
Reduction
Oxidation
6 O26 CO2 6 H2O C6H12O6
C6H12O6 6 CO2
Learning Check
• If H2O is losing electrons than it is being reduced/oxidized
• Co2 is being reduced/oxidized, which means it is gaining/losing electrons.
Photosynthesis Overview
• Light reactions– Depend on light– Occur in Thylakoid
Membrane
• Light Independent (“Dark”) reactions– Does NOT need light– Occurs in the Stroma
Learning Target
12.Compare & contrast the structure & function of mitochondria & chloroplast
15. Determine what factors affect the process of photosynthesis & cellular respiration
Location, location, location
Where does the Light Dependent Reaction occur?The Light Independent reaction?
Chloroplast Structure
• Found in mesophyll – 1 mesophyll
cell may have 30 chloroplasts
• Stomata regulate passage of CO2, O2 and H2O
Learning Check
Where does the Light Dependent Reaction occur?
The Light Independent reaction?
• What factors could affect the process of photosynthesis?
Learning Targets
11. Describe the purpose of Chlorophyll & Accessory pigments.
Pigments• Pigments
– Absorb light energy– Boost e- become unstable!
• Chlorophyll– Chlorophyll a main pigment
blue-green– Chlorophyll b accessory
pigment yellow-green• Other accessory pigments
absorb different wavelengths of light– Carotenoids yellow-orange– Xanthophyll yellow– Rhodophyll red– Fucoxanthin brown
Why are plants
green?
Why are plants changing color?
Photosystems• Pass energy
reaction center (chlorophyll a molecule) transfers energy to primary electron acceptor
• antenna pigments are primarily chlorophyll b, carotenoids & xanthophyll
Learning Check
• What is the purpose/function of pigments?
Photosynthesis Overview• Light reactions
– light energy chemical energy (ATP and NADPH) and produce O2
• Light Independent (“Dark”) reactions– Using ATP and NADPH
from the light reactions form sugar from CO2
Learning Target
7. Contrast Chemiosmosis in Cellular Respiration and Photosynthesis
6. Explain how electron transport chains (ETC) establish an electrochemical gradient across membranes.
ETC, Chemiosmosis & ATP Synthase
• Powers ATP synthesis in light reactions• electrons (e-) are passed along a chain of proteins (called the ETC) in
the membrane H+ pumped into Thylakoid space (chemiosmosis)
• H+ diffuse back across the membrane through ATP synthase powers the phosphorylation of ADP to produce ATP (photophosphorylation)
Photophosphorylation http://vcell.ndsu.nodak.edu/animations/atpgradient/movie.htm
Learning Check!
• ETC uses the energy of e- being passed along to pump _______ from the ________ into the thylakoid _______
• Chemiosmosis is the movement of ______ to create a ________concentration.
Learning Target
3. Identify the inputs and outputs and location of the light reactions and Calvin Cycle.
4. Explain the role of NADH, FADH2, and NADPH.
14. Summarize how energy is transferred during photosynthesis and cellular respiration.
Electron Carriers• NAD+
– Reacts with C-H bonds to become NADH
• NADP+– Reacts with free e- and H+ ions
• ADP ATP– diffusion of H+ through ATP Synthase
LDR
• Inputs?• Outputs?
• Two types:– Noncyclic
Photophosphorylation – Cyclic
Photophosphorylation
Non-cyclic photophosphorylation
Learning Target
12. Describe the connection between PS2 & PS1
LIGHTREACTOR
NADP+
ADP
ATP
NADPH
CALVINCYCLE
[CH2O] (sugar)STROMA(Low H+ concentration)
Photosystem II
LIGHT
H2O CO2
Cytochromecomplex
O2
H2OO2
1
1⁄2
2
Photosystem I
Light
THYLAKOID SPACE(High H+ concentration)
STROMA(Low H+ concentration)
Thylakoidmembrane
ATPsynthase
PqPc
Fd
NADP+
reductase
NADPH + H+
NADP+ + 2H+
ToCalvincycle
ADP
P
ATP
3
H+
2 H++2 H+
2 H+
Light Dependent RXN animation
• http://www.science.smith.edu/departments/Biology/Bio231/ltrxn.html
• http://vcell.ndsu.nodak.edu/animations/photosynthesis/movie-flash.htm
Cyclic Photophosphorylation
• Primitive used by bacteria
• Electron boosted out of P1 ETC returned to P1
• Electron drives proton pumps chemiosmosis ATP
Learning Targets
3. Identify the inputs and outputs and location of the light reactions and Calvin Cycle.
4. Explain the role of NADH, FADH2, and NADPH.
15. Summarize how energy is transferred during photosynthesis and cellular respiration.
Calvin Cycle/Light Independent Reactions
• Occur in the dark or the light• Light independent reactions• 3 steps
– Carbon fixation– Reduction– Regeneration of RuBP
Step 1:Carbon Fixation
• RuBP (ribulose bisphosphate)– 5 C sugar– Catalyzed by Rubisco
(RuBP carboxylase)
– Adds CO2
• Creates an unstable 6 C molecule that splits
• Creates PGA (3 C moleucle
Step 2:Reduction
• PGA gets phosphorylated by ATP (gets it’s energy)
• Reduced by NADPH (gets it’s e-)
• Produces G3P (PGAL)
– some G3P glucose
– most G3P regenerate RuBP
Step 3:Regeneration of RuBP
• 1 G3P moves out to eventually become glucose
• G3P rearranged into RuBP
• Requires input of 3 ATP• Takes 6 turns of cycle
1 glucose
http://www.science.smith.edu/departments/Biology/Bio231/calvin.html
Alternative mechanisms:Photorespiration
• C3 plants rice, wheat, soybeans
• Uses Co2 directly to make PGA
• On hot, dry days they close their stomata– no CO2 taken in and O2 builds up
– rubisco substitutes O2 for CO2
– Creates a 2 C compound
• 2 C compound gets broken down releases CO2 & water
• Called photorespiration– Uses light, releases CO2 and water
– Doesn’t make glucose
Alternative mechanisms:C4 Plants
• Sunny ecosystems • C is fixed into 4 C molecule• Carbon fixed outside cells (in
bundle sheath cells very efficient requires extra ATP
• Only fixes C, not oxygen• Donates the carbon to Calvin
Cycle• Balances out photorespiration &
saves water
• Corn and sugarcane are a C4 plants
Alternative mechanisms:CAM Plants
• Crassulacean acid metabolism Hot/dry climates
• Orchids, cacti, pineapple etc.
• Stomates open at night to reduce water loss evaporation
• CO2 is fixed into a 4 C compound, used later