1. Quiz over cellular respiration
Objective:
I can explain how plants use photosynthesis to create oxygen and sugar.
Agenda:
Quiz over cellular respiration
Notes over photosynthesis

2. Photosynthesis

3. Photosynthesis: An Overview
Photosynthesis is the process by which some organisms convert the energy in sunlight into the energy stored in sugar (and other organic molecules)

4. Photosynthesis Autotrophs and Heterotrophs Autotroph = “self-feeder”
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Able to produce their own food
Heterotroph = “other-feeder”
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Cannot produce their own food
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5. Chloroplast & Leaf Structure
Most photosynthesis occurs in the leaves of plants
Mesophyll is the interior section of the leaf, where most photosynthesis occurs
Gases (O2 and CO2) enter and exit the leaves through stomata (tiny pores in leaf surface)
Chloroplasts
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Thylakoids – individual disc-shaped sac
Granum (plural – grana) – a stack of thylakoids

7. Photosynthesis The Big Picture:
The process by which plants convert light energy into chemical energy
Overall equation:
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2 Stages:
The Light Reactions
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8. The Nature of Light Wavelength = Photons =
distance between two identical places on a wave
Photons =
discrete particles of light
As wavelength gets longer, energy gets lower
Therefore, the color of light with the most energy is .

9. The Light Reactions Step 1 of 2 in Photosynthesis
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Overall Function:
Conversion of light energy (sunlight) into chemical energy (NADPH and ATP) to drive the Calvin Cycle

10. Photosynthetic Pigments
substances that absorb visible light
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3 main pigments involved in photosynthesis:
Chlorophyll a
Chlorophyll b – accessory pigment
Carotenoids – accessory pigment
Each pigment absorbs light energy at its own specific wavelength
Can catch more with 3 “buckets” than just 1

11. Photosystems
Photosystems are made up of pigments (to absorb light) bound to proteins
There are 2 photosystems:
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absorbs light best at wavelength of 700
absorbs light best at wavelength of 680
Named in order of their discovery

12. Photosystems Photosystems:
Chlorophyll is organized along with other molecules into photosystems
“Made up of several hundred pigment molecules
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Working as a team!

13. Photosystems Reaction Center:
Made up of a certain chlorophyll a molecule and the primary electron acceptor
Once a photon strikes the photosystem, an electron is “excited” to a higher energy level
Excited electron is passed from one pigment molecule to another until it gets to this particular chlorophyll a molecule
“hot potato”
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14. Noncyclic Electron Flow
Photosystem II absorbs light, and therefore loses an electron to the PEA.
- PSII is now one electron short of what it needs
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–O2 is released as a
byproduct.

15. Noncyclic Electron Flow
Excited electron leaves PEA and goes to Photosystem I, travelling via an electron transport chain.
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- This ETC harnesses the energy from the electron to produce ATP by chemiosmosis.
4. When the electron gets down to the bottom of the ETC, it replaces an electron that has been lost from Photosystem I because of photoexcitation.

16. Noncyclic Electron Flow
5. The PEA of PS I passes the excited electron to ferredoxin
- (part of ETC #2)
6. The enzyme NADP+ reductase transfers the electrons from ferredoxin to NADP+.
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17. The Light Reactions

18. ***Chemiosmosis in Chloroplasts
ATP is generated using the process of chemiosmosis
Protons (H+) are pumped from stroma into thylakoid space
Pumping energy comes from energy lost by electrons
Potential energy (rock at top of hill idea)

19. ***Chemiosmosis
As protons diffuse through ATP synthase (enzyme) in the thylakoid membrane, the potential energy (in H+ concentration) is used to form a bond between ADP (dead battery) + a phosphate group
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20. ***Chemiosmosis

21. The Calvin Cycle Step 2 of 2 in Photosynthesis
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Big Picture:
Uses CO2 (from atmosphere) and energy (from the Light Reactions) to make SUGAR

22. The Calvin Cycle Carbon Fixation:
The incorporation of CO2 into organic material
Making carbon “stick” – part of a complex molecule for energy storage
Sugar (useful) not just carbon dioxide (un-useful )

23. Phase I: Carbon Fixation
5-carbon RuBP is attached to 1 CO2 molecule to produce 1 6-carbon molecule
This reaction is catalyzed by Rubisco
6-carbon molecule splits into (2) 3-carbon molecules
3-phosphoglycerate

24. Phase II: Reduction
Each 3-phosphoglycerate gets a phosphate added to it from ATP (light reactions)
NADPH donates electrons to convert 3-phosphoglycerate to G3P
G3P is a carbohydrate/ stores more energy than 3-phosphoglycerate

25. Phase II: Reduction Now… However…
For every 3 molecules of CO2 that entered the cycle, we have 6 molecules of G3P
However…
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This 1 “extra” G3P exits the cycle to be used by the cell

26. Phase III: Regeneration of RuBP
The Calvin CYCLE
5 G3P molecules (3-C each) are rearranged into 3 RuBP molecules (5-C each)
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27. An Overview: Light Reactions & the Calvin Cycle
Provide the energy (ATP and NADPH) required to run the Calvin Cycle
Calvin Cycle:
Uses the energy (ATP and NADPH) from the light reactions and carbon dioxide (from the atmosphere) to make carbohydrates
You can’t have one without the other! 