1. Chapter 10
Photosynthesis

2. The feeding of the biosphere
Life on Earth is solar powered
Photosynthesis nourishes almost the entire Earth
Almost all plants are autotrophs
Self-feeders

3. Autotrophs vs. heterotrophs
Autotrophs –sustain themselves without eating anything derived from other organisms. They produce organic molecules from CO2 and other raw materials
Hetertrophs – obtain organic material by consuming other organisms

4. Photosynthetic vs. chemosynthetic
Autotrophs can be photosynthetic or chemosynthetic
Photosynthetic autotrophs use light as source of energy to synthesize organic substances
Chemosynthetic autotrophs use chemical energy to synthesize organic substances

5. Photosynthesis: overview
Occurs in two stages
Light reactions- conversion of solar energy to chemical energy to produce NADPH and ATP
Calvin Cycle or dark cycle – the synthesis part of photosynthesis, the incorporation of CO2 from the air into organic molecules.

6. The chloroplast The site of photosynthesis Found in green plants
Mainly in the mesophyll tissue of the leaf.

7. Chloroplast structure
Double membranes enclose the stroma – dense fluid inside the chloroplast. A system of interconnected membranous sacs called thylakoids separates the stroma
Chlorophyll is located inside the thylakoids

8. The pigment chlorophyll is located in the thylakoids of the chloroplasts. The pigment absorbs light energy to produce ATP and NADPH.
The Calvin cycle occurs in the stroma
Chloroplast function

9. Photosynthesis equation
6 CO2 + 6 H20 + LIGHT ENERGY
C6H12O6 + 6O2

10. THE ROLE OF REDOX REACTIONS
Like cellular respiration, photosynthesis involve redox reactions
Photosynthesis reverses the direction of electron flow. Water is split and electrons are transferred along with H+s from H2O(oxidized)
CO2 is reduced to sugar

11. Absorption spectrum vs action spectrum
Absorption spectrum is the wavelength of light best absorbed by the pigment
Action spectrum profiles the relative effectiveness of different wavelengths of radiation.

12. Why does chlorophyll’s absorption spectrum differ from action spectrum
Accessory pigments with different absorption spectra are in chloroplasts
Chlorophyll b- yellow-green
Carotenoids have various shades of yellow and orange. Contain antioxidants

13. Effective wavelengths of light
Light in the violet-blue and red portions of the spectrum.

14. Absorption photons
Absorption of a photon boosts electrons to an orbital of higher energy. The pigment molecule is in an excited state

15. Components of photosystem
Photosystem I and Photosystem II (named in the order discovered)
Consists of a reaction center and light – harvesting complexes. The reaction center is a protein complex
Light-harvesting complex consists of pigment molecules bound to protein

16. Flow of light through psI and psii
Photon of light strikes a pigment molecule in light-harvesting complex. It is relayed to other pigment molecules until it reaches P680 chlorophyll molecule in PS II reaction center. P680 is excited to higher energy level
The electron is captured by primary electron acceptor
An enzyme splits a water molecule into 2 electrons (2H+ and an O). Electrons are supplied one by one to P680 molecule ( O combines with another O to form O2)
Photoexcited electron passes from the primary electron acceptor of PSII to PS I via an electron transport chain.

17. The exergonic “fall” of electrons to lower energy level provides energy for ATP synthesis.
Light energy is transferred to a light harvesting complex in PSI exciting a P700 chlorophyll molecule. The excited electron goes to primary electron acceptor.
Photo excited electrons are passed from PSI primary acceptor through a second electron transport chain.
NADP+ is reduced to NADPH.

18. PS I and PS II

19. Carbon-fixing reactions of the calvin cycle
The Calvin Cycle is anabolic, building sugar from smaller molecules and consuming energy
CO2 enters
End product is G3P
To produce 1 G3P, the Calvin Cycle consumes 9 ATP, 6 NADPH

20. The role of Atp and nadph in the calvin cycle
The Calvin Cycle spends ATP as an energy source and consumes NADPH as a reducing power for adding high-energy electrons to make sugar

21. Photorespiration
A metabolic pathway that consumes O2 and releases CO2.
Generates no ATP
No production of sugar
Decreases photosynthetic output by siphoning the organic material from the Calvin Cycle.

22. Photosynthetic adaptations
In most plants the initial fixation of carbon occurs via rubisco.
C3 plants – rice, wheat, soybeans
Their stomata partially close on hot, dry days.
Decrease CO2 leads to lower sugar production

23. C4 plants Use distinctive photosynthetic cells Sugarcane and corn
Bundle-sheath cells and mesophyll cells
Mesophyll cells export 4-Carbon compound to Bundle-sheath cells where it is converted to CO2 and enters the Calvin cycle.
Sugarcane and corn

24. CAM plants Open stomata during the night and close them during the day
CO2 is converted into organic compound and stored in the vacuoles of mesophyll cells until morning
Light reactions can supply ATP, NADPH for the Calvin Cycle
The process takes place within the same cell.

25. Fate of photosynthetic products
50% of organic material made by photosynthesis is consumed as fuel for cellular respiration in the mitochondria of the plant
Carbohydrates are transported in the form of sucrose
Some sugar is linked together to form cellulose.