1. Photosynthesis
CHAPTER 10

2. LIGHT ENERGY
Photons – a discrete bundle of light energy that is always in motion
Energy Levels of photons are measured in wavelengths
Plants absorb most light energy in the red and blue ranges of colors
LOW ENERGY HIGH ENERGY

3. Engelmann's photosynthetic action spectrum
Engelmann's photosynthetic action spectrum. Aerotactic bacteria move toward areas of high oxygen concentration indicative of photosynthesis, stimulated by red and blue light. The black and white drawing is from (Engelmann, 1882), and it has been superimposed on a spectrum to show photosynthetically active wavelengths.

5. PIGMENTS
Photosynthetic organisms capture free energy present in sunlight using pigments.
Chlorophyll – green pigment
Absorbs red and blue wavelengths – reflects green
There are 3 types of chlorophylls
Chlorophyll a – green
Chlorophyll b/c – green and orange
PHOTOSYSTEMS
Groups of photosynthetic pigments
Photosystem I (P700) absorbs light in the 700nm range
Photosystem II (P680) absorbs light in the 680mm range

6. REACTIONS OF PHOTOSYNTHESIS
LIGHT DEPENDENT
Occurs in the Thylakoids
Chlorophyll absorbs light
Light energy drives the production of ATP and NADPH
Water is split to form H+ ions and oxygen
Chemisomotic production of ATP
LIGHT INDEPENDENT
Occurs in the stroma
ATP and NADPH provide the energy input to form carbohydrates

7. The Thylakoids

8. Thylakoid Structure

9. The Light Dependent Reactions
During photosynthesis, chlorophylls absorb free energy from light, boosting electrons to a higher energy level in Photosystems I and II.
Photosystems I and II are embedded in the internal membranes of chloroplasts (thylakoids) and are connected by the transfer of higher free energy electrons through an electron transport chain (ETC).

10. The Light Dependent Reactions
When electrons are transferred between molecules in a sequence of reactions as they pass through the ETC, an electrochemical gradient of hydrogen ions (protons) across the thylakoid membrane is established.
The formation of the proton gradient is a separate process, but it is linked to the synthesis of ATP from ADP and inorganic phosphate via ATP synthase.

11. The Light Independent Reaction
The energy captured in the light reactions as ATP and NADPH powers the production of carbohydrates from carbon dioxide in the Calvin cycle, which occurs in the stroma of the chloroplast.

12. Hatch-Slack Pathway (C4)
Used by heat-tolerant plants
Desert plants, crabgrass, weeds
Separate the photolysis and carbon fixation into different cells
In C3 plants photolysis and carbon fixation occur in a single chloroplast

13. Hatch-Slack Pathway (C4)
In C4 plants the photosynthesis takes place in a chloroplast of a thin-walled mesophyll cell and a 4-carbon acid is handed off to a thick-walled bundle sheath cell where the Calvin cycle occurs in a chloroplast of that second cell.
This protects the Calvin cycle from the effects of photorespiration.

14. C4 versus C3 Leaf Structure
C4 Leaf Anatomy C3 Leaf Anatomy

16. CAM PLANTS
Photosynthesis and initial carbon fixation occur at night and a 4-carbon acid is stored in the cell's vacuole. During the day, the Calvin cycle operates in the same chloroplasts.

17. FACTORS AFFECTING PHOTOSYNTHESIS
The graph shows the relationship of photo­synthetic rate and irradiance (light intensity) as it is influenced by both temperature and carbon dioxide level.

18. Factor Affecting Photosynthesis
EFFECT
Light Intensity
Increased light increases rate
Temperature
Increases rate – excessive temperature denatures photosystems
Carbon Dioxide
Increases to Vmax – limited by rate of Rubisco activity
Water
Increases rate
Oxygen
As level increase, rate decreases due to competitive inhibition of Rubisco pH
Denature photosystems