1. Photosynthesis

3. Structures of Photosynthesis

4. Leaves
 Flattened leaf shape exposes large surface
area to catch sunlight
 Upper and lower leaf surfaces of a leaf
comprise the epidermis
 Waxy, waterproof cuticle on outer surfaces
reduces water evaporation

5.  Adjustable pores called stomata allow for entry of air
with CO2
 Inner mesophyll cell layers contain majority of
chloroplasts (40- 200 each mesophyll cell)
 Vascular bundles (veins) supply water and minerals to
the leaf while carrying sugars away from the leaf
 Chloroplasts- double-membrane (inner and outer)

6. 6
Chloroplast Structure

7. Pigments
 Pigment absorbs visible light
 Chlorophyll a and b absorb violet, blue, and red
light but reflect green light (hence they appear green)
 Carotenoids absorb blue and green light but reflect
yellow, orange, or red (what color would they appear?)

8. Photophosphorylation
 Process that creates ATP using a proton gradient
created by the energy of sunlight
 Similar to electron transport chain in respiration
 Is light dependent, therefore called
photophosphorylation
 2 types-non-cyclic and cyclic

9. Non-cyclic photophosphorylation

10. Light Dependent Reaction

11. Path of Electron

12. Path of electron

15. Non-Cyclic
Photophosphorylation
 ATP is generated by the protons moving across the
thylakoid membranes to create a proton gradient
 Proton gradient is used to generate ATP during
chemiosmosis
 NADPH2 is formed
 Oxygen released due to photolysis of water
 PSII and PSI working together
 Needs external source of electrons
 Performs best under optimum light, with CO2 present
and aerobic conditions
 Continues to light independent reactions to fix carbon

16. Chemiosmosis
 Process that uses the movement of a proton (H+) to
join ADP and Pi to form ATP
 ATP synthase is needed
 H+ ions create a proton-motive force

17. Cyclic Photophosphorylation
 Electrons are recycled, return back to PS I
 Proton gradient is formed, therefore ATP formation
happens
 No reduction of NADP+ occurs, only ATP is made
 Requires only PS I
 Typical of low light situations, limited CO2 and/or
anaerobic conditions
 Not very common, except with photosynthetic
bacteria

18. Light Independent Reactions
a.k.a. the Calvin Cycle

21. Light Independent Reactions
 CO2 diffuses into the stroma of the cloroplasts
 CO2 is fixed to a 5-carbon molecule (ribulose
biphosphate) to form a 6 carbon molecule
 Rubisco, an enzyme, catalyzes this reaction
 6-carbon molecule is not stable, and splits to form
3PGA
 Energy from ATP and NADPH is used to remove a
phosphate group from 3PGA to form G3P
 RuBP is regenerated from G3P

22. Light Independent Reactions
 Occurs in the stroma
 Depleted carriers (ADP and NADP+) return to light-
dependent reactions for recharging
 6 CO2 used to synthesize 1 glucose (C6H12O6)

24. Quick Review
1. How is the structure of a chloroplast related to its
function?
2. Why do plant cells need mitochondria if they can
make ATP in chloroplasts?
3. Explain the role of water in photosynthesis.
4. Explain why light-independent reactions of
photosynthesis can only continue for a short time
in darkness.