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)
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
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
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)
23.
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.
Editor's Notes
Diagram to show the light dependent reactions with photosytems II and ICommonly referred to as a Z-scheme
P680- photosystem is sensitive to 680nm wavelength of light, P700 to 700nm of light
PS II produces ATP and PS I produces NADPHPhotolysis of water is associated with PS II
4. Light indeprxns involve ATP/NADPH + H+/ intermediates which are made in light reactions, supply of ATP/NADPH intermediates is used up/ runs out in the dark, GP therefore not reduced/ converted to triose phosphate, RuBP therefore not regenerated, CO2 fixation therefore stops, stomata close in the dark, CO2 therefore not absorbed.
