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.
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
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)
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?)
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
Non-CyclicPhotophosphorylation 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
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
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
Light Independent Reactions a.k.a. the Calvin Cycle
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
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)
Quick Review1. 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.