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4.3 Photosynthesis. Photosynthesis in Plants. What is the simple word equation for photosynthesis?. Chloroplasts.
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Photosynthesis in Plants • What is the simple word equation for photosynthesis?
Chloroplasts Thylakoids are a phospholipidbilayer membrane-bound compartment. A granum is a stack of thylakoids folded on top of one another. The stroma is the fluid space within the chloroplast. The lumen is the fluid filled space within a thylakoid. An average green plant cell has between 10 – 50 chloroplast
Chlorophyll • Chlorophyll is actually made up of 5 pigments • Chlorophyll a & b • Carotenoids (carotene and xanthophyll) • Phaeophytin (a grey breakdown product of the others)
There are 2 distinct chlorophyll complexes • Photosystem I (PSI) • Photosystem II (PSII) • Each system has a different combination of pigments • They therefore absorb light in different areas of the spectrum • PSI absorbs around 700 nm • PSII absorbs around 680 nm • Each system has a different role in photosynthesis
Biochemistry of Photosynthesis • Photosynthesis is a two stage process involving a series of reactions. • Light-dependent stage can only take place during daylight. • It produces products which are used by the light-independent stages. • The whole process occurs all the time during daylight hours. But the light-independent stage can also occur in the dark.
Light-Dependent • Takes place on thylakoid membranes • 2 functions: • Produce ATP • Split water in a photochemical reaction providing hydrogen ions to reduce CO2 and make carbohydrates • Light is made of photons, photons hit chlorophyll and excite them (give them more energy) • excited electrons are picked up by electron acceptors • ATP can then be made by photophosphorylationvia an electron transport chain.
Non-Cyclic Photophosphorylation NADP (electron acceptor) +2H+ Reduced NADP (used in light-independent reaction) Electron transport chain
Light-independent Stage CO2 Glucose RUBISCO Calvin Cycle