BIOLOGY - CLUTCH CH.10 - PHOTOSYNTHESIS

[Pages:17]BIOLOGY - CLUTCH CH.10 - PHOTOSYNTHESIS

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BIOLOGY - CLUTCH CH.10 - PHOTOSYNTHESIS CONCEPT: PHOTOSYNTHESIS Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy. Photosynthetic organisms are autotrophs (self-feeders). Heterotrophs consume other organisms EXAMPLE:

The chloroplast, the organelle of photosynthesis, is the site of light absorption, and the subsequent reactions. Chloroplasts are found in high density in the tissue inside leaves, called the mesophyll EXAMPLE:

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BIOLOGY - CLUTCH CH.10 - PHOTOSYNTHESIS CONCEPT: PHOTOSYNTHESIS Chloroplast anatomy:

Double membrane Stroma ? the fluid in the chloroplast, surrounding the internal structures Thylakoids are the membrane bound compartments in which the light reactions occur EXAMPLE:

Photosynthesis has two stages: Light reactions (photo) ? ATP is produced in chloroplasts via chemiosmosis Calvin cycle (synthesis) ? CO2 is turned into the 3-carbon sugar G3P

EXAMPLE:

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BIOLOGY - CLUTCH CH.10 - PHOTOSYNTHESIS CONCEPT: PHOTOSYNTHESIS Light energy from the sun is radiated in discrete packets called photons. Photons can be perceived as fluctuations in the electromagnetic field. EXAMPLE:

The electromagnetic spectrum is the full range of electromagnetic radiation. Electromagnetic radiation is measured by wavelength and frequency

Visible light accounts for only a small fragment of the spectrum EXAMPLE:

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BIOLOGY - CLUTCH CH.10 - PHOTOSYNTHESIS CONCEPT: PHOTOSYNTHESIS Photosynthetic pigments absorb light energy, exciting their electrons

Chlorophyll a ? the main pigment of photosynthesis Accessory pigments ? chlorophyll b and carotenoids broaden the spectrum of light that can be used

Carotenoids provide photoprotection, protection from damaging frequencies of light EXAMPLE:

Pigments have characteristic absorption spectrums. The plot of photosynthetic activity against wavelength of light is called the action spectrum. EXAMPLE:

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BIOLOGY - CLUTCH CH.10 - PHOTOSYNTHESIS CONCEPT: LIGHT REACTIONS The light reactions occur in the thylakoids, and use light energy to drive the processes The light reactions have two functions:

Produce ATP via chemiosmosis Reduce NADP+ to NADPH. EXAMPLE:

Electrons are excited by sunlight, and moved through an electron transport chain. EXAMPLE:

The proton gradient powers ATP synthase to synthesize ATP via photophosphorylation. EXAMPLE

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BIOLOGY - CLUTCH CH.10 - PHOTOSYNTHESIS CONCEPT: LIGHT REACTIONS Photosystems ? complexes of proteins, photopigments, and organic molecules embedded in the thylakoid membrane. Light-harvesting complex (antenna complex) ? system of photopigments and proteins

Resonance energy transfer EXAMPLE:

Reaction-center complex ? specialized pair of chlorophyll molecules that transfer e- to e- acceptor Primary electron acceptor (pheophytin) Page 7

BIOLOGY - CLUTCH CH.10 - PHOTOSYNTHESIS CONCEPT: LIGHT REACTIONS Photosystem II is the start of linear electron flow

P680 ? the reaction-center chlorophyll pair of photosystem II that transfers electrons to primary electron acceptor. Water is split supplying electrons to replace those transferred by P680

H+ is pumped into thylakoid space EXAMPLE:

The primary electron acceptor gives electrons to plastiquinone (PQ) the start of the electron transport chain. PQ gives the electrons to a cytochrome complex (cytochrome/b6-f complex) that pumps protons into thylakoid space Electrons are passed to plastocyanin (PC), then to reaction center in photosystem I EXAMPLE:

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