Chapter 10

Chapter 10 - 1 of 5 Chapter 10: Photosynthesis Leaves are...

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1 of 5 Chapter 10: Photosynthesis Leaves are the major sites of photosynthesis in most plants The color of the leaf is from chlorophyll, the green pigment within chloroplasts Light energy absorbed by chlorophyll drives synthesis of organic molecules in the chloroplast, which is found mostly in the cells of the mesophyll, the tissue in the interior of the leaf CO2 enters the leaf, and O2 exits, by way of stomata 6CO2 + 6H20 + Light Energy C6H12O6 + 6O2 O2 given off by plants is derived from H2O and not CO2 Photosnythesis reverses the direction of electron flow o Water is split, and electrons are transferred along with hydrogen ions from water to carbon dioxide, reducing it to sugar. Electrons increase in potential energy, so the process requires energy (endergonic) Light Reactions [grana] o Convert solar energy to chemical energy o Water is split, providing a source of electrons and protons with O2 as a byproduct o Light absorbed by chlorophyll drives a transfer of electrons and hydrogen ions from water to an acceptor called NADP+ o Light reactions use solar power to reduce NADP+ to NADPH by adding a pair of electrons along with an H+ o Light reactions also generate ATP using chemiosmosis to power the addition of P to ADP ( photophosphorylation) Calvin Cycle or Dark Reactions [stroma] o Produce the sugar o Begin by incorporating CO2 from the air into organic molecules ( carbon fixation ) o Reduces fixed carbon to carbohydrate by the addition of electrons o Reducing power is provided by NADPH, which acquired its cargo of electrons in the light reactions; to convert CO2 to carbohydrate, the Calvin Cycle requires chemical energy in the form of ATP (from light reactions)
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2 of 5 Light is a form of energy known as electromagnetic energy Substances that absorb visible light are known as pigments Spectrophotometer directs beams of light of different wavelengths through a solution of the pigment and measures the fraction of the light transmitted at each wavelength Violet-blue and red light work best for photosynthesis; green is the least effective Accessory pigments with different absorption spectra are photosynthetically important Chlorophyll a is blue green and chlorophyll b is olive green (absorb different wavelengths) Carotenoids (yellow and orange because they absorb violet and blue green light) o Used for photoprotection- absorb and dissipate excessive light energy that would otherwise damage chlorophyll
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Chapter 10 - 1 of 5 Chapter 10: Photosynthesis Leaves are...

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