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Photosynthesis

Photosynthesis. Cellular Energy Unit Part I. Autotrophs. Producers Photosynthesizing plants, bacteria, and some eukaryotic single celled organisms. The base of every food chain/web possible. Overview. Overall Reaction: 6CO 2 + 6H 2 O + sunlight → C 6 H 12 O 6 + 6O 2

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Photosynthesis

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  1. Photosynthesis Cellular Energy Unit Part I

  2. Autotrophs • Producers • Photosynthesizing plants, bacteria, and some eukaryotic single celled organisms. • The base of every food chain/web possible.

  3. Overview Overall Reaction: 6CO2 + 6H2O + sunlight → C6H12O6 + 6O2 Affected by: Intensity of light, concentration of CO2 and temperature.

  4. Chloroplasts Two important sites of photosynthesis: thylakoid membranes and the stroma.

  5. Plant Pigments • There are many pigments in the chloroplasts of plant cells. They are present in different proportions at different times of year which accounts for the many colors of leaves we see. • The two classes are chlorophylls and carotenoids. Chlorophylls are green and carotenoids run a spectrum from yellow to red but are most commonly called orange. • We see colors because these pigments absorb the white light and reflect the wavelength of light they do not absorb. For example, we see green because chlorophyll absorbs red, orange, yellow, blue, indigo and violet and reflects green back to us.

  6. Light Reactions • Light Reaction: • ADP + NADP+ + H2O+ Sunlight→ATP + NADPH + O2 • Occurs in the Thylakoid Membranes of Chloroplasts • Includes Photosystem II where chlorophyll is excited by light and loses electrons. Water is split to provide more electrons to chlorophyll and oxygen is given off it diffuses out of the stoma. • The electrons travel to the electron transport chain where NADP+ recharged to NADPH using one of the hydrogens from water. • Then Photosystem I where more chlorophyll is excited by light and more water is split to create a H+ gradient that ATP synthase uses to recharge ADP to ATP.

  7. ATP Synthase

  8. Dark Reactions • ATP + NADPH + CO2 → C6H12O6 + ADP + NADP+ • Occurs in the stroma of the chloroplasts. • Does not depend on light • Carbon dioxide diffuses into the stoma. • Uses the calvin cycle for carbon fixation to create a 6 carbon glucose from carbon dioxide. • It takes 6 spins of the calvin cycle to make 1 glucose and it uses 18 ATP and 12 NADPH’s to power the process. • Glucose is stored in the vacuole as starch or it is used to feed the plant or make plant cell parts.

  9. Calvin Cycle • Also known as carbon fixation. • Uses ATP at two points in each turn of the cycle. In the first point it uses 2 ATP’s and the second it uses 1 ATP for a total of 3 ATP’s for each turn of the cycle. • It uses 2 NADPH’s at one point in each cycle for a total of 12 NADPH’s used during the 6 cycles it takes to make one glucose. • It then feeds the used ADP and NADP+ back into the thylakoid for the light reactions recharge them back to ATP and NADPH.

  10. Photosynthesis Review Light Dark Occurs in the stroma Uses carbon dioxide, ATP, and NADPH Produces glucose Recycles ADP and NADP+ Glucose is food and made into cell parts. • Occurs in the thylakoid • Uses water, sunlight and the recycled ADP and NADP+ • Produces ATP, NADPH, and OXYGEN • Oxygen leaves the plant through the stoma.

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