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PHOTOSYNTHESIS Converts light energy into chemical energy through a complex series of biochemical reactions 6CO 2 + 6H 2 O -> C 6 H 12 O 6 + 6O 2 Photosynthesis.

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Presentation on theme: "PHOTOSYNTHESIS Converts light energy into chemical energy through a complex series of biochemical reactions 6CO 2 + 6H 2 O -> C 6 H 12 O 6 + 6O 2 Photosynthesis."— Presentation transcript:

1 PHOTOSYNTHESIS Converts light energy into chemical energy through a complex series of biochemical reactions 6CO 2 + 6H 2 O -> C 6 H 12 O 6 + 6O 2 Photosynthesis occurs inside the chloroplasts White light from the sun is composed of different colors of different wavelengths – visible spectrum

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8 CHLOROPLAST STRUCTURE Outer, double membrane Inner Membrane system: –THYLAKOIDS – flattened sacs –GRANA – stacks of thylakoids Light harvesting pigments embedded in thylakoid membrane Surrounding thylakoids, liquid: STROMA

9 Photosynthesis depends upon green pigment CHLOROPHYLL (absorbs light in the blue-violet and orange-red and reflects light in green region Accessory pigments help harvest light energy

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12 LIGHT DEPENDENT RXNS Visible light (traveling in “photons”, packets of energy) is changed into chemical energy H 2 O is split into O 2 and H PS I and II absorb light energy This light energy is transferred to reaction center, a Chlorophyll a that donates e- to electron carrier

13 LIGHT DEP. RXNS cont’d Lost e- from PSII is replaced by e- from H 2 O At end of electron flow, electrons combine with NADP+ to form NADPH As electrons flow along electron transport chain, protons build up inside thylakoids

14 H3C HC1"/,H C C H CHJ H CH3 H H H H H C CH1J,,/HJI I I I I I I I II! I/c, /C"", /c""' /C, /C, /C""' /c, /C"", /c~ /c, /c" /CH1H1C C C C C C C C C C C /C"I I I I I I I I I I H3C CHJH1C, /C H H H H H CHJ H CH3 HC "H1 CH3f,'-caroteneH3C HC1"/,H C C H CHJ H CH3 H H H H H C CH1J,,/HJI I I I I I I I II! I/c, /C"", /c""' /C, /C, /C""' /c, /C"", /c~ /c, /c" /CH1H1C C C C C C C C C C C /C"I I I I I I I I I I H3C CHJH1C, /C H H H H H CHJ H CH3 HC "H1 CH3f,'-carotene

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16 LIGHT DEP. RXNS cont’d These built up protons will diffuse down concentration gradient through ATP synthase TAH-DAH!! ATP is made!!! PRODUCTS: –O 2, ATP and NADPH!!!!

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19 CALVIN CYCLE Pathway that produces organic compounds, using energy stored in ATP and NADPH from the light reactions Occurs in the stroma CO 2 is “fixed” into organic compounds RuBP (ribulose bisphosphate) is the 5 carbon sugar that CO 2 is bound to by the enzyme rubisco

20 More CALVIN… The new 6 carbon molecule is immediately split into 2 3-carbon molecules (PGA) PGA converted to PGAL by addition of the phosphate from ATP and the hydrogen from NADPH ADP, NADP+ and phosphate are used again in the light reactions to form more ATP and NADPH

21 To make one molecule of G3P, three turns of the cycle + 3 CO 2 molecules CO 2 is fixed to RuBP by rubisco – produces unstable intermediate -> 3- phosphoglycerate RuBP is regenerated – one per each trip through the cycle Uses 9 ATP and 6 NADPH

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24 ALTERNATIVE PATHWAYS Calvin cycle plants = C 3 because of PGAL that is formed (3 carbon) Water loss through stomates is big problem When air is hot and dry, stomates close to prevent water loss BAD THING – CO 2 levels fall and O 2 levels rise, resulting in carbon fixation inhibition

25 C 4 PATHWAY During hottest part of day, C 4 plants partially close stomates A special enzyme fixes CO 2 into 4- carbon compounds that is stored in bundle sheath cells and can then enter the Calvin cycle Corn, sugar cane and crabgrass

26 CAM Photosynthesis Adaptation to hot, dry climates Open stomates at night and close them during the day (minimizes water loss) CO 2 that enters at night is fixed into a variety of organic compounds and stored in vacuoles; in morning, stomates close and CO2 is then released during the day and enters Calvin cycle These plants grow very slowly – cactuses, pineapples

27 Rates of Photosynthesis 4 limiting factors: –Light intensity, temperature, [CO 2 ], [O 2 ] Active site of Rubisco can bind to O 2 or CO 2 : Photorespiration – results in release of previously fixed CO 2 that would otherwise remain in organic form

28 RATES OF PHOTOSYNTHESIS As light intensity increases, so does rate of photosynthesis Levels off at a max rate, when all electrons are excited Same thing for CO 2 levels Temperature increase, rate increases to a point; then, enzymes denature and stomates close to prevent water loss, thus decreasing rate at high temperatures


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