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Photosynthesis

Photosynthesis. How do photoautotrophs use light to make their own food?. Autotrophs. Literally means “self-feeders” Include all plants, some bacteria, archaea, and protists (algae) make organic food molecules (e.g. glucose) from inorganic raw materials (e.g. water and carbon dioxide).

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Photosynthesis

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  1. Photosynthesis How do photoautotrophs use light to make their own food?

  2. Autotrophs • Literally means “self-feeders” • Include all plants, some bacteria, archaea, and protists (algae) • make organic food molecules (e.g. glucose) from inorganic raw materials (e.g. water and carbon dioxide)

  3. Leaf Section http://iusd.k12.ca.us/uhs/cs2/ images/Leaf%20Cross-section.jpg Chloroplast

  4. How can carbon dioxide get into the leaf? Leaf Structure • Through tiny holes on leaf surface called stomata • Oxygen produced from photosynthesis can also escape out of leaves through stomata

  5. lab bench Stomata Regulation of Guard Cells Closed Stomate http://www.macleans.school.nz/students/science/F4/plants/closed_stoma.jpg

  6. A. Open stoma B. Closed stoma http://www.phschool.com/science/biology_place/labbench/lab9/images/stoma1.gif

  7. How can we tell if a plant is actively photosynthesizing? http://www.bbc.co.uk/schools/ks3bitesize/science/images/image33.gif

  8. Photosynthesis and oxygen atoms 6 CO2 + 12 H2O  C6H12O6 + 6H2O + 6O2 No label 6 CO2 + 12 H2O C6H12O6 + 6H2O + 6O2 Label

  9. Redox reactions…Which one is photosynthesis? reduction 6 CO2 + 12 H2O C6H12O6 + 6H2O + 6O2 oxidation oxidation C6H12O6+6O2 6 CO2 + 6 H2O reduction

  10. Electromagnetic Spectrum http://upload.wikimedia.org/wikipedia/en/thumb/8/8a/Electromagnetic- Spectrum.png/350px-Electromagnetic-Spectrum.png

  11. Green plants are green because… • Chlorophyll reflectsgreen light, but absorbs light in the red, orange, blue, indigo and violet wavelength range • Other pigments absorb light of different wavelengths, e.g. carotenoids are yellow-orange pigments

  12. Chlorophyll embedded in a photosystem

  13. Two photosystems • Photosystem I was discovered first and the chlorophyll a of its reaction center absorbs light best at 700 nanometers (far-red zone) • Photosystem II reaction center chlorophyll absorbs best at 680 nm (red zone) Chemiosmosis

  14. Electron flow in the light reactions http://library.thinkquest.org/C004535/media/photosystem.gif

  15. Two types of photosystems cooperate in the light reactions Photon ATP mill Photon Water-splitting photosystem NADPH-producing photosystem

  16. Light Reactions takes place in thylakoid membranes (grana) of chloroplasts Dark Reactions (Calvin Cycle) takes place in the stroma (thick fluid inside chloroplasts) Two stages of Photosynthesis

  17. Input: H2O (from roots) NADP+ ADP and Phosphate photons (packets of light energy) Output: O2 NADPH (carrying electrons) ATP I. Light Reactions

  18. Cyclic Photophosphorylation http://student.ccbcmd.edu/courses/bio141/lecguide/unit6/metabolism/photosyn/images/u4fg45.jpg

  19. Input: CO2 ATP NADPH RuBP (ribulose biphosphate: a 5-carbon sugar) Output: G3P (glyceraldehyde 3-phosphate) used to make glucose NADP+ ADP and Phosphate II. Calvin Cycle

  20. http://www.daviddarling.info/images/Calvin_cycle.jpg

  21. http://edu.tebyan.net/biology/Cells/images/calvin_cycle.gif

  22. Calvin Cycle • Carbon is reduced to glucose (carbon fixation) • Electrons and protons are added to carbon • NADP+ is regenerated so it can be reused in the Light Reactions

  23. Alternate Mechanisms of Carbon Fixation C3 plants like rice, wheat, and soybeans Rubisco can accept O2 instead of CO2 resulting in photorespirationStomates on hot dry days decrease carbon dioxide in leaf starves Calvin Cycle oxygen concentrations in the leaf overtake CO2 photorespiration occurs decreasing photosynthetic output taking organic material away from Calvin Cycle http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/C4plants.html

  24. C3 95 percent of the plant species on earth The equation for the Calvin Cycle: CO2 (Carbon dioxide in from stomata) + RuBP (Ribulose bisphosphate already in plant) + the enzyme RUBISCO (Ribulose bisphosphate carboxylase) “fixes” carbon from the atmosphere  2PGA (phospholygerate) PGA enters Calvin cycle in Mesophyll cells  more RuBP (to fix more CO2) + sugar (CH2O) C3 are inefficient at CO2 fixation because RUBISCO has a greater affinity for oxygen than CO2 Mesophyll cells are packed with RUBISCO Stomata open during day (CO2, oxygen, and water can all flow out) Photorespiration undoes CO2 assimilation 2PGA  CO2 + RuBP increases when there is lots of O2, low levels of CO2, and increased temperature http://wc.pima.edu/~bfiero/tucsonecology/plants/plants_photosynthesis.htm

  25. C4 crop plants—sugar cane and corn 2nd most prevalent photosynthetic type C4plants—carbon fixation and photosynthesis split between the mesophyll cells and bundle sheath cells. The equation: In mesophyll (carbon fixation): CO2 + PEP (phosphoenol pyruvate) + PEP carboxylase fixes carbon  OAA (oxaloacetic acid) OAA diffuses to bundle sheath cells In bundle sheath (Calvin Cycle): OAA  malic acid and aspartic acid is decarboxylated  CO2 + pyruvate Then the Calvin Cycle CO2 + RuBP + the enzyme RUBISCO  2PGA RuBP + CH2O Pyruvate with ATP is moved back to mesophyll and turned into PEP (to fix more CO2)

  26. C4 Photosynthesis

  27. Feature of many grasses (i.e. big blue stem back campus), corn, and many arid/semi arid shrubs Calvin cycle in bundle sheath cells where there is no oxygen to be bound by RUBISCO Very high concentration of CO2 in bundle sheath cells PEP carboxylase has a high affinity for CO2 so plants must open their stomata less to get CO2 and hence lose less water (especially important in arid regions) Low levels of photorespiration and higher net photosynthesis than C3 because of low photorespiration Costly adaptation because it requires lots of ATP (energy)— however, benefits outweigh energy costs. Stomata are open during the day Fixation and the Calvin cycle are physically separate C4

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