Ch 10. Photosynthesis

Ch 10. Photosynthesis - Photosynthesis Energy from the Sun...

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Photosynthesis: Energy from the Sun Biology 1A Chapter 10 Capturing energy from the Sun Autotrophs (Self-feeding) Photoautotrophs (use light energy) Chemoautotrophs (use chemical energy) Autotrophs provide all the food (energy) for heterotrophs! Nearly all carbon and energy enter living things through photosynthesis. Photosynthesis converts light energy into chemical energy Carbon and energy are released through fermentation and aerobic respiration Organization of the chloroplast Photosynthesis occurs in the chloroplast (in eukaryotes) Chloroplasts have two membranes Stroma is the liquid inner compartment Thylakoid membranes are stacked and contain chlorophyll, a light-absorbing pigment, as well as two photosystems Thylakoid interior contains a low pH (lots of H+) Structure of a Plant leaf Most photosynthesis occurs in leaves Mesophyll cells contain many chloroplasts The leaf’s outer surfaces are largely water and air-tight because they are covered by a waxy cuticle Stomata are microscopic pores in the leaf’s surface, that let water and other gases in and out In general, stomata are open during the day and closed at night so that water is not lost when photosynthesis is not occuring Where does O2 come from? CO2 + H2O -> (CH2O)n + O2 Oxygen could come from CO2 or H2O a. CO2 --> C + O2 b. H2O --> H2 + 1/2O2 Van Niel proposed (b), although (a) was the accepted idea at the time (1930s) CO2 + H2X -> CH2O + X2 Sulfur bacteria use Sulfur in place of X Plants use oxygen in place of X His hypothesis was confirmed using O18 and C14 20 years later Two Stages of Photosynthesis: 6CO2 + 6H2O -> C6H12O6 + 6O2 1. Light reaction = Photophosphorylation Creation of ATP with light (photons) Two sub-pathways: a. Non-cyclic = seen in Cyanobacteria, Algae and Plants ATP and NADPH produced ; Oxygen is a waste product b. Cyclic (only ATP produced) Primitive method, in anaerobic bacteria and higher plants
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2. Calvin Cycle or Light-independent reaction CO2 is fixed to Form “Carbos” (Anabolism) takes a lot of ATP and NADPH2 Q: Light can be described as A: A wave and particle How can light contain energy? Light is electromagnetic radiation It has a dual wave-particle nature Energy varies with wavelength, which we perceive as color Blue light has a shorter wavelength and more energy than red light. Energy is carried in packets termed photons Different plant pigments absorb photons with different energies. Q: Which contains more energy: Blue or red light? A: Blue! Pigments absorb light energy Pigments such as chlorophyll absorb certain photons of light (in the visible range), gaining energy from them Chlorophyll a and b absorb blue and red light, so they appear green Protective functions of accessory pigments Accessory pigments absorb other colors of light Caretenoids absorb mostly blue and blue-green, so they appear yellow-orange Caretenoids and xanthophylls also protect plants from free radicals! Flavanoids also play a role
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Ch 10. Photosynthesis - Photosynthesis Energy from the Sun...

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