Lecture 7 (Spring) - Biology 172 Lecture 7 Wednesday Todays...

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Lecture 7: Wednesday, May 20, 2015 Biology 172 Today’s Outline Photosynthesis - Overview - Light Reactions Noncyclic photophosphorylation Cyclic photophosphorylation - Calvin Cycle Announcements Quiz 4 due today, 11:59 This week’s discussion: Photosynthesis
Lecture Objectives Understand the reactions of photosynthesis. Know input and output of light reactions and Calvin cycle. Know where each occurs in prokaryotes and eukaryotes. Be able to trace the path of electrons as they move move through the Z scheme. Understand resonance and redox reactions and the difference between antenna pigments and the reaction centers Understand why a plant undergoes cyclic photo- phosphorylation and what is involved. Know the 3 phases of Calvin cycle Understand why rubisco is inefficient and the adaptations that C4 and CAM plants have made Understand the similarities between the mitochondria and the chloroplasts with respect to what is happening in each compartment
Plants Unicellular protist Multicellular algae Cyanobacteria Purple sulfur bacteria 10 μm 1.5 μm 40 μm Photoautotrophs: producers for most ecosystems
Photosynthesis Glucose Converts light energy into chemical energy Light Reactions: Use the energy from sunlight to generate high energy molecules ATP and NADPH Calvin Cycle: Uses the high energy molecules ATP and NADPH to reduce 6 CO 2 Into 1 C 6 H 12 O 6 Photoautotrophs are photosynthetic organisms that make their own food from ions and simple molecules using the energy from the sun
Photosynthesis - the use of light energy to generate organic molecules - occurs in chloroplasts (plants/algae) or plasma membrane and cytosol (some prokaryotes)
How is gas exchange accomplished in leaf cells? CO 2 must diffuse into the cell for photosynthesis, while water is lost. This is accomplished by stomata (stomates),openings or pores in leaf epidermal cells. The size of the pores is regulated by a pair of specialized cells known as guard cells. Paradox of having stomates open?
Leaf surfaces contain stomata. Carbon dioxide diffuses into leaves through stomata. Guard cells Pore Stoma Stoma CO 2 Extracellular space Photosynthetic cells O 2 H 2 O Leaf surface Interior of leaf Leaf surface
Chloroplasts have 3 membranes, the outer membrane, inner membrane and the thylakoid membrane. The thylakoid membranes contain the pigment chlorophyll, which absorbs blue and red light and reflects green light.
Light reactions that take place in the chloroplasts rely on pigments embedded in the thylakoid membrane; two of the pigments being chlorophyll a and chlorophyll b. Chlorophylls a and b absorb slightly different wavelengths of light but have similar structures Light microscope image
Accessory pigments such as carotenoids absorb other wavelengths of light in the visible spectrum. It has been demonstrated that blue and red photons of light are the most effective at driving photosynthesis. Because chlorophylls a and b absorb these wavelengths, chlorophylls are the main photosynthetic pigments.
CO 2 CALVIN CYCLE O 2 [CH 2 O] (sugar)

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