Chapter 8 - BSC 1010 Dr. Presley Chapter 8 PHOTOSYNTHESIS...

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BSC 1010 Dr. Presley Chapter 8 PHOTOSYNTHESIS Photosynthesis: - means synthesis with energy from light - converts light energy into chemical energy (stored in bonds of organic molecules) - carried out by photoautotrophs = producers these include green plants, algae, and a few bacteria - the flow of energy in the ecosystem: autotrophs are the producers photoautotrophs - use light energy to fuel the production of organic food chemoautotrophs - use inorganic chemicals to fuel the production of organic food heterotrophs are the consumers need organic material to fuel metabolic processes decomposers live on remains of dead organisms - ecological sustainability is highly dependent on the process of photosynthesis - importance of photosynthesis: - ultimate source of food for living things - produces oxygen - provides energy through undecomposed ancient plants & animals (fossil fuels) REACTION OF PHOTOSYNTHESIS: light CO 2 + 12 H 2 0 ----------------------> CH 2 0 + 6 0 2 + 6 H 2 0 chlorophyll - anabolic reaction ** NOT simply the reverse of cellular respiration pathway - experiments to determine source of oxygen Fig. 8.2, p.146 - isotope tracer used to identify water as the source of oxygen - input for photosynthesis: Fig. 8.1, p.146 - H 2 0 comes from soil, lost from leaves by evaporation thru stomata - CO 2 taken in through open stomata (also where 0 2 and H 2 0 can escape) - light is essential for the production of oxygen and carbohydrate source of energy for endergonic process - oxidation - reduction reactions water is split, electrons move along with H + to reduce coenzymes and produce ATP, CO 2 is fixed and then reduced it to form a three- carbon sugar OVERVIEW OF TWO MAIN COMPONENTS OF PHOTOSYNTHESIS : Light reactions (light-dependent reactions) = convert light energy to chemical bond energy in ATP and NADPH + H+ -occur in the thylakoid membranes in the stacks of grana in chloroplast Calvin cycle (“dark reactions”) - carbon-fixation reactions that reduces atmospheric carbon dioxide to form a carbohydrate (3-C sugar) **uses ATP and NADPH + H + from the light reactions as energy source - occurs in the stroma of the chloroplast (usually of mesophyll cells except for C-4 plants) KNOW and be able to diagram from memory Figure 8.3 on page 147. CHLOROPLAST: -- Study Figure 8.2 on page 147 found in the mesophyll region of leaves, in green stems, in unripened fruit leaves have breathing pores called stomata (singular = stoma) that allow the exchange of gases between the atmosphere and spaces in the leaf chloroplast envelope compartmentalizes photosynthesis in eukaryotes, prokaryotes have thylakoid lamellae but no enclosure stroma - dense fluid inside the chloroplast envelope, contains the enzymes for the Calvin cycle (“dark” reactions ) of photosynthesis thylakoids consist of the thylakoid membrane and the enclosed thylakoid space - stacks of thylakoids make up a granum (grana = pleural) - light-trapping pigments are attached to the thylakoid membrane - pigments include: chlorophyll a
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Chapter 8 - BSC 1010 Dr. Presley Chapter 8 PHOTOSYNTHESIS...

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