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Chapter 8 - Photosynthesis 6CO 2 + 6H 2 O + light C 6 H 12 O 6 + 6O 2 The capture and conversion of solar energy to chemical bond energy
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Photosynthesis occurs in… Plants, algae, some bacteria
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Not all plants are photosynthetic Some parasitic plants are not photosynthetic
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Photosynthesis occurs in chloroplasts
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Photosynthetic products are utilized in respiration
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Chlorophyll is the primary photosynthetic pigment
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Chlorophyll absorbs specific wavelengths of visible light
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1883 – T.W. Englemann Red and blue light most effective for producing oxygen during photosynthesis
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Wavelength and photosynthesis
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Accessory pigments
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Chlorophyll in photosystems absorb light energy and release electrons
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What happens when light is absorbed by a molecule? “Free” electrons are a source of kinetic energy
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Z-scheme & energy flow
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Chemiosmosis drives ATP synthesis
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Photolysis and chemiosmosis Photolysis replaces electrons removed from chlorophyll Electron flow “pumps” H+ ions through membrane
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Light reactions animation
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Chemiosmosis animation
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ATP synthase phosphorylates ADP (photophosphorylation) H + ions
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Chlorophyll 1. Is the organelle in which photosynthesis takes place 2. Absorbs green wavelengths of light 3. Is the primary photosynthetic pigment 4. All of these 5. Both 1 and 2
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When light energy is absorbed by chlorophyll 1. Chlorophyll produces oxygen 2. Chlorophyll becomes an accessory pigment 3. Chlorophyll is destroyed 4. Chlorophyll becomes radioactive 5. Chlorophyll releases an electorn
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Active transport of hydrogen ions into the thylakoid space 1. Occurs during chemiosmosis 2. Involves the electron transport chain of photosystem II 3. Occurs by the process of photolysis 4. Involves the electron transport chain of photosystem I
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Photolysis 1. Occurs when light energy splits a chlorophyll molecule in half 2. Is when light splits open a chloroplast to release sugars 3. Splits water molecules to resupply chlorophyll with electrons 4. Is the production of ATP utilizing a hydrogen ion gradient 5. Occurs when absorbed light causes an electron to be removed from a chlorophyll molecule
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The hydrogen ion gradient inside the thylakoid membrane forms as a result of 1. Photosystem II 2. Photolysis 3. Chemiosmosis 4. Photophosphorylation 5. Both 1 and 2
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Dr. Calvin, Nobel prize in chemistry, 1961
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Calvin’s experiment (see Fig. 8.9)
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Calvin’s results
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The Calvin cycle produces G3P Occurs in the stroma Several enzyme- catalyzed steps Requires energy Produces sugars
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Calvin Cycle Animation
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Summary of photosynthesis
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Photosynthesis animation
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Rate of photosynthesis varies with environmental conditions What is meant by the “rate of photosynthesis”? What environmental conditions affect the rate of photosynthesis?
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Factors influencing the rate of photosynthesis Carbon dioxide concentration Water availability Light intensity Temperature
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Variations of photosynthesis 85% of plants use “C 3 ” photosynthesis –C 3 cycle = Calvin cycle C 4 photosynthesis –C 4 plants include many tropical monocots, other grasses (0.4% of plants) Crassulacean Acid Metabolism (CAM) –CAM plants – cacti, orchids, bromeliads, succulents (~10% of plants)
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C 4 photosynthesis is more efficient than C 3 under certain conditions
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Photorespiration and rubisco Rubisco – Ribulose 1,5- bisphosphate carboxylase/oxygenase –Most abundant protein on earth (25-40% of total plant protein) –Activity depends on carbon dioxide concentration in the leaf
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Rubisco activity and CO 2 concentration
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When would photorespiration occur and why? When are CO 2 concentrations low? –When stomata close Hot days Moisture stress
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C 4 vs. CAM
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Crassulacean Acid Metabolism Evolved in areas of high light intensity, little precipitation Stomata closed during the day, open at night
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Which of the following are true of the Calvin cycle? 1. Occurs in the cytoplasm 2. RUBP reacts with oxygen to form Rubisco 3. RUBP reacts with CO2 to form Rubisco 4. All of these are true 5. None of these are true
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The Calvin cycle occurs 1. In C3 plants but not C4 or CAM plants 2. In the mesophyll of all plants 3. In the bundle sheath of C4 plants 4. In C4 and CAM plants, but not C3 plants
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Photorespiration is most likely to occur 1. On cool, cloudy days 2. In plants adapted to desert habitats 3. In C3 plants 4. In C4 plants and CAM plants 5. Both 2 & 4
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During photorespiration 1. Plants react O 2 with glucose to make ATP 2. Plants react O 2 with ATP to make glucose 3. Plants use the energy of light to make ATP 4. RUBP reacts with CO 2 to make sugars 5. RUBP reacts with O 2 to make CO 2
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CAM plants 1. Use their bundle sheath cells to run the Calvin cycle at night 2. Use their bundle sheath cells to run the Calvin cycle during the day 3. Absorb CO 2 during the day, and make sugars during the night 4. Absorb CO 2 during the night, and make sugars during the day 5. Both 1 and 3
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Photosynthesis research Why study photosynthesis? Photosynthesis Center at Arizona State Photosynthesis Center at Arizona State
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