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AP BIOLOGY: Chapter Ten Review Answers 
1. van Helmont grew a tree over a period of years in soil to which he added only water. When the tree was weighed after five years, it had gained 74.4 kilograms, while the soil had only lost a few grams in weight. The weight of the tree clearly came from some place other than the soil. 2. The overall equation is 6CO2 + 12H2O _ C6H12O6 + 6H2O + 6O2. The final oxygen comes from the lysis of water. This was ascertained through comparable studies of photosynthesis in purple sulfur bacteria. 3. The photon is the basic unit. The short wavelength blue is most energetic; the long wavelength red is least energetic. 4. Pigments absorb light energy when their electrons become excited by photons. Green is not absorbed at all by the plant, so green light is reflected back to our eyes. 5. Englemann used aerobic bacteria as indicators of oxygen production in a strand of alga exposed to all wavelengths of light in the visible spectrum. The aerobic bacteria congregated next to those regions of the alga most photosynthetically active: the regions of red and violet light, the wavelengths most strongly absorbed by chlorophyll. 6. Three main stages in the "light reactions" in photosynthesis are 1) capture of photon by a pigment,2) shuttling of an electron through a series of electron carriers to an acceptor, and 3) proton-pump driven chemiosmosis. Reaction center chlorophyll molecules pass excitation energy to the primary electron acceptor. The primary electron acceptor serves as an energy-channeling site for excitation energy, in the form of electrons. 7. Light causes ejection of the high-energy electron and it travels through the photosynthetic unit, and drives the proton pump to generate ATP; the electron is then returned to the pigment. The ejected electron is high-energy and the returned one is not, so it is not a precise cycle. Two electrons yield one ATP. 8. The photocenter works as follows: a photon is absorbed by P680 of PS II, light excites an electron, the high-energy electron drives the proton pump to make ATP, the electron returns to its normal energy state and is passed to PS I where another photon re-excites it, and it is channeled to ferredoxin, causing NADP+ to become NADPH. The PS II system generates ATP, and the PS I system NADPH. 9. In the dark reaction, CO2 is fixed, forming carbohydrates. ATP provides energy for the conversion of RuMP to RuBP, and two NADPH and two ATP are used to make one fructose-6-phosphate from 2,3-phosphoglycerates. Another name for this reaction is the Calvin cycle. 10. 1,5 bisphosphate (RuBP) binds to CO2 during the dark stage of photosynthesis to generate two molecules of PGA. Glyceraldehyde phosphate combines with fructose-6-phosphate prior to this to produce the RuBP. 11. In a C3 plant, thylakoid membranes within the chloroplasts are the sites of the light reactions, which generate the ATP and NADPH that fuel the dark reactions. The stroma contains the Calvin cycle enzymes that carry out the carbon-fixing dark reactions. 12. Photorespiration is the oxidation of ribulose 1,5-bisphosphate, releasing CO2 without producing ATP or NADPH. The advantage of C4 photosynthesis is the fact that bundle sheath cells concentrate CO2 and inhibit photorespiration. C4 photosynthesis requires use of ATP to concentrate CO2 in bundle sheath cells, so it is not as energy-efficient as C3 photosynthesis, but is still worth the "expenditure" because it conserves glucose molecules that would otherwise be converted back into CO2 by photorespiration in the consistently higher temperatures in warmer climates. | ||||||||||||
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