10.1 What is photosynthesis?
The Chloroplast as a Photosynthetic Machine
• The equation for photosynthesis is: carbon dioxide + water + light yields glucose + water + oxygen. (p. 187)
• The light-dependent reactions occur within thylakoid membranes within chloroplasts. (p. 187)
10.2 Learning about photosynthesis: An experimental journey.
The Role of Soil and Water
• Jan Baptista van Helmont demonstrated that soil did not add mass to a growing plant, while Priestly, Ingenhousz, and other chemists worked out the basic formula for photosynthesis: carbon dioxide + water + light yields sugar and oxygen. (p. 188)
Discovery of the Light-Independent Reactions
• In the early 1900s, Blackman showed that capturing photosynthetic energy requires the input of sunlight, but building organic molecules does not. (p. 188)
The Role of Light and Reducing Power
• Van Niel discovered that photosynthesis splits water molecules, incorporating the carbon atoms of carbon dioxide gas and the hydrogen atoms of water into organic molecules and oxygen gas. (p. 189)
• Hill showed that plants can use light energy to generate reducing power. (p. 189)
• Carbon fixation refers to the incorporation of carbon dioxide into organic molecules in the light-independent reactions. (p. 189)
10.3 Pigments capture energy from sunlight.
The Biophysics of Light
• Short-wavelength light contains photons of higher energy than long-wavelength light. (p. 190)
• Sunlight reaching the earth's surface contains a significant amount of ultraviolet light, which possesses considerably more energy than visible light. (p. 191)
• In photosynthesis, photons are absorbed by plant pigments, and specific pigments absorb specific wavelengths. (p. 191)
• Chlorophyll a is the main photosynthetic pigment, although chlorophyll b and carotenoids also play important roles. (p. 191)
Chlorophylls and Carotenoids
• Chlorophylls absorb photons by means of an excitation process. (p. 192)
• The wavelengths absorbed by a pigment depend on the available energy level to which light-excited electrons can be boosted. (p. 193)
Organizing Pigments into Photosystems
• The light-dependent reactions take place in four stages: primary photoevent, charge separation, electron transport, and chemiosmosis. (p. 194)
• Pigments within photosystems transfer energy to reaction centers where the energy excites electrons that are channeled to perform chemical work. (p. 195)
How Photosystems Convert Light to Chemical Energy
• Plants employ two photosystems in series, which generate power to reduce NADP+ to NADPH. (p. 196)
How the Two Photosystems of Plants Work Together
• Plants use photosystems II and I in series (noncyclic phosphorylation). (p. 198)
• High-energy electrons generated by photosystem II are used to synthesize ATP and then passed to photosystem I to drive the production of NADPH. (p. 199)
10.4 Cells use the energy and reducing power captured by the light-dependent reactions to make organic molecules.
The Calvin Cycle
• The Calvin cycle is also known as C3 photosynthesis. (p. 200)
• CO2 binds to RuBP in carbon fixation, forming two three-carbon molecules of PGA. (pp. 200—201)
• Plants incorporate carbon dioxide into sugars in the Calvin cycle, which is driven by the ATP and NADPH produced in the light-dependent reactions. (p. 202)
Photorespiration
• Photorespiration releases CO2 and results in decreased yields of photosynthesis. (p. 203)
• C4 photosynthesis circumvents photorespiration by creating high local levels of CO2 in bundle sheath cells. (p. 203)
• CAM plants isolate CO2 temporally by opening stomata at night instead of during the day. (p. 204)