Photosynthesis (ch 10) Key Concepts Photosynthesis converts light energy to chemical energy in the bonds of carbohydrates. It has two sets of reactions. In the light reactions , excited electrons are used to produce the electron carrier NADPH or are donated to an electron transport chain, to produce ATP via chemiosmosis. In the dark reactions, the enzyme rubisco catalyzes the addition of CO2 to a 5-carbon compound. The Calvin cycle uses ATP and NADPH from the light reactions, for carbohydrate production. In plants, CO2 enters photosynthetic tissue through stomata . The CAM and C4 pathways increase CO2 concentrations inside the leaves of some species and make photosynthesis more efficient. An Overview of Photosynthesis Photosynthesis is the process of using sunlight to produce carbohydrate. This process requires sunlight, carbon dioxide, and water, and produces oxygen as a by-product. The overall reaction when glucose is the carbohydrate can be written as: Photosynthesis contrasts with cellular respiration. o Photosynthesis is endergonic and reduces CO2 to sugar o Cellular respiration is exergonic and oxidizes sugar to CO2 Photosynthesis: Two Linked Sets of Reactions (key Concept) Photosynthesis consists of two linked sets of reactions: light-dependent reactions produce O2 from H2O, and dark or Calvin cycle reactions produce sugar from CO2 . The reactions are linked by electrons, which are released in the light-dependent reactions when water is split to form oxygen gas and then transferred to the electron carrier NADP+ , forming NADPH. The Calvin cycle then uses these electrons and the potential energy in ATP to reduce CO2 to make sugars.
What Do You Think? Why would life use two slightly different forms of nicotinamide adenine dinucleotide electron carriers for photosynthesis and oxidation? o Two different versions of the electron carrier would each be recognized by different sets of enzymes The Structure of the Chloroplast Photosynthesis occurs in the chloroplasts of green plants, algae, and other photosynthetic organisms. Chloroplasts are surrounded by two membranes. The internal membranes of chloroplasts form flattened, vesicle-like structures called thylakoids , some of which form stacks called grana . o Thylakoid membranes contain large quantities of pigments . o The most common pigment is chlorophyll . The fluid-filled space between the thylakoids and the inner membrane is the stroma.
The Nature of Light Energy Electromagnetic radiation is a form of energy. Light is a type of energy - electromagnetic radiation that acts both particle-like and wave- like. o As a particle, light exists in discrete packets called photons. o As a wave, light can be characterized by its wavelength o the distance between two successive wave crests.
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