Photosynthesis
Chemical Cycling between Photosynthesis and Cellular Respiration –The ingredients for photosynthesis are carbon dioxide and water. CO 2 is obtained from the air by a plant’s leaves. H 2 O is obtained from the damp soil by a plant’s roots. –Chloroplasts rearrange the atoms of these ingredients to produce sugars (glucose) and other organic molecules. Oxygen gas is a by-product of photosynthesis.
–Both plants and animals perform cellular respiration. Cellular respiration is a chemical process that harvests energy from organic molecules. Cellular respiration occurs in mitochondria. –The waste products of cellular respiration, CO 2 and H 2 O, are used in photosynthesis.
The Basics of Photosynthesis –Almost all plants are photosynthetic autotrophs, as are some bacteria and protists. They generate their own organic matter through photosynthesis.
Chloroplasts: Sites of Photosynthesis –Chloroplasts Are found in the interior cells of leaves. Contain stroma, a thick fluid. Contain thylakoids, membranous sacs.
The Overall Equation for Photosynthesis –The reactants and products of the reaction Solar energy (sunlight) energizes electrons that are then added to carbon dioxide to make sugar.
A Photosynthesis Road Map –Photosynthesis is composed of two processes: The light reactions convert solar energy to chemical energy. The Calvin cycle adds that chemical energy to carbon dioxide to make the high-energy molecule sugar.
The Nature of Sunlight –Sunlight is a type of energy called radiation Or electromagnetic energy. –The full range of radiation is called the electromagnetic spectrum.
The Light Reactions –Chloroplasts are chemical factories powered by the sun that convert solar energy into chemical energy. Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings - Chloroplasts absorb select wavelengths of light that drive photosynthesis.
Chloroplast Pigments –Chloroplasts contain several pigments: Chlorophyll a Chlorophyll b Carotenoids
How Photosystems Harvest Light Energy –Light behaves as photons, discrete packets of energy. –Chlorophyll molecules absorb photons. Electrons in the pigment gain energy. Image from Purves et al., Life: The Science of Biology, 4th Edition, by Sinauer Associates ( and WH Freeman (
Figure 7.9 Check out:
–A photosystem Is an organized group of chlorophyll and other molecules. Is a light-gathering antenna.
How the Light Reactions Generate ATP and NADPH
–An electron transport chain Connects the two photosystems. Uses energy in electrons to make ATP
–Two types of photosystems cooperate in the light reactions.
How the Light Reactions Generate ATP and NADPH
The Calvin Cycle –The Calvin cycle Functions like a sugar factory within a chloroplast. Adds the energy and H+ stored in ATP and NADPH to carbon dioxide to make sugar. Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings
A review of photosynthesis