CHAPTER 10 PHOTOSYNTHESIS

CHAPTER 10 PHOTOSYNTHESIS - CHAPTER 10 PHOTOSYNTHESIS I...

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CHAPTER 10 PHOTOSYNTHESIS I. Photosynthesis in Nature Photosynthesis transforms solar light energy trapped by chloroplasts into chemical bond energy stored in sugar and other organic molecules. This process: - Synthesizes energy-rich organic molecules from the energy-poor molecules, C02 and H20 - Uses C02 as a carbon source and light energy as the energy source - Directly or indirectly supplies energy to most living organisms A. Plants and other autotrophs are the producers of the biosphere Organisms acquire organic molecules used for energy and carbon skeletons by one of two nutritional modes: 1) autotrophic nutrition or 2) heterotrophic nutrition. Autotrophic nutrition = (Auto = self; trophos = feed); nutritional mode of synthesizing organic molecules from inorganic raw materials - Examples of autotrophic organisms are plants, which require only CO 2 , H 2 O and minerals as nutrients. - Because autotrophic organisms produce organic molecules that enter an ecosystem's food store, autotrophs are also known as producers. - Autotrophic organisms require an energy source to synthesize organic molecules. That energy source may be from light (photoautotrophic) or from the oxidation of inorganic substances (chemoautotrophic). - Photoautotrophs = Autotrophic organisms that use light as an energy source to synthesize organic molecules. Examples are photosynthetic organisms such as plants, algae, and some prokaryotes. - Chemoautotrophs = Autotrophic organisms that use the oxidation of inorganic substances, such as sulfur or ammonia, as an energy source to synthesize organic molecules. Unique to some bacteria, this is a rarer form of autotrophic nutrition.
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Heterotrophic nutrition = (Heteros = other; trophos = feed); nutritional mode of acquiring organic molecules from compounds produced by other organisms. Heterotrophs are unable to synthesize organic molecules from inorganic raw materials. Heterotrophs are also known as consumers. Examples are animals that eat plants or other animals. Examples also include decomposers, heterotrophs that decompose and feed on organic litter. Most fungi and many bacteria are decomposers. - Most heterotrophs depend on photoautotrophs for food and oxygen (a by product of photosynthesis). B. Chloroplasts are the sites of photosynthesis in plants Although all green plant parts have chloroplasts, leaves are the major sites of photosynthesis in most plants. - Chlorophyll is the green pigment in chloroplasts that gives a leaf its color and that absorbs the light energy used to drive photosynthesis. Leaf cross-section: - Chloroplasts are primarily in cells of mesophyll, green tissue in the leafs interior. - CO 2 enters and O 2 exits the leaf through microscopic pores called stomata. - Water absorbed by the roots is transported to leaves through veins or
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CHAPTER 10 PHOTOSYNTHESIS - CHAPTER 10 PHOTOSYNTHESIS I...

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