BIOL 1010 Lecture Notes - Hydrogen Sulfide, Endergonic Reaction, Electronegativity
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Photosynthesis
Lecture 20
Photosynthesis in Nature
- Photosynthesis transforms solar light energy trapped by chloroplasts into chemical bond energy
stored in sugar and other organic molecules
- This process:
o Synthsizes energy-rich organic molecules from the energy-poor molecules, CO2 and H2O
o Directly or indirectly supplies energy to most living organisms
Plants and other autotrophs are the producers of the biosphere
- Organisms aquire organic molecules used for energy and carbon skeleton by one of two
nutritional modes:
o Autotrophic nutrition
o Heterotrophic nutrition
- Autotrophic nutrition: nutritional mode of synthesizing organic molecules from inorganic raw
materials
o Examples of autotrophic organisms are plants, which require only CO2, H2O and
minerals as nutrients
o Because autotrophic organisms produce organic molecules that enter an ecosystem’s
food store, autotrophs are also known as producers
- The energy source may be from light (photoautotrophic) or the oxidation or 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.
- Chemoautotroph- 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
- Heterotrophic nutrition- nutritional mode of acquiring organic molecules from compounds
produced by other organisms. Are unable to synthesize organic molecules from inorganic raw
materials
o Heteroptrophs are known as consumers
o Examples are animal that eat plants or other animals
o Examples also include decomposers Heterotrophs that decompose and feed on organic
matter. Most fungi and many bacteria are decomposers.
o Most heterotrophs depend on photoautotroph for food and oxygen (a by-product of
photosynthesis)