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Oxygenic and Anoxygenic Phototrophs: Definition and Examples

Instructor: Jeremy Battista

Jeremy has a master of science degree in education.

Most animals gather and take in their energy via some form of eating similar to humans, but some organisms cannot simply 'eat' like we can. In this lesson, we look at two types of phototrophic organisms who get their energy in a different way.

What Are Phototrophs?

When you hear the word 'phototrophs' one assumes that you are automatically talking about plants. Most plants, if you recall are photoautotrophs in that they go through photosynthesis, which takes is the process of taking in light, water, and carbon dioxide to create food for the plant to use. So plants are photoautotrophs meaning they use sunlight (photo) to make their own food (autotroph).

We have to make a slight distinction here as phototrophs are organisms that capture sunlight and use it to complete various metabolic functions not just limited to making food. In fact, some phototrophs, as we will see, actually don't make their own food at all.

We refer to these as photoheterotrophs. These organisms usually consist of different bacteria that use sunlight as an energy source. However, unlike organisms, such as plants, they need a way in which to get carbon through other sources. It is very similar to photosynthesis but utilizing different carbon sources than a plant would.

Restating what was said (because it is important!) phototrophs are those organisms that utilize the photons (packets of light energy) from sunlight to carry out certain functions inside of them. Sometimes this includes creating energy. Sometimes it is just a way for the organism to function similar to how we take in oxygen for use in various metabolic functions. Similarly some people could be caffeine-otrophs (made up term) and need to drink their coffee in the morning to wake up and function, whereas other humans do not. I guess that isn't the best example but I hope it conveys the message that phototrophs just use sunlight to function, whether it be making their own food and other metabolic functions.

As you will see in the next section, we split our phototrophs into photoautotrophs and photoheterotrophs. Photoautotrophs can further be broken into oxygenic and anoxygenic. For our purposes here, we will be focusing on photoautotrophs and their designations as either oxygenic or anoxygenic.

Oxygenic Phototrophs

Plants are what we refer to as oxygenic phototrophs and are actually photoautotrophic. These organisms can take in light energy from the sun as photons. These photons are collected by chlorophyll, which acts like a magnet, pulling in the photons. This occurs in the leaves of the plant where carbon dioxide also gathers along with water. Together, these can combine to form glucose or sugar that the plant uses for energy.

Don't forget, though, that these are 'oxygenic' so oxygen comes into play here. The plant needs some oxygen uptake in order to use that oxygen to break apart or oxidize the water molecule of the plant, releasing the energy and atmospheric oxygen from it to be used later on during 'respiration' where the plant goes back and destroys the sugar it made. So the plant makes its own food, then breaks down that food for use as energy later on when needed.

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