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AP Bio



Unit 8

8.2 Energy Flow Through Ecosystems

2 min readjanuary 29, 2021


Caroline Koffke

All organisms in an ecosystem need energy. Remember, all the energy that we have on Earth originates from the sun. Photosynthetic bacteria convert this energy into usable energy through photosynthesis. Energy flows through ecosystems, starting with energy from the sun and traveling through photosynthetic organisms and the organisms that consume them. The majority of energy is lost in the form of heat between levels of the ecosystem. This is because energy is used by the individual in order to produce heat, digest, and go through basic daily functioning.

Trophic Levels

As energy flows through an ecosystem it travels through trophic levels. A trophic level is the energy level in which an organism exists based on what it eats. Autotrophs produce their own energy (think: plants and photosynthetic bacteria). Heterotrophs get their energy from other organisms (think: everyone else).

Image courtesy of Static Flickr.

The maintenance of energy levels is essential to the survival of all organisms. If an organism is using more energy than it is consuming, creating a net loss of energy, the organism will lose mass and may eventually die. An organism that gains more energy than it uses has a net positive in energy and will be able to grow and store energy. The increase in energy is essential to an organism surviving and reproducing.

Maintaining Energy

Along with storing energy, organisms also have different strategies for maintaining heat and energy within their bodies. Endotherms maintain an even temperature in their bodies. We are examples of endotherms, as we maintain a body temperature between 97 and 99°F. These organisms use a great deal of the energy that they get from food sources in order to maintain their internal temperature.
Ectotherms do not maintain an even temperature in their bodies. Snakes and fish are examples of ectotherms. These organisms must change their behaviors in order to maintain an internal temperature. This may involve hibernating in the winter and lying in a sunny spot during the summer. Along with how an organism maintains its energy and heat, the mass of an organism is usually correlated to the amount of energy that that organism metabolizes. Typically, the smaller that an organism is, the higher its metabolic rate. This would mean that a mouse metabolizes things much more quickly than a human.

Image courtesy of WikiMedia Commons.

Lastly, the overall availability of energy in an ecosystem determines the growth, population density, and overall health of the ecosystem. If there are a number of high volume producers in the area, an ecosystem is more capable of survival and reproduction.
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