How organisms on Earth sustain themselves
| All mobile living creatures on our planet need oxygen and water to survive. But all animals (and even some plants) need to consume another fuel type to continue living - food. This food can be a plant, another animal, or both. Both food sources provide carbohydrates, fats, proteins and nutrients needed by organisms to grow their own bodies, repair them, and to reproduce offspring. But an organism also needs to consume foods to process energy to regulate body temperature at all times. For animals, these foods usually come in the form of smaller animals. These smaller animals likely fed on even smaller prey to continue living, which in turn may have fed on plants. This linear arrangement of feeding is sometimes referred to as a "food chain," and can be easily pictured with the following real-world example. Phytoplankton are small, microscopic plants floating just under the ocean surface, preferably in cool, nutrient-rich waters, such as off the coast of Alaska. These tiny plants are eaten by very small organisms called zooplankton. These zooplankton are then consumed by shrimp. In turn, the shrimp are caught by large fish, and those fish may be consumed by sea lions. As with this example, many "food chains" have a direct progression of size of an organism from one "link" to the next. Since foods can be thought of as energy, it is easy to imagine energy "moving up" each "link" (or stage) of the "food chain." These stages are often referred to as trophic levels. |
Credit: GSFC/NASA
For more info: http://seawifs.gsfc.nasa.gov/SEAWIFS/sanctuary_4.html