Study Guide

Ecology: Organisms and Their Environments - The Water Cycle

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The Water Cycle

In the previous section, you learned how the community portion of an ecosystem interacts with energy, an essential abiotic factor in the habitat. In these next sections, we will look at how communities interact with a few other abiotic factors: the essential chemicals water, carbon, nitrogen, and phosphorous.


Water is perhaps the most important component of any ecosystem. All living organisms need water to grow and survive. In an ecosystem, water cycles through the atmosphere, soil, rivers, lakes, and oceans. Some water is stored deep in the earth. Surface water, on the other hand, is the source that sustains life on land. In many cases, water also structures the physical habitat of an ecosystem. Polar bears, for example, rely on ocean ice in order to successfully hunt and capture seals. Rivers, lakes, and other bodies of water divide environments into different habitats, effectively defining where some organisms can live and others cannot. What’s more, most of the life on Earth actually lives completely submerged in the waters of the oceans. Water is truly a powerful factor in all ecosystems.

Brain Snack

The largest freshwater body of water in the world is lake Baikal in Russia. It is the oldest and deepest lake as well, at 30 million years old and 744.4 metres on average in depth, respectively.

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