The Role of Water On Earth

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  • 0:00 What Is Water?
  • 0:32 Biological Processes
  • 1:27 The Water Cycle
  • 2:20 Modern Uses
  • 2:54 Lesson Summary
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Lesson Transcript
Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

What is water? It is a small molecule essential to human life! After completing this lesson, you will be able to describe the role of water on Earth: from human uses of water, to plants, to the water cycle.

What Is Water?

Water is a substance that is liquid at most temperatures on Earth and is necessary for life. It consists of molecules made up of two hydrogen atoms and one oxygen atom. This might not seem altogether exciting, but many scientists believe it may be a requirement for the development of complex life. It really is that important! Today, we're going to talk about the role of water on Earth, how water moves and how it is used by humans and other animals.

Biological Processes

Earth has been called the blue planet. When you look at the Earth from a long way away, that's what you see: a little blue speck. A full 71% of the Earth's surface is covered with water. And most mammals, like humans, are made up of 55-75% water. Plants also contain large amounts of water.

Some people might argue that life on Earth relies on water precisely because there is so much of it here. Perhaps life on other planets won't need it. But it's hard for us even to imagine how organisms could exist without it. That's because water is vital for biological processes, from chemical reactions, to the transport of nutrients in the blood, to moving nutrients between cells. Without water, our bodies would have to operate completely differently. Plants need water in a similar way, and in the case of small plants, water also creates tension in their stalks, allowing them to stand up straight and reach for the sunlight. This is called turgor pressure.

The Water Cycle

Water is also a big part of how our world functions as a whole. The water cycle isn't literally what makes the world go around, but it's still a big deal. Water evaporates from the oceans, rivers and lakes, and is carried through plants and trees to their leaves. Gaseous water, called water vapor then rises from the plants' leaves until it gets cold enough to form clouds. Those clouds ultimately release their water as rain or snow, and the cycle continues.

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