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Figure 10.
Most of the water on Earth consists of saltwater in the oceans. What percent of Earth’s water is
freshwater? Where is most of the freshwater found?
Structure and Properties of Water
No doubt, you are already aware of some of the properties of water. For example, you probably know
that water is tasteless and odorless. You also probably know that water is transparent, which means that light
can pass through it. This is important for organisms that live in the water because some of them need sunlight
to make food.
1.3 Reading Resource #3: Water and Life
The human body is about 70% water (not counting the water in body fat, which varies from person to
person). The body needs all this water to function normally. Just why is so much water required by human
beings and other organisms? Water can dissolve many substances that organisms need, and it is necessary for
many biochemical reactions. The examples below are among the most important biochemical processes that
occur in living things, but they are just two of many ways that water is involved in biochemical reactions.
•
Photosynthesis—In this process, cells use the energy in sunlight to change carbon dioxide and water
to glucose and oxygen. Water is a reactant in this process. The reactions of photosynthesis can be
represented by the chemical equation
6CO
2
+ 6H
2
O + Energy → C
6
H
12
O
6
+ 6O
2
•
Cellular respiration—In this process, cells break down glucose in the presence of release carbon
dioxide
and oxygen, water (a product), and energy. The reactions of
cellular respiration can be
represented by the chemical equation
C
6
H
12
O
6
+ 6O
2
→ 6CO
2
+ 6H
2
O + Energy
Water is involved in many other biochemical reactions.
As a result, just about all
life processes depend on
water. Clearly, without water, life as
we know it could not exist
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