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By the end of this section, you will be able to:
  • Describe the properties of water that are critical to maintaining life
  • Explain why water is an excellent solvent
  • Provide examples of water’s cohesive and adhesive properties
  • Discuss the role of acids, bases, and buffers in homeostasis

Why do scientists spend time looking for water on other planets? Why is water so important? It is because water is essential to life as we know it. Water is one of the more abundant molecules and the one most critical to life on Earth. Approximately 60–70 percent of the human body is made up of water. Without it, life as we know it simply would not exist.

The polarity of the water molecule and its resulting hydrogen bonding make water a unique substance with special properties that are intimately tied to the processes of life. Life originally evolved in a watery environment, and most of an organism’s cellular chemistry and metabolism occur inside the watery contents of the cell’s cytoplasm. Special properties of water are its high heat capacity and heat of vaporization, its ability to dissolve polar molecules, its cohesive and adhesive properties, and its dissociation into ions that leads to the generation of pH. Understanding these characteristics of water helps to elucidate its importance in maintaining life.

Water’s polarity

One of water’s important properties is that it is composed of polar molecules: the hydrogen and oxygen within water molecules (H 2 O) form polar covalent bonds. While there is no net charge to a water molecule, the polarity of water creates a slightly positive charge on hydrogen and a slightly negative charge on oxygen, contributing to water’s properties of attraction. Water’s charges are generated because oxygen is more electronegative than hydrogen, making it more likely that a shared electron would be found near the oxygen nucleus than the hydrogen nucleus, thus generating the partial negative charge near the oxygen.

As a result of water’s polarity, each water molecule attracts other water molecules because of the opposite charges between water molecules, forming hydrogen bonds. Water also attracts or is attracted to other polar molecules and ions. A polar substance that interacts readily with or dissolves in water is referred to as hydrophilic    (hydro- = “water”; -philic = “loving”). In contrast, non-polar molecules such as oils and fats do not interact well with water, as shown in [link] and separate from it rather than dissolve in it, as we see in salad dressings containing oil and vinegar (an acidic water solution). These nonpolar compounds are called hydrophobic    (hydro- = “water”; -phobic = “fearing”).

Image shows oil droplets floating in water. The oil droplets act like prisms that bend the light into all the colors of the rainbow.
Oil and water do not mix. As this macro image of oil and water shows, oil does not dissolve in water but forms droplets instead. This is due to it being a nonpolar compound. (credit: Gautam Dogra).

Water’s states: gas, liquid, and solid

The formation of hydrogen bonds is an important quality of the liquid water that is crucial to life as we know it. As water molecules make hydrogen bonds with each other, water takes on some unique chemical characteristics compared to other liquids and, since living things have a high water content, understanding these chemical features is key to understanding life. In liquid water, hydrogen bonds are constantly formed and broken as the water molecules slide past each other. The breaking of these bonds is caused by the motion (kinetic energy) of the water molecules due to the heat contained in the system. When the heat is raised as water is boiled, the higher kinetic energy of the water molecules causes the hydrogen bonds to break completely and allows water molecules to escape into the air as gas (steam or water vapor). On the other hand, when the temperature of water is reduced and water freezes, the water molecules form a crystalline structure maintained by hydrogen bonding (there is not enough energy to break the hydrogen bonds) that makes ice less dense than liquid water, a phenomenon not seen in the solidification of other liquids.

Questions & Answers

what is biology
enock Reply
what type of fluid is filled in hydroskeretal system
Ngenda Reply
The phenomenon by which Protoplasm of a cell shrinks from the wall is 
test Reply
which vein connective from harm to Brian
Burton Reply
which nevel succulate blood system from harm to hear
if an organism is cartilaginous is fully capable of a protecting the internal organs
Verah Reply
what is different between cell and tissue
Rose Reply
cell is the functional and structural unit of life while tissue is a group of cells aggregate to perform a similar or particular function
cell is the basic unit of life while tissue is group of related cells that perform the same function Eg. the nerve tissue is made up of nerve cells
please what is meant by mutation
Kyere Reply
mutation is the change in DNA which results in the evolution
what is binominal nomenclature?
Furaha Reply
the system of naming organisms depending on their xtics of origin
The system of naming organisms using two-words Latin names
what is the fate of reduced NAD in cell metabolism
namirembe Reply
what is plant cell
what is the importance of meoisis
Kamasa Reply
it also aids in formation of pollen grain in anther and formation of ovules in ovary of flowering plant
it also aids in formation of sperm or ova in animals
explain the function of the skeleton
Jonathan Reply
skeleton is mainly the infrastructure of the organisms
what 's different between immunity and vaccination
Symon Reply
vaccination simply refers to as drugs usually injected,most times in a liquid form given to a person or an animal,while immunity refers to a source of prevention usually in a liquid form that help in disease prevention
In children
Golgi apparatus helps in the formation of lysosomes
what is the difference between placenta and umbilical cord?
Grace Reply
No difference
what's golgi apparatus.
What is biology
Rita Reply
is the study of living things
biology is the study of living and non living things
Biology is the study of living things
the study of living organisms
Biology is the study of living organism or things
Biology is the study of both living and non living things

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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