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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

Do you ever wonder why scientists spend time looking for water on other planets? It is because water is essential to life; even minute traces of it on another planet can indicate that life could or did exist on that planet. Water is one of the more abundant molecules in living cells and the one most critical to life as we know it. Approximately 60–70 percent of your body is made up of water. Without it, life simply would not exist.

Water is polar

The hydrogen and oxygen atoms within water molecules form polar covalent bonds. The shared electrons spend more time associated with the oxygen atom than they do with hydrogen atoms. There is no overall charge to a water molecule, but there is a slight positive charge on each hydrogen atom and a slight negative charge on the oxygen atom. Because of these charges, the slightly positive hydrogen atoms repel each other and form the unique shape seen in [link] . Each water molecule attracts other water molecules because of the positive and negative charges in the different parts of the molecule. Water also attracts other polar molecules (such as sugars), forming hydrogen bonds. When a substance readily forms hydrogen bonds with water, it can dissolve in water and is referred to as hydrophilic    (“water-loving”). Hydrogen bonds are not readily formed with nonpolar substances like oils and fats ( [link] ). These nonpolar compounds are hydrophobic    (“water-fearing”) and will not dissolve in water.

Picture of oil in water.
As this macroscopic image of oil and water show, oil is a nonpolar compound and, hence, will not dissolve in water. Oil and water do not mix. (credit: Gautam Dogra)

Water stabilizes temperature

The hydrogen bonds in water allow it to absorb and release heat energy more slowly than many other substances. Temperature is a measure of the motion (kinetic energy) of molecules. As the motion increases, energy is higher and thus temperature is higher. Water absorbs a great deal of energy before its temperature rises. Increased energy disrupts the hydrogen bonds between water molecules. Because these bonds can be created and disrupted rapidly, water absorbs an increase in energy and temperature changes only minimally. This means that water moderates temperature changes within organisms and in their environments. As energy input continues, the balance between hydrogen-bond formation and destruction swings toward the destruction side. More bonds are broken than are formed. This process results in the release of individual water molecules at the surface of the liquid (such as a body of water, the leaves of a plant, or the skin of an organism) in a process called evaporation    . Evaporation of sweat, which is 90 percent water, allows for cooling of an organism, because breaking hydrogen bonds requires an input of energy and takes heat away from the body.

Conversely, as molecular motion decreases and temperatures drop, less energy is present to break the hydrogen bonds between water molecules. These bonds remain intact and begin to form a rigid, lattice-like structure (e.g., ice) ( [link] a ). When frozen, ice is less dense than liquid water (the molecules are farther apart). This means that ice floats on the surface of a body of water ( [link] b ). In lakes, ponds, and oceans, ice will form on the surface of the water, creating an insulating barrier to protect the animal and plant life beneath from freezing in the water. If this did not happen, plants and animals living in water would freeze in a block of ice and could not move freely, making life in cold temperatures difficult or impossible.

Questions & Answers

what Is taxonom
Don Reply
Taxonom is the the laws and principles guiding the classification of living things either plant 🌿 or animal
Samuel
protein synthesis began with what?
Kesselly Reply
What structures does a plant cell have that an animal cell does not hav
Martin Reply
A plant cell has a cell wall, a large central vacuole, and chloroplasts, which an animal cell does not have.
AI-Robot
what is the function of the cytoskeleton?
Martin
truly. Al-robot
Mark
why is it advantageous for the cell membrane to be fluid in nature?
Martin Reply
The fluid nature of the cell membrane allows for flexibility and dynamic changes in its structure. This allows for the movement of molecules and ions in and out of the cell, as well as the ability to respond to external stimuli. The fluidity of the membrane also allows for the formation of specialized structures such as receptor proteins, which are important for cell-cell communication.
AI-Robot
What is used as a visual marker for successful gene transfer into transgenic animals?
rhonda Reply
Parts of the body involved in homeostasis
Favour Reply
liver
Kirk
A collection of similar-typed cells working together to perform a specific function is called what?
Rachel Reply
tissue
Van
which structure consists of a phospholipid bilayers and it is known as the mosaic model?
Jamar Reply
cell membrane
Abanoub
what is diffusion
Patricia Reply
a passive process of transport
Jamar
Random movement of gas molecule from region of high concentration to a low concentration.
praise
10 difference between male and female reproductive system
Ina Reply
if a phase is omitted ,what will happen to the cell
Ewemoje Reply
discribe advantages and disadvantages of asexual and sexual reproduction
basi Reply
Compared to separate sexes and assuming self-fertilizing is not possible, what might be one advantage and one disadvantage to hermaphroditism?
Gift Reply
is nature of their environment among
basi
cool 😎
Precious
why are the laws of thermodynamics considered laws of nature and not scientific theories
Yolonda Reply
archea were given their own separate domain because they are?
Yolonda
which of the following is a basic component of all of the others?
Yolonda
which of the following organization levels is the least inclusive
Yolonda
which cell feature is absent in bacterial cells
Yolonda
which metric movies the base unit of measurement by one thousandth (0.001)?
Yolonda
What is biology?
Blessing Reply
List the branches of biology
Blessing
List the branches of biology
Blessing
List the branches of biology
Blessing
List the branches of biology
Blessing
Ecology,Anatomy,genetics,biophysics,biochemistry,microbiology and biotechnology.
praise

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Source:  OpenStax, Concepts of biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11487/1.9
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