Water is Essential to Living Systems
Name:
Date:
The tiny three-atom water molecule has unusual features that make it essential to all
organisms, which explains why the search for __________________________ begins
with the search for _______________. Certainly, ______ organism on Earth can live
without it.
Water molecules are made up of a central oxygen atom bonded by
__________________ bonds to two hydrogen atoms. Water is made up of polar
molecules. This means that the water molecule has one end with a slight
______________ charge and one end with a slight _______________ charge. A
hydrogen bond forms __________________ water molecules and is responsible for
many of water’s unusual properties.
Water’s Unusual Properties
1. Water dissolves many substances
(aka. the universal solvent)
2. Water expands and is less dense in its frozen state
3. Water is cohesive (wants to stick together) creating a
skin like surface
4. Water regulates temperature – resists temperature
changes and it requires a lot of energy to increase the
temperature or change its state from liquid to gas
5. Nearly all life’s chemical reactions occur in the watery solution in and around cells.
Hydrophillic substances (water loving) _______________ in water. This is because
they are made up of _____________ _______________ or ions. Ex. Sugar and salt
Hydrophobic molecules (water hating) such as fats do not _______________ ___
water.
Water and the pH scale
Water solutions are ______________, _________________ or _______________
depending on their properties. Acids increase H+ ions in solution, taste _____________
and turn litmus paper ______________. Examples of common acids include stomach
acid (1.6-1.8), juice and pop (3) Bases increase OH- ions in solution, taste
____________ and feel _______________. Bases turn litmus paper
_______________. Common bases are baking soda (8.1) and soap (10). When acids
and bases are mixed they react to form ________________ and ________________.