AP Chapter 3

Chapter 3

Water and the Fitness of
the Environment

Overview: The Molecule That Supports All of Life

          _______________is the biological medium on Earth

          All living organisms require _________________more than any other substance

          Most cells are surrounded by water, and cells themselves are about ________________ water

          The abundance of water is the main reason the Earth is ______________________________

Concept 3.3: Acidic and basic conditions affect living organisms

          A hydrogen atom in a ­­­­­­­­­­­_____________________________ between two water molecules can shift from one to the other:

          The hydrogen atom leaves its electron behind and is transferred as a proton, or _______________________________________

          The molecule with the extra proton is now a ___________________________________, though it is often represented as H+

          The molecule that lost the proton is now a _________________________________

          Water is in a state of ___________________________________ in which water molecules dissociate at the same rate at which they are being reformed

          Though statistically rare, the dissociation of water molecules has a great effect on organisms

          Changes in _______________________________ of H+ and OH can drastically affect the chemistry of a cell

Effects of Changes in pH

          Concentrations of H+ and OH are __________________ in pure water

          Adding certain solutes, called _____________________ and ____________________, modifies the concentrations of H+ and OH

          Biologists use something called the ____________________________________ to describe whether a solution is acidic or basic (the opposite of acidic)


Acids and Bases

          An _____________________________ is any substance that increases the _______

_____________________________________ of a solution

          A _______________________________ is any substance that ______________________ the H+ concentration of a solution

The pH Scale

          In any aqueous solution at 25°C the product of H+ and OH is constant and can be written as                                                                                            ___________________________________________

          The pH of a solution is defined by the negative logarithm of H+ concentration, written as                                               ___________________________________________

          For a neutral aqueous solution                                            


          Acidic solutions have pH values _______________________ than 7

          Basic solutions have pH values _________________________ than 7

          Most biological fluids have pH values in the range of _______________________________


          The internal pH of most living cells must remain close to ________________________

          _______________________________ are substances that minimize changes in concentrations of H+ and OH in a solution

          Most buffers consist of an acid-base pair that reversibly combines with H+

Threats to Water Quality on Earth

          ________________________________________ refers to rain, snow, or fog with a pH lower than 5.6

          Acid precipitation is caused mainly by _______________________________________________
________________________________________ and can fall at some distance from the source of pollutants

          Acid precipitation can damage life in lakes and streams

          Effects of acid precipitation on _____________________________________ are contributing to the decline of some forests

          Human activities such as ________________________________________ threaten water quality

          _______________________ is released by fossil fuel combustion and contributes to:

          A warming of earth called the ___________________________________________

          Acidification of the oceans; this leads to a decrease in the ability of corals to form calcified reefs