Most cells are surrounded by water, and cells themselves are about
A water molecule is held together by strong, polar covalent bonds
between oxygen and hydrogen atoms.
The partially charged regions of a polar water molecule are attracted
to oppositely charged parts of neighboring molecules.
Each molecule can form weak hydrogen bonds to multiple partners,
conferring water unique properties.
Water molecules are also attracted to other substances, such as cell
walls, by adhesion.
These properties help transport water up against gravity in plants.
Water molecules form hydration shells around ions, separating them
from the crystal and dissolving the salt and forming a solution.
A solution with water as the solvent is called an aqueous solution.
Substances dissolved in solution are called solutes.
For simplicity, HO^+ can be viewed as HO plus a H^+ (hydrogen
ion), or proton.
The H^+ concentration at 25°C ranges from 1 Molar (10^0, or pH=0) to
10^-14 M (pH=14).
These concentrations are plotted on a negative logarithmic scale: each
unit change in pH is a 10-fold change in H^+ ion concentration.
An acid has a high concentration of H^+ ions (low pH).
A base has a low H^+ concentration (high pH).
In human blood, dissolved CO forms Carbonic acid (HCO).
Carbonic acid acts as a buffer by dissociating to yield a bicarbonate
ion (HCO^-) and a hydrogen ion (H^+) in a dynamic equilibrium.
Humans have dug up these carbon fuels to burn as energy sources, releasing excess carbon,
sulfur, and nitrogen into the atmosphere.