A compound or solution that is a base releases  ions or takes up  ions.  It is not a nonpolar molecule with covalent bonds and does not mix well with oil, which is nonpolar.

Iron  is important for many organisms but it isn't found in quantities large enough for it to be a major component. It is part of the trace minerals. Carbon, nitrogen, sulfur and oxygen are all part of the bulk elements, elements that are found in the largest quantities (they make up 96% of organisms). 

Water is a polar molecule because the bonds between oxygen and hydrogen are polar covalent bonds. This means that although they form covalent bonds (normally non-polar) the difference in electronegativity is great enough to make one side more negative (oxygen side) and the other side more positive (hydrogen side). However, the polarity isn't as strong as the polarity in ionic bonds so we donate the charges with the greek letter delta to show that they are partial charges. 

Catabolism means to break something down, usually from a larger starting point to one or more smaller byproducts. Hydrolysis is the most common reaction in the human body. Hydrolysis means "breaking" through the addition of a water molecule. You will see hydrolysis as an important reaction in many pathways in the human body.

An alcohol group is written as  (hydroxide) in the structural formation of a molecule. The hydroxide group is an oxygen and carbon molecule held together by a covalent bond. Hydroxide is a minor constituent of water. Remember water is usually in the form, .

When there is a concentration gradient, water will move across a membrane unassisted by ATP or channel proteins. In contrast, solutes (the dissolved substances) cannot cross the membrane unassisted.

Carbon is phenomenally important to life as we understand it. The ability to form bonds with up to four different atoms gives carbon an incredible chemical diversity, and allows for carbon to make long chains and aromatic compounds. The ability to make long chains and aromatic compounds accounts for the formation of nucleic acids, proteins, and lipids (macromolecules that are absolutely essential to life). Binding properties of carbon also relate to the structure and orientation of biological compounds, which are important aspects of organic chemistry.

In its ground state carbon has four valence electrons, two its full s subshell and two in a partially filled p subshell. Normally, this would indicate that carbon forms two bonds, since only two of the electrons are in orbitals that are not already paired. Carbon, however, is able to form hybrid orbitals by combining the three p orbitals and one s orbital to form four identical sp³ orbitals, each containing one electron. This means that carbon can form four bonds, allowing it to achieve a stable octet.

For biology, the important note is that carbon can make four bonds. Organic chemistry is the study of carbon and how these bonds function to create organic and biological materials.

Carbon has four valance electrons, allowing it to form a wide range of bonds with other atoms.

When carbon bonds to four separate substituents, it forms a tetrahedral structure. Because of its ability to hybridize orbitals, carbon can also bond to three substituents by forming a double bond, or to two substituents via two double bonds or the combination of a single bond and a triple bond. This variability in molecular bonding and shape allows carbon to exist in numerous compounds, exhibiting a number of different properties and functions.

Carbon is incapable of forming a quadruple bond, and it is not magnetic. Though carbon has a relatively low atomic mass, one would expect hydrogen to be the most relevant element if low mass was the most pertinent property of carbon. Carbon can form ionic bonds (generally with metals), but is most commonly found in organic molecules where it forms covalent bonds.

Life is "carbon-based" or predominantly carbon because it can form stable bonds with itself, but also with a variety of other types of elements. Electronegativity increases from left to right on the periodic table, but also from bottom to top. While carbon is relatively high and right on the periodic chart, there are still elements like oxygen or fluorine (the most electronegative) that have a great pull for electrons. While carbon makes up a lot of the universe, it pales in comparison to hydrogen which is the most common element (three fourths of the mass of our universe). Therefore ratios do not matter. The polar and nonpolar nature of molecules are important for the functions of life (like membranes), but were it not for the bonding of carbon to itself, the nonpolar molecules would not be able to form. Thus, its bonding versatility is the main reason for life being carbon based.