Hippocampus Biology: The Chemical Basis of Life: Summary

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Living organisms use only a small fraction of the known chemical elements to carry out all of their biological functions. Six elements make up more than 99% of matter in living systems: hydrogen, carbon, nitrogen, oxygen, phosphorous, and calcium. Five elements are found in much smaller amounts: sodium, magnesium, sulfur, chlorine, and potassium. Finally, 14 elements are known as "trace" elements because living organisms require them in minute quantities.

An atom is the fundamental unit of chemical matter. An atom consists of a nucleus, containing positively charged protons and uncharged neutrons, surrounded by a cloud of negatively charged electrons. Atoms of the same element that differ in the number of neutrons are called isotopes.

Ions are charged species resulting from the gain or loss of electrons from a neutral atom or molecule. Some atoms, like sodium, readily lose electrons, while other atoms, such as fluorine, readily gain electrons.

We saw how atoms and ions combine through chemical bonding. Bonding can be covalent, where electrons are shared, or it can be ionic, where an attraction between oppositely charged ions holds them together.

We learned that chemistry involves both the structure and the transformation of matter. A chemical reaction is a process in which a substance or substances is converted into one or more new substances with different properties and composition. The substances we start with are called the reactants, and the substances we obtain are called the products. An important feature of chemical equations is that they must be balanced. This equation is balanced because both sides of the equation have one carbon atom, 4 hydrogen atoms, and 4 oxygen atoms.

Finally, we learned that some chemical reactions produce energy and some reactions consume energy. Energy is produced when the reactants have more energy than the products, and energy is consumed when the reactants have less energy than the products.