absorption spectrum
A chart indicating which wavelengths of light are absorbed by a given pigment.
wikipedia reference

Acetyl-CoA
Coenzyme A (CoA) is adapted from pantothenic acid and adenosine triphosphate and used in metabolism in areas such as fatty acid oxidization and citric acid cycles. Its main function is to carry acyl groups such as acetyl as thioesters. A molecule of Coenzyme A carrying an acetyl group is also referred to as Acetyl-CoA.
wikipedia reference

action spectrum
A chart indicating the activity of a metabolic process, such as photosynthesis, in relation to different wavelengths of light.
wikipedia reference

activation energy
The activation energy in chemistry is the energy needed by a system to initiate a particular process. Activation energy is often used to denote the minimum energy needed for a specific chemical reaction to occur.
wikipedia reference

active sites
The location on an enzyme where catalysis takes place; location of substrate binding.
wikipedia reference

active transport
Active transport is transport across a membrane that relies on chemical energy. In this form of transport, molecules move against either an electrical or concentration gradient (collectively termed an electrochemical gradient). There are two main types, primary and secondary. Primary transport involves the consumption of metabolic energy (often in the form of ATP) and is directly coupled to movement across a membrane, independent of any other species. Secondary transport concerns the diffusion of one species across a membrane to drive the transport of another. Transporters generally are membrane-spanning or "transmembrane" or integral membrane proteins.
wikipedia reference

ADP
Adenosine diphosphate is formed when ATP is hydrolyzed and gives up a phosphate.  It can also be formed by a condensation reaction binding adenosine monophosphate (AMP) with a phosphate.
wikipedia reference

Aerobic Respiration
The stepwise process by which organisms oxidize glucose to produce ATP and reduced cofactors; includes glycolysis, pyruvate oxidation, the Krebs cycle, and oxidative phosporylation. Oxygen is the final electron acceptor in this process.
wikipedia reference

allele
An allele is any one of a number of alternative forms of the same gene occupying a given locus (position) on a chromosome. An example is the gene for blossom color in many species of flower - a single gene controls the color of the petals, but there may be several different versions of the gene. One version might result in red petals, while another might result in white petals.

Many organisms are diploid - that is, they have two sets of homologous chromosomes in their somatic cells, and thus contain two copies of each gene. An organism in which both copies of the gene are identical - that is, have the same allele - is said to be homozygous for that gene. An organism which has two different alleles of the gene is said to be heterozygous. Often one allele is "dominant" and the other is "recessive" - the "dominant" allele will determine what trait is expressed. For example, in the case of blossom color, if the "red" allele is dominant to the "white" allele, in a heterozygous flower (with one red and one white allele), the petals will be red. An exception is "codominance", where both alleles are active - a blending of traits may result, e.g. pink petals.

A wild type allele is an allele which is considered to be "normal" for the organism in question, as opposed to a mutant allele which is usually a relatively new modification.
wikipedia reference

allosteric enzymes
Enzymes with multiple binding sites for substrates and/or repressors; binding of one molecule of substrate or repressor makes binding of a second molecule more likely to occur.
wikipedia reference

amino acid
In chemistry, an amino acid is any molecule that contains both amino and carboxylic acid functional groups.

In biochemistry, this term is frequently used to refer to alpha amino acids, that is, those amino acids in which the amino and carboxylate functionalities are attached to the same carbon.

There are 20 amino acids which are directly expressed in the genetic code. If a protein contains a different amino acid it must have been modified after translation. These modifications are often essential for the function of the protein. Over 500 amino acids have been found in nature.

The generalized structure of alpha amino acids is:

    COOH
    |
  H-C-R
    |
    NH2

Where "R" represents a side chain specific to each particular amino acid. Amino acids are usually classified by properties of the side chain into four groups: acidic, basic, hydrophilic (polar), and hydrophobic (nonpolar).
wikipedia reference

anabolism
Anabolism encompasses the processes of cell metabolism in which the cell uses energy and reducing power to construct complex molecules and perform other biological functions.
wikipedia reference

anti-parallel
Refers to the nature of the two strands of the DNA double helix - one strand runs in the 5' to 3' direction, while the other runs in the 3' to 5' direction.
wikipedia reference

antiports
Integral membrane proteins that move two or more substances across a membrane, but in opposite directions.
wikipedia reference

asexual reproduction
Asexual reproduction is a biological process by which an organism creates a genetically similar copy of itself without the combination of genetic material with another individual. For example, the Hydra (invertebrates of the order Hydroidea) and yeast are able to reproduce by budding. Most plants are capable of vegetative reproduction.
wikipedia reference

ATP
Adenosine triphosphate (commonly called ATP) is the "molecular currency" of intracellular energy transfers. It is a means of storing and transporting chemical energy within the cell and a precursor for RNA formation. Chemically, adenosine triphosphate consists of the adenosine nucleotide (which is ribose sugar and adenine base) plus three phosphate groups.
wikipedia reference

ATP Synthase
A large protein complex embedded in certain membranes that uses the potential energy of a proton gradient to synthesize ATP; important in photosynthetic electron transport and aerobic respiration electron transport.
wikipedia reference

autosomes (wikipedia reference) redirected to chromosome

autotroph
An autotroph is an organism that produces its own organic compounds from inorganic substances (e.g., minerals) using either light or chemical bonds as a source of energy. Plants and other organisms using photosynthesis are photoautotrophs; bacteria that use utilize inorganic compounds, such as hydrogen sulfide or ferric iron, for energy are chemoautotrophs.

Autotrophs are a vital part of the food chain. They take energy from the sun or from inorganic sources and convert it into a form (organic molecules) that other organisms (heterotrophs) can use as food, obtaining energy by breaking down the organic molecules. Heterotrophs, like animals, fungi, and most bacteria and protozoa, depend on autotrophs for energy and for the raw materials to make complex organic molecules. Even carnivorous animals ultimately rely on autotrophs because the energy gained from the prey comes from the autotrophs eaten by the prey.
wikipedia reference