Dr. Paul's Virtually Biology Show.

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B

B lymphocyte(B cell) Cells in the immune system that can antibodies. These are the only cells in the immune system that can produce antibodies.
Bacillus. A rod shaped bacterium.
Bacteriophage. A virus that uses bacteria as its host.

Barr Body. An inactivated X chromosome. In mammals during development one X chromosome in a lineage of cells is randomly placed in a Barr body, making females in a sense, genetic mosaics.

Base. A substance that when added to water, lowers the concentration of hydrogen ions in a solution. Bases may be either weak or strong. Strong bases include sodium and potassium hydroxide. Weak bases include urea and other nitrogen containing organic compounds. See acid, pH

Base substitution. A kind of mutation in which a nucleotide with one nitrogen base, Thymine for instance, replaces another. Often this leads to a different amino acid in translation of a codon.

Basophil. A white blood cell that releases histamine and other chemical messengers as part of the inflammatory response. The name comes from the fact that these cells take up certain alkaline(basic) stains.

Behavior. An organism's coordinated response to internal and external stimuli. Sometimes behavior is defined so as to refer only to animals but this is now often considered to be excessively narrow. Even bacteria can show coordinated responses to stimuli.

Bilateral Symmetry. A body plan in which both haves of the body are mirror images of each other such that this can only be done in one way. We are bilaterally symmetric.
Bile. A substance produced by the liver and that contains cholesterol lecithin(a phospholipid) and various salts. The function of bile(aside from looking really gross) is to emulsify fats so that the fats can be more easily digested. Remember , bile is produced by the liver and stored by the gall bladder.
Binary fission. Non mitotic division of a bacterial cell and its DNA into two identical daughter cells.

Biogeography. The study of the distribution of plants, animals and other organisms on the earth and the development of theories to explain these distributions.

Bioluminescence. The conversion of chemical energy in a "cold" light that happens in certain organisms. Aside from the familiar "fireflies", this process happens in many other insects, bacteria, fungi, protista as well as various animals including deep sea fish. The significance of bioluminescence is not known in many of these cases.
Biome. A large scale terrestrial ecosystem characterized by certain forms of vegetation adapted to the amounts of light, moisture and the temperature found in a particular broad region.
Biosphere. The regions on, the surface, below the surface and up into the atmosphere where life is found. Sometimes considered to be the global ecosystem or ecosphere.
Biosynthetic pathway. A series, often complex, of chemical reactions which lead to the production of a chemical from simpler reactants that occurs within cells. Examples of biosynthetic pathways would be protein synthesis and the synthesis of glucose in photosynthesis.
Biotic potential. The maximum rate of increase of a population assuming ideal conditions.
Blind spot. In vertebrates, the region of the retina where there are no rods and or cones.
Bottleneck effect. A loss of genetic variability in a population brought about by a population crash(the bottle neck). When the population increases again, much of the population's genetic variation has been lost by passage through the bottle neck. This is important because the new population, even though it may seem healthy, is endangered because it has lost critical genetic variation to help it evolve when environmental conditions change.

Bowman's capsule. In the kidney, this is the cup shaped structure at the beginning of the nephron that receives water, urea and other substances from the blood.
Bronchiole. A "small bronchus". The smallest of a series of finer and finer branchings from the bronchi. The bronchioles terminate in the alveoli where gas exchange between the lungs takes place.
Bronchus. In the lung, the bronchi are the primary, secondary and tertiary branchings from the trachea.
Bryophyte. A member of the plant kingdom that lacks vascular tissue and that has a photosynthetic gametophyte from which grows the spore producing stages. Mosses and Liverworts are typical bryophytes.
Buffer. In biology a buffer is a substance that helps a solution maintain a certain pH even though hydrogen ions are being added to or subtracted from the solution. They do this by either taking up the excess hydrogen ions or by releasing more as needed. Buffers are important because the cell's pH must typically be maintained within a narrow range for the enzymes to function properly.
Bulk flow. Movement of water or other substance which is due to pressure or density differences from one region of the solution to another.