Science / Biology Glossary

Biomass: The total weight of living tissue in a community.

Biome: A large-scale grouping that includes many communities of a similar nature.

Biosphere: All ecosystems on Earth as well as the Earths crust, waters, and atmosphere on and in which organisms exist; also, the sum of all living matter on Earth.

Birds: Taxonomic class of terrestrial vertebrates that are characterized by endothermy and feathers; descended from some group of reptiles (or possibly dinosaurs).

Birth Rate: The ratio between births and individuals in a specified population at a particular time.

Bladder: A hollow, distensible organ with muscular walls that stores urine and expels it through the urethra.

Blastocoel: The fluid-filled cavity at the center of a blastula.

Blastocyst: The developmental stage of the fertilized ovum by the time it is ready to implant; formed from the morula and consists of an inner cell mass, an internal cavity, and an outer layer of cells . . . View Full Definition

Blastula: A ball of cells surrounding a fluid-filled cavity (the blastocoel) that is produced by the repeated cleavage of a zygote.

Blending: Term applied to 19th century belief that parental traits blended in their offspring; disproven by Mendels work.

Blood Group Or Type: One of the classes into which blood can be separated on the basis of the presence or absence of certain antigens; notably, the ABO types and the Rh blood group.

Body Fossil: The actual remains (however permineralized, compressed or otherwise post-mortem altered) of an organism; includes bones, shells, and teeth.

Bolus: A mass of chewed food mixed with salivary secretions that is propelled into the espohagus during the swallowing phase of digestion.

Bony Fish: A term applied collectively to all groups of fish with bony (as opposed to cartilaginous) skeletons.

Bottlenecks: Drastic short-term reductions in population size caused by natural disasters, disease, or predators; can lead to random changes in the populations gene pool.

Brachiopods: A phylum of hinge-shelled animals that have left an excellent fossil record; brachiopods live on or in the ocean floor.

Brachydactly: Human genetic disorder that causes production of an extra digit; an autosomal dominant trait. Sometimes referred to as polydactly.

Brain: The most anterior, most highly developed portion of the central nervous system.

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