Biosystematices. Aspect of systematic concerned with variation and evolution of species. More or less equivalent to experimental taxonomy.

Biota. It refers to the animals and plants of a particular region.

Biotic factors. Environment influences that arise from activities of living organisms, as distinct from e.g. climate factors.

Biotin. A vitamin in the vitamin B complex. It is a coenzyme concerned in carboxylation and decarboxylation. Widely distributed in organisms.

Biotype.
(1) Naturally occurring group of individuals having the same genetic composition.
(2) Physiologic race.

Bipolar. A neuron having two axons which are emerging form opposite sides of soma.

Bisexual. Hermaphrodite or Monoecious, where both the male and female sexes are borne by the same individual; most plants and same lower animals like sponges, some coelenterates, flat worms, earthworms and leeches.

Blastema. (Zool). Mass of undifferentiated cells which later develop into an organ. One of the two main ways by which an animal regenerates a lost part by initial formation of blastema (e.g. limb or tail of newt, head of flatworm); the other way being by remodeling of remaining tissue (morphallaxis).

Blastocoele. Cavity which appears within the mass of cells formed towards the end of the period of cleavage of the egg of many animals.

Blastocyst. Stage in mammalian development resulting from cleavage, which is roughly the equivalent of a blastula. A thin-walled hollow sphere (trophoblost) containing at one side a knob of cells destined to become the embroyo proper.

Blastomeres. Refers to cell which are formed by the division of zygote during cleavage.

Blastogenesis. The process development of the off spring in a sexual reproduction from buds or fragments.