Secondary succession
A type of succession that occurs where an existing community has been severely cleared by
some disturbance.
Secretion
(1) The discharge of molecules synthesized by the cell.
(2) In the vertebrate kidney, the discharge of wastes from the blood into the filtrate from
the nephron tubules.
Secretory tissue
Secretory tissue in the interior of the gland is made up of: Secretory tissue - This is made up
of secretory epithelial cells.
Secondary cell wall
The secondary cell wall is a structure found in many plant cells, located between the
primary cell wall and the plasma membrane. The cell starts producing the secondary cell
wall only after the primary cell wall is complete and the cell has stopped growing.
Secondary xylem
Xylem produced by cambium, composed of two interpenetrating systems, the horizontal
(ray) and vertical (axial).
Sedimentary rock
Rock formed from sand and mud that once settled in layers on the bottom of seas, lakes,
and marshes. Sedimentary rocks are often rich in fossils.
Seed
An adaptation for terrestrial plants consisting of an embryo packaged along with a store of
food within a resistant coat.
Segmentation
The subdivision of an organism or of an organ into more or less equivalent parts.
Segregation
The separation of paired alleles during meiosis so that members of each pair of alleles
appear in different gametes.
Selection
The process by which the forms of organisms in a population that are better adapted to the
environmental conditions increase in frequency relative to less well-adapted forms over a
number of generations.
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