Passive transport
The diffusion of a substance across a biological membrane.
Pathogen
An organism or a virus that causes disease.
Parthenocarpic
The production of fruit without fertilization.
Pattern formation
The ordering of cells into specific three-dimensional structures, an essential part of shaping
an organism and its individual parts during development.
Pericardium
He membranous sac filled with serous fluid that encloses the heart and the roots of the
aorta and other large blood vessels
Pectin
Pectin is a gummy polysaccharide constituent of the cell walls of plants that is used as a
thickening agent in jams and jellies. Pectin’s mucilaginous qualities are useful in treating
diarrhea and high cholesterol and it may have beneficial effects on radiation sickness as
well.
Pedigree
A family tree describing the occurrence of heritable characters in parents and offspring
across as many generations as possible.
Pelagic zone
The area of the ocean past the continental shelf, with areas of open water often reaching to
very great depths.
Pelvic girdle
A bony or cartilaginous structure in vertebrates, attached to and supporting the hind limbs
or fins.
Penis
The male organ of copulation in higher vertebrates, homologous with the clitoris (female).
In mammals, it also serves as the male organ of urinary excretion.
Pentadactyl
Having five fingers or toes on each hand or foot.
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