The ocher star (Pisaster orchraceous) is a keystone
predator because it prevents mussels, its prey, from tak-
ing over intertidal areas. Sea otters are a keystone
predator in kelp beds, since they eat the urchins that
feed on kelp, whose beds maintain a diversity of other
organisms.
The removal of a keystone predator from an
ecosystem causes a reduction of the species diversity
among its former prey.
Keystone species increase or decrease the diversity
of a system because they play a dominant role and
affect many other organisms, including the death and
disappearance of the dependent species.
kidney An organ, paired, in vertebrates that regu-
lates secretion and osmoregulation as part of the uri-
nary system. Filtration takes place at the site of the
glomerulus in the Bowman’s capsule, while the loops
of Henle are responsible for taking waste material to
be excreted. Millions of nephrons within the renal
cortex and renal medulla filter the blood and regulate
thevolume and composition of body fluids during
the formation of urine. A ureter from each kidney
carries urine produced in the kidney to the bladder
for elimination.
kilocalorie (kcal) One kilocalorie is equal to 1,000
calories, a unit of heat equal to the amount of heat
required to raise the temperature of 1 kilogram of
water by 1 degree at one atmosphere pressure; used to
measure the energy value in food and labor; usually
just called calorie: 1 kilocalorie (kcal) = 1 Calorie
(Cal) = 1,000 calories (cal). However, in the Interna-
tional System of Units (ISU), the universal unit of
energy is the joule (J). One kilocalorie = 4.184 kilo-
joules (kJ).
kilogram The basic unit of mass (not of weight or of
force). A kilogram is equal to the mass of 1.000028
cubic decimeters of water at the temperature of its
maximum density.
kinematics A division of mechanics that studies
objects in motion (like an animal’s gait) and their
changes in position and the effects of motion on dis-
tance and time of travel. Differs from the study of
mechanics, which also includes the effects of mass and
force.kinesis When an animal finds itself in an unwanted
environment, kinesis is its ability to respond to the
intensity of this stimulus by undirected movement in a
random way (trial and error).kinetic energy Energy of motion; kinetic energy
depends on the object’s mass and velocity and can
be described mathematically as K.E. = 1/2mv^2.
Moving matter, be it a rolling rock, flowing water,
or falling ball, transfers a portion of its kinetic energy
to other matter. For example, an inelastic collision
is one in which at least a portion of the kinetic
energy of the colliding particles is lost. Potential ener-
gy, energy stored in a body, can be converted to
kinetic energy.kinetochore A specialized region or structure on the
centromereof chromosomes, the region that joins two
sister chromatids; links each sister chromatid to the
mitotic spindle. The mitotic spindle is the specialized
region on the chromatid where kinetochores and sister
chromatids attach. When a chromosome replicates
after mitosis or meiosis, it produces two side-by-side
chromatids, with each eventually becoming a separate
chromosome.
See alsoCENTROMERE.kinetochore fibers The microtubules that connect
kinetochores to spindle polar fibers.kinetosome(basal body) The structure at the base
of a flagellum or cilium that rises from the centriole
and consists of a cylinder composed of nine longitudi-
nally oriented, evenly spaced, triplet microtubules sur-
rounding one central pair, called the axoneme. Usually
found in pairs. Also called a blepharoplast. The type of
kinetosomes—based on number, structure, and posi-
tion—are used to type ciliates.kinetosome 187