have the ability to regenerate lost limbs and demon-
strated that corals were animals, not plants. In 1735 he
introduced the concept of growing degree-days, later
known as Réaumur’s thermal constant of phenology.
This idea led to the heat-unit system used today to
study plant-temperature relationships.
In 1737 Réaumur became an honorary member of
the Russian Academy of Sciences, and the following
year he became a fellow of the Royal Society.
After studying the chemical composition of Chi-
nese porcelain, in 1740 he formulated his own Réau-
mur porcelain. In 1750 while investigating the animal
world, he designed an egg incubator. Two years later, in
1752, he discovered that digestion is a chemical process
by isolating gastric juice and studied its role in food
digestion by studying hawks and dogs.
Réaumur died in La Bermondière on October 18,
1757, and bequeathed to the Academy of Science his
cabinet of natural history with his collections of miner-
als and plants.
recapitulation The repetition of stages of evolution
in the stages of development in the individual organism
(ONTOGENY). The history of the individual develop-
ment of an organism.
receptor Amolecule or a polymeric structure in or
on a cell that specifically recognizes and binds a com-
pound acting as a molecular messenger (neurotransmit-
ter,HORMONE, lymphokine, lectin, DRUG, etc.).
receptor mapping The technique used to describe
the geometric and/or electronic features of a binding
site when insufficient structural data for this RECEPTOR
orENZYMEare available. Generally the active-site cavi-
ty is defined by comparing the superposition of active
molecules with that of inactive molecules.
receptor-mediated endocytosis Cells use RECEPTOR-
mediated endocytosis—a method where specific
molecules are ingested into the cell—for ingestion of
nutrients, hormones, and growth factors. The specifici-
ty results from a receptor-LIGAND(a molecule or ion
that can bind another molecule) interaction. Other lig-
ands that can be ingested include toxins and lectins,
viruses, and serum transport proteins and antibodies. A
receptor, a specific binding protein such as clathrin, on
the plasma membrane of the target tissue will specifi-
cally bind to ligands on the outside of the cell. An
endocytotic process results, i.e., the cell folds inward
with a portion of the plasma membrane, and the result-
ing clathrin-coated pit is pinched off to form a mem-
brane-enclosed bubble or vesicle, called an endosome.
After entering the cytoplasm, the endocytotic vesicle
loses its clathrin coat, and the ligand (multiple ligands
can enter the cell in the same coated pit) is ingested.
The receptor can be recycled to the surface by vesicles
that bud from the endosome targeting the plasma mem-
brane. After these recycling vesicles fuse with the plas-
ma membrane, the receptor is returned to the cell
surface for binding and activity once more.receptor potential(end-plate potential) A change in
a neuron’s membrane potential (a change in voltage
across the receptor membrane) caused by redistribution
of ions responding to the strength of the stimulus. If
the potential is high enough, an action potential will be
fired in an afferent neuron. The more action potentials
fired, the more neurotransmitters released, and stronger
the signals reaching the brain.recessive allele An allele that is not expressed
phenotypically in a heterozygote due to the presence
of a dominant or masking allele. However, it will be
expressed in a specific phenotype when a counterpart
recessive gene is present. However, often when indi-
viduals inherit two mutant copies of a gene on one of
the autosomes, they suffer from autosomal recessive
disorders. Examples like hemophilia occur where
the recessive gene associated with it lies on part of the
X chromosome (X-linked recessive disorder). Most
genetic mutations produce recessive alleles.recessive disorder A disorder associated with a
recessive allele.reciprocal altruism The belief that if one acts
kindly toward another unrelated individual, thatreciprocal altruism 287