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26.17: R

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radial symmetry
symmetry of a body plan in which there is a distinct top and bottom but not distinct head and tail ends, so the body can be divided into two halves like a pie
reactant
starting material in a chemical reaction
recessive allele
allele that is masked by the presence of another allele for the same gene when they occur together in a heterozygote
recombinant DNA
DNA that results when DNA from two organisms is combined
red blood cell
type of cell in blood that contains hemoglobin and carries oxygen
reflex
rapid motor response to a sensory stimulus in which nerve impulses travel in an arc that includes the spinal cord but not the brain
regeneration
regrowing of tissues, organs, or limbs that have been lost or damaged
regulatory element
region of DNA where a regulatory protein binds
regulatory protein
protein that regulates gene expression
relative dating
method of dating fossils by their location in rock layers; determines which fossils are older or younger but not their age in years
renewable resource
natural resource that can be replenished by natural processes as quickly as humans use it
reproduction
process by which living things give rise to offspring
reproductive system
system of organs that produces gametes and secretes sex hormones
reptile
ectothermic, tetrapod vertebrate that lays amniotic eggs; includes crocodiles, lizards, snakes, and turtles
reservoir
part of a biogeochemical cycle that holds an element or water for a long period of time
respiration
exchange of gases between the body and the outside air
respiratory system
organ system that brings oxygen into the body and releases carbon dioxide into the atmosphere
resting potential
difference in electrical charge across the plasma membrane of a neuron that is not actively transmitting a nerve impulse
rhizoid
hair-like structure in a nonvascular plant that absorbs water and minerals and anchors the plant to a surface
ribosomal RNA
type of RNA that helps form ribosomes and assemble proteins
ribosome
organelle inside all cells where proteins are made
ringworm
skin infection caused by the fungus Trichophyton that causes a characteristic ring-shaped rash
RNA (ribonucleic acid)
single-stranded nucleic acid that helps make proteins
RNA world hypothesis
hypothesis that RNA was the first organic molecule to evolve and that early life was based on RNA, rather than DNA or protein
root hair
tiny hairlike structure that extends from an epidermal cell of a plant root and increases the surface area for absorption
root system
all the roots of a plant, including primary roots and secondary roots
r-selected
species in which population growth is rapid but death rates are high so population size is generally below the carrying capacity
runoff
precipitation that falls on land and flows over the surface of the ground

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Feb 23, 2012

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Aug 22, 2014
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CK.SCI.ENG.SE.1.Biology.26.18
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