Q–T R recessive
Refers to an allele that cannot control the
phenotype unless it is the only kind of allele
present, as in a homozygote or hemizygote. Also
refers to the trait or phenotype produced when
only a recessive allele is present. The opposite of recessive is dominant.
reproductive isolation
The inability of individuals within a species to create
offspring with members of any other species. The
mark of a species is its reproductive isolation from
all other species. respiratory system
The organ system responsible for the intake of
oxygen and diffusion of that gas into the blood
and the elimination of carbon dioxide from the
body. Important structures of the system are the
pharynx, larynx, trachea, bronchi, bronchioles, and lungs. Alveoli in
the lungs are the location of gas
exchange with the blood. The movement of the
muscular diaphragm allows the lungs to inhale and
exhale.
ribonucleic acid (RNA)
One type of nucleic acid polymer. RNA nucleotides' sugars contain one
more oxygen atom than DNA
nucleotides' sugars. RNA nucleotides can have the
nitrogenous bases adenine, cytosine, guanine, and
uracil.
ribosome
Organelle responsible for protein synthesis. Ribosomes are located in
cytoplasm or endoplasmic
reticulum.
root
The part of a plant beneath the soil; responsible for
collecting water and minerals from the soil, storing
nutrients, and securing the plant to the ground. Can be fibrous or a taproot.
root hair
An outgrowth of a plant root that provides an
increased surface area for the absorption of water
and dissolved minerals from the soil.
runner Slender horizontal stem that can form new plants
via specialized nodes. S saprophytes
See decomposers.
segregation
Mendel's conclusion that individuals have two
copies of each gene, and that these copies separate
randomly during gamete formation, one copy per gamete. This law is
true except for genes on sex
chromosomes in males, who have only one copy of
each such gene. It is often called Mendel's first law.
semicircular canal
Fluid-filled structure within the ear that can detect
balance. sepal
Green, leaflike structure that encloses and protects
the unopened flower bud.
sex cells
See gamete.
sex chromosome Refers to a chromosome involved in defining the
sex of an individual. Humans have two sex
chromosomes and 44 autosomes. In females, both
sex chromosomes are X chromosomes. Males have
one X chromosome and one Y chromosome.
sex-linked Refers to a gene located on a sex chromosome or
to a trait defined by such a gene. Such traits will
appear with different frequencies in males and
females, and males and females will differ in their
ability to transmit the trait to their offspring. In
order for a recessive sex-linked trait such as hemophilia or color
blindness to manifest in the
phenotype of a woman, it must be inherited from
both mother and father; such diseases will be
present in the phenotype of a man if he inherits it
just from his mother.
somatic cell Any plant or animal cell that is not a germ cell,
meaning it is not passed down to offspring. The
class of cell formed during mitosis.
somatic nervous system
One half of the motor system of the peripheral
nervous system. Responsible for voluntary, or conscious, movement.
Neurons in this system
target skeletal muscles and release the
neurotransmitter acetylcholine.
speciation
The development of a species through evolution. A
species forms when its members become reproductively isolated from all
other organisms.
Speciation can occur through geographic
separation that eliminates gene flow or through
adaptive radiation.
species
A group of organisms defined by their ability to interbreed with only
each other.
sperm
The male gamete in sexual reproduction.
spermatogenesis
The process in which haploid sperm cells form
through meiotic division. spinal cord
A long cylinder of nervous tissue that extends
along the vertebral column from the head to the
lower back. It controls some autonomic responses
and connects the brain to the peripheral nervous
system. spores
Usually unicellular and microscopic, spores are
produced by protist molds, fungi, and plants and
are able to develop into new individuals. Spores are
able to survive without food or water for long
periods. Most fungi spend part of their life cycle as hyphae and part as spores.
sporophyte
A diploid plant or plant structure that produces
haploid spores through meiosis.
stabilizing selection
When selection pressures favor the average form of a trait.
stamen
The male reproductive organ of the flower,
consisting of an anther and filament.
stigma
The top part of the pistil, where pollen grains are received.
stomata
Small epidermal pores, surrounded by two guard
cells, through which gases diffuse and water
transpires in and out of a leaf.
stop codon A codon on mRNA that signals the termination of
DNA translation. There are three stop codons: UAA,
UAG, or UGA.
style
The shaft of the pistil that leads from the stigma
down into the ovary. substrate
The starting material that will undergo chemical
change in a chemical reaction facilitated by an
enzyme.
symbiosis
A type of interaction within a community that falls into one of three
categories: a parasitic relationship
benefits one organism and hurts the other; a
commensal relationship benefits one and does not
affect the other; a mutualistic relationship benefits
both organisms.
synapse The gap between two neurons, spanning the space
between the axon of one and the dendrites of the
other. In order to pass an impulse across a
synapse, neurons must release neurotransmitters. T taste buds
Structures on the tongue that contain
chemoreceptors, which respond to four main
sensations—sour, salty, bitter, and sweet—to
create the sense of taste.
taxonomy The study of biological classification.
telophase
The final stage of mitosis before cytokinesis. In
telophase, the nuclear envelope re-forms around
separated sister chromatids and kinetochore
microtubules disappear. Cell elongation also occurs during this phase.
The final stage of the first meiotic
division (meiosis I), during which chromosomes
arrive at the poles of the cell and begin to
recondense; the final stage of the second meiotic
division (meiosis II), during which chromosomes
arrive at the poles of the cell, the nuclear envelope begins to
re-form, and the chromosomes begin to
recondense.
tendon
Connective tissue between bones and muscles.
testes
The male gonads; sperm and testosterone are produced here.
testosterone
A hormone necessary for sperm production in men.
Also responsible for developing and maintaining
the secondary sex characteristics of males, starting
at puberty. thyroid
Gland that produces the hormone thyroxine, which
increases the metabolism of most of the cells in the
body. Located in the neck.
tissue
A group of closely connected and similar cells that cooperate to
generate a specific structure or
specialized function within an organism.
tracheophyte
A terrestrial plant with a vascular system.
trait
Any observable feature or characteristic of an organism.
transfer RNA (tRNA)
An RNA molecule used in protein synthesis as a link
helping to convert messenger RNA into amino
acids.
Refers to an allele that cannot control the
phenotype unless it is the only kind of allele
present, as in a homozygote or hemizygote. Also
refers to the trait or phenotype produced when
only a recessive allele is present. The opposite of recessive is dominant.
reproductive isolation
The inability of individuals within a species to create
offspring with members of any other species. The
mark of a species is its reproductive isolation from
all other species. respiratory system
The organ system responsible for the intake of
oxygen and diffusion of that gas into the blood
and the elimination of carbon dioxide from the
body. Important structures of the system are the
pharynx, larynx, trachea, bronchi, bronchioles, and lungs. Alveoli in
the lungs are the location of gas
exchange with the blood. The movement of the
muscular diaphragm allows the lungs to inhale and
exhale.
ribonucleic acid (RNA)
One type of nucleic acid polymer. RNA nucleotides' sugars contain one
more oxygen atom than DNA
nucleotides' sugars. RNA nucleotides can have the
nitrogenous bases adenine, cytosine, guanine, and
uracil.
ribosome
Organelle responsible for protein synthesis. Ribosomes are located in
cytoplasm or endoplasmic
reticulum.
root
The part of a plant beneath the soil; responsible for
collecting water and minerals from the soil, storing
nutrients, and securing the plant to the ground. Can be fibrous or a taproot.
root hair
An outgrowth of a plant root that provides an
increased surface area for the absorption of water
and dissolved minerals from the soil.
runner Slender horizontal stem that can form new plants
via specialized nodes. S saprophytes
See decomposers.
segregation
Mendel's conclusion that individuals have two
copies of each gene, and that these copies separate
randomly during gamete formation, one copy per gamete. This law is
true except for genes on sex
chromosomes in males, who have only one copy of
each such gene. It is often called Mendel's first law.
semicircular canal
Fluid-filled structure within the ear that can detect
balance. sepal
Green, leaflike structure that encloses and protects
the unopened flower bud.
sex cells
See gamete.
sex chromosome Refers to a chromosome involved in defining the
sex of an individual. Humans have two sex
chromosomes and 44 autosomes. In females, both
sex chromosomes are X chromosomes. Males have
one X chromosome and one Y chromosome.
sex-linked Refers to a gene located on a sex chromosome or
to a trait defined by such a gene. Such traits will
appear with different frequencies in males and
females, and males and females will differ in their
ability to transmit the trait to their offspring. In
order for a recessive sex-linked trait such as hemophilia or color
blindness to manifest in the
phenotype of a woman, it must be inherited from
both mother and father; such diseases will be
present in the phenotype of a man if he inherits it
just from his mother.
somatic cell Any plant or animal cell that is not a germ cell,
meaning it is not passed down to offspring. The
class of cell formed during mitosis.
somatic nervous system
One half of the motor system of the peripheral
nervous system. Responsible for voluntary, or conscious, movement.
Neurons in this system
target skeletal muscles and release the
neurotransmitter acetylcholine.
speciation
The development of a species through evolution. A
species forms when its members become reproductively isolated from all
other organisms.
Speciation can occur through geographic
separation that eliminates gene flow or through
adaptive radiation.
species
A group of organisms defined by their ability to interbreed with only
each other.
sperm
The male gamete in sexual reproduction.
spermatogenesis
The process in which haploid sperm cells form
through meiotic division. spinal cord
A long cylinder of nervous tissue that extends
along the vertebral column from the head to the
lower back. It controls some autonomic responses
and connects the brain to the peripheral nervous
system. spores
Usually unicellular and microscopic, spores are
produced by protist molds, fungi, and plants and
are able to develop into new individuals. Spores are
able to survive without food or water for long
periods. Most fungi spend part of their life cycle as hyphae and part as spores.
sporophyte
A diploid plant or plant structure that produces
haploid spores through meiosis.
stabilizing selection
When selection pressures favor the average form of a trait.
stamen
The male reproductive organ of the flower,
consisting of an anther and filament.
stigma
The top part of the pistil, where pollen grains are received.
stomata
Small epidermal pores, surrounded by two guard
cells, through which gases diffuse and water
transpires in and out of a leaf.
stop codon A codon on mRNA that signals the termination of
DNA translation. There are three stop codons: UAA,
UAG, or UGA.
style
The shaft of the pistil that leads from the stigma
down into the ovary. substrate
The starting material that will undergo chemical
change in a chemical reaction facilitated by an
enzyme.
symbiosis
A type of interaction within a community that falls into one of three
categories: a parasitic relationship
benefits one organism and hurts the other; a
commensal relationship benefits one and does not
affect the other; a mutualistic relationship benefits
both organisms.
synapse The gap between two neurons, spanning the space
between the axon of one and the dendrites of the
other. In order to pass an impulse across a
synapse, neurons must release neurotransmitters. T taste buds
Structures on the tongue that contain
chemoreceptors, which respond to four main
sensations—sour, salty, bitter, and sweet—to
create the sense of taste.
taxonomy The study of biological classification.
telophase
The final stage of mitosis before cytokinesis. In
telophase, the nuclear envelope re-forms around
separated sister chromatids and kinetochore
microtubules disappear. Cell elongation also occurs during this phase.
The final stage of the first meiotic
division (meiosis I), during which chromosomes
arrive at the poles of the cell and begin to
recondense; the final stage of the second meiotic
division (meiosis II), during which chromosomes
arrive at the poles of the cell, the nuclear envelope begins to
re-form, and the chromosomes begin to
recondense.
tendon
Connective tissue between bones and muscles.
testes
The male gonads; sperm and testosterone are produced here.
testosterone
A hormone necessary for sperm production in men.
Also responsible for developing and maintaining
the secondary sex characteristics of males, starting
at puberty. thyroid
Gland that produces the hormone thyroxine, which
increases the metabolism of most of the cells in the
body. Located in the neck.
tissue
A group of closely connected and similar cells that cooperate to
generate a specific structure or
specialized function within an organism.
tracheophyte
A terrestrial plant with a vascular system.
trait
Any observable feature or characteristic of an organism.
transfer RNA (tRNA)
An RNA molecule used in protein synthesis as a link
helping to convert messenger RNA into amino
acids.
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