A–D A abiotic
Nonliving materials in the environment—such as
elements, sunlight, and soil—that influence and are
influenced by living (biotic) entities on the planet.
acetylcholine
A neurotransmitter released by neurons to excite an action potential
or trigger a muscle to contract.
acids
Hydrogen ion (H+) donors. Acids are very important in the chemical
reactions of life because
they are highly reactive. Acids have pH values
below 7. They are the opposite of bases.
actin
Protein filaments that, along with myosin, allow
muscles to contract. active site
The part of an enzyme that interacts with, or binds
to, a substrate.
active transport
The movement of molecules across a cell
membrane from a region of lower concentration to a region of higher
concentration. Because active
transport involves moving the molecule against the
natural flow of the concentration gradient, the
process requires energy.
adaptive radiation
The evolutionary process by which ancestral forms of an organism are
diversified through adaptation
to new environments.
adenosine triphosphate (ATP) The energy storage molecule for the cell.
ATP consists of an adenosine molecule bonded to three
phosphate groups. Each phosphate bond contains
energy; by breaking these bonds, the cell can get
the energy it needs for chemical reactions. Cells
build ATP during cell respiration, using the raw material of glucose.
adrenal glands
Two glands, the adrenal cortex and adrenal
medulla, located on the kidney.
aerobic respiration
A form of cell respiration requiring oxygen (as opposed to anaerobic
respiration, which does not
need oxygen). Aerobic respiration is much more
efficient than anaerobic respiration; it produces 36 ATP for every
molecule of glucose. Aerobic respiration proceeds in three stages:
glycolysis, the
Krebs cycle, and the electron transport chain.
allele
A specific form or possible version of a gene having
multiple versions. Alleles may be dominant or
recessive. allelic frequency
The frequency with which a particular allele for a
certain characteristic appears among all possible
alleles for that characteristic in a population.
alternation of generations
The fluctuation between the diploid (sporophyte) and haploid
(gametophyte) life stages that occur in
plants.
amino acid
The monomer of a protein. A central carbon
attached to an amino group (–NH2), a carboxyl group (–COOH), and a
hydrogen atom (–H). The fourth group is variable and defines the amino
acid's chemical identity.
anaerobic respiration
A form of cell respiration that does not use oxygen
(as opposed to aerobic cell respiration). Anaerobic
respiration is less efficient than the aerobic variety and produces
just 2 ATP per molecule of glucose. Anaerobic respiration has two
stages: glycolysis
and fermentation.
analogous trait
A trait that is morphologically and functionally
similar to that of a different species but that arose
from a distinct, ancestral condition. anaphase
The stage of mitosis in which sister chromosomes
are separated and pulled to opposite ends of the
cell by microtubules; the fourth stage of the first
meiotic division (meiosis I), during which maternal
and paternal homologous pairs are separated on microtubules; the
fourth stage of the second
meiotic division (meiosis II), during which either
maternal or paternal sister chromatids are
separated on microtubules.
angiosperm
A vascular flowering plant in which seeds are enclosed inside
protective ovaries, such as fruit or
flowers. Angiosperms can be monocots or dicots.
anther
Pollen-producing structure at the top of the stamen,
the male reproductive organ of flowers.
anticodon The sequence of three nucleotides on tRNA that
pairs with a codon of mRNA at the A site of a
ribosome during translation.
antigen
A protein coat on the surface of red blood cells; a
red blood cell may have a protein coat of type A, B, or AB. If the
cell has no antigens, it is called type O.
The presence of a foreign antigen in a body will
cause blood to clot.
aorta
The largest artery in the body; carries oxygenated
blood from the left ventricle of the heart. aphotic zone
Literally, zone without light. The aphotic zone is part
of the marine pelagic zone and begins 600 feet
below the surface of the ocean. Only
chemosynthetic organisms, scavengers, and
predators are able to survive in this habitat. artery
Vessel that carries blood away from the heart and
has thick, elastic, muscular walls that can dilate or
contract to control blood pressure within the
vessels. Blood in arteries is oxygenated, with the
exception of the blood in the pulmonary artery. autonomic nervous system
The involuntary half of the peripheral nervous
system. The autonomic nervous system is in two
antagonistic parts: the sympathetic and
parasympathetic nervous systems. Their
interactions control smooth and cardiac muscle, glands, and organs and
processes such as
heartbeat, the movements of the digestive tract,
and the contraction of the bladder.
autosome
Any chromosome that is not a sex chromosome.
Humans have 44 autosomes, in 22 homologous pairs. The two sex
chromosomes are the twenty-
third pair of chromosomes.
autotroph
An organism that can produce the organic
molecules and energy necessary for life through
the processes of photosynthesis or chemosynthesis. Autotrophs do not
rely on other
organisms for food. In a food web, autotrophs are
producers.
auxin
One in a class of plant hormones that stimulates
(among other things) cell elongation, secondary tissue growth, and
fruit development. B base
An ion or compound that removes H+ ions from solution. Often bases are
substances that release
hydroxide ions (OH–). Bases have pH values above 7. They are the
opposite of acids.
bile
An emulsifier of fats secreted by the liver and stored
in the gallbladder for release in the small intestine.
binary fission
Asexual reproduction found in prokaryotes in which a cell divides into
two equal daughter cells
by a nonmitotic process.
biomass
The amount of living matter in a given ecosystem.
Because only 10 percent of energy is transferred
between trophic levels, the biomass of lower trophic levels is greater
than the biomass of
subsequent trophic levels: biomass of producers >
biomass of primary consumers > biomass of
secondary consumers > biomass of tertiary
consumers.
biome A particular geographic area with a common
climate and characteristic plant and animal life.
There are six major terrestrial biomes and two
aquatic biomes. The six terrestrial biomes are
tropical rain forest, savanna, desert, temperate
deciduous forest, taiga, and tundra. The two aquatic biomes are marine
and freshwater. Each
biome is characterized by specific climax
communities.
blood
The liquid that carries nutrients and oxygen to the
cells and carries carbon dioxide and nitrogenous wastes away. The
liquid fluid of blood is called
plasma. Red blood cells contain hemoglobin, an
iron-containing protein that binds oxygen. White
blood cells fight disease. Platelets clot to prevent
extreme blood loss resulting from injury.
bone Rigid structures composed of living cells rooted in a
matrix of calcium, phosphate salts, and collagen
fibers. Bones are the primary component of most
vertebrate skeletons.
brain
The center of the central nervous system. The brain coordinates the
processes of the body. It is
composed of various distinct regions, all of which
have different functions, including the cerebrum,
cerebellum, medulla oblongata, and hypothalamus.
bryophyte
A lower terrestrial plant (often a moss or liverwort) that lacks a
vascular system and is dependent on
environmental moisture for reproductive and
nutritive functions.
budding
Asexual reproductive process in which a small
portion of the cell membrane and cytoplasm receive a nucleus and pinch
off from the parent cell.
buffer
Solutions that resist change in pH even when acids
and bases are added.
bulb
Roughly spherical underground bud containing additional buds that can
develop asexually into
new plants. C Calvin cycle
Light-independent phase of photosynthesis, where
carbon dioxide is fixed to a three-carbon
compound used to form glucose. ATP and NADH are consumed in this
cycle. Also called the Calvin-
Benson cycle or the dark reactions.
capillary
Tiny blood vessels able to branch through the body
and deliver oxygen and nutrients to every cell.
carbon The central element of life. Carbon has the ability to
form bonds with up to four other elements or
molecules at the same time.
carrying capacity
The maximum number of individuals in a
population that can be sustained in a given environment. As
populations become increasingly
concentrated, competition for food and space,
predation, and disease all determine carrying
capacity.
cartilage
A firm but flexible substance, found in regions of vertebrate
skeletons, such as the ribs, that need to
bend.
cell
The smallest unit of life, consisting of a solution of
organic molecules enclosed by a plasma
membrane. cell cycle
A process in which cells reproduce. First the cell
replicates its DNA and then divides into two
daughter cells. The two main phases of the cell
cycle are interphase and mitosis.
cell membrane The phospholipid bilayer that surrounds all cells,
regulating the passage of molecules in and out of
the cell.
cellular respiration
The process in which the cell burns glucose to
create ATP with the aid of oxygen. Cells have two different methods of
turning food into usable fuel:
aerobic respiration and anaerobic respiration.
cell theory
The doctrine that every living organism is
composed of cells and that all cells come only from
other preexisting cells. cell wall
A rigid structure that surrounds the outer
membrane of some cells and helps maintain their
shape. In plants the cell wall contains cellulose; in
fungi it contains chitin; in prokaryotes it typically
contains peptidoglycan. cellulose
A complex carbohydrate that constitutes the cell
walls of plants and protist molds.
central nervous system (CNS)
The brain and the spinal cord. The CNS acts as the
central command center of the body. Mostly made up of interneurons.
centriole
A structure in the cell that plays an important role in
cell replication. During prophase, the centrioles
migrate to the poles of the cell and form the mitotic
spindle, which allows the chromosomes to be organized and split when
the cell divides.
cerebellum
Part of the brain. Makes sure that movements are
coordinated and balanced.
cerebrum
Part of the brain. Controls all voluntary movement, sensory
perception, speech, memory, and creative
thought.
chemical cycles
The cycles in which inorganic elements move
through the biotic and abiotic aspects of an
ecosystem. The two most important chemical cycles are the carbon and
nitrogen cycles.
chemosynthesis
Synthesizing organic compounds by energy
derived from chemical reactions rather than from
the energy of the sun. Chemosynthetic organisms
are autotrophs. chitin
A rough polysaccharide that constitutes the cell
wall of fungi and exoskeleton of arthropods.
chlorophyll
A pigment located within a chloroplast that absorbs
light in plant cells, helping to convert light energy into biological
energy through the process of
photosynthesis.
chloroplast
A double-membrane-bound organelle that
contains chlorophyll and is found in plant cells.
Chloroplasts are responsible for mediating photosynthesis.
chromatin
The stringy web of genetic material and histone
proteins found in the nucleus of eukaryotic cells.
During cell division, each strand of DNA coils to
form a chromosome. chromosome
A physical structure composed of a single long
strand of DNA (and associated proteins), containing
along its length many genes. The human genome
consists of 46 chromosomes contained within the
nucleus of each cell. cilia
Short, hairlike projections found on eukaryotic cells
that can help the cell move or can sweep food
particles toward the mouth.
circadian rhythms
Behavior cycles that depend on time of day. circulatory system
System of organs and blood that brings nutrients
and oxygen to cells and carries away wastes. In
higher vertebrates, the system has a pulmonary
and systemic circuit. The pulmonary circuit carries
blood to the lungs to be oxygenated, while the systemic circuit
carries oxygenated blood to the
body. Vertebrates have a closed circulatory system,
while arthropods have an open system.
citric acid cycle
See Krebs cycle.
climax community A combination of plant and animal forms that
dominate mature ecological communities. Climax
communities are unique and shaped by various
factors, including temperature, rainfall, and soil
acidity.
codominance A phenomenon in which two alleles of the same
gene are fully expressed in the phenotype when
both are present in a heterozygote. Blood type is an
example of codominance.
codon
A three-nucleotide sequence in a DNA or mRNA molecule. Each codon
specifies a single amino acid.
coenzyme
A compound that regulates activity by binding to
an enzyme to tell it when to catalyze a reaction.
cold-blooded
Animals that are unable to retain heat produced by metabolic
activities. Also known as ectothermic. The
metabolism of cold-blooded animals is greatly
influenced by climate and temperature.
community
The many populations that interact in a given
geographical locale constitute ecological communities. Communities
exhibit particular
interactions such as competition, symbiosis,
predation, and food relationships. They also
undergo ecological succession.
competition
The struggle for survival between organisms or populations that use
similar resources and occupy
similar niches. Interspecific competition refers to
competition between populations that may drive a
population out of a community or push it to evolve
a different niche to reduce competition.
Intraspecific competition refers to competition between individuals of
the same species.
consumer
Consumers are heterotrophic organisms within the
food web of a community. In the trophic levels of
the food chain, primary consumers consume
producers, secondary consumers consume primary consumers, and tertiary
consumers consume
secondary consumers.
contractile vacuole
An organelle often found in protozoa that pumps
excess water out of the cell to keep the cell from
bursting in a hypotonic environment (like freshwater).
corpus luteum
After releasing its ovum (ovulation), the follicle
becomes the corpus luteum, which produces
progesterone for the continued buildup of the
uterine wall. crossing-over
The exchange of genetic information between
homologous chromosomes during meiosis I.
Crossing-over can disrupt the normal linkage
between genes on the same chromosome.
cytokinesis The final part of mitosis, in which a cell with
duplicated contents splits into two independent
cells.
cytoplasm
The entire content of the cell outside the nucleus,
including the membrane-bound organelles and the cytosol.
cytoskeleton
A system of protein filaments found throughout the
cytoplasm of eukaryotic cells, which provides
structural support for the cell. The cytoskeleton also
helps with the movement of organelles within the cell. It is composed
of microfilaments and
microtubules.
cytosol
The main component of the cytoplasm. It is a
grayish, gel-like liquid containing the nucleus,
organelles, and cytoskeleton. D Darwin, Charles
English naturalist (1809–1882) who proposed the
modern theory of evolution through natural
selection. Darwin traveled aboard the HMS Beagle to
the Galápagos Islands, where his revolutionary
observations took shape. decomposer
Organisms that consume waste products and dead
organic material and constitute part of the food
web, which also includes producers and
consumers. Also called saprophytes. Decomposers
liberate inorganic elements such as nitrogen and carbon and allow
those elements to move back into
their respective chemical cycles. Examples of
decomposers are bacteria and fungi.
dehydration synthesis
A common biochemical reaction in which a new
compound is formed by the joining of two compounds to release water.
Occurs in the
synthesis of polysaccharides and polypeptides. The
reverse of hydrolysis.
deoxyribonucleic acid (DNA)
A type of nucleic acid polymer built from sugar-
phosphate backbones and nitrogenous bases. DNA's sugar, deoxyribose,
has one fewer oxygen
atom than ribose, found in RNA. The nitrogenous
bases adenine, cytosine, guanine, and thymine are
used in DNA.
dicot
A flowering plant (angiosperm) that possesses two cotyledons during
embryonic development. Usually
has taproots, flower parts in multiples of fours and
fives, and branching veins in leaves.
diffusion
The transport or natural drift of molecules traveling
from an area of higher concentration to an area of lower
concentration. Diffusion does not require
outside energy from the cell.
digestive system
The system of organs that converts food to usable
nutrients through mechanical and chemical
breakdown. Important components of the system are the alimentary
canal, glands, esophagus,
stomach, small intestine, large intestine, and rectum.
diploid number
The total number of chromosomes present in a
somatic cell. The diploid number is twice the
haploid number. In humans, the diploid number is 46.
disaccharide
A sugar compound consisting of two carbohydrate
monomers.
dominant
Refers to an allele that controls the phenotype even when a different
allele is also present, as in a
heterozygote. Can also refer to the trait or
phenotype produced by a dominant allele. Also
known as Mendel's law of dominance, based on
Gregor Mendel's observations that when two
purebred individuals with different forms of the same trait are mated,
only one of the two forms
appears in the first generation of offspring. Mendel
called the apparent form dominant and the
suppressed form recessive.
No comments:
Post a Comment