Glossary ❮ 317bileSubstance that contains bile salts, phospholipids,
cholesterol, and bile pigments such as bilirubin, is
stored in the gallbladder, and is dumped into the
small intestine on the arrival of the food.
bile saltsHelp to mechanically digest fat by emulsi-
fying it into small droplets contained in water.
binary fission Mechanism by which prokaryotic cells
divide. The cell elongates and pinches into two
new daughter cells.
binomial system of classification System created by
Linnaeus in which each species is given a two-word
name: Genus +species (e.g., Homo sapiens).
biogeochemical cycles Cycles that represent the
movement of elements, such as nitrogen and
carbon, from organisms to the environment and
back in a continuous cycle.
biomass pyramidBiomassrepresents the cumulative
weight of all of the members at a given trophic
level.
biome The various geographic regions of the earth
that serve as hosts for ecosystems.
biosphere The entire life-containing area of a
planet—all ecosystems and communities.
biotic componentsLiving organisms of an ecosystem.
biotic potential The maximum growth rate for a
population given unlimited resources, unlimited
space, and lack of competition or predators.
birth rate Offspring produced per a specific time
period.
bivalves Mollusks with hinged shells such as oysters
and clams.
blastula As a morula undergoes its next round of cell
divisions, fluid fills its center to create this hollow-
looking structure.
“blending” hypothesis Theory that the genes con-
tributed by two parents mix as if they are paint
colors and the exact genetic makeup of each parent
can never be recovered; the genes are as insepara-
ble as blended paint.
bottleneckA dramatic reduction in population size
that increases the likelihood of genetic drift.
bronchiTunnels that branch off the trachea that
lead into the individual lungs and divide into
smaller branches called bronchioles.
bronchioles Tiny lung tunnels that branch repeat-
edly until they conclude as tiny air pockets con-
taining alveoli.
brush border Large numbers of microvilli that
increase the surface area of the small intestine to
improve absorption efficiency.
bryophytes The first land plants to evolve from the
chlorophytes. Members of this group include
mosses, liverworts, and hornworts.
bundle sheath cells Cells that are tightly wrapped
around the veins of a leaf. They are the site for the
Calvin cycle in C 4 plants.
C 4 photosynthesis Photosynthetic process that alters
the way in which carbon is fixed to better deal with
the lack of CO 2 that comes from the closing of the
stomata in hot, dry regions.
C 4 plant Plant that has adapted its photosynthetic
process to more efficiently handle hot and dry
conditions.
Calvin cycle A name for the light-independent
(dark) reactions of photosynthesis.
CAM (crassulacean acid metabolism) photosynthesis
Plants close their stomata during the day, collect
CO 2 at night, and store the CO 2 in the form
of acids until it is needed during the day for
photosynthesis.
capsidA protein shell that surrounds genetic material.
carbohydrate Organic compound used by the cells
of the human body in energy-producing reactions
and as structural material. The three main types of
carbohydrates are monosaccharides, disaccharides,
and polysaccharides.
carbon cycleThe movement of carbon from the
atmosphere to living organisms and back to the
environment in a continuous cycle.
carbon fixation The attachment of the carbon from
CO 2 to a molecule that is able to enter the Calvin
cycle, assisted by rubisco.
carbonyl groupA functional group that is hydrophilic
and polar. It has a central carbon connected to
R groups on either side. If both Rs are carbon
chains, it is a ketone. If one R is a hydrogen and the
other a carbon chain, it is an aldehyde.
carboxyl group An acidic functional group
(COOH). This functional group shows up along
with amino groups in amino acids.
cardiac muscleInvoluntary muscle of the heart that
is striated in appearance and contains multiple
nuclei.
carnivore A consumer that obtains energy and nutri-
ents through consumption of other animals.
carotenoid A photosynthetic pigment.
carrying capacity The maximum number of
individuals a population can sustain in a given
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