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posterior part of an arthropod's body

abiotic factor

physical, or nonliving, factor that shapes an ecosystem

abscission layer

layer of cells at the petiole that seals off a leaf from the vascular system

accessory pigment

compound other than chlorophyll that absorbs light at different wavelengths than chlorophyll

acellular slime mold

slime mold that passes through a stage in which its cells fuse to form large cells with many nuclei


neurotransmitter that diffuses across a synapse and produces an impulse in the cell membrane of a muscle cell


compound that forms hydrogen ions (H+) in solution

acid rain

rain containing nitric and sulfuric acids


animal lacking a coelom, or body cavity


a protein that mainly makes up the thin filaments in striations in skeletal muscle cells

action potential

reversal of charges across the cell membrane of a neuron; also called a nerve impulse

activation energy

energy needed to get a reaction started

active immunity

immunity produced by exposure to an antigen, as a result of the immune response

active transport

energy-requiring process that moves material across a cell membrane against a concentration difference


inherited characteristic that increases an organism's chance of survival

adaptive radiation

process by which a single species or small group of species evolves into several different forms that live in different ways; rapid growth in the diversity of a group of organisms


uncontrollable dependence on a drug

adenosine triphosphate (ATP)

one of the principal chemical compounds that living things use to store and release energy


attraction between molecules of different substances; in plants, attraction between unlike molecules


process that requires oxygen

age-structure diagram

graph of the numbers of males and females within different age groups of a population


threatening behavior that one animal uses to gain control over another


the practice of farming

air sac

one of several sacs attached to a bird's lungs into which air moves when a bird inhales; allows for the one-way flow of air through the respiratory system

algal bloom

an immediate increase in the amount of algae and other producers that results from a large input of a limiting nutrient


one of a number of different forms of a gene


overreaction of the immune system to antigens

alternation of generations

process in which many algae switch back and forth between haploid and diploid stages of their life cycles


tiny air sac at the end of a bronchiole in the lungs that provides surface area for gas exchange to occur

amino acid

compound with an amino group (−NH2) on one end and a carboxyl group (−COOH) on the other end

amniotic egg

egg composed of shell and membranes that create a protected environment in which the embryo can develop out of the water

amoeboid movement

type of locomotion used by amoebas


vertebrate that, with some exceptions, lives in water as a larva and on land as an adult, breathes with lungs as an adult, has moist skin that contains mucus glands, and lacks scales and claws


enzyme in saliva that breaks the chemical bonds in starches


process that does not require oxygen

anal pore

region of the cell membrane of a ciliate where waste-containing food vacuoles fuse and are then emptied into the environment


the third phase of mitosis, during which the chromosome pairs separate and move toward opposite poles


flowering plant; bears its seeds within a layer of tissue that protects the seed


kingdom of multicellular eukaryotic heterotrophs whose cells do not have cell walls


flowering plant that completes a life cycle within one growing season


flower structure in which haploid male gametophytes are produced


male reproductive structure in some algae and plants


primate group made up of humans, apes, and most monkeys


compound that blocks the growth and reproduction of bacteria


protein that helps destroy pathogens


group of three bases on a tRNA molecule that are complementary to an mRNA codon


substance that triggers an immune response


opening through which wastes leave the digestive tract


large blood vessel in mammals through which blood travels after it leaves the left ventricle

aphotic zone

permanently dark layer of the oceans below the photic zone

apical dominance

phenomenon in which the closer a bud is to the stem's tip, the more its growth is inhibited

apical meristem

group of undifferentiated cells that divide to produce increased length of stems and roots


structure, such as a leg or antenna, that extends from the body wall


the raising of aquatic organisms for human consumption


domain of unicellular prokaryotes that have cell walls that do not contain peptidoglycan


kingdom of unicellular prokaryotes whose cell walls do not contain peptidoglycan


specialized cell in a sponge that makes spicules


female reproductive structure in some plants, including mosses and liverworts


large blood vessel that carries blood from the heart to the tissues of the body

artificial selection

selection by humans for breeding of useful traits from the natural variation among different organisms


haploid spore produced within the ascus of ascomycetes


structure within the fruiting body of an ascomycete in which two nuclei of different mating types fuse

asexual reproduction

process by which a single parent reproduces by itself


chronic respiratory disease in which the air passageways become narrower than normal


condition in which fatty deposits called plaque build up on the inner walls of the arteries


basic unit of matter

ATP synthase

large protein that uses energy from H+ ions to bind ADP and a phosphate group together to produce ATP


upper chamber of the heart that receives and holds blood that is about to enter the ventricle


chromosome that is not a sex chromosome


organism that can capture energy from sunlight or chemicals and use it to produce its own food from inorganic compounds; also called a producer


substance produced in the tip of a seedling that stimulates cell elongation


long fiber that carries impulses away from the cell body of a neuron


rod-shaped prokaryote


domain of unicellular prokaryotes that have cell walls containing peptidoglycans


virus that infects bacteria


tree structure that includes all tissues outside the vascular cambium, including phloem, the cork cambium, and cork


compound that produces hydroxide ions (OH+) in solution

base pairing

principle that bonds in DNA can form only between adenine and thymine and between guanine and cytosine


spore in basidiomycetes that germinates to produce haploid primary mycelia


spore-bearing structure of a basidiomycete


the way an organism reacts to changes in its internal condition or external environment

behavioral isolation

form of reproductive isolation in which two populations have differences in courtship rituals or other types of behavior that prevent them from interbreeding


organisms that live attached to or near the ocean floor


flowering plant that completes its life cycle in two years

bilateral symmetry

body plan in which only a single, imaginary line can divide the body into two equal halves; characteristic of worms, arthropods, and chordates

binary fission

"type of asexual reproduction in which an organism replicates its DNA and divides in half, producing two identical daughter cells

binocular vision

ability to merge visual images from both eyes, which provides depth perception and a three-dimensional view of the world

binomial nomenclature

classification system in which each species is assigned a two-part scientific name


biological diversity; the sum total of the variety of organisms in the biosphere

biogeochemical cycle

process in which elements, chemical compounds, and other forms of matter are passed from one organism to another and from one part of the biosphere to another

biological magnification

increasing concentration of a harmful substance in organisms at higher trophic levels in a food chain or food web


science that seeks to understand the living world


total amount of living tissue within a given trophic level


group of ecosystems that have the same climate and dominant communities


part of Earth in which life exists including land, water, and air or atmosphere

biotic factor

biological influence on organisms within an ecosystem


term used to refer to two-footed locomotion


endothermic animal that has an outer covering of feathers, two legs covered with scales that are used for walking or perching, and front limbs modified into wings


thin, flattened section of a plant leaf that collects sunlight


hollow ball of cells formed when a zygote undergoes a series of divisions

bone marrow

soft tissue inside the cavities within bones

book lung

organ that has layers of respiratory tissue that is used by some terrestrial arthropods for the exchange of gases

Bowman's capsule

cup-shaped structure in the upper end of a nephron that encases the glomerulus

brain stem

structure that connects the brain and spinal cord; includes the medulla oblongata and the pons


passageway leading from the trachea to a lung


nonvascular plant; examples are mosses and their relatives


plant structure containing undeveloped tissue that can produce new stems and leaves


asexual process by which yeasts increase in number; process of attaching a bud to a plant to produce a new branch


weak acid or base that can react with strong acids or bases to help prevent sharp, sudden changes in pH


term used by scientists to measure the energy stored in foods; 1000 calories


amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius

Calvin cycle

reactions of photosynthesis in which energy from ATP and NADPH is used to build high-energy compounds such as sugars


disorder in which some of the body's own cells lose the ability to control growth


dense covering formed by the leafy tops of tall rain forest trees


smallest blood vessel; brings nutrients and oxygen to the tissues and absorbs carbon dioxide and waste products

capillary action

tendency of water to rise in a thin tube


outer protein coat of a virus


in crustaceans, the part of the exoskeleton that covers the cephalothorax; in turtles and tortoises, the dorsal part of the shell


compound made up of carbon, hydrogen, and oxygen atoms; major source of energy for the human body


chemical compound known to cause cancer


organism that obtains energy by eating animals


innermost part of a flower that produces the female gametophytes

carrying capacity

largest number of individuals of a population that a given environment can support


strong connective tissue that supports the body and is softer and more flexible than bone

Casparian strip

waterproof strip that surrounds plant endodermis cells


group of individual insects specialized to perform particular tasks, or roles


substance that speeds up the rate of a chemical reaction


collection of living matter enclosed by a barrier that separates the cell from its surroundings; basic unit of all forms of life

cell body

largest part of a typical neuron; contains the nucleus and much of the cytoplasm

cell culture

group of cells grown in a nutrient solution from a single original cell

cell cycle

series of events that cells go through as they grow and divide

cell division

process by which a cell divides into two new daughter cells

cell fractionation

technique in which cells are broken into pieces and the different cell parts are separated

cell membrane

thin, flexible barrier around a cell; regulates what enters and leaves the cell

cell specialization

the process in which cells develop in different ways to perform different tasks

cell theory

idea that all living things are composed of cells, cells are the basic units of structure and function in living things, and new cells are produced from existing cells

cell wall

strong supporting layer around the cell membrane in plants, algae, and some bacteria

cell-mediated immunity

immunity against abnormal cells and pathogens inside living cells

cellular respiration

process that releases energy by breaking down glucose and other food molecules in the presence of oxygen

cellular slime mold

slime mold whose individual cells remain separated during every phase of the mold's life cycle


one of two tiny structures located in the cytoplasm of animal cells near the nuclear envelope


area where the chromatids of a chromosome are attached


concentration of sense organs and nerve cells at the front of an animal's body


region of a crustacean formed by the fusion of the head with the thorax


region of the brain that coordinates body movements

cerebral cortex

outer layer of the cerebrum of a mammal's brain; center of thinking and other complex behaviors

cerebrospinal fluid

fluid in the space between the meninges that acts as a shock absorber that protects the central nervous system


area of the brain responsible for all voluntary activities of the body


pair of mouthparts in chelicerates that contain fangs and are used to stab and paralyze prey

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