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Unit 1:
Ch. 1
Ch. 2
Ch. 3
Interlude A
Unit 2:
Ch. 4
Ch. 5
Ch. 6
Ch. 7
Ch. 8
Ch. 9
Interlude B
Unit 3:
Ch. 10
Ch. 11
Ch. 12
Ch. 13
Ch. 14
Ch. 15
Interlude C
Unit 4:
Ch. 16
Ch. 17
Ch. 18
Ch. 19
Interlude D
Unit 5:
Ch. 20
Ch. 21
Ch. 22
Ch. 23
Ch. 24
Ch. 25
Ch. 26
Ch. 27
Ch. 28
Ch. 29
Ch. 30
Interlude E
Unit 6:
Ch. 31
Ch. 32
Interlude F
Unit 7:
Ch. 33
Ch. 34
Ch. 35
Ch. 36
Ch. 37
Ch. 38
Interlude G
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  • acid A chemical compound that can give up a hydrogen ion. Compare base and buffer.
  • acid rain Rainfall with a low pH. Acid rain is a consequence of the release of sulfur dioxide and other pollutants into the atmosphere, where they are converted to acids that then fall back to Earth in rain or snow.
  • acrosome The front tip of a sperm, which contains enzymes that digest the outer covering of the unfertilized ovum.
  • actin A protein found in the cytoskeleton, in muscle tissue, and in bacterial flagella.
  • actin filament One of the two types of filaments that make up muscle, consisting of two molecules of the protein actin. Compare myosin filament.
  • action potential An electrical signal generated by the flow of ions across the plasma membrane of a neuron. Action potentials are self-sustaining and can travel down a neuron in only one direction.
  • activation energy The small input of energy required for a chemical reaction to proceed.
  • active carrier protein A protein in the plasma membrane of a cell that, using energy from an energy storage molecule such as ATP, changes its shape to transfer a molecule across the plasma membrane. Compare passive carrier protein.
  • active immunity The immunity of an organism to a pathogen that depends on the production of antibodies specific to that pathogen by the organism's own body. Compare passive immunity.
  • active site The specific region on the surface of an enzyme where substrate molecules bind.
  • active transport Movement of molecules that requires an input of energy. Compare passive transport.
  • adaptation A characteristic of an organism that improves that organism's performance in its environment.
  • adaptive evolution The process by which natural selection improves the match between organisms and their environment over time.
  • adaptive radiation An evolutionary expansion in which a group of organisms takes on new ecological roles and forms new species and higher taxonomic groups.
  • adenosine triphosphate See ATP.
  • adrenal gland One of a pair of endocrine glands that sit atop the mammalian kidney and which release the hormones epinephrine and norepinephrine.
  • adrenaline See epinephrine.
  • aerobic Of or referring to a metabolic process or organism that requires oxygen gas. Compare anaerobic.
  • aerobic respiration A general term used to describe a series of oxidation reactions that use oxygen to produce ATP.
  • allele One of several alternative versions of a gene. Each allele has a DNA sequence different from that of all other alleles of the same gene.
  • allele frequency The proportion (percentage) of a particular allele in a population.
  • allopatric speciation The formation of new species from populations that are geographically isolated from one another. Compare sympatric speciation.
  • altruism A behavior that benefits another individual but has a cost to the individual performing the behavior.
  • alveolus (pl. alveoli) A small sac in the mammalian lung where gas exchange takes place.
  • amino acid An organic compound that has an amino group, a carboxyl group, and a variable R group attached to a single carbon atom. Proteins are polymers of amino acids.
  • amniocentesis A procedure in which a needle is inserted through the abdomen into the uterus to extract a small amount of amniotic fluid from the pregnancy sac that surrounds the fetus; this fluid contains fetal cells that can be used to test for genetic disorders.
  • amnion A sac filled with a watery fluid that surrounds and protects the developing vertebrate embryo.
  • amplification The chain of events set in motion when the binding of a single hormone molecule to a receptor activates thousands of proteins in the target cell.
  • anabolic See biosynthetic.
  • anaerobic Of or referring to a metabolic process or organism that does not require oxygen gas. Compare aerobic.
  • analogous Of or referring to a characteristic shared by two groups of organisms because of convergent evolution, not common descent. Compare homologous.
  • anaphase The stage of mitosis during which sister chromatids separate and move to opposite poles of the cell.
  • anchoring junction A protein structure that acts as a “hook” between two animal cells or between a cell and the extracellular matrix.
  • androgen One of a class of steroid hormones that stimulate cells to develop the characteristics of maleness. The primary androgen is testosterone. Compare estrogen.
  • angiosperms The flowering plants, a group that includes most plants on Earth today; named for the protective tissues covering the plant's embryo in the seed. Compare gymnosperms.
  • Animalia The kingdom made up of animals, multicellular eukaryotes that have evolved specialized tissues, organs and organ systems, body plans, and behaviors.
  • annual A plant that completes its entire life cycle in one year.
  • antagonistic Of or referring to the opposing effects of two hormones that together serve to regulate a process.
  • antenna complex An arrangement of chlorophyll molecules in the thylakoid membrane of a chloroplast that harvests energy from sunlight.
  • antibody A protein that is produced by a B cell and binds specifically to a particular antigen.
  • anticodon A sequence of three nitrogen bases on a transfer RNA molecule that can bind to a particular codon on an mRNA molecule. Compare codon.
  • antigen A characteristic membrane protein or molecule produced by an invading pathogen that is recognized by particular lymphocytes and the antibodies produced by those lymphocytes.
  • anus The opening of the digestive system through which undigested food and other solid wastes leave the body.
  • apical dominance Inhibition of the growth of lateral buds by the apical meristem.
  • apical meristem A region of rapidly dividing cells in the tips of plant branches and roots that gives rise to new stem and root tissues.
  • apoptosis Programmed or intentional cell death.
  • appendicular skeleton A collective term for the bones of the arms, legs, and pelvis. Compare axial skeleton.
  • aquaculture Managed agricultural systems in which fish and shellfish are cultivated for human consumption.
  • aquifer An underground body of water that is sometimes bounded by impermeable layers of rock.
  • Archaea A domain of microscopic, single-celled prokaryotes that arose after the Bacteria.
  • artery A blood vessel that carries blood from the heart. Compare vein.
  • arthropods A group of animals characterized by a hard exoskeleton; includes millipedes, crustaceans, insects, and spiders.
  • artificial selection A process in which only individuals that possess certain characteristics are allowed to breed; used to guide the evolution of crop plants and domestic animals in ways that are advantageous for people.
  • asexual reproduction The production of genetically identical offspring without the exchange of genetic material with another individual. Compare sexual reproduction.
  • atmospheric cycle A type of nutrient cycle in which the nutrient enters the atmosphere easily. Compare sedimentary cycle.
  • atom The smallest unit of a chemical element that still has the properties of that element.
  • atomic mass number The sum of the number of protons and neutrons found in the nucleus of an atom of a particular chemical element.
  • atomic number The number of protons found in the nucleus of an atom of a particular chemical element.
  • ATP Adenosine triphosphate, a molecule that is commonly used by cells to store energy and to transfer energy from one chemical reaction to another.
  • atrioventricular (AV) node A signaling center in the heart that relays the signal for cardiac muscle to contract from the sinoatrial node to the ventricles.
  • atrium (pl. atria) A chamber in a heart that receives blood from the body and pumps it into the ventricle. Compare ventricle.
  • auditory canal The tubular opening leading from the ear pinna to the eardrum.
  • autoimmune disease A disease caused when the body destroys some of its own tissues that the immune system misidentifies as foreign tissues.
  • autosome Any chromosome that is not a sex chromosome. Compare sex chromosome.
  • auxin A plant hormone that causes apical dominance and has other important effects, such as controlling the way plants bend toward sunlight and stimulating the differentiation of vascular tissue.
  • axial skeleton A collective term for the skull, the spinal column, and the ribs. Compare appendicular skeleton.
  • axon An extension of a neuron that carries action potentials through an animal's body.

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