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26.1: A

Difficulty Level: At Grade Created by: CK-12
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abiotic factor
nonliving aspect of the environment such as sunlight and soil
absolute dating
carbon-14 or other method of dating fossils that gives an approximate age in years
process in which substances such as nutrients pass into the blood stream
solution with a pH lower than 7
acid rain
low-pH precipitation that forms with air pollution combines with water
acquired immunodeficiency syndrome (AIDS)
disorder characterized by frequent opportunistic infections that eventually develops in people who are infected with human immunodeficiency virus (HIV)
action potential
reversal of electrical charge across the membrane of a resting neuron that travels down the axon of the neuron as a nerve impulse
activation energy
energy needed to start a chemical reaction
active immunity
ability to resist a pathogen that results when an immune response to the pathogen produces memory cells
active transport
movement of substances across a plasma membrane that requires energy
characteristic that helps living things survive and reproduce in a given environment
adaptive radiation
process by which a single species evolves into many new species to fill available niches
period of transition between the beginning of puberty and adulthood during which significant physical, mental, emotional, and social changes occur
adolescent growth spurt
period of rapid growth that occurs during puberty
adrenal glands
pair of endocrine glands located above the kidneys that secrete hormones such as cortisol and adrenaline
aerobic respiration
type of cellular respiration that requires oxygen
age-sex structure
number of individuals of each sex and age in a population
behavior that is intended to cause harm or pain
air pollution
chemical substances and particles released into the air mainly by human actions such as burning fossil fuels
Air Quality Index (AQI)
assessment of the levels of pollutants in the outdoor air that is based on their human health effects
alcoholic fermentation
type of anaerobic respiration that includes glycolysis followed by the conversion of pyruvic acid to ethanol and carbon dioxide and the formation of NAD+
algae (singular, alga)
plant-like protists such as diatoms and seaweeds
algal bloom
excessive growth of algae in bodies of water because of high levels of nutrients, usually from fertilizer in runoff
one of two or more different versions of the same gene
allele frequency
how often an allele occurs in a gene pool relative to the other alleles for that gene
any antigen that causes an allergy
disease in which the immune system makes an inflammatory response to a harmless antigen
allopatric speciation
evolution of a new species that occurs when some members of an original species become geographically separated from the rest of the species
alternation of generations
change back and forth from one generation to the next between haploid gametophyte and diploid sporophyte stages in the life cycle of plants
alveoli (singular, alveolus)
tiny sacs at the ends of bronchioles in the lungs where pulmonary gas exchange takes place
type of protozoa, such as Amoeba, that moves with pseudopods
amino acid
small molecule that is a building block of proteins
animal that produces eggs with internal membranes that allow gases but not water to pass through so the embryo can breathe without drying out (reptile, bird, or mammal)
amniotic sac
enclosed membrane containing fluid that surrounds and protects a fetus
ectothermic, tetrapod vertebrate that may live on land but must return to water in order to reproduce
anabolic reaction
endothermic reaction in organisms
anaerobic respiration
type of cellular respiration that does not require oxygen
analogous structure
structure that is similar in unrelated organisms because it evolved to do the same job, not because it was inherited from a common ancestor
third phase of mitosis during which sister chromatids separate and move to opposite poles of the cell
type of seed plant that produces seeds in the ovary of a flower
heterotrophic, multicellular eukaryote with cells that lack cell walls; member of the animal kingdom
animal behavior
any way that animals interact with each other or the environment
invertebrate phylum of segmented worms such as earthworms
antheridia (singular, antheridium)
male reproductive organs of the gametophyte generation of plants that produce motile sperm
antibiotic drug
drug that kills bacteria and cures bacterial infections and diseases
antibiotic resistance
ability to withstand antibiotic drugs that has evolved in some bacteria
large, Y-shaped proteins produced by B cells that recognize and bind to antigens in a humoral immune response
molecule that the immune system identifies as foreign and responds to by forming antibodies
aphotic zone
area in aquatic biomes deeper than 200 meters
aquatic biome
water-based biomes, defined by the availability of sunlight and the concentration of dissolved oxygen and nutrients in the water
underground layer of rock that stores water
of or pertaining to trees, as in arboreal, or tree-living, mammal
one of two prokaryote domains that includes organisms that live in extreme environments
archegonia (singular, archegonium)
female reproductive organs of the gametophyte generation of plants that produce eggs
type of blood vessel that carries blood away from the heart toward the lungs or body
invertebrate in the phylum Arthropoda, characterized by a segmented body, hard exoskeleton, and jointed appendages
artificial selection
process in which organisms evolve traits useful to humans because people select which individuals are allowed to reproduce and pass on their genes to successive generations
asexual reproduction
reproduction that involves a single parent and results in offspring that are all genetically identical to the parent
respiratory system disease in which air passages of the lungs periodically become too narrow, making breathing difficult
condition in which plaque builds up inside arteries
athlete’s foot
infection of the skin between the toes by the fungus Trichophyton
ATP (adenosine triphosphate)
energy-carrying molecule that cells use to power their metabolic processes
autoimmune disease
type of disease, such as type 1 diabetes, in which the immune system attacks the body’s cells as though they were pathogens
autonomic nervous system (ANS)
division of the peripheral nervous system that controls involuntary activities not under conscious control such as heart rate and digestion
chromosomes 1–22 in humans that contain genes for characteristics unrelated to sex
organism that makes its own food
long extension of the cell body of a neuron that transmits nerve impulses to other cells

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Date Created:
Feb 23, 2012
Last Modified:
Sep 13, 2016
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