abiotic nonliving parts of the environment 
acid a compound that releases hydrogen ions when dissolved in water; a substance, such as vinegar, with a sour taste 
acid rain rain that is more acidic than normal 
active transport the process by which cells use energy to transport molecules through the cell membrane from areas of low concentration to areas of high concentration 
adaptive value any trait that helps an organism survive and reproduce under a given set of environmental conditions 
agarose a gel-like substance used in bacterial cultures 
AIDS (.acquired immunodeficiency syndrome) the disease that results when the HIV virus attacks the human immune system 
allergy a condition in which a person's immune system is overly sensitive to environmental substances that are normally harmless 
amino acid anyone of several building blocks of protein 
animal a complex, multicellular organism with specialized tissues and organs, but no cell walls; a heterotroph that obtains energy by consuming other organisms

antibody a protein, produced by the immune system  that either attacks invading pathogens or marks them for killing 
antigen a molecule found on the outer surfaces of cells that the immune system recognizes as either part of the body or an outside invader 
antihistamine a substance that reduces the effects of histamines and the symptoms they cause 
artificial selection the process of breeding two organisms with desirable characteristics to produce offspring that have the advantages of both parents 

asexual reproduction a method of reproduction in which all the genes passed on to the offspring come from a single individual or parent 

assumption something accepted as true that may or may not actually be true 
ATP (.adenine triphosphate) a compound that stores energy in cells 
autotroph an organism that produces its own food; the source of energy for all other living things on Earth 
bacterium anyone of many single-celled organisms without a distinct nucleus 
balance a tool that measures mass by comparing the unknown mass of an object with an object of known mass 
base a compound that produces hydroxide ions when dissolved in water 
bias a tendency to favor something; prejudice 
biochemical process a chemical process that occurs in a living thing 

biodiversity the variety of species in an area 
biome large groups of ecosystems with similar climates and organisms; examples include the tundra, taiga, temperate forest, 
chaparral, tropical rain forest, desert, temperate grassland, tropical savanna grassland, and polar and high-mountain ice 
biosphere all of Earth's ecosystems, collectively; the biologically inhabited portions of Earth, including all of the water, land, and air in which organisms survive 
biotechnology the combination of technology and biological sciences 
biotic the living parts of the environment 
bond the chemical link between atoms that hold molecules together 
calibrate to adjust the scale of a measurement tool 
carnivore an organism that survives by eating animals 
carrying capacity the largest population of any single species that an area can support 
catalyst a substance that can speed up the rate of a chemical reaction without being changed or used up during the reaction 

cell the basic unit of structure and function that makes up all organisms 
cell membrane the thin boundary between the cell and its environment 
cellular respiration the process in which nutrients are broken apart, releasing the chemical energy stored in them 
Celsius a temperature scale based on 100 equal units, with 0 as the freezing point of water and 100 as the. boiling point of water 
chloroplast the green organelle that contains chlorophyll; where photosynthesis takes place 
chromatography a laboratory technique used to separate mixtures of molecules 
chromosome a thick, threadlike structure that contains genetic information in the form of DNA 
circulation the flow of materials within a cell as well as between parts of a multicellular organism 
classify to group things based upon their similarities 
climax community a relatively diverse and stable ecosystem that is the end result of succession 
clone an organism that is genetically identical to the organism from which it was produced 
cloning a technique used to make identical organisms 
 
community a combination of all the different populations that live and interact in the same environment 
competition the struggle between organisms for the same limited resources in a particular area 

compound light microscope a tool that uses more than one lens and a light source to magnify an object 
conclusion the decision made about the outcome of an experiment; usually based on how well the actual result matches the 
predicted result 
consumer an organism that obtains its energy from producers 
control that group in an experiment in which everything except the variable to be tested is identical; the standard of comparison in an experiment 
controlled experiment an experiment in which all variables except for the one being tested- are exactly the same 

coverslip a thin slice of glass that covers the specimen on a slide 
cytoplasm the jellylike substance that is between the cell membrane and the nucleus and that contains specialized structures 
data the results of specific trials or tests completed during experiments 
decomposer an organism, generally a bacterium or fungus, that consumes dead organisms and organic waste 
decomposition the process whereby dead organisms, as well as the wastes produced by living organisms, are broken down into their raw materials and returned to the ecosystem 
deforestation forest destruction that results from human activity 
dependent variable the part of an experiment that is changed to test a hypothesis 
depletion a serious decline or reduction 
detrimental damaging; harmful 
deviation a change from normal circumstances
dichotomous key a guide that compares pairs of observable traits to help the user identify an organism 
differentiation the process that transforms developing cells into specialized cells with different structures and functions 
diffusion the movement of molecules from areas of high concentration to areas of low concentration 
digestion the process that breaks down large food molecules into simpler molecules that the organism can use 
direct harvesting the destruction of an organism, or the removal of an organism from its habitat 
disease a condition, other than injury, that prevents the body from working as it should 
dissection the act of cutting apart a dead organism to examine its internal structure 
DNA (deoxyribonucleic acid) the material found in all cells that contains genetic information about that organism 
dynamic equilibrium the constant small corrections that normally occur to keep an organism's internal environment within the limits needed for survival 

ecological niche the specific role played by an organism or a population of organisms in the ecosystem 
ecological succession the process by which an existing community is replaced by another community 
ecology the study of how living things interact with one another and with their environment 
ecosystem all the living and nonliving things that interact in a specific area; a subdivision of the environment 
egg a sex cell produced by a female 
electronic balance a balance that measures mass automatically 
electrophoresis a tool that allows scientists to separate mixtures of molecules according to size 
element a substance consisting of only one kind of atom 
embryo an organism in the early stages of development (prior to birth) 
endocrine glands various hormone-producing glands that secrete substances directly into the blood or lymph 
endoplasmic reticulum an organelle that transports proteins and other materials from one part of the cell to another 
energy flow the movement of energy through an ecosystem 
energy pyramid a diagram showing how food energy moves through the ecosystem 
environment every living and nonliving thing that surrounds an organism 
environmental impact statement a statement that includes an analysis of how a new project or technology might affect the environment 
enzymes proteins that speed up the rate of chemical reactions in living things 
equilibrium a state of balance and stability 
estrogen a hormone (produced by the ovaries) that controls female sexual development and the reproductive process 
evidence support for the idea that something is true 
evolution the process by which species have changed over time 

excretion the removal of all the wastes produced by the cells of the body 
experiment a series of trials or tests that are done to support or refute a hypothesis 
expressed the way that an unseen gene is seen in an organism as an actual physical trait 
extinction the disappearance of all members of a species from Earth 
Fallopian tubes that part of the female reproductive system where the egg cell is fertilized by the sperm cell 
feedback mechanism a cycle in which the output of a system either modifies or reinforces the first action taken by the system 
fertilization the process that combines a sperm cell and an egg cell 
fetus the unborn, developing young of an animal during the later stages of development 
finite limited 
flow of energy the movement of energy through an ecosystem 
food chain a representation that identifies the specific feeding relationships among organisms 
food web a representation of many interconnected food chains that shows the feeding relationships among producers, consumers, and decomposers 
forceps a tool used mainly during dissection to lift out small parts, to move structures, and to pry parts open 
fossil the preserved remains of ancient organisms 
fossil fuel a fuel, such as coal and gas, that comes from the remains of organisms that lived millions of years ago 
fossil record a collection of fossils used to represent Earth's history 
fungus the kingdom of organisms that are mostly multicellular, have cell walls made of chitin, and are heterotrophic 
gamete an egg or sperm cell; a sex cell 
gas exchange the process of obtaining oxygen from the environment and releasing carbon dioxide 
gene a segment of DNA (on a chromosome) that contains the code for a specific trait 

gene expression the result of activated genes 
genetic engineering a set of technologies that humans use to alter the genetic instructions of an organism by substituting DNA molecules 
genetic recombination the formation of a new combination of genes during sexual reproduction 
genetic variation the normal differences found among offspring 
geologic time Earth's history as revealed by layers of rock 
global warming a increase in Earth's average surface temperature caused by an increase in green- house gases 
glucose a sugar that is a major source of energy for cells 
graduated cylinder a tool used to measure the volume of a liquid 
greenhouse effect the trapping of heat by gases in the atmosphere 
greenhouse gas an atmospheric gas that traps heat 
growth an increase in the size or number of cells 
guard cells specialized cells that control the opening and closing of the pores on the surface of a leaf
habitat the place where an animal or plant lives 
herbivore an organism that eats only plants 
heredity the passing of traits from parent to offspring 
heterotroph organism that cannot make its own food; a consumers 
histamine a chemical that is released as the immune system's reaction to an allergy 
homeostasis the ability of an organism to maintain a stable internal environment even when the external environment changes 
hormone a chemical produced in the endocrine glands 
host the organism in a parasitic relationship that provides a home and/or food for the parasite 
hot water bath in the science laboratory, usually a large beaker of water heated on a hot plate; used to heat test tubes that contain a flammable liquid, such as alcohol 
humerus the long bone in the upper part of the arm 
hypothesis a statement that predicts a relationship between cause and effect in a way that can be tested 
immune system the body's primary defense against disease causing pathogens 
immunity the body's ability to destroy pathogens before they cause disease 
independent variable a factor that might influence the dependent variable in an experiment 
indicator a substance that changes color when it encounters certain chemical conditions 
industrialization the process of converting an economy into one in which large scale manufacturing is the primary economic base 
inference a conclusion or deduction based on observations 
infinite without limits or bounds 
inorganic a type of molecule that does not contain both carbon and hydrogen but can contain any other combination of elements 
insulin a hormone that prompts glucose to move from the blood into body cells, resulting in a lower glucose level in the blood 
limiting factor any factor in the environment that limits the size of a population 
lipid anyone of a group of organic compounds that includes oils, fats, and waxes 
magnification the ability of a microscope to make an object appear larger 
mass a measure of the quantity of matter in an object 
meiosis the process that results in the production of sex cells (sperm and egg) 
meniscus the curved surface at the top of a column of liquid 
metabolism all the chemical reactions that occur within the cells of an organism 
metric ruler a tool used to measure the length of an object 
microbe any microscopic organism 
micrometer a unit of length equal to one millionth of a meter 

microscope a tool that uses a lens or a combination of lenses to magnify an object 
mitochondria pod shaped organelles that contain enzymes used to extract energy from nutrients 
mitosis the process that divides the cell's nucleus into two, each with a complete set of genetic material from the parent cell 
model a representation used to explain or demonstrate a process or structure; also used to predict what might occur in a new situation 
molecule a particle in which two or more atoms combine to form a single unit; the smallest unit of a compound 
muscular system a body system comprised of tissue that contracts when it is stimulated; the combination of muscles that enables the body to move 
mutation any alteration in the sequence of DNA 
natural selection the process by which the organisms that are best adapted to a specific environment survive and produce more offspring than organisms that are not as well adapted 
niche the specific role played by an organism in its ecosystem 
nitrogen cycle the movement of nitrogen from the atmosphere to the soil and organisms and then back to the atmosphere 
nitrogen fixation the process by which nitrogen forms compounds that can be used by living things 
nonrenewable resource any resource, such as fossil fuels and minerals, that cannot be replaced 
nuclear fuel an energy source that results from splitting atoms 
nucleus a large structure within a cell that controls the cell's metabolism and stores genetic information, including chromosomes and DNA 
nucleic acids large, complex organic molecules that contain the instructions cells need to carry out their life processes 
nutrient a substance that provides the body with the materials and energy needed to carry out the basic life of cells 
objective one of the lenses of a microscope 
observation any information that is collected with any of the senses 
ocular the eyepiece lens of a microscope 

opinion ideas people have that may not be based in fact 
optimum the most favorable condition 
organ a body structure made of different kinds of tissues combined to perform a specific function 
organ system several organs that work together to perform a major function in the body 
organelle a structure within the cell that carries out a specific function 
organic term used to describe molecules that contain both hydrogen and carbon 
organic compound a compound that contains both hydrogen and carbon 
ovary the organ of the human female reproductive system that produces an egg cell, the female gamete 
overproduction the potential for a species to increase its numbers beyond the area's carrying capacity 
oviduct the part of the female reproductive system where the egg cell is fertilized by the sperm 
oxygen-carbon dioxide cycle the movement of oxygen and carbon dioxide between living things and the environment 
ozone shield the layer of ozone gas in the upper atmosphere that protects Earth from some of the sun's radiation 
pancreas an endocrine organ that secretes insulin 
parasite an organism that survives by living and feeding on other organisms 
parasitic relationship an arrangement in which one organism lives in or on a host organism, deriving some or all of its nourishment from the host, to the host's detriment 
pathogen an organism that invades the body, causing disease 
peer review the process by which scientists carefully examine the work of other scientists to look for possible flaws in their experimental design or their interpretation of results 
pH a measure of whether a substance is acidic, neutral, or basic 
photosynthesis the process by which some organisms are able to capture light energy and use it to make food from carbon dioxide and water 

pioneer species the first organisms to become established in a new habitat 
pipette a laboratory tool that looks like a slender tube but works something like an eyedropper 
placenta the organ that enables nutrients and oxygen to pass from the mother's blood to the fetus, and waste products to pass from the fetus to the mother's blood 
plant any complex, multicellular organism that obtains energy through photosynthesis and consists of cell walls and specialized tissues and organs 
poaching illegally capturing or killing an organIsm 
pollution a harmful change in the chemical make up of the soil, water, or air 
population all the individuals of a single species that live in a specific area 
predator an animal that hunts and kills other animals for food 
predator-prey relationship the connection between predators and prey that limits the growth of both populations 
prey an animal that is hunted and killed by predators 
primary succession the first group of communities that moves into a previously lifeless habitat 
producer an organism that makes its own food from light energy and inorganic materials 
progesterone a hormone associated with sexual development and the reproductive system 
proportion the relationship of one thing to another in terms of size, number, amount, or degree 
protist a single-celled organism with both its genetic materials and its organelles enclosed in membranes 
quarantine confined isolation 
radius one of the two long bones of the lower forearm 
receptor molecule certain protein molecules in the cell membrane that can receive chemical messages from other cells 
recombination the additional mixing of genetic material from a sperm and egg which results in a unique combination of genes 

refute to disprove 
replicate to copy 
renewable resource Earth's resources, such as our food supply and solar energy, which, given time, can be replaced 
research plan the initial stage of an experiment that involves finding background information, developing a hypothesis, and devising an experimental method for testing the hypothesis 
respiration the process by which the chemical bond energy stored in nutrients is released for use in cells 
reproduction the process by which organisms produce new organisms of the same type 
ribosome one of the tiny structures in the cell that is the site of protein production 
rider one of the devices that is moved along the beam of a balance 
scavenger a carnivore that feeds on the bodies of dead organisms 
science a way of learning about the natural world and the knowledge gained through that process 
scientific literacy a basic knowledge of the natural world combined with an understanding of the diverse ways that scientists gain knowledge 
scientific theory a concept, which has been tested and confirmed in many different ways, that explains a wide variety of observations 
secondary succession a type of change that occurs when a disturbance empties an existing habitat without destroying the soil 
selective breeding the process of choosing a few organisms with desirable traits to serve as the parents of the next generation 
sensor a structure that reacts to stimuli by sending a nerve impulse to the brain 
sex cell an egg (female) or a sperm (male) 
sexual reproduction a method of reproduction that involves two parents to produce offspring that are genetically different from either parent 
sibling a brother or sister 
simple sugar the result of digested starches 
skeletal system the body system that contains the bones, provides shape and support, and protects internal organs 

smog a kind of air pollution that results when certain pollutants react with sunlight 
species a group of organisms that share certain characteristics and can mate with one another, producing fertile offspring 
sperm the male sex cell 
splice to join two things together 
stain a chemical used to make cell structures more visible when viewed under a microscope 
steady state the condition in which something remains relatively constant in spite of minor fluctuations 
stereoscope a microscope that uses two eyepieces; often used for dissections 
stimulus any change in the environment that causes an organism to react 
stomata a tiny pore found on the underside of most leaves 
subunit the section of a DNA molecule that contains a sugar, a phosphate, and a base 
symbiotic a kind of long-term association between members of different species in which at least one species benefits and neither species is harmed 
synthesis a life process that involves combining simple substances into more complex substances 
tare button a function on an electronic balance that returns the mass reading to zero 
technology all of the practical scientific knowledge that has been used to meet human needs 
template the pattern for a new molecule 
testes the male reproductive organ that produces sperm and the hormone testosterone 
testosterone a hormone associated with male sexual development and reproduction 
theory an explanation, supported by many observations and/or experiments, that can be used to accurately explain related occurrences 
thermal pollution a kind of water pollution in which the temperature of the water increases 
tissue a group of specialized cells that perform a specific function 
toxic poisonous 
trait a characteristic that is passed from parent to offspring through the genes 

trade-off an exchange or agreement made to reach a compromise 
transpiration the process whereby plants absorb water through their roots and eliminate it through tiny pores on the undersides of their leaves 
triple-beam balance a tool, with a single pan and three bars calibrated in grams, used to measure mass 
tumor a clump of cells that develops when cancerous cells divide uncontrollably 
ulna one of the two long bones in the lower forearm 
uterus the organ, in female animals, where the embryo develops into a fetus 
vaccine a substance made of weakened, killed, or partial pathogens and designed to protect the body from future invasions of that pathogen 
vacuole storage sacs within the cytoplasm of a cell that may contain either wastes or useful materials, such as water or food 
vertebrate an animal with a backbone 
virus a nonliving particle of protein and genetic material that reproduces by invading the cell of a living organism 
volume the space occupied by something 
water cycle the process by which water continuously moves from Earth's surface to the atmosphere and back 
zygote the cell that results from the joining of the egg and sperm