Like this study set? Create a free account to save it.

Sign up for an account

Already have a Quizlet account? .

Create an account

Biology: Principles & Explorations Holt, Rinehart, and Winston


The study of life.


Highly organized, tiny structures with thin coverings called membranes. The smallest unit capable of life functions.


The process by which organisms make more of their own kind from one generations to the next.


The sum of all chemical reactions carried out in an organism. Almost all energy used by living organisms is captured from sunlight.


The maintenance of stable internal conditions despite changes in the external environment.


Sets of inherited instructions for making proteins. Control when proteins are made and what proteins are made.


The passing of traits from parent to offspring.


A change in the DNA of a gene.


Change in the inherited traits of a species over time.


A group of genetically similar organisms that can produce fertile offspring.

natural selection

The process in which organisms with favorable genes are more likely to survive and reproduce.


The science that studies the interactions of living organisms with one another and with the nonliving part of their environment.


A virus that destroys the immune system, causing acquired immune deficiency disorder, or AIDS.

cystic fibrosis

A fatal disorder in which abnormally thick mucus builds up in many organs, including the lungs. Caused by a defective gene.


A growth disorder of cells that occurs when cells divide uncontrollably in the body.


The act of noting or perceiving objects or events using the senses.


An explanation that might be true-a statement that can be tested by additional observations or experimentation.


The expected outcome of a test, assuming the hypothesis is correct.


A description of how acidic a solution is. Measured on a scale of 0-14 with 7 being neutral. Solutions measuring below 7 are more acidic and those measuring above 7 are more basic.


A planned procedure to test a hypothesis.

control group

A group in an experiment that receives no experimental treatment.

independent variable

The factor that is varied in an experiment.

dependent variable

The variable that is measured in an experiment.


A set of related hypotheses that have been tested and confirmed many times by many scientists.


The smallest unit of matter than cannot be broken down by chemical means.


A substance made of only one kind of atom, and therefore a pure substance.


A substance made of the joined atoms of two or more different elements.


A group of atoms held together by covalent bonds.


a charged atom or molecule that has lost or gained one or more electrons.


Attraction between substances of the same kind.


Attraction between different substances.


A mixture in which one or more substances are evenly distributed in another substance.


Compounds that form hydrogen ions when dissolved in water.


Compounds that reduce the concentration of hydrogen ions in a solution.


Organic compounds made of carbon, hydrogen, and oxygen atoms in the proportion of 1:2:1.


The building blocks of carbohydrates: simple sugars such as glucose and fructose.


Nonpolar molecules that are not soluble in water including fats, phospholipids, steroids, and waxes.


A chain of amino acids linked together and folded into compact shapes.

amino acids

Molecules that are the building blocks of proteins.

nucleic acid

A long chain of smaller molecules called nucleotides.


Has three parts: a sugar, a base, and a phosphate group, which contains phosphorous and oxygen atoms.


Deoxyribonucleic acid. Consists of two strands of nucleotides that spiral around each other. The two strands are held together by hydrogen bonds between bases across from one another. Make up chromosomes.


Ribonucleic acid. Consists of a single strand of nucleotides. Plays several roles in cell function, including the manufacture of proteins.


Adeonsine triphosphate. A single nucleotide with two extra energy-storing phosphate groups. The main energy currency of cells.


The ability to move or change matter.

activation energy

The energy needed to start a chemical reaction.


Substances that increase the speed of chemical reactions. Most are proteins.


A substance on which an enzyme acts during a chemical reaction.

active sites

The pockets formed by the folds in a protein enzyme.

light microscope

A microscope in which light passes through one or more lenses to produce an enlarged image of a specimen.

electron microscope

A microscope which forms an image of a specimen using a beam of electrons.


The ability to make an image appear larger than its actual size.


A measure of the clarity of an image.

scanning tunneling microscope

Uses a needle-like probe to measure differences in voltage caused by electrons that leak, or tunnel, from the surface of the object being viewed.

cell theory

1. All living things are made of one or more cells.
2. Cells are the basic units of structure and function in organisms.
3. All cells arise from existing cells.

cell membrane

The outer boundary of a cell. Encloses the cell and separates the cell interior, called the cytoplasm, from its surroundings. Regulates what enters and leaves a cell-including gases, nutrients, and waste.


The interior of a cell.


A system of microscopic fibers in which the structures inside a cell are suspended.


The cellular structures on which proteins are made.


A single-celled organism that lacks a nucleus and other internal compartments. The modern version would be a bacterium.

cell wall

In bacteria, fungi, and plants, surrounds the cell membrane providing structure and support.


Long, threadlike structures that protrude from the cell's surface and enable movement.


An organism whose cells have a nucleus.


An internal compartment that houses the cell's DNA.


A structure that carries out specific activities in the cell.


Short hairlike structures protruding from the surface of some eukaryotic cells.


A lipid made of a phosphate group and two fatty acids.

lipid bilayer

A double layer of phospholipids. This arrangement forms the cell membrane.

endoplasmic reticulum

An extensive system of internal membranes that move proteins and other substances through the cell. It is made of a lipid bilayer with embedded proteins.


A small, membrane-bound sac that transports substances in cells.

golgi apparatus

A set of flattened, membrane-bound sacs that serves as the packaging and distribution center of the cell.


Small, spherical organelles that contain the cell's digestive enzymes.


An organelle that harvests energy from organic compounds to make ATP.


Organelles that use light energy to make carbohydrates from carbon dioxide and water.

central vacuole

A large, membrane-bound space taking up much of the space of a plant cell. When full it presses the cytoplasm against the cell wall, making the cell rigid, which enables plants to stand upright.

passive transport

Movement across the cell membrane that does not require energy from the cell.

concentration gradient

A difference in the concentration of a substance across a space.


A condition in which the concentration of a substance is equal throughout a space.


The movement of a substance from an area of high concentration to an area of lower concentration caused by the random motion of particles of the substance.


The diffusion of water through a selectively permeable membrane.

hypertonic solution

A solution that causes a cell to shrink because of osmosis.

hypotonic solution

A solution that causes a cell to swell because of osmosis.

isotonic solution

A solution that produces no change in cell volume because of osmosis.

ion channel

A doughnut shaped transport protein with a polar pore through which ions can pass.

carrier protein

A transport protein that can bind to a specific substance on one side of the cell membrane, carry the substance across the cell membrane, and release it on the other side.

facilitated diffusion

Transport of substances through a cell membrane down a concentration gradient aided by carrier proteins.

active transport

The transport of a substance across the cell membrane against its concentration gradient.

sodium-potassium pump

In a complete cycle transports three sodium ions, Na+, out of a cell and two potassium ions, K+, into the cell.


The movement of a substance into a cell by a vesicle.


the movement of a substance by a vesicle to the outside of a cell.

receptor protein

A protein that binds to a specific signal molecule, enabling the cell to respond to the signal molecule.

second messenger

A signal molecule in the cytoplasm.


The process by which light energy is converted to chemical energy.


Organisms that use energy from sunlight or inorganic substances to make organic compounds.


Organisms that must get energy from food instead of directly from sunlight or inorganic substances.

cellular respiration

A metabolic process similar to burning fuel. Releases much of the energy in food to make ATP.


Light-absorbing substances.


The primary pigment involved in photosynthesis. Absorbs mostly blue and red light and reflects green and yellow light.


Pigments that produce yellow and orange fall leaf colors, as well as the colors of many fruits, vegetables and flowers. Absorbs wavelengths of light different from those absorbed by chlorophyll.


Disk-shaped structures in the membranes of plants where clusters of pigments are stored.

electron transport chains

The series of molecules through which excited electrons are passed along a thylakoid membrane.


An electron carrier that provides the high energy electrons needed to make carbon-hydrogen bonds in the third stage of photosynthesis.

carbon dioxide fixation

The transfer of carbon dioxide to organic compounds.


Metabolic process that require oxygen.


Metabolic processes that do not require oxygen.


A process in which glucose is broken down in the cytoplasm. An enzyme-assisted anaerobic process that breaks down one six-carbon molecule of glucose to two three-carbon pyruvates.


An electron carrier formed when a glucose is broken down, transferring some of its hydrogen atoms to an electron receptor called NAD+.

krebs cycle

A series of enzyme-assisted reactions involving Acetyl-CoA that produces electron carriers that temporarily store energy.


An electron carrier created during the Krebs cycle.


The recycling of NAD+ using an organic hydrogen acceptor.


An organism's reproductive cells, such as sperm or egg cells.

binary fission

A form a sexual reproduction that produces identical offspring.


A segment of DNA that codes for a protein or RNA molecule.


A coiled structure containing long strands of DNA and proteins.


The two exact copies of DNA that make up each chromosome.


The point where to two chromatids of a chromosome are attached.

homologous chromosomes

Chromosomes that are similar in size, shape, and genetic content.


When a cell, such as a somatic cell, contains two sets of chromosomes.


When a cell, such as a gamete, contains one set of chromosomes.


A fertilized egg cell, the first cell of a new individual.


Chromosomes that are not directly involved in determining the sex of an individual.

sex chromosome

One of the 23 pairs of chromosomes in humans containing genes that will determine the sex of the individual.


A photo of the chromosomes in a dividing cell that shows the chromosomes arranged by size.

cell cycle

A repeating sequence of cellular growth and division during the life of an organism.


The first three phases of the cell cycle occurring before mitosis and cytokinesis.


The process during cell division in which the nucleus of a cell is divided into two nuclei.


The process during cell division in which the cytoplasm divides.


Cell structures made up of both centrioles and individual microtubule fibers that are involved in moving chromosomes during cell division.


A form of cell division that halves the number of chromosomes when forming specialized reproductive cells, such as gametes or spores.


Occurs when portions of a chromatid on one homologous chromosome broken and exchanged with the corresponding portions on one of the chromotids of the other homologous chromosome.

independent assortment

The random distribution of homologous chromosomes during meiosis.


The process by which sperm are produced in male animals.


Male gametes.


The process by which gametes are produced in female animals.


The female gamete, more commonly known as an egg.

asexual reproduction

Reproduction in which a single parent passes copies of all of its genes to each of its offspring.


An individual produced by asexual reproduction.

sexual reproduction

Reproduction in which two parents each form haploid reproductive cells.

life cycle

The entire span in the life of an organism from one generation to the next.


A process in which the gametes (sperm and egg cells) join during the diploid life cycle.


In plants, the diploid phase in the life cycle that produces spores.


A haploid reproductive cell produced by meiosis that is capable of developing into an adult without fusing with another cell.


The haploid phase that produces gametes by mitosis.


The passing of traits from parents to offspring.


The branch of biology that focuses on heredity.

monohybrid cross

A cross that involves one pair of contrasting traits.


Breeding in which all of the offspring display only one form of a particular trait.

P generation

the first of two individuals that are crossed in a breeding experiment.

F1 generation

The first offspring of the P generation.

See more

Please allow access to your computer’s microphone to use Voice Recording.

Having trouble? Click here for help.

We can’t access your microphone!

Click the icon above to update your browser permissions and try again


Reload the page to try again!


Press Cmd-0 to reset your zoom

Press Ctrl-0 to reset your zoom

It looks like your browser might be zoomed in or out. Your browser needs to be zoomed to a normal size to record audio.

Please upgrade Flash or install Chrome
to use Voice Recording.

For more help, see our troubleshooting page.

Your microphone is muted

For help fixing this issue, see this FAQ.

Star this term

You can study starred terms together

Voice Recording