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anything takes up space and has mass


substance consisting of two or more elements in a fixed ratio


any substance that cannot be broken down to any other substance

trace elements

an element indispensable for life but required in extremely minimum amounts


smallest unit of matter that retains property of an element


an electrically neutral particle found in the nucleus of an atom


a subatomic particle with single positive charge found in nucleus of an atom


a subatomic particle with a single negative charge; one or more electrons move around the nucleus


one of several atomic forms of an element each containing different number of neutrons and different in atomic mass

valence electrons

the electrons in the outermost electron shell

chemical bonds

an attraction between two atoms resulting from a sharing of outer shell electrons or the presence of opposite charges on the atom; the bonded atoms gain compounds outer electron shells

covalent bonds

a type of strong chemical bond in which two atoms share one pair of valence electrons

polar covalent bonds

a type of covalent bond between atoms that differ in electronegativity. the shared electrons are pulled closer to the more electronegative atom. making one slightly negative and the other slightly positive


the attraction of an atom for the electrons of a covalent bond


a negatively charged ion


an ion with a positive charge produced by the loss of one or more electrons

hydrogen bond

a type of weak chemical bond formed when the slightly positive hydrogen atom of a polar covalent bond in one molecules is attracted to the slightly negative atom of a polar covalent in another bond


the binding together of like molecules often by hydrogen bonds


the attraction between different kinds of molecules

surface tension

a measure of how difficult it is to stretch or break the surface of a liquid


total amount of kinetic energy due to molecular motion in a body of matter. It is energy in most random form


a measure of the intensity of heat in degrees reflecting molecules average kinetic energy

specific heat

the amount of heat that must be absorbed lost for one gram of a substance to change its temperature by one degree


a homogeneous mixture of two or more substance (liquid)


dissolving agent of a solution


a substance that is dissolved in a solution

aqueous solution

a solution in which water is the solvent


a substance that increases the hydrogen ion concentration of a solution


a substance that reduces the hydrogen ion concentration of a solution


having an affinity to water


having aversion to water tend to coalesce and form droplets of water


A measure of hydrogen ion concentration equal to -log [H+] and ranging in value from 0 to 14.


A substance that consists of acid and base forms in a solution and that minimizes changes in pH when extraneous acids or bases are added to the solution.

acid precipitation

Rain, snow, or fog that is more acidic than pH 5.6.

organic chemistry

The study of carbon compounds (organic compounds).


An organic molecule consisting only of carbon and hydrogen.


One of several organic compounds with the same molecular formula but different structures and therefore different properties. The three types are structural , geometric and enantiomers.

structural isomers

Compounds that have the same molecular formula but differ in the covalent arrangements of their atoms.

geometric isomers

Compounds that have the same molecular formula but differ in the spatial arrangements of their atoms.


Molecules that are mirror images of each other.

functional groups

A specific configuration of atoms commonly attached to the carbon skeletons of organic molecules and usually involved in chemical reactions.

hydroxyl groups

A functional group consisting of a hydrogen atom joined to an oxygen atom by a polar covalent bond. Molecules possessing this group are soluble in water and are called alcohols.

carbonyl groups

A functional group present in aldehydes and ketones and consisting of a carbon atom double-bonded to an oxygen atom.


An organic molecule with a carbonyl group located at the end of the carbon skeleton.


An organic compound with a carbonyl group of which the carbon atom is bonded to two other carbons.

carboxyl group

A functional group present in organic acids and consisting of a single carbon atom double-bonded to an oxygen atom and also bonded to a hydroxyl group.

amino group

A functional group that consists of a nitrogen atom bonded to two hydrogen atoms; can act as a base in solution, accepting a hydrogen ion and acquiring a charge of +1.

sulfhydryl group

A functional group consisting of a sulfur atom bonded to a hydrogen atom (—SH).

phosphate group

A functional group important in energy transfer.


A giant molecule formed by the joining of smaller molecules, usually by a condensation reaction. Polysaccharides, proteins, and nucleic acids are macromolecules.


A long molecule consisting of many similar or identical monomers linked together.


The subunit that serves as the building block of a polymer.

condensation reaction

A reaction in which two molecules become covalently bonded to each other through the loss of a small molecule, usually water; also called dehydration reaction.

dehydration reaction

A chemical reaction in which two molecules covalently bond to each other with the removal of a water molecule.


A chemical process that lyses, or splits, molecules by the addition of water; an essential process in digestion.


A sugar (monosaccharide) or one of its dimers (disaccharides) or polymers (polysaccharides).


The simplest carbohydrate, active alone or serving as a monomer for disaccharides and polysaccharides. Also known as simple sugars, the molecular formulas of are generally some multiple of CH2O.


A double sugar, consisting of two monosaccharides joined by dehydration synthesis.


A storage polysaccharide in plants consisting entirely of glucose.


An extensively branched glucose storage polysaccharide found in the liver and muscle of animals; the animal equivalent of starch.


A structural polysaccharide of cell walls, consisting of glucose monomers joined by b-1, 4-glycosidic linkages.

fatty acid

A long carbon chain carboxylic acid. vary in length and in the number and location of double bonds; three fatty acids linked to a glycerol molecule form fat.

saturated fatty acid

A fatty acid in which all carbons in the hydrocarbon tail are connected by single bonds, thus maximizing the number of hydrogen atoms that can attach to the carbon skeleton.

unsaturated fatty acid

A fatty acid possessing one or more double bonds between the carbons in the hydrocarbon tail. Such bonding reduces the number of hydrogen atoms attached to the carbon skeleton.


A molecule that is a constituent of the inner bilayer of biological membranes, having a polar, hydrophilic head and a nonpolar, hydrophobic tail.


A steroid that forms an essential component of animal cell membranes and acts as a precursor molecule for the synthesis of other biologically important steroids.


A type of lipid characterized by a carbon skeleton consisting of four rings with various functional groups attached.


A polymer of up to over a thousand monosaccharides, formed by dehydration reactions.

glycosidic linkage

A covalent bond formed between two monosaccharides by a dehydration reaction.


constructed from glycerol and fatty acids

amino acid

An organic molecule possessing both carboxyl and amino groups. Amino acids serve as the monomers of proteins.


A three-dimensional biological polymer constructed from a set of 20 different monomers called amino acids.

peptide bond

The covalent bond between two amino acid units, formed by a dehydration reaction

beta (B) pleated sheet

One form of the secondary structure of proteins in which the polypeptide chain folds back and forth, or where two regions of the chain lie parallel to each other and are held together by hydrogen bonds.


For proteins, a process in which a protein unravels and loses its native conformation, thereby becoming biologically inactive. For DNA, the separation of the two strands of the double helix. Denaturation occurs under extreme conditions of pH, salt concentration, and temperature.


A type of nucleic acid consisting of nucleotide monomers with a ribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and uracil (U); usually single-stranded; functions in protein synthesis and as the genome of some viruses.


A double-stranded, helical nucleic acid molecule capable of replicating and determining the inherited structure of a cell's proteins.

nucleic acid

A polymer (polynucleotide) consisting of many nucleotide monomers; serves as a blueprint for proteins and, through the actions of proteins, for all cellular activities. The two types are DNA and RNA.


One of two families of nitrogenous bases found in nucleotides. Adenine (A) and guanine (G) are purines.


One of two families of nitrogenous bases found in nucleotides. Cytosine (C), thymine (T), and uracil (U) are pyrimidines.


One of several formed bodies with specialized functions, suspended in the cytoplasm of eukaryotic cells.

electron microscope

A microscope that focuses an electron beam through a specimen, resulting in resolving power a thousandfold greater than that of a light microscope. A transmission electron microscope (TEM) is used to study the internal structure of thin sections of cells. A scanning electron microscope (SEM) is used to study the fine details of cell surfaces.

cell fractionation

The disruption of a cell and separation of its organelles by centrifugation.

ultra centrifuges

A machine that spins test tubes at the fastest speeds to separate liquids and particles of different densities.


The semifluid portion of the cytoplasm.

prokaryotic cell

A type of cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles; found only in the domains Bacteria and Archaea.


A dense region of DNA in a prokaryotic cell.


The entire contents of the cell, exclusive of the nucleus, and bounded by the plasma membrane.

plasma membrane

The membrane at the boundary of every cell that acts as a selective barrier, thereby regulating the cell's chemical composition.


(1) An atom's central core, containing protons and neutrons. (2) The chromosome-containing organelle of a eukaryotic cell. (3) A cluster of neurons.

nuclear lamina

A netlike array of protein filaments that maintains the shape of the nucleus.


The complex of DNA and proteins that makes up a eukaryotic chromosome. When the cell is not dividing,exists as a mass of very long, thin fibers that are not visible with a light microscope.

food vacuoles

A membranous sac formed by phagocytosis.

contractile vacuoles

A membranous sac that helps move excess water out of the cell.


One of a family of closely related plant organelles, including chloroplasts, chromoplasts, and amyloplasts (leucoplasts).

central vacuole

A membranous sac in a mature plant cell with diverse roles in reproduction, growth, and development.


A membrane that encloses the central vacuole in a plant cell, separating the cytosol from the cell sap


An organelle in eukaryotic cells that serves as the site of cellular respiration.


An organelle found only in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water.


(plural, cristae) An infolding of the inner membrane of a mitochondrion that houses the electron transport chain and the enzyme catalyzing the synthesis of ATP.


A flattened membrane sac inside the chloroplast, used to convert light energy to chemical energy.


A stacked portion of the thylakoid membrane in the chloroplast. Grana function in the light reactions of photosynthesis


The fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water.


A microbody containing enzymes that transfer hydrogen from various substrates to oxygen, producing and then degrading hydrogen peroxide.


A network of microtubules, microfilaments, and intermediate filaments that branch throughout the cytoplasm and serve a variety of mechanical and transport functions.


Material present in the cytoplasm of all eukaryotic cells, important during cell division; the microtubule-organizing center.


A long cellular appendage specialized for locomotion, formed from a core of nine outer doublet microtubules and two inner single microtubules, ensheathed in an extension of plasma membrane.


A short cellular appendage specialized for locomotion, formed from a core of nine outer doublet microtubules and two inner single microtubules ensheathed in an extension of plasma membrane.


A globular protein that links into chains, two of which twist helically about each other, forming microfilaments in muscle and other contractile elements in cells.

cell wall

A protective layer external to the plasma membrane in plant cells, bacteria, fungi, and some protists. In plant cells, the wall is formed of cellulose fibers embedded in a polysaccharide-protein matrix. The primary cell wall is thin and flexible, whereas the secondary cell wall is stronger and more rigid and is the primary constituent of wood.

extracellular matrix

The substance in which animal tissue cells are embedded consisting of protein and polysaccharides.


A glycoprotein in the extracellular matrix of animal cells that forms strong fibers, found extensively in connective tissue and bone; the most abundant protein in the animal kingdom.


A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins.


A specialized structure in the nucleus, formed from various chromosomes and active in the synthesis of ribosomes.


A cell organelle constructed in the nucleolus and functioning as the site of protein synthesis in the cytoplasm; consists of rRNA and protein molecules, which make up two subunits

smooth ER

That portion of the endoplasmic reticulum that is free of ribosomes.

Rough ER

That portion of the endoplasmic reticulum studded with ribosomes.

endoplasmic reticulum

An extensive membranous network in eukaryotic cells, continuous with the outer nuclear membrane and composed of ribosome-studded (rough) and ribosome-free (smooth) regions.


A protein covalently attached to a carbohydrate.

golgi apparatus

An organelle in eukaryotic cells consisting of stacks of flat membranous sacs that modify, store, and route products of the endoplasmic reticulum.

transport vesicles

A tiny membranous sac in a cell's cytoplasm carrying molecules produced by the cell.


A membrane-enclosed bag of hydrolytic enzymes found in the cytoplasm of eukaryotic cells.


A type of endocytosis involving large, particulate substances.

selective permeability

(the ability to allow some sub. to cross the plasma membrane more easily) A property of biological membranes that allows some substances to cross more easily than others.

fluid mosaic model

The currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of individually inserted protein molecules drifting laterally in a fluid bilayer of phospholipids.

integral proteins

Typically transmembrane proteins with hydrophobic regions that completely span the hydrophobic interior of the membrane.

peripheral proteins

Protein appendages loosely bound to the surface of the membrane and not embedded in the lipid bilayer.


The spontaneous tendency of a substance to move down its concentration gradient from a more concentrated to a less concentrated area.

concentration gradient

An increase or decrease in the density of a chemical substance in an area. Cells often maintain concentration gradients of ions across their membranes. When a gradient exists, the ions or other chemical substances involved tend to move from where they are more concentrated to where they are less concentrated

passive transport

The diffusion of a substance across a biological membrane


In comparing two solutions, referring to the one with a greater solute concentration.


In comparing two solutions, the one with a lower solute concentration.


Having the same solute concentration as another solution.


The control of water balance in organisms living in hypertonic, hypotonic, or terrestrial environments.


The diffusion of water across a selectively permeable membrane.


Firm. Walled cells become turgid as a result of the entry of water from a hypotonic environment.


Limp. Walled cells are limp in isotonic surroundings, where there is no tendency for water to enter.


A phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall when the cell loses water to a hypertonic environment

facilitated diffusion

The spontaneous passage of molecules and ions, bound to specific carrier proteins, across a biological membrane down their concentration gradients


(water channel proteins that facilitate the amount of diffusion)A transport protein in the plasma membrane of a plant or animal cell that specifically facilitates the diffusion of water across the membrane (osmosis).

gated channels

A protein channel in a cell membrane that opens or closes in response to a particular stimulus.

active transport

The movement of a substance across a biological membrane against its concentration or electrochemical gradient with the help of energy input and specific transport proteins.

sodium potassium pump

A special transport protein in the plasma membrane of animal cells that transports sodium out of the cell and potassium into the cell against their concentration gradients.

electrochemical gradient

The diffusion gradient of an ion, representing a type of potential energy that accounts for both the concentration difference of the ion across a membrane and its tendency to move relative to the membrane potential.

proton pump

An active transport mechanism in cell membranes that consumes ATP to force hydrogen ions out of a cell and, in the process, generates a membrane potential


The coupling of the "downhill" diffusion of one substance to the "uphill" transport of another against its own concentration gradient.


The cellular secretion of macromolecules by the fusion of vesicles with the plasma membrane.


The cellular uptake of macromolecules and particulate substances by localized regions of the plasma membrane that surround the substance and pinch off to form an intracellular vesicle.


A type of endocytosis involving large, particulate substances.

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