AP BIO VOCAB #1

Polar molecule

A molecule (such as water) with an uneven distribution of charges in different regions of the molecule.

Hydrogen bond

A type of weak chemical bond that is formed when the slightly positive hydrogen atom of a polar covalent bond in one molecule is attracted to the slightly negative atom of a polar covalent bond in another molecule or in another region of the same molecule.

Cohesion

The linking together of like molecules, often by hydrogen bonds.

Adhesion

The clinging of one substance to another, such as water to plant cell walls by means of hydrogen bonds.

Surface tension

A measure of how difficult it is to stretch or break the surface of a liquid. Water's is high because of the hydrogen bonding of surface molecules.

Specific heat

The amount of heat that must be absorbed or lost for 1 g of a substance to change its temperature by 1°C

Evaporative cooling

The process in which the surface of an object becomes cooler during evaporation, a result of the molecules with the greatest kinetic energy changing from the liquid to the gaseous state.

Hydrophilic

Having an affinity for water.

Hydrophobic

Having no affinity for water; tending to coalesce and form droplets in water.

Polymer

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

Monomer

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

Hydrolysis

A chemical reaction that breaks bonds between two molecules by the addition of water; functions in disassembly of polymers to monomers.

Dehydration reaction

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

Carbohydrate

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

Lipid

Any of a group of large biological molecules, including fats, phospholipids, and steroids, that mix poorly, if at all, with water.

Protein

A biologically functional molecule consisting of one or more polypeptides folded and coiled into a specific three-dimensional structure.

Nucleic acid

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

Nucleotide

The building block of a nucleic acid, consisting of a five-carbon sugar covalently bonded to a nitrogenous base and one or more phosphate groups.

Antiparallel

Referring to the arrangement of the sugar-phosphate backbones in a DNA double helix (they run in opposite 5′ → 3′ directions).

Denaturation

In proteins, a process in which a protein loses its native shape due to the disruption of weak chemical bonds and interactions, thereby becoming biologically inactive; in DNA, the separation of the two strands of the double helix. It occurs under extreme (noncellular) conditions of pH, salt concentration, or temperature.

Prokaryotic cell

A type of cell lacking a membrane-enclosed nucleus and membrane-enclosed organelles. Organisms with prokaryotic cells (bacteria and archaea) are called prokaryotes.

Eukaryotic cell

A type of cell with a membrane-enclosed nucleus and membrane-enclosed organelles. Organisms with these types of cells (protists, plants, fungi, and animals) are called eukaryotes.

Endosymbiont theory

The theory that mitochondria and plastids, including chloroplasts, originated as prokaryotic cells engulfed by an ancestral eukaryotic cell. The engulfed cell and its host cell then evolved into a single organism.

Vesicle

A membranous sac in the cytoplasm of a eukaryotic cell.

Plasma membrane

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

Phospholipid

A lipid made up of glycerol joined to two fatty acids and a phosphate group. The hydrocarbon chains of the fatty acids act as nonpolar, hydrophobic tails, while the rest of the molecule acts as a polar, hydrophilic head. They form bilayers that function as biological membranes.

Selective permeability

A property of biological membranes that allows them to regulate the passage of substances across them.

Fluid mosaic model

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

Integral protein

A transmembrane protein with hydrophobic regions that extend into and often completely span the hydrophobic interior of the membrane and with hydrophilic regions in contact with the aqueous solution on one or both sides of the membrane (or lining the channel in the case of a channel protein).

Peripheral protein

A protein loosely bound to the surface of a membrane or to part of an integral protein and not embedded in the lipid bilayer.

Transport protein

A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane.

Glycoprotein

A protein with one or more covalently attached carbohydrates.

Diffusion

The spontaneous movement of a substance down its concentration or electrochemical gradient, from a region where it is more concentrated to a region where it is less concentrated.

Concentration gradient

A region along which the density of a chemical substance increases or decreases.

Passive transport

The diffusion of a substance across a biological membrane with no expenditure of energy.

Hypertonic solution

Referring to a solution that, when surrounding a cell, will cause the cell to lose water.

Hypotonic solution

Referring to a solution that, when surrounding a cell, will cause the cell to take up water.

Isotonic solution

Referring to a solution that, when surrounding a cell, causes no net movement of water into or out of the cell.

Osmosis

The diffusion of free water across a selectively permeable membrane.

Turgid

Swollen or distended, as in plant cells. (A walled cell becomes like this if it has a lower water potential than its surroundings, resulting in entry of water.)

Flaccid

Limp. Lacking turgor (stiffness or firmness), as in a plant cell in surroundings where there is a tendency for water to leave the cell. (A walled cell becomes like this if it has a higher water potential than its surroundings, resulting in the loss of water.)

Plasmolysis

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

Facilitated diffusion

The passage of molecules or ions down their electrochemical gradient across a biological membrane with the assistance of specific transmembrane transport proteins, requiring no energy expenditure.

Aquaporin

A channel protein in the plasma membrane of a plant, animal, or microorganism cell that specifically facilitates osmosis, the diffusion of free water across the membrane.

Active transport

The movement of a substance across a cell membrane against its concentration or electrochemical gradient, mediated by specific transport proteins and requiring an expenditure of energy.

Exocytosis

The cellular secretion of biological molecules by the fusion of vesicles containing them with the plasma membrane.

Endocytosis

Cellular uptake of biological molecules and particulate matter via formation of vesicles from the plasma membrane.

Phagocytosis

A type of endocytosis in which large particulate substances or small organisms are taken up by a cell. It is carried out by some protists and by certain immune cells of animals (in mammals, mainly macrophages, neutrophils, and dendritic cells).

Pinocytosis

A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.

Receptor

mediated Endocytosis - The movement of specific molecules into a cell by the inward budding of vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances.

Contractile vacuole

A membranous sac that helps move excess water out of certain freshwater protists.

Osmoregulation

An animal that controls its internal osmolarity independent of the external environment.