Biology Honors Midterm Study Guide

Element

A substance that cannot be broken down to other substances by chemical means.

Compound

A substance containing two or more elements in a fixed ratio.

Proton

A particle with a positive charge, found in the nucleus of an atom.

Electron

A particle with a negative electrical charge; move around the nucleus of an atom.

Neutron

A particle having no electrical charge, found in the nucleus of an atom.

Nucleus

An atom's central core, containing protons and neutrons.

Atomic number

The number of protons in each atom of a particular element.

Mass number

The total number of protons and neutrons in the nucleus of an atom

Atomic mass

The average mass of all the isotopes of an element.

Isotopes

One of several atomic forms of an element; each has the same number of protons but different number of neutrons.

Radioactive isotopes

An isotope whose nucleus decays spontaneously, giving off particles and energy.

Electron shells

Depicted as simple circles around nucleus; each shell holds differing numbers of electrons.

Chemical bonds

An attraction between two atoms resulting from a sharing of outershell electrons or the presence of opposite charges on the atoms.

Covalent bond

A type of strong chemical bond in which atoms share one or more pairs of valence electrons

Molecule

Two or more atoms connected by covalent bonds.

Electronegativity

A measure of the ability of an atom in a chemical compound to attract electrons.

Nonpolar covalent bond

A type of covalent bond in which electrons are shared equally between two atoms of similar electronegativity.

Polar covalent bond

A covalent bond between atoms that differ in electronegativity. The shared electrons are pulled closer to the more electronegative atom, making it slightly negative and the other atom slightly positive.

Ion

An atom or group of atoms that has gained or lost one or more electrons, thus acquiring a charge.

Ionic bond

A chemical bond resulting from the attraction between oppositely charged ions.

Hydrogen bond

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

Polar molecule

A molecule containing a polar covalent bond and having unequal distribution of charges (water is an example).

Chemical reactions

The making and breaking of covalent bonds, leading to changes in matter.

Reactants

The starting material in a chemical reaction.

Product

The ending material in a chemical reaction.

Cohesion

The sticking together of molecules of the same kind, often by hydrogen bonds.

Adhesion

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.

Does water have a high surface tension?

Yes because of the hydrogen bonding of surface molecules.

Evaporative cooling

Surface of an object becomes cooler during evaporation.

Solution

A liquid that is homogeneous mixture of two or more substances

Solvent

The dissolving agent of a solution.

What is the most versatile solvent?

Water

Solute

A substance that is dissolved in a solution.

Acid

A substance that increases the hydrogen ion concentration in a solution.

Base

A substance that reduces the hydrogen ion (H+)concentration of a solution

PH scale

Describes how acidic or basic a solution is

Organic Compounds

Carbon-based molecules that usually contain hydrogen atoms in addition to carbon.

Hydrocarbons

An organic compound composed only of the elements carbon and hydrogen.

Carbon Skeleton

The chain of carbon molecules that forms the structural backbone of an organic molecule.

Isomers

Organic compounds with the same molecular formula but different structures and, therefore, different properties.

Functional Groups

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

Hydrophilic

"Water-loving"; pertaining to polar or charged molecules (or parts of molecules) that are soluble in water.

Hydroxyl Group

(-OH) consists of a H atom bonded to an O atom which in turn is bonded to a C.

Phosphate Group

-OPO3^2-

a P atom bonded to four O atoms.

Macromolecules

A large molecule formed by the joining of smaller molecules, usually by a dehydration reaction: a protein, carbohydrate, or nucleic acid.

Polymers

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

Monomers

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

Dehydration Reaction

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

Hydrolysis

A chemical reaction that breaks bonds between two molecules by the addition of water; process by polymers are broken down and an essential part of digestion.

Enzyme

A macromolecule, usually a protein, that serves as a biological catalyst, changing the rate of chemical reaction without being consumed by the reaction.

Carbohydrate

Member of the class of biological molecules consisting of single-monomer sugars (monosaccharides), two-monomer sugars (disaccharides), and polymers (polysaccharides).

Monosaccharide

The simplest carbohydrate; a simple sugar with a molecular formula that is generally some multiple of CH2O. Monosaccharides are the building blocks of disaccharides and polysaccharides.

Disaccharide

A sugar molecule consisting of two monosaccharides linked by a dehydration reaction.

Starch

A storage polysaccharide found in the roots of plants and certain other cells; a polymer of glucose.

Cellulose

A large polysaccharide composed of many glucose monomers linked into cable-like fibrils that provide structural support in plant cell walls.

Chitin

A structural polysaccharide found in many fungal cell walls and in the exoskeletons of arthropods.

Lipid

An organic compound consisting mainly of carbon and hydrogen atoms linked by nonpolar convalent bonds, making the compound mostly hydrophobic. Lipids include fats, phospholipids, and steroids and are insoluble in water.

Hydrophobic

"Water-fearing"; pertaining to nonpolar molecules (or parts of molecules) that do not dissolve in water.

Fat

A large lipid molecule made from an alcohol called glycerol and three fatty acids; a triglyceride. Most fats function as energy-storage molecules.

Unsaturated Fatty Acid

Pertaining to fats and fatty acids whose hydrocarbon chains lack the maximum number of hydrogen atoms and therefore have one or more double covalent bonds. Unsaturated fats and fatty acids do not solidify at room temperature.

Saturated Fatty Acid

Pertaining to fats and fatty acids whose hydrocarbon chains contain the maximum number of hydrogens and therefore have no double covalent bonds. Saturated fats and fatty acids solidify at room temperature.

Trans Fats

An unsaturated fat, formed artificially during hydrogenation of vegetable oils, which is linked to health risks.

Phospholipid

A lipid made up of glycerol joined to two fatty acids and a phosphate group, giving the molecule a nonpolar hydrophobic tail and a polar hydrophilic head. Phospholipids form bilayers that function as biological membranes.

Steroid

A type of lipid whose carbon skeleton is in the form of four fused rings with various chemical groups attached; examples are cholesterol, testosterone, and estrogen.

Cholesterol

A steroid that is an important component of animal cell membranes and that acts as a precursor molecule for the synthesis of other steroids such as hormones.

Anabolic Steroids

A synthetic variant of the male hormone testosterone that mimics some of its effects.

Protein

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

Amino Acid

An organic molecule containing a carboxyl group and an amino group; serves as the monomer of proteins.

Peptide Bond

The covalent linkage between two amino acid units in a polypeptide; formed by a dehydration reaction.

Polypeptide

A polymer (chain) of amino acids linked by peptide bonds.

Denaturation

A process in which a protein unravels, losing its specific structure and hence function; can be caused by changes in pH or salt concentration or by high temperature. Also refers to the separation of the two strands of the DNA double helix, caused by similar factors.

Gene

A discrete unit of hereditary information consisting of a specific nucleotide sequence in DNA (or RNA, in some viruses). Most of the genes of a eukaryote are located in its chromosomal DNA; a few are carried by the DNA of mitochondria and chloroplasts.

DNA

A double-stranded helical nucleic acid molecule consisting of nucleotide monomers with deoxyribose sugar and the nitrogenous bases adenine (A), cytosine (C), guanine (G), and thymine (T). Capable of replicating, is an organism's genetic material. See also gene.

Nucleic Acid

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

RNA

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.

Nucleotides

An organic monomer consisting of a five-carbon sugar covalently bonded to a nitrogenous base and a phosphate group. Nucleotides are the building blocks of nucleic acids.

Double helix

The form of native DNA, referring to its two adjacent polynucleotide strands wound into a spiral shape.

light microscope

An optical instrument with lenses that refract (bend) visible light to magnify images and project them into a viewer's eye or onto photographic film.

magnification

The increase in an object's image size compared with its actual size.

resolution

The ability to distinguish two nearby objects as separate.

cell theory

The theory that all living things are composed of cells and that all cells come from other cells.

electron microscope

A microscope that uses magnets to focus an electron beam through, or onto the surface of, a specimen. Achieves a hundredfold greater resolution than a light microscope.

scanning electron microscope

A microscope that uses an electron beam to study the surface details of a cell or other specimens.

transmission electron microscope

A microscope that uses an electron beam to study the internal structure of thinly sectioned specimens.

prokaryotic cell

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

eukaryotic cell

A type of cell that has a membrane-enclosed nucleus and membrane-enclosed organelles. All organisms except bacteria and archaea are composed of these types of cells.

cytosol

The semifluid portion of the cytoplasm.

chromosome

A gene-carrying structure found in the nucleus of a eukaryotic cell and most visible during mitosis and meiosis; also, the main gene-carrying structure of a prokaryotic cell. Consists of one very long DNA molecule and associated proteins.

ribosome

A cell structure consisting of RNA and protein organized into two subunits and functioning as the site of protein synthesis in the cytoplasm. In eukaryotic cells, the subunits are assembled in the nucleolus.

cytoplasm

The contents of a eukaryotic cell between the plasma membrane and the nucleus; consists of a semifluid medium and organelles; can also refer to the interior of a prokaryotic cell.

nucleoid

A non-membrane-bounded region in a prokaryotic cell where the DNA is concentrated.

flagellum

A long cellular appendage specialized for locomotion.

cell wall

A protective layer external to the plasma membrane in plant cells, bacteria, fungi, and some protists; protects the cell and helps maintain its shape.

plasma membrane

The membrane at the boundary of every cell that acts as a selective barrier to the passage of ions and molecules into and out of the cell; consists of a phospholipid bilayer with embedded proteins.

organelle

A membrane-enclosed structure with a specialized function within a cell.

cellular metabolism

All the chemical activities of a cell.

nucleus

The organelle of a eukaryotic cell that contains the genetic material in the form of chromosomes, made of chromatin.

nuclear envelope

A double membrane that enclosed the nucleus, perforated with pores that regulate traffic with the cytoplasm.