Quiz Bowl Science

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Nucleus

Membrane-bound organelle that houses the cell's DNA and controls gene expression; surrounded by a double membrane called the nuclear envelope.

Nucleolus

Dense region inside the nucleus where ribosomal RNA is made and ribosome subunits are assembled.

Mitochondria

The "powerhouse of the cell"; site of aerobic respiration where ATP is produced; has its own DNA and inner membrane folds called cristae.

Ribosome

Site of protein synthesis (translation); made of rRNA and protein; found free in the cytoplasm or attached to the rough ER.

Rough endoplasmic reticulum

ER studded with ribosomes; synthesizes and folds proteins bound for secretion or membranes.

Smooth endoplasmic reticulum

ER without ribosomes; makes lipids, stores calcium, and detoxifies drugs.

Golgi apparatus

Stack of flattened membranes that modifies, sorts, and packages proteins and lipids into vesicles for shipment.

Lysosome

Organelle full of digestive enzymes that break down waste, debris, and worn-out organelles; has an acidic interior.

Chloroplast

Organelle in plant and algal cells where photosynthesis occurs; contains chlorophyll and thylakoid stacks called grana.

Vacuole

Storage sac; the large central vacuole in plant cells maintains turgor pressure.

Cell membrane

Phospholipid bilayer that controls what enters and leaves the cell; described by the fluid mosaic model.

Cell wall

Rigid outer layer in plants (cellulose), fungi (chitin), and bacteria (peptidoglycan) that provides structure.

Cytoskeleton

Network of microtubules, microfilaments, and intermediate filaments that gives a cell shape and enables movement.

Peroxisome

Organelle that breaks down fatty acids and neutralizes hydrogen peroxide using the enzyme catalase.

Prokaryote vs. eukaryote

Prokaryotes (bacteria) lack a nucleus and membrane-bound organelles; eukaryotes have both.

Carbohydrates

Sugars and starches made of carbon, hydrogen, and oxygen; a quick energy source; monomers are monosaccharides like glucose.

Lipids

Fats, oils, phospholipids, and steroids; store energy, form membranes, and are hydrophobic.

Proteins

Polymers of amino acids joined by peptide bonds; act as enzymes, structural material, and transporters.

Nucleic acids

DNA and RNA; polymers of nucleotides that store and transmit genetic information.

ATP

Adenosine triphosphate, the cell's main energy currency; releases energy when its terminal phosphate bond breaks.

Enzyme

Protein catalyst that speeds up reactions by lowering activation energy; binds a specific substrate at its active site.

Amino acid

Building block of proteins; 20 standard types, each with an amino group, a carboxyl group, and a variable side chain.

DNA

Deoxyribonucleic acid; a double helix carrying the genetic code in bases A, T, G, and C; structure found by Watson and Crick using Franklin's X-ray data.

RNA

Ribonucleic acid; single-stranded, uses uracil instead of thymine; types include mRNA, tRNA, and rRNA.

Central dogma

The flow of genetic information: DNA is transcribed into RNA, which is translated into protein.

Transcription

Copying a DNA gene into messenger RNA, carried out by RNA polymerase.

Translation

Ribosomes reading mRNA codons and assembling the matching chain of amino acids.

Codon

A three-base sequence of mRNA that specifies one amino acid or a stop signal.

Complementary base pairing

Adenine pairs with thymine (or uracil in RNA); guanine pairs with cytosine.

Chromosome

Threadlike structure of DNA and protein that carries genes; humans have 46.

Gene

A segment of DNA that codes for a protein or trait.

Mutation

A change in DNA sequence that can alter an organism's traits.

Mitosis

Cell division producing two genetically identical diploid cells; phases are prophase, metaphase, anaphase, telophase.

Meiosis

Division producing four genetically diverse haploid gametes; includes two rounds of division and crossing over.

Gregor Mendel

The "father of genetics"; studied pea plants and derived the laws of segregation and independent assortment.

Allele

One of the alternative versions of a gene.

Genotype vs. phenotype

Genotype is the genetic makeup; phenotype is the observable trait it produces.

Dominant vs. recessive

A dominant allele masks a recessive one; a recessive trait appears only when both alleles are recessive.

Punnett square

Diagram used to predict the probability of offspring genotypes from a cross.

Photosynthesis

Process converting carbon dioxide and water into glucose and oxygen using light energy; occurs in chloroplasts.

Light-dependent reactions

Stage of photosynthesis in the thylakoid that captures light to make ATP and NADPH and releases oxygen.

Calvin cycle

Light-independent stage of photosynthesis in the stroma that fixes carbon dioxide into sugar.

Cellular respiration

Breaking down glucose to release ATP; its stages are glycolysis, the Krebs cycle, and the electron transport chain.

Glycolysis

First stage of respiration in the cytoplasm; splits glucose into two pyruvate molecules and yields a little ATP.

Krebs cycle

Also called the citric acid cycle; runs in the mitochondrial matrix and produces electron carriers (NADH, FADH2) and CO2.

Electron transport chain

Final respiration stage on the inner mitochondrial membrane; makes most of the ATP using oxygen as the final electron acceptor.

Charles Darwin

Proposed evolution by natural selection in "On the Origin of Species" (1859); studied finches on the Galapagos.

Natural selection

Mechanism of evolution in which organisms better suited to their environment survive and reproduce more.

Taxonomy

Science of naming and classifying organisms; the hierarchy is domain, kingdom, phylum, class, order, family, genus, species.

Binomial nomenclature

Two-part Latin naming system (genus plus species) devised by Carl Linnaeus.

Three domains

The broadest classification level: Bacteria, Archaea, and Eukarya.

Bacteria vs. virus

Bacteria are living single-celled organisms; viruses are nonliving particles that need a host cell to reproduce.

Neuron

Nerve cell that transmits electrical impulses; parts include dendrites, a cell body, and an axon.

Homeostasis

Maintenance of a stable internal environment despite external changes.

Antibody

Immune-system protein that recognizes and binds a specific antigen.

Diffusion

Movement of particles from an area of high concentration to low concentration.

Osmosis

Diffusion of water across a semipermeable membrane.

Atom

Smallest unit of an element; protons and neutrons in a nucleus with electrons around it.

Atomic number

Number of protons in an atom's nucleus; it defines the element.

Isotope

Atoms of the same element that have different numbers of neutrons.

Valence electrons

Electrons in an atom's outermost shell; they determine how it bonds.

Periodic table

Arrangement of elements by increasing atomic number into periods (rows) and groups (columns); organized by Dmitri Mendeleev.

Alkali metals

Group 1 elements (except hydrogen); soft, highly reactive metals with one valence electron.

Alkaline earth metals

Group 2 elements; reactive metals with two valence electrons.

Halogens

Group 17 elements; highly reactive nonmetals that form salts, such as fluorine and chlorine.

Noble gases

Group 18 elements; nonreactive gases with full valence shells, like helium and neon.

Transition metals

The central block of metals (groups 3-12) that often form colored compounds and multiple oxidation states.

Electronegativity

An atom's tendency to attract shared electrons; fluorine is highest (about 4.0) and francium is lowest.

Ionization energy

Energy needed to remove an electron; it increases across a period and decreases down a group.

Atomic radius

Size of an atom; it decreases across a period and increases down a group.

Ionic bond

Bond formed by transferring electrons from a metal to a nonmetal, creating charged ions.

Covalent bond

Bond formed by sharing electrons between nonmetal atoms.

Metallic bond

Bond in metals where electrons move freely in a "sea" around positive ions.

Hydrogen bond

Weak attraction between hydrogen and an electronegative atom like oxygen or nitrogen; key in water and DNA.

Mole

Unit for amount of substance; one mole holds Avogadro's number of particles.

Avogadro's number

The number of particles in one mole, about 6.022 times 10 to the 23rd.

Stoichiometry

Calculating amounts of reactants and products using a balanced chemical equation.

Chemical equation

Symbolic representation of a reaction; it must be balanced so atoms are conserved.

Catalyst

Substance that speeds a reaction without being used up, by lowering activation energy.

Oxidation

Loss of electrons by a substance in a reaction.

Reduction

Gain of electrons by a substance in a reaction.

Conservation of mass

Matter is neither created nor destroyed in a chemical reaction.

Chemical vs. physical change

A chemical change forms new substances; a physical change alters form but not identity.

Acid

Substance that donates protons (H+) or has a pH below 7; examples include hydrochloric and sulfuric acid.

Base

Substance that accepts protons or releases hydroxide ions; has a pH above 7.

pH scale

Measures acidity from 0 to 14, with 7 neutral; it is logarithmic, so each unit is a tenfold change.

States of matter

Solid, liquid, gas, and plasma; they differ in particle arrangement and energy.

Ideal gas law

PV = nRT, relating a gas's pressure, volume, moles, and temperature.

Boyle's law

At constant temperature, a gas's pressure and volume are inversely proportional.

Charles's law

At constant pressure, a gas's volume is directly proportional to its absolute temperature.

Density

Mass per unit volume.

Dmitri Mendeleev

Created the modern periodic table and predicted the properties of undiscovered elements.

Antoine Lavoisier

The "father of modern chemistry"; established the law of conservation of mass and named oxygen.

Marie Curie

Pioneer of radioactivity; discovered polonium and radium; the only person to win Nobel Prizes in two different sciences.

Newton's first law

An object stays at rest or in uniform motion unless acted on by a net force (the law of inertia).

Newton's second law

Force equals mass times acceleration (F = ma).

Newton's third law

For every action there is an equal and opposite reaction.

Inertia

An object's resistance to changes in its motion; it is proportional to mass.

Momentum

The product of mass and velocity; it is conserved in a closed system.

Velocity

Speed in a given direction; a vector quantity.