- Prokaryotic cell
- A cell with no membrane-bound nucleus or organelles; DNA sits in the cytoplasm. Bacteria are prokaryotes — smaller and simpler than eukaryotic cells.
- Eukaryotic cell
- A cell with a membrane-bound nucleus and organelles (mitochondria, ER, Golgi). Animal, plant, fungal, and protist cells are eukaryotic.
- Cell membrane (plasma membrane)
- A phospholipid bilayer with embedded proteins that controls what enters and leaves the cell; selectively permeable and fluid (the fluid-mosaic model).
- Mitochondrion
- The organelle that makes ATP through aerobic cellular respiration — the cell's 'powerhouse.' It has its own DNA and a folded inner membrane (cristae).
- Smooth endoplasmic reticulum (SER)
- The organelle that synthesizes lipids and detoxifies drugs and poisons; it lacks ribosomes (unlike the rough ER).
- Rough endoplasmic reticulum (RER)
- ER studded with ribosomes; it synthesizes and folds proteins destined for secretion or membranes.
- Ribosome
- The cellular machine that builds proteins by translating mRNA into a chain of amino acids; found free in the cytoplasm or on the rough ER.
- Golgi apparatus
- The organelle that modifies, sorts, and packages proteins and lipids into vesicles for secretion or delivery — the cell's 'post office.'
- Lysosome
- A membrane-bound organelle full of digestive enzymes that break down waste, debris, and worn-out organelles.
- Nucleus
- The organelle that houses the cell's DNA and controls gene expression and cell division; bounded by the nuclear envelope.
- S phase
- The phase of interphase in which the cell replicates its DNA, so each chromosome ends up with two sister chromatids before mitosis.
- Mitosis
- Division of a somatic cell's nucleus into two genetically identical diploid daughter nuclei; stages are prophase, metaphase, anaphase, telophase.
- Meiosis
- A two-stage division producing four genetically diverse haploid gametes; it halves the chromosome number and includes crossing over.
- Helicase
- The enzyme that unwinds and separates the two strands of the DNA double helix at the replication fork.
- DNA polymerase
- The enzyme that builds a new DNA strand by adding nucleotides complementary to a template, in the 5' to 3' direction.
- Microtubules
- Hollow cytoskeletal tubes of tubulin that form the mitotic spindle and move chromosomes during cell division; also tracks for organelle transport.
- Glycolysis
- The catabolic pathway that splits one glucose into two pyruvate in the cytoplasm, producing a net 2 ATP and 2 NADH — no oxygen required.
- Catabolic reaction
- A metabolic reaction that breaks larger molecules into smaller ones and releases energy (e.g., glycolysis); the opposite of an anabolic reaction.
- ATP (adenosine triphosphate)
- The cell's main energy currency; energy is released when its terminal phosphate bond is broken to form ADP.
- Cellular respiration
- The process that converts glucose and oxygen into ATP, carbon dioxide, and water through glycolysis, the Krebs cycle, and the electron transport chain.
- Uniporter
- A membrane transport protein that moves a single type of molecule down its concentration gradient (facilitated diffusion) — no energy required.
- Active transport
- Movement of a substance against its concentration gradient using energy (ATP), as in the sodium-potassium pump.
- Osmosis
- The passive diffusion of water across a selectively permeable membrane, from lower to higher solute concentration.
- Second messenger (cAMP)
- An intracellular signaling molecule, such as cyclic AMP, that relays a signal from a membrane receptor to targets inside the cell.
- Lac operon
- A cluster of E. coli genes for lactose metabolism; lactose acts as an inducer, turning the genes on when lactose is present.
- Enzyme
- A protein catalyst that speeds a reaction by lowering its activation energy; it is specific to its substrate and is not consumed.
- Antioxidant
- A molecule that neutralizes free radicals, preventing the oxidative damage they can cause to cells, proteins, and DNA.
- B lymphocyte (B cell)
- A white blood cell of the adaptive immune system that produces antibodies against specific antigens.
- T lymphocyte (T cell)
- A white blood cell of cell-mediated immunity; helper T cells coordinate the response and cytotoxic T cells kill infected cells.
- Antibody
- A Y-shaped protein made by B cells (plasma cells) that binds a specific antigen to mark it for destruction.
- Dominant allele
- An allele whose trait appears in the phenotype even when only one copy is present (heterozygous); written with a capital letter.
- Recessive allele
- An allele whose trait appears only when two copies are present (homozygous recessive); written with a lowercase letter.
- Genotype vs. phenotype
- Genotype is the genetic makeup (e.g., Aa); phenotype is the observable trait that results from the genotype and environment.
- Homeostasis
- The maintenance of a stable internal environment (temperature, pH, glucose) despite external change, often via negative feedback.
- Diffusion
- The passive net movement of particles from an area of higher concentration to lower concentration until equilibrium; no energy required.
- Atomic number
- The number of protons in an atom's nucleus; it defines the element and equals the number of electrons in a neutral atom.
- Mass number
- The total number of protons plus neutrons in an atom's nucleus.
- Isotope
- Atoms of the same element with the same number of protons but different numbers of neutrons (different mass numbers).
- Electronegativity
- The tendency of an atom to attract bonding electrons. Fluorine is the most electronegative element; it increases up and to the right on the periodic table.
- Ionization energy
- The energy required to remove an electron from a gaseous atom; it increases across a period as effective nuclear charge (Zeff) rises.
- Effective nuclear charge (Zeff)
- The net positive charge an electron actually experiences after accounting for shielding by inner electrons; it rises across a period.
- Ionic bond
- A bond formed by the transfer of electrons from a metal to a nonmetal, creating oppositely charged ions held together by electrostatic attraction.
- Covalent bond
- A bond formed when two atoms share a pair of electrons; nonpolar if shared equally, polar if shared unequally.
- VSEPR theory
- Valence Shell Electron Pair Repulsion: electron pairs around a central atom arrange to minimize repulsion, which predicts molecular shape (e.g., bent, trigonal, tetrahedral).
- sp² hybridization
- The hybridization of a carbon forming three sigma bonds and one pi bond (a double bond), as in ethylene ($\ce{C2H4}$); geometry is trigonal planar (120°).
- Intermolecular forces
- Attractions between molecules (London dispersion, dipole-dipole, hydrogen bonding) that determine boiling point, melting point, and solubility.
- Hydrogen bonding
- A strong dipole-dipole attraction between H bonded to N, O, or F and a lone pair on N, O, or F; it gives water its high boiling point.
- Chemical equilibrium
- The state in a reversible reaction where forward and reverse rates are equal and concentrations stay constant.
- Le Chatelier's principle
- If a system at equilibrium is disturbed (concentration, pressure, temperature), it shifts to counteract the change and re-establish equilibrium.
- pH
- A measure of acidity, $pH = -\log[H^+]$. A 0.01 M HCl solution has pH 2. Below 7 is acidic, 7 is neutral, above 7 is basic.
- Brønsted-Lowry acid
- A proton ($H^+$) donor. In acid-base salt formation the acid donates a proton to the base.
- Brønsted-Lowry base
- A proton ($H^+$) acceptor.
- Precipitation reaction
- A reaction in which two soluble ionic solutions combine to form an insoluble solid (precipitate), e.g., $\ce{AgNO3}$ + $\ce{NaCl}$ → $\ce{AgCl}$ (s).
- Stoichiometry
- The use of balanced-equation mole ratios to calculate the amounts of reactants and products in a chemical reaction.
- Mole
- The SI unit for amount of substance; one mole contains Avogadro's number ($6.022 \times 10^{23}$) of particles.
- Ideal gas law
- $PV = nRT$: at constant pressure and moles, a gas's volume increases as temperature increases (Charles's law).
- Oxidation
- The loss of electrons by a species (its oxidation number increases). Remember 'OIL RIG' — Oxidation Is Loss.
- Reduction
- The gain of electrons by a species (its oxidation number decreases). Remember 'OIL RIG' — Reduction Is Gain.
- Molarity
- Concentration expressed as moles of solute per liter of solution ($mol/L$).
- Endothermic vs. exothermic
- Endothermic reactions absorb heat (positive ΔH); exothermic reactions release heat (negative ΔH).
- Catalyst
- A substance that speeds a reaction by lowering its activation energy without being consumed; it does not shift the equilibrium position.
- Periodic trend: atomic radius
- Atomic radius decreases across a period (rising Zeff pulls electrons in) and increases down a group (added shells).
- Avogadro's number
- $6.022 \times 10^{23}$ — the number of particles (atoms, molecules, ions) in one mole of a substance.
- Sum of interior angles of a polygon
- $(n - 2) \times 180°$, where $n$ is the number of sides. A sum of 1,800° means 12 sides.
- Volume of a cylinder
- $V = \pi r^2 h$ — the base area ($\pi r^2$) times the height.
- Probability from odds
- If the odds against an event are a to b, the probability it occurs is $\frac{b}{a + b}$. Odds of 5 to 3 against give probability $\frac{3}{8}$.
- Sum of an infinite geometric series
- $S = \frac{a}{1 - r}$ when $|r| < 1$. For $1 + \tfrac12 + \tfrac14 + \cdots$, $a=1, r=\tfrac12$, so the sum is 2.
- Effect of adding a constant on mean and SD
- Adding a constant to every value shifts the mean by that constant but leaves the standard deviation unchanged.
- Mean (average)
- The sum of all values divided by the number of values; a measure of central tendency.
- Median
- The middle value of an ordered data set (or the average of the two middle values); less affected by outliers than the mean.
- Standard deviation
- A measure of how spread out data are around the mean; a larger value means more variability.
- Mixture / concentration problem
- The amount of pure substance is conserved: amount = volume × concentration. Set the substance before evaporation equal to the substance after.
- Perimeter of a rectangle
- $P = 2(l + w)$. With length three times the width and $P = 64$, the width is 8 and the length is 24.
- nth term of a sequence
- Substitute the position $n$ into the term formula. For $3n^2 - 2n + 1$, the 5th term is $3(25) - 10 + 1 = 66$.
- Slope of a line
- $m = \frac{y_2 - y_1}{x_2 - x_1}$ — the change in y over the change in x ('rise over run').
- Quadratic formula
- For $ax^2 + bx + c = 0$, $x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$.
- Pythagorean theorem
- In a right triangle, $a^2 + b^2 = c^2$, where $c$ is the hypotenuse.
- Area of a circle
- $A = \pi r^2$; the circumference is $C = 2\pi r$.
- Percent change
- $\frac{\text{new} - \text{old}}{\text{old}} \times 100\%$. A positive result is an increase, a negative one a decrease.
- Ratio and proportion
- A proportion sets two ratios equal ($\frac{a}{b} = \frac{c}{d}$); solve by cross-multiplying ($ad = bc$).
- Probability of independent events
- The probability that two independent events both occur is the product of their individual probabilities: $P(A \text{ and } B) = P(A) \times P(B)$.
- Exponent rules
- $x^a \cdot x^b = x^{a+b}$; $\frac{x^a}{x^b} = x^{a-b}$; $(x^a)^b = x^{ab}$.
- Simple interest
- $I = Prt$ — principal times rate times time. Distinct from compound interest, which earns interest on accrued interest.
- Perceptual ability
- The skill of accurately perceiving the dimensions of objects and mentally manipulating them in space — the core ability the ATDH Perceptual Ability section tests.
- Spatial reasoning
- The mental ability to visualize and manipulate two- and three-dimensional shapes; the most important skill for the Perceptual Ability section.
- Apertures (keyholes) subtest
- A PAT task: choose the single opening through which a 3D object could pass straight through, in any orientation.
- View recognition subtest
- A PAT task: given two of the top, front, and side (orthographic) views of an object, identify the correct missing view.
- Angle discrimination subtest
- A PAT task: rank a set of four angles from smallest to largest.
- Paper folding (hole punching) subtest
- A PAT task: a sheet is folded, hole-punched, then unfolded — predict the resulting pattern of holes.
- Cube counting subtest
- A PAT task: in a stack of cubes, count how many cubes have a given number of painted or exposed faces.
- 3D form development (pattern folding) subtest
- A PAT task: identify the three-dimensional shape that a flat pattern produces when folded.
- Pattern recognition
- The skill of identifying recurring features, similarities, or regularities — used to match objects or images, such as dental X-rays to patients.
- Mental rotation
- Imagining how an object would look when rotated to a new orientation; central to comparing 3D forms and orthographic views.
- Orthographic views
- Two-dimensional projections of an object from the top, front, and side; used in the view-recognition subtest.
- Sequential reasoning
- Putting steps or images in the correct logical order — for example, arranging a series of procedural images in sequence.
- Detecting minute differences
- The ability to spot small visual distinctions between similar images — key to comparing normal and abnormal conditions in a set of images.
- Spatial organization
- Mentally arranging objects within a space, such as visualizing a new furniture or equipment layout in a room.
- Reading comprehension (ATDH)
- The skill of reading, understanding, and analyzing basic scientific information. ATDH passages run about 450–500 words with roughly eight questions each.
- Main idea
- The central point a passage makes; usually stated in or summarized by the topic sentence and supported by the rest of the text.
- Supporting detail
- A fact, example, or piece of evidence in a passage that develops or backs up the main idea.
- Inference
- A logical conclusion drawn from evidence in a passage that is implied but not stated outright. Answer from the text, not outside knowledge.
- Author's tone
- The author's attitude toward the subject, conveyed through word choice — e.g., objective, critical, enthusiastic, cautious.
- Author's purpose
- The reason a passage was written — to inform, persuade, describe, or analyze. Identifying it guides how you interpret the text.
- Context clues
- Surrounding words and sentences that reveal the meaning of an unfamiliar term — the intended way to define vocabulary in a science passage.
- Methodology (in a study)
- How a study was designed and conducted; examining it is critical to judging whether a paper's conclusions are valid.
- Statistical validity
- Whether the statistical methods used to analyze data justify a study's conclusions — the most critical element when evaluating research claims.
- Search-and-find strategy
- A reading approach: skim the questions first, then scan the passage for the relevant section rather than reading every word closely up front.
- Subject-verb agreement
- A verb must match its subject in number. With 'neither/nor,' the verb agrees with the nearer subject (e.g., 'Neither the dentist nor the hygienists HAVE arrived').
- Semicolon
- Joins two closely related independent clauses without a conjunction, often before a conjunctive adverb (e.g., 'brushing helps; however, flossing matters too').
- Comma in a series
- Separates three or more items in a list (e.g., 'brushing, flossing, and using mouthwash'); the final comma before 'and' is the Oxford comma.
- Independent clause
- A group of words with a subject and verb that expresses a complete thought and can stand alone as a sentence.
- Dependent (subordinate) clause
- A clause with a subject and verb that does NOT express a complete thought and cannot stand alone (e.g., 'because she flossed daily').
- Relative clause
- A clause beginning with a relative pronoun (who, which, that) that adds information about a noun (e.g., 'patients WHO neglect their health').
- Appositive
- A noun phrase that renames or explains an adjacent noun, set off by commas (e.g., 'the periodontist, a gum-disease specialist, will join us').
- Passive voice
- A construction in which the subject receives the action (e.g., 'the guidelines were published'); useful for emphasis or when the actor is unknown.
- Active voice
- A construction in which the subject performs the action (e.g., 'the association published the guidelines'); usually clearer and more direct.
- Conditional sentence
- A sentence expressing a hypothetical situation and its result, using 'if' (or inverted 'should') plus a result clause.
- Subjunctive mood
- A verb form expressing a wish, demand, or hypothetical; uses the base verb (e.g., 'It is essential that each professional BE informed').
- Misplaced modifier
- A descriptive word or phrase positioned so it seems to modify the wrong word, creating confusion; place modifiers next to what they describe.
- Dangling modifier
- A modifier whose intended subject is missing from the sentence (e.g., 'Walking in, the chair was empty'); fix by naming the subject.
- Parallel structure
- Using the same grammatical form for items in a series (e.g., 'brushing, flossing, and rinsing' — all gerunds).
- Comma splice
- The error of joining two independent clauses with only a comma; fix with a period, semicolon, or a coordinating conjunction.
- Run-on sentence
- Two or more independent clauses joined with no punctuation or conjunction; fix by separating or properly connecting them.
- Apostrophe
- Marks possession (the dentist's chair) or a contraction (it's = it is); 'its' (possessive) takes no apostrophe.
- Pronoun-antecedent agreement
- A pronoun must match the noun it refers to in number and gender (a singular antecedent takes a singular pronoun).
- Colon
- Introduces a list, explanation, or quotation after a complete independent clause (e.g., 'Bring three things: a pen, an ID, and a confirmation').
