Your FREE ATDH Flashcards 2026 – 100+ Cards

A cell with no membrane-bound nucleus or organelles; DNA sits in the cytoplasm. Bacteria are prokaryotes — smaller and simpler than eukaryotic cells.

A cell with a membrane-bound nucleus and organelles (mitochondria, ER, Golgi). Animal, plant, fungal, and protist cells are eukaryotic.

A phospholipid bilayer with embedded proteins that controls what enters and leaves the cell; selectively permeable and fluid (the fluid-mosaic model).

The organelle that makes ATP through aerobic cellular respiration — the cell's 'powerhouse.' It has its own DNA and a folded inner membrane (cristae).

The organelle that synthesizes lipids and detoxifies drugs and poisons; it lacks ribosomes (unlike the rough ER).

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

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.

The organelle that modifies, sorts, and packages proteins and lipids into vesicles for secretion or delivery — the cell's 'post office.'

A membrane-bound organelle full of digestive enzymes that break down waste, debris, and worn-out organelles.

The organelle that houses the cell's DNA and controls gene expression and cell division; bounded by the nuclear envelope.

The phase of interphase in which the cell replicates its DNA, so each chromosome ends up with two sister chromatids before mitosis.

Division of a somatic cell's nucleus into two genetically identical diploid daughter nuclei; stages are prophase, metaphase, anaphase, telophase.

A two-stage division producing four genetically diverse haploid gametes; it halves the chromosome number and includes crossing over.

The enzyme that unwinds and separates the two strands of the DNA double helix at the replication fork.

The enzyme that builds a new DNA strand by adding nucleotides complementary to a template, in the 5' to 3' direction.

Hollow cytoskeletal tubes of tubulin that form the mitotic spindle and move chromosomes during cell division; also tracks for organelle transport.

The catabolic pathway that splits one glucose into two pyruvate in the cytoplasm, producing a net 2 ATP and 2 NADH — no oxygen required.

A metabolic reaction that breaks larger molecules into smaller ones and releases energy (e.g., glycolysis); the opposite of an anabolic reaction.

The cell's main energy currency; energy is released when its terminal phosphate bond is broken to form ADP.

The process that converts glucose and oxygen into ATP, carbon dioxide, and water through glycolysis, the Krebs cycle, and the electron transport chain.

A membrane transport protein that moves a single type of molecule down its concentration gradient (facilitated diffusion) — no energy required.

Movement of a substance against its concentration gradient using energy (ATP), as in the sodium-potassium pump.

The passive diffusion of water across a selectively permeable membrane, from lower to higher solute concentration.

An intracellular signaling molecule, such as cyclic AMP, that relays a signal from a membrane receptor to targets inside the cell.

A cluster of E. coli genes for lactose metabolism; lactose acts as an inducer, turning the genes on when lactose is present.

A protein catalyst that speeds a reaction by lowering its activation energy; it is specific to its substrate and is not consumed.

A molecule that neutralizes free radicals, preventing the oxidative damage they can cause to cells, proteins, and DNA.

A white blood cell of the adaptive immune system that produces antibodies against specific antigens.

A white blood cell of cell-mediated immunity; helper T cells coordinate the response and cytotoxic T cells kill infected cells.

A Y-shaped protein made by B cells (plasma cells) that binds a specific antigen to mark it for destruction.

An allele whose trait appears in the phenotype even when only one copy is present (heterozygous); written with a capital letter.

An allele whose trait appears only when two copies are present (homozygous recessive); written with a lowercase letter.

Genotype is the genetic makeup (e.g., Aa); phenotype is the observable trait that results from the genotype and environment.

The maintenance of a stable internal environment (temperature, pH, glucose) despite external change, often via negative feedback.

The passive net movement of particles from an area of higher concentration to lower concentration until equilibrium; no energy required.

The number of protons in an atom's nucleus; it defines the element and equals the number of electrons in a neutral atom.

The total number of protons plus neutrons in an atom's nucleus.

Atoms of the same element with the same number of protons but different numbers of neutrons (different mass numbers).

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.

The energy required to remove an electron from a gaseous atom; it increases across a period as effective nuclear charge (Zeff) rises.

The net positive charge an electron actually experiences after accounting for shielding by inner electrons; it rises across a period.

A bond formed by the transfer of electrons from a metal to a nonmetal, creating oppositely charged ions held together by electrostatic attraction.

A bond formed when two atoms share a pair of electrons; nonpolar if shared equally, polar if shared unequally.

Valence Shell Electron Pair Repulsion: electron pairs around a central atom arrange to minimize repulsion, which predicts molecular shape (e.g., bent, trigonal, tetrahedral).

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°).

Attractions between molecules (London dispersion, dipole-dipole, hydrogen bonding) that determine boiling point, melting point, and solubility.

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.

The state in a reversible reaction where forward and reverse rates are equal and concentrations stay constant.

If a system at equilibrium is disturbed (concentration, pressure, temperature), it shifts to counteract the change and re-establish equilibrium.

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.

A proton ($H^+$) donor. In acid-base salt formation the acid donates a proton to the base.

A proton ($H^+$) acceptor.

A reaction in which two soluble ionic solutions combine to form an insoluble solid (precipitate), e.g., $\ce{AgNO3}$ + $\ce{NaCl}$ → $\ce{AgCl}$ (s).

The use of balanced-equation mole ratios to calculate the amounts of reactants and products in a chemical reaction.

The SI unit for amount of substance; one mole contains Avogadro's number ($6.022 \times 10^{23}$) of particles.

$PV = nRT$: at constant pressure and moles, a gas's volume increases as temperature increases (Charles's law).

The loss of electrons by a species (its oxidation number increases). Remember 'OIL RIG' — Oxidation Is Loss.

The gain of electrons by a species (its oxidation number decreases). Remember 'OIL RIG' — Reduction Is Gain.

Concentration expressed as moles of solute per liter of solution ($mol/L$).

Endothermic reactions absorb heat (positive ΔH); exothermic reactions release heat (negative ΔH).

A substance that speeds a reaction by lowering its activation energy without being consumed; it does not shift the equilibrium position.

Atomic radius decreases across a period (rising Zeff pulls electrons in) and increases down a group (added shells).

$6.022 \times 10^{23}$ — the number of particles (atoms, molecules, ions) in one mole of a substance.

$(n - 2) \times 180°$, where $n$ is the number of sides. A sum of 1,800° means 12 sides.

$V = \pi r^2 h$ — the base area ($\pi r^2$) times the height.

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 $\frac{3}{8}$.

$S = \frac{a}{1 - r}$ when $|r| < 1$. For $1 + \tfrac12 + \tfrac14 + \cdots$, $a=1, r=\tfrac12$, so the sum is 2.

Adding a constant to every value shifts the mean by that constant but leaves the standard deviation unchanged.

The sum of all values divided by the number of values; a measure of central tendency.

The middle value of an ordered data set (or the average of the two middle values); less affected by outliers than the mean.

A measure of how spread out data are around the mean; a larger value means more variability.

The amount of pure substance is conserved: amount = volume × concentration. Set the substance before evaporation equal to the substance after.

$P = 2(l + w)$. With length three times the width and $P = 64$, the width is 8 and the length is 24.

Substitute the position $n$ into the term formula. For $3n^2 - 2n + 1$, the 5th term is $3(25) - 10 + 1 = 66$.

$m = \frac{y_2 - y_1}{x_2 - x_1}$ — the change in y over the change in x ('rise over run').

For $ax^2 + bx + c = 0$, $x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$.

In a right triangle, $a^2 + b^2 = c^2$, where $c$ is the hypotenuse.

$A = \pi r^2$; the circumference is $C = 2\pi r$.

$\frac{\text{new} - \text{old}}{\text{old}} \times 100\%$. A positive result is an increase, a negative one a decrease.

A proportion sets two ratios equal ($\frac{a}{b} = \frac{c}{d}$); solve by cross-multiplying ($ad = bc$).

The probability that two independent events both occur is the product of their individual probabilities: $P(A \text{ and } B) = P(A) \times P(B)$.

$x^a \cdot x^b = x^{a+b}$; $\frac{x^a}{x^b} = x^{a-b}$; $(x^a)^b = x^{ab}$.

$I = Prt$ — principal times rate times time. Distinct from compound interest, which earns interest on accrued interest.

The skill of accurately perceiving the dimensions of objects and mentally manipulating them in space — the core ability the ATDH Perceptual Ability section tests.

The mental ability to visualize and manipulate two- and three-dimensional shapes; the most important skill for the Perceptual Ability section.

A PAT task: choose the single opening through which a 3D object could pass straight through, in any orientation.

A PAT task: given two of the top, front, and side (orthographic) views of an object, identify the correct missing view.

A PAT task: rank a set of four angles from smallest to largest.

A PAT task: a sheet is folded, hole-punched, then unfolded — predict the resulting pattern of holes.

A PAT task: in a stack of cubes, count how many cubes have a given number of painted or exposed faces.

A PAT task: identify the three-dimensional shape that a flat pattern produces when folded.

The skill of identifying recurring features, similarities, or regularities — used to match objects or images, such as dental X-rays to patients.

Imagining how an object would look when rotated to a new orientation; central to comparing 3D forms and orthographic views.

Two-dimensional projections of an object from the top, front, and side; used in the view-recognition subtest.

Putting steps or images in the correct logical order — for example, arranging a series of procedural images in sequence.

The ability to spot small visual distinctions between similar images — key to comparing normal and abnormal conditions in a set of images.

Mentally arranging objects within a space, such as visualizing a new furniture or equipment layout in a room.

The skill of reading, understanding, and analyzing basic scientific information. ATDH passages run about 450–500 words with roughly eight questions each.

The central point a passage makes; usually stated in or summarized by the topic sentence and supported by the rest of the text.

A fact, example, or piece of evidence in a passage that develops or backs up the main idea.

A logical conclusion drawn from evidence in a passage that is implied but not stated outright. Answer from the text, not outside knowledge.

The author's attitude toward the subject, conveyed through word choice — e.g., objective, critical, enthusiastic, cautious.

The reason a passage was written — to inform, persuade, describe, or analyze. Identifying it guides how you interpret the text.

Surrounding words and sentences that reveal the meaning of an unfamiliar term — the intended way to define vocabulary in a science passage.

How a study was designed and conducted; examining it is critical to judging whether a paper's conclusions are valid.

Whether the statistical methods used to analyze data justify a study's conclusions — the most critical element when evaluating research claims.

A reading approach: skim the questions first, then scan the passage for the relevant section rather than reading every word closely up front.

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').

Joins two closely related independent clauses without a conjunction, often before a conjunctive adverb (e.g., 'brushing helps; however, flossing matters too').

Separates three or more items in a list (e.g., 'brushing, flossing, and using mouthwash'); the final comma before 'and' is the Oxford comma.

A group of words with a subject and verb that expresses a complete thought and can stand alone as a sentence.

A clause with a subject and verb that does NOT express a complete thought and cannot stand alone (e.g., 'because she flossed daily').

A clause beginning with a relative pronoun (who, which, that) that adds information about a noun (e.g., 'patients WHO neglect their health').

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').

A construction in which the subject receives the action (e.g., 'the guidelines were published'); useful for emphasis or when the actor is unknown.

A construction in which the subject performs the action (e.g., 'the association published the guidelines'); usually clearer and more direct.

A sentence expressing a hypothetical situation and its result, using 'if' (or inverted 'should') plus a result clause.

A verb form expressing a wish, demand, or hypothetical; uses the base verb (e.g., 'It is essential that each professional BE informed').

A descriptive word or phrase positioned so it seems to modify the wrong word, creating confusion; place modifiers next to what they describe.

A modifier whose intended subject is missing from the sentence (e.g., 'Walking in, the chair was empty'); fix by naming the subject.

Using the same grammatical form for items in a series (e.g., 'brushing, flossing, and rinsing' — all gerunds).

The error of joining two independent clauses with only a comma; fix with a period, semicolon, or a coordinating conjunction.

Two or more independent clauses joined with no punctuation or conjunction; fix by separating or properly connecting them.

Marks possession (the dentist's chair) or a contraction (it's = it is); 'its' (possessive) takes no apostrophe.

A pronoun must match the noun it refers to in number and gender (a singular antecedent takes a singular pronoun).

Introduces a list, explanation, or quotation after a complete independent clause (e.g., 'Bring three things: a pen, an ID, and a confirmation').