IB Biology HL flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Three-domain system

Classification into Bacteria, Archaea, and Eukarya based on ribosomal RNA sequence comparisons. Archaea and Eukarya are more closely related to each other than either is to Bacteria.

Binomial nomenclature

Two-part naming system where the genus is capitalized and the species name is lowercase; both are italicized in print or underlined when handwritten, for example Homo sapiens.

Synapomorphy

A shared derived character inherited from a common ancestor that defines a clade. Cladograms group organisms by synapomorphies rather than by analogous features produced by convergent evolution.

Biological species concept

A species is a group of populations whose members can interbreed to produce fertile offspring and are reproductively isolated from other such groups. It does not apply to asexual organisms.

Prezygotic isolation

A reproductive barrier that prevents fertilization from occurring, including temporal, habitat, behavioral, mechanical, and gametic isolation. These barriers stop hybrid zygotes from ever forming.

Molecular clock

The assumption that neutral mutations accumulate at a roughly constant rate, allowing DNA or protein sequence differences to estimate the time since two lineages diverged from a common ancestor.

Surface area to volume ratio

The ratio of exchange surface to body volume, which decreases as organism size increases. Small or flattened organisms rely on diffusion; large ones need specialized exchange and transport systems.

Competitive inhibition

An inhibitor binds the enzyme active site, competing with substrate. It raises apparent Km because more substrate is needed, but Vmax is unchanged at saturating substrate concentration.

Non-competitive inhibition

An inhibitor binds a site other than the active site and alters enzyme shape. Vmax decreases because fewer enzyme molecules are functional, while Km is generally unchanged.

Water potential equation

Water potential equals solute potential plus pressure potential (Ψ = Ψs + Ψp). Water moves by osmosis from higher to lower water potential, meaning from less negative to more negative values.

Bohr shift

A rightward shift of the hemoglobin oxygen dissociation curve caused by higher CO2, lower pH, or higher temperature. It reduces oxygen affinity and promotes oxygen unloading in respiring tissues.

Sliding filament model

Muscle contraction in which myosin heads bind actin and pull filaments past each other. Calcium binds troponin, moving tropomyosin to expose binding sites, and ATP powers the cross-bridge cycle.

Pressure flow hypothesis

Phloem transport driven by active loading of sucrose at the source, lowering water potential so water enters by osmosis. Increased pressure pushes sap toward the sink.

Negative pressure ventilation

Breathing in mammals where diaphragm and external intercostal contraction increase thoracic volume, lowering pressure below atmospheric so air flows into the lungs.

Logistic growth equation

dN/dt = rN(K − N)/K, where r is the intrinsic growth rate and K is carrying capacity. Population growth slows as N approaches K and is fastest at K/2.

Ten percent rule

Only about 10 percent of energy at one trophic level is transferred to the next, with the rest lost through respiration, heat, and excretion. This limits food chain length.

Nitrogen fixation

Conversion of atmospheric N2 into ammonia by bacteria such as Rhizobium in root nodules and by cyanobacteria. It makes nitrogen available for synthesis of amino acids and nucleic acids.

Nitrification

Oxidation of ammonium to nitrite by Nitrosomonas and then to nitrate by Nitrobacter. Plants absorb the resulting nitrate and ammonium ions from soil for growth.

Keystone species

A species whose removal causes disproportionate change in community structure, often through trophic cascades. Sea otters controlling sea urchin populations that graze kelp are a classic example.

Greenhouse effect

Greenhouse gases absorb outgoing long-wave infrared radiation and re-emit it, warming the lower atmosphere. Carbon dioxide, methane, nitrous oxide, and water vapor are the main contributors.

Semi-conservative replication

Each new DNA molecule contains one original parental strand and one newly synthesized strand. DNA polymerase adds nucleotides only in the 5' to 3' direction.

Okazaki fragments

Short DNA segments synthesized discontinuously on the lagging strand during replication, later joined by DNA ligase. They arise because polymerase can only extend away from the replication fork.

Crossing over

Exchange of DNA segments between non-sister chromatids of homologous chromosomes during prophase I of meiosis. It creates new allele combinations and increases genetic variation in gametes.

Independent assortment

Random orientation of homologous chromosome pairs at metaphase I means maternal and paternal chromosomes are distributed independently, producing genetically varied haploid gametes.

Frameshift mutation

Insertion or deletion of a number of bases not divisible by three, shifting the reading frame. All downstream codons change, usually producing a non-functional protein.

Hardy–Weinberg equilibrium

Allele frequencies remain constant across generations if there is no mutation, migration, selection, genetic drift, or non-random mating. Genotype frequencies follow p² + 2pq + q² = 1.

X-linked recessive inheritance

A trait carried on the X chromosome that appears mostly in males, who have only one X. Affected fathers pass the allele to daughters as carriers, not to sons.

Polymerase chain reaction

Repeated cycles of denaturation near 95 degrees Celsius, primer annealing near 55 degrees, and extension by Taq polymerase near 72 degrees, exponentially amplifying a specific DNA sequence.

Gel electrophoresis

Separation of DNA fragments in an electric field through a gel. Negatively charged DNA moves toward the positive electrode, and smaller fragments migrate farther than larger ones.

Chi-squared test

A statistical test comparing observed with expected frequencies using χ² = Σ(O − E)²/E. Degrees of freedom are (rows − 1)(columns − 1); the null hypothesis is rejected above the critical value.

Validity versus reliability

Validity means the investigation measures the intended variable; reliability means repeated trials give consistent results. Accurate results are close to the true value, which requires valid methods.

Dilution series formula

C1V1 = C2V2 relates stock concentration and volume to the diluted concentration and volume. It is used to prepare a series of known concentrations for a controlled independent variable.