VCE Biology Units 3 & 4 Comprehensive Review

Comprehensive vocabulary flashcards covering the key definitions, biological processes, and quantitative data across VCE Biology Units 3 & 4.

Index fossils

Distinctive, widespread, abundant, and short-lived fossil species used to correlate and date the relative ages of rock strata (e.g., ammonites).

Transitional fossils

Fossils that exhibit physical characteristics common to both an ancestral group and its derived descendant group, providing evidence of evolutionary transitions (e.g., Archaeopteryx).

Faunal succession

The predictable chronological sequence in which distinct fossilised organisms appear and disappear throughout vertical layers of geological strata.

Relative dating

The science of determining the chronological order of past events and fossil specimens using the law of superposition in undisturbed strata, without providing an exact numerical age in years.

Absolute dating

A technique that calculates a specific numerical age in years for an object or fossil, typically through radiometric methods measuring the decay of radioactive isotopes.

Carbon-14 radiometric dating

An absolute dating method that calculates the ratio of radioactive ${}^{14}\text{C}$ to its decay product ${}^{14}\text{N}$ in once-living organic matter, accurate for samples up to approximately $60{,}000\text{ years}$ old with a half-life of $5{,}730\text{ years}$.

Allopatric speciation

Speciation that occurs when biological populations become geographically isolated from each other, preventing gene flow and allowing divergent selection pressures to accumulate reproductive barriers (e.g., Galapagos finches).

Sympatric speciation

The divergence of populations into distinct species within the same geographic area without physical isolation, driven by reproductive isolating mechanisms like differing flowering times or habitat niches (e.g., Howea palms on Lord Howe Island).

Homologous structures

Morphological features across different species that share the same fundamental anatomical structure due to inheritance from a common ancestor, regardless of whether their functions have diverged (e.g., vertebrate pentadactyl limb).

Vestigial structures

Reduced and often non-functional anatomical remnants of organs or structures that performed an active, necessary function in an organism's evolutionary ancestors.

Molecular homology

The degree of similarity in DNA nucleotide sequences or amino acid sequences among different species, where higher sequence alignment indicates a more recent common ancestor.

Phylogenetic tree node

A branch point on a phylogenetic tree that represents the most recent shared common ancestor from which descendant evolutionary lineages diverged.

Pathogen

A biological agent capable of causing disease; categorised into cellular agents (such as bacteria, fungi, protists, and parasites) and non-cellular agents (such as viruses and prions).

Allergen

A normally harmless environmental antigen that can trigger an inappropriate or exaggerated immune response in sensitive individuals.

Antigen

A molecule, often a protein, recognised by immune system receptors that allows discrimination between self-markers and foreign (non-self) targets.

Physical barriers

Structural defence mechanisms that physically block or impede the entry of pathogens into an organism (e.g., intact skin and mucous membranes in animals; thick bark, waxy cuticles, and cell walls in plants).

Chemical barriers

Chemical secretions that destroy, neutralize, or inhibit pathogen growth (e.g., lysozyme in tears/saliva and stomach acid in animals; defensins and antimicrobial enzymes in plants).

Microbiota barriers

Populations of harmless or non-pathogenic commensal microorganisms residing on internal or external host surfaces that outcompete potential invaders for vital space and nutrients.

Mast cells

Innate immune tissue cells that degranulate upon activation or allergen binding to surface IgE, releasing histamine and cytokines to promote vasodilation and inflammation.

Neutrophils

Abundant, rapid-response circulating white blood cells of the innate immune system that exit the bloodstream to engulf and destroy invading pathogens via phagocytosis.

Macrophages

Large, phagocytic tissue-resident cells of the innate immune system that engulf cellular debris and pathogens, also functioning as professional antigen-presenting cells (APCs).

Dendritic cells

Professional antigen-presenting phagocytes found in epithelial tissues that internalise pathogens, migrate to secondary lymphoid organs, and present non-self antigen fragments on MHC II to initiate adaptive immunity.

Natural killer (NK) cells

Granular cytotoxic innate lymphocytes that detect and kill abnormal, cancerous, or virus-infected host cells by releasing death signals that induce programmed cell death (apoptosis).

Eosinophils

Innate granulocytic immune cells that release toxic chemical mediators from their granules to combat large extracellular parasites, also participating in allergic responses.

Complement proteins

A group of circulating blood plasma proteins that activate in a biochemical cascade to lyse pathogens, promote inflammation, and coat pathogens (opsonisation) to attract phagocytes.

Interferons

A family of signalling cytokine proteins secreted by virus-infected host cells to stimulate surrounding uninfected cells to heighten their internal anti-viral defences.

MHC class I markers

Cell surface glycoproteins expressed on all nucleated body cells that present endogenous peptides to display self-status and signal abnormal internal proteins to cytotoxic T cells.

MHC class II markers

Cell surface proteins expressed exclusively by professional antigen-presenting cells (macrophages, dendritic cells, and B cells) used to present processed exogenous peptide fragments to helper T cells.

Humoral immune response

The branch of adaptive immunity mediated by B lymphocytes, plasma cells, and secreted antibodies directed primarily against extracellular pathogens and toxins.

Cell-mediated immune response

The adaptive immune pathway driven by T lymphocytes, specifically cytotoxic T cells, aimed at identifying and eliminating intracellular threats, virus-infected cells, and cancerous cells.

Helper T cells (CD4+)

Lymphocytes of the adaptive immune system that bind complementary peptide-MHC II complexes on APCs and release cytokines to stimulate clonal expansion of B cells and cytotoxic T cells.

Cytotoxic T cells (CD8+)

Effector T lymphocytes that identify specific non-self peptide antigens displayed on MHC I of abnormal or infected cells, subsequently delivering cytotoxins to induce apoptosis.

Plasma cells

Effector B lymphocytes generated following clonal selection and expansion that synthesise and secrete vast amounts of antigen-specific antibodies into body fluids.

Memory cells

Long-lived, antigen-primed T and B lymphocytes that persist in the body following an initial immune challenge to orchestrate a faster, stronger secondary immune response upon re-exposure.

Natural active immunity

Acquired immunity arising when an individual encounters a pathogen naturally through infection, launching their own immune response and generating immunological memory cells.

Artificial passive immunity

Temporary immunity established by injecting pre-formed, ready-made antibodies into an individual, offering immediate defence without stimulating memory cell production.

Hominoids

A taxonomic superfamily of primates that encompasses modern and ancestral apes and humans, characterised by the absence of a tail, a broad chest, flexible shoulder joints, and relatively long arms.

Hominins

A taxonomic group comprising modern humans and all extinct bipedal ancestor species, defined by anatomical specialisations for habitual bipedalism, an S-shaped spine, and an arched foot.

Putative species

A newly proposed organismal species whose taxonomic status remains provisional and not yet fully ratified by definitive scientific evidence (e.g., Homo luzonensis).

Denisovans

An extinct group of archaic hominins known initially through DNA sequence retrieval from sparse fossil remains, whose genetic variants persist in certain modern indigenous human genomes.

"Denny"

An ancient hominin fossil individual confirmed by nuclear genomic analysis to be the first-generation offspring of a Neanderthal mother and a Denisovan father.

Sahul

The single Pleistocene continent connecting Australia, New Guinea, and Tasmania during low sea levels, settled by modern humans approximately $50{,}000\text{--}65{,}000\text{ years ago}$.

Homo floresiensis

An extinct small-bodied, small-brained hominin species from Indonesia with an adult cranial capacity of approximately $360\,\text{cm}^3$, illustrating an evolutionary exception to the hominin trend toward expanding brain volume.

Biochemical pathway

A linked sequence of intracellular, enzyme-catalysed reactions where the chemical product of one reaction functions directly as the substrate for the next step.

Coenzymes

Non-protein organic helper molecules (such as ATP, NAD, and NADPH) that reversibly bind enzymes to facilitate biochemical reactions by shuttling electrons, hydrogen, or energy.

Rubisco

The primary enzyme in the Calvin cycle that fixes atmospheric $\text{CO}_2$ into organic compounds, but can also competitively fix $\text{O}_2$, precipitating wasteful photorespiration.

Photorespiration

A counterproductive biochemical pathway initiated when Rubisco oxygenates RuBP using $\text{O}_2$ instead of $\text{CO}_2$, reducing overall photosynthetic glucose output in hot, arid conditions.

C4 plants

Plants that bypass photorespiration by spatially segregating initial carbon capture in mesophyll cells via PEP carboxylase from Rubisco-driven Calvin cycle reactions inside bundle sheath cells.

CAM plants

Arid-adapted plants that temporally separate carbon fixation by opening stomata only at night to fix $\text{CO}_2$ into stored malate, which is subsequently released during daylight to run the Calvin cycle.

Glycolysis

The initial, anaerobic stage of cellular respiration in the cytosol that cleaves one glucose molecule into two pyruvate molecules, yielding a net $2\text{ ATP}$ and $2\text{ NADH}$.

Krebs cycle

The second stage of aerobic cellular respiration occurring within the mitochondrial matrix, processing acetyl-CoA derivatives to produce $2\text{ ATP}$, $\text{NADH}$, $\text{FADH}_2$, and $\text{CO}_2$.

Electron transport chain (mitochondrial)

A series of protein complexes embedded in the inner mitochondrial cristae that use electrons from $\text{NADH}$ and $\text{FADH}_2$ alongside terminal oxygen to generate $26\text{ or }28\text{ ATP}$ and water.

Competitive inhibitor

A regulatory or inhibitory molecule with structural similarity to a substrate that directly occupies an enzyme's active site, an effect that can be outcompeted by higher substrate concentrations.

Non-competitive inhibitor

An inhibitor that binds to an allosteric site on an enzyme rather than its active site, inducing a conformational shift that impairs catalytic function regardless of substrate availability.

Anaerobic fermentation

A cytosolic anaerobic pathway that accepts electrons from $\text{NADH}$ to reduce pyruvate (forming lactate in animals or ethanol and $\text{CO}_2$ in yeast), regenerating $\text{NAD}^+$ to sustain glycolysis without yielding extra ATP.

Restriction endonuclease

A bacterial enzyme that cuts double-stranded DNA by hydrolysing phosphodiester bonds at specific palindromic recognition sequences, producing either sticky or blunt ends.

DNA ligase

An enzyme that catalyses the formation of covalent phosphodiester bonds to join adjacent DNA fragments together, sealing nicks in the sugar-phosphate backbone.

Taq polymerase

A heat-resistant DNA polymerase originally isolated from Thermus aquaticus, employed in PCR to synthesize complementary DNA strands at an optimal temperature of $72^\circ\text{C}$.

Polymerase Chain Reaction (PCR)

An in vitro molecular technique used to exponentially amplify specific target DNA fragments through successive cycles of thermal denaturation ($90\text{--}95^\circ\text{C}$), primer annealing ($\sim 55^\circ\text{C}$), and enzymatic extension ($72^\circ\text{C}$).

CRISPR-Cas9

An adaptive bacterial endonuclease defence system that uses guide RNA sequences to direct Cas9 to cleave complementary invading viral DNA adjacent to a PAM sequence, adapted for targeted eukaryotic genome editing.

Gel electrophoresis

A technique that uses an electric current to separate negatively charged DNA fragments across an agarose gel matrix, where smaller fragments migrate faster and farther toward the positive electrode.

Recombinant plasmid

A small circular bacterial DNA molecule engineered by inserting a foreign gene of interest using restriction enzymes and DNA ligase, acting as a vector to transform host bacteria.

Genetically modified organism (GMO)

Any organism whose genetic material has been deliberately modified, inserted, or knocked out using modern recombinant gene technology.

Transgenic organism

A distinct subcategory of genetically modified organism that contains functional, heritable foreign DNA introduced from an entirely different species.