NCEA Level 3 Biology cheat sheet

A valid investigation states a hypothesis that is a testable prediction linking the independent variable to the dependent variable, plus a biological reason for the prediction.

Independent variable = what the investigator deliberately changes; dependent variable = what is measured; control variables = everything else held constant and listed with how each was controlled.

Reliability is increased by repeating measurements and calculating the mean; it is not the same as validity, which concerns whether the method actually measures the intended variable.

Validity improves with a control group, randomised or systematic sampling, and controls that remove confounding variables such as temperature, light intensity, or time of day.

Precision = closeness of repeated measurements to each other (small range); accuracy = closeness to the true value. Use a range or standard deviation to report spread.

Use a suitable statistical test: chi-square for frequencies in categories, t-test for comparing two means, correlation coefficient for relationship between two measured variables.

A conclusion must refer back to the hypothesis and use the data (means, ranges, statistical result) as evidence; it must distinguish correlation from causation.

Ethical and safety considerations relevant to biology include animal welfare approval, informed consent, aseptic technique, disposal of biological material, and avoiding harm to organisms or habitats.

Sources of error are classified as random (affects precision, reduced by repeats) or systematic (shifts all readings, e.g. uncalibrated instrument, not fixed by repeating).

A socio-scientific issue involves biological evidence plus economic, cultural, ethical, legal, or political considerations; a strong response addresses at least two of these dimensions explicitly.

Structure: state the issue and its biological basis, present evidence for and against, evaluate the reliability of each source, then give a justified personal position with trade-offs acknowledged.

Distinguish scientific evidence (peer-reviewed data, statistics) from opinion, anecdote, advocacy, and commercial interest; note who funded a source and whether it has a stake in the outcome.

Biological concepts commonly used: gene expression and mutation, natural selection and resistance, ecosystem services, biodiversity, carrying capacity, and dose-response relationships.

Resistance to antibiotics or pesticides is a standard example: selection pressure favours resistant variants already present in the population; resistance is not caused by the exposure itself.

Economic trade-offs include cost of regulation versus cost of harm, externalities, and who bears the risk versus who gains the benefit; cultural considerations include indigenous knowledge and food sovereignty.

Use risk language precisely: hazard (potential to cause harm) versus risk (probability of harm under defined exposure); mention uncertainty and the precautionary approach.

A justified recommendation links the chosen action to the evidence, states the likely consequences for each stakeholder group, and identifies what further data would change the decision.

Tropisms are directional growth responses: phototropism (light), geotropism/gravitropism (gravity, roots positive, shoots negative), thigmotropism (touch), hydrotropism (water).

Auxin (IAA) is produced in shoot and root tips; it moves by diffusion and polar transport, accumulates on the shaded or lower side, and at high concentration inhibits root elongation but promotes shoot elongation.

Nastic responses are non-directional and reversible, e.g. Mimosa leaf folding (rapid turgor loss) and nyctinasty (day/night leaf movement); they are not growth responses.

Photoperiodism: short-day (long-night) plants flower when the dark period exceeds a critical length; long-day plants flower when dark is shorter; phytochrome red/far-red interconversion detects night length.

Taxes are directional movement of the whole organism (phototaxis, chemotaxis); kineses are non-directional changes in activity rate in response to stimulus intensity.

Orientation behaviours: homing (return to a home site), migration (seasonal long-distance movement), navigation using sun compass, stars, magnetic fields, landmarks, and olfactory cues.

Biological timing: circadian rhythms (~24 h) are endogenous and entrained by environmental cues (zeitgebers) such as light; they persist under constant conditions for a period before free-running drift.

Plant responses to water and temperature include stomatal closure via abscisic acid under drought, heat-shock protein expression, and vernalisation (cold exposure required for flowering in some species).

Animal responses to temperature include behavioural thermoregulation (basking, burrowing, huddling) and physiological responses (vasoconstriction, shivering, torpor, hibernation, aestivation).

Homeostasis is maintenance of internal conditions within tolerable limits despite external change; it usually involves a receptor, a control centre, and an effector linked by negative feedback.

Negative feedback reverses a deviation from the set point; positive feedback amplifies a change and is not used for steady-state regulation (e.g. oxytocin in labour, blood clotting).

Thermoregulation: hypothalamus detects blood temperature; responses include vasodilation/vasoconstriction of skin arterioles, sweating, shivering, piloerection, and metabolic rate change (thyroxine, adrenaline).

Endotherms generate heat metabolically and regulate it; ectotherms rely mainly on behaviour and have variable body temperature; both use behavioural and physiological mechanisms.

Blood glucose: insulin from beta cells of the islets of Langerhans lowers glucose (uptake, glycogenesis, fat synthesis); glucagon from alpha cells raises it (glycogenolysis, gluconeogenesis).

Diabetes mellitus: type 1 is autoimmune destruction of beta cells (no insulin); type 2 is reduced receptor sensitivity/insulin resistance; both cause hyperglycaemia and osmotic diuresis.

Osmoregulation: hypothalamus osmoreceptors trigger ADH release; ADH increases collecting duct water permeability via aquaporins, concentrating urine; aldosterone increases Na+ reabsorption.

Gas and pH homeostasis: chemoreceptors detect CO2/pH; medulla sets breathing rate; carbonic anhydrase converts CO2 and water to carbonic acid, buffering blood pH near 7.4.

Negative feedback is described as a loop: stimulus, receptor, afferent pathway, control centre, efferent pathway, effector, response, and return toward the set point.

Evolution is change in allele frequency in a population over generations; the gene pool is the total set of alleles in a population.

Sources of variation: mutation (ultimate source of new alleles), meiosis (independent assortment, crossing over), and random fertilisation; variation is not created by need.

Natural selection requires heritable variation, differential survival or reproduction, and a selection pressure; allele frequencies change if the trait affects fitness.

Types of selection: directional, stabilising, disruptive; sexual selection acts through mate choice or competition and can produce traits that reduce survival.

Genetic drift is random change in allele frequency, strongest in small populations; bottleneck and founder effects reduce diversity and are non-adaptive.

Speciation requires reproductive isolation. Allopatric: geographic barrier separates populations. Sympatric: isolation without a barrier, e.g. polyploidy, habitat or temporal isolation, behavioural isolation.

Prezygotic barriers include habitat, temporal, behavioural, and mechanical isolation plus gamete incompatibility; postzygotic barriers include hybrid inviability, hybrid sterility, and hybrid breakdown.

Evidence for evolution includes fossil succession, homologous and vestigial structures, biogeography, comparative DNA and protein sequences, and observed change (antibiotic resistance, Darwin's finches).

The biological species concept (interbreeding populations producing fertile offspring) does not apply to asexual organisms or fossils; alternatives include morphological and phylogenetic species concepts.

Hominins are distinguished from other apes by bipedalism; key skeletal indicators are a forward-placed foramen magnum, S-shaped spine, bowl-shaped pelvis, valgus knee, and non-opposable big toe.

Trend of increasing cranial capacity: Australopithecus roughly 400-500 cm3, Homo habilis ~600-700 cm3, Homo erectus ~900-1100 cm3, Homo sapiens ~1300-1400 cm3.

Trend of decreasing prognathism (flatter face), reduced brow ridges, smaller molars and jaw, and a more parabolic dental arcade through the genus Homo.

Trend toward smaller, less robust skeletons and longer limbs relative to trunk in later Homo, associated with endurance locomotion and reduced thermoregulatory stress.

Homo erectus is associated with fire use, Acheulean hand axes, and expansion out of Africa; Homo neanderthalensis had a robust build, large brain, and Mousterian tools.

Cultural evolution (tools, fire, language, art, agriculture) can buffer environmental selection pressure and is transmitted non-genetically, so it is not explained by natural selection alone.

Dating and evidence: radiometric dating (K-Ar, C-14), stratigraphy, and comparative anatomy; C-14 is limited to organic material younger than about 50,000 years.

Molecular evidence places the human-chimpanzee divergence around 6-7 million years ago; mtDNA and Y-chromosome data support an African origin for modern humans.

Interpretation caution: hominin phylogeny is a branching bush, not a ladder; many species coexisted, and new fossil finds revise relationships.

Techniques: PCR amplifies DNA; gel electrophoresis separates fragments by size (negative DNA moves to positive electrode); restriction enzymes cut at specific recognition sequences; DNA ligase joins fragments.

Recombinant DNA requires a vector (often a plasmid), restriction digestion, ligation, transformation into a host cell, and selection using antibiotic resistance or marker genes.

CRISPR-Cas9 uses a guide RNA to target a sequence and Cas9 to cut DNA; repair by non-homologous end joining (knockout) or homology-directed repair (insertion or correction).

Transgenic organisms carry genes from another species, e.g. Bt cotton (pest resistance) and golden rice (beta-carotene pathway); gene editing usually alters existing genes without adding foreign DNA.

Applications: human insulin from bacteria, gene therapy (somatic vs germline; germline edits are heritable), vaccines, and agricultural traits such as drought tolerance.

Risks and issues: off-target edits, mosaicism, gene flow to wild populations, resistance evolution in pests, allergenicity, loss of biodiversity, and unequal access to therapy.

Ethical and regulatory dimensions: informed consent, privacy of genetic data, insurance and employment discrimination, embryo status, animal welfare, labelling of GM food, and the precautionary principle.

Whole organism cloning (somatic cell nuclear transfer) produces genetically identical individuals; it has high failure rates and raises welfare and identity concerns.

Predictive genetic testing detects alleles such as BRCA variants; results are probabilistic, so counselling and interpretation limits matter.