WACE ATAR Biology cheat sheet

Controlled variables are held constant across treatment groups; the independent variable is manipulated by the investigator and the dependent variable is measured as the response.

Validity: a method is valid if it measures the intended quantity and controls confounders; reliability: repeated trials under identical conditions give consistent results.

Accuracy is closeness to the true value (systematic error shifts it); precision is closeness of repeated measurements to each other (random error scatters them).

Random sampling reduces selection bias; a sample size increase reduces the standard error of the mean by a factor of the square root of n.

A null hypothesis states no difference or no association; it is rejected when the probability of the observed data under that assumption is below the chosen significance level (conventionally 0.05).

Correlation between two variables does not establish causation; causation requires a controlled manipulation or a plausible mechanism plus elimination of confounders.

Personal protective equipment, aseptic technique, ethical approval and animal ethics review are required before biological investigations involving microorganisms, tissues or vertebrates.

A line graph suits continuous independent variables; a bar chart suits categorical or discrete categories; error bars represent spread (SD) or uncertainty of the mean (SE).

In a valid conclusion, state the direction of the effect, the magnitude, the statistical support, and the limits of extrapolation beyond the tested range.

Peer review is the mechanism by which scientific claims are checked by independent experts before publication; it filters error but does not guarantee correctness.

A scientific theory is a well-supported explanatory framework that has survived repeated testing, not a guess; a law describes a consistent relationship, often mathematically.

Scientific knowledge is provisional: conclusions are revised when new evidence or improved methods appear, so consensus reflects current best evidence, not final truth.

Collaboration across institutions and nations accelerates discovery; the Human Genome Project and COVID-19 vaccine development both relied on open data sharing.

Funding sources, patents and commercial interests can create conflicts of interest; disclosure and independent replication are the standard safeguards.

Indigenous and local ecological knowledge contributes long-term observational data to land and fire management, and is increasingly incorporated alongside Western scientific methods.

Technologies such as PCR, CRISPR and genome sequencing move from research tools to applied practice only after validation, safety assessment and regulatory approval.

Ethical frameworks (informed consent, privacy of genetic data, equitable access) shape which applications of biological science are permitted or publicly accepted.

Biodiversity has three levels: genetic diversity within populations, species diversity within communities, and ecosystem diversity across landscapes.

Species richness is the count of species present; species evenness describes how similar their abundances are; indices such as Simpson's combine both.

Natural selection requires heritable variation, differential reproductive success and selection pressure from the environment; it acts on phenotypes and changes allele frequencies.

A keystone species has a disproportionately large effect on community structure relative to its abundance; its removal triggers cascading changes.

Trophic levels transfer roughly 10% of energy to the next level; energy flows one way and is lost as heat, while matter cycles through biogeochemical pathways.

Symbiosis includes mutualism (both benefit), commensalism (one benefits, other unaffected) and parasitism (one benefits at the host's expense).

Primary succession begins on substrate lacking soil (bare rock, lava); secondary succession follows disturbance where soil and propagules remain.

Population growth: exponential when resources are unlimited (dN/dt = rN); logistic when density dependence applies (dN/dt = rN(K−N)/K), with carrying capacity K.

Major threats to biodiversity include habitat fragmentation and loss, introduced species, overexploitation, pollution and climate change; small populations also suffer inbreeding depression and loss of genetic variation.

Prokaryotes lack membrane-bound organelles and a nucleus; eukaryotes have a nucleus, mitochondria, and in plants chloroplasts and a cellulose cell wall.

Surface area to volume ratio constrains cell size: as a cell enlarges, volume rises faster than surface area, limiting diffusion, so cells stay small or become compartmentalised.

Mitosis produces two genetically identical diploid cells for growth and repair; meiosis produces four genetically distinct haploid gametes via crossing over and independent assortment.

DNA replication is semi-conservative; transcription makes mRNA from a template strand; translation at ribosomes uses codons read against tRNA anticodons to assemble amino acids.

Monohybrid cross of heterozygotes gives a 3:1 phenotype ratio; dihybrid cross of heterozygotes gives 9:3:3:1 when genes assort independently.

Codominance (both alleles expressed, e.g. AB blood type) differs from incomplete dominance (intermediate phenotype); sex-linked traits show different ratios in males and females.

Mutation, gene flow, genetic drift (including founder and bottleneck effects) and natural selection all change allele frequencies in populations.

Hardy-Weinberg equilibrium requires no mutation, no migration, random mating, large population and no selection; genotype frequencies follow p² + 2pq + q² = 1.

Evidence for evolution includes the fossil record, homologous and vestigial structures, comparative embryology, biogeography and molecular sequence similarity; speciation occurs when gene flow between populations is blocked.