SACE Stage 2 Biology cheat sheet

DNA replication is semi-conservative: each daughter molecule keeps one parental strand and one newly synthesised strand, following complementary base pairing (A-T, G-C).

Transcription copies a gene's DNA template into mRNA in the nucleus; translation at the ribosome reads mRNA codons three bases at a time, each codon specifying one amino acid.

Enzyme activity rises with temperature to an optimum then falls sharply as denaturation destroys the active site; pH shifts produce similar denaturation curves.

Cellular respiration: glycolysis in cytosol yields 2 ATP and 2 pyruvate per glucose; aerobic stages in mitochondria yield far more ATP than anaerobic fermentation.

Photosynthesis light-dependent reactions split water, release O2 and produce ATP and NADPH; the Calvin cycle fixes CO2 using those products to build carbohydrate.

Homeostasis uses negative feedback: a receptor detects deviation, a control centre compares to a set point, and an effector counteracts the change, restoring the variable toward the set point.

Natural selection requires heritable variation, differential reproductive success and change across generations in allele frequencies within a population.

Mendelian ratios follow from segregation of alleles and independent assortment of unlinked genes; test crosses reveal unknown genotypes by offspring ratios.

Cell signalling and transport depend on membrane structure: the fluid mosaic model with phospholipid bilayer, channel and carrier proteins, and selective permeability.

Scientific knowledge is provisional: claims are accepted to the degree the evidence supports them and can be revised when new reproducible evidence conflicts with them.

Peer review before publication checks methods, analysis and interpretation; it filters weak claims but does not guarantee correctness.

A hypothesis must be falsifiable - there must exist an observation that would count as evidence against it.

Correlation between variables does not establish causation; confounding variables and reverse causation must be excluded by design or controls.

Ethical review boards assess human and animal research on informed consent, minimisation of harm, welfare and benefit before approval.

Funding sources, publication bias and replication failures are recognised influences on which scientific claims reach public attention.

Models and simulations are approximations: their predictions are only as reliable as the assumptions built into them.

Scientific consensus emerges from convergence of independent lines of evidence, not from the authority of any single researcher.

Communication of science to policy and public audiences involves uncertainty, risk framing and the difference between hazard and exposure.

Independent variable is deliberately changed; dependent variable is measured; controlled variables are held constant to prevent confounding.

A controlled experiment includes a control group receiving no treatment or a placebo so the effect of the treatment can be isolated.

Validity concerns whether the investigation measures what it claims; reliability concerns whether repeated measurements give consistent results.

Accuracy is closeness to the true value; precision is closeness of repeated measurements to each other; random error affects precision, systematic error affects accuracy.

Repeat trials and adequate sample size reduce the influence of random variation; averaging reduces random error but not systematic error.

Uncertainty of a mean is commonly reported as standard deviation or standard error; overlapping error bars suggest differences may not be meaningful.

A line graph suits continuous independent variables; a column graph suits categorical variables; axes require labels, units and consistent scale.

Conclusions must be limited to the range of conditions tested; extrapolation beyond the data range is unsupported.

Risk assessment identifies hazards, rates likelihood and severity, and states specific controls before practical work begins.

Use aseptic technique: sterilise loops and spreaders, flame the vessel mouth, work near a flame, and dispose of cultures by autoclaving.

Microscope magnification = eyepiece magnification × objective magnification; field of view diameter is inversely proportional to total magnification.

When preparing a wet mount, lower the coverslip at an angle to avoid air bubbles, and focus on low power before switching to higher objectives.

Benedict's test for reducing sugars gives a brick-red precipitate on heating; iodine detects starch as blue-black; Biuret detects protein as purple.

Colorimeters quantify colour change: zero with a blank, select the wavelength of maximum absorbance, and convert absorbance to concentration with a standard curve.

Serial dilutions multiply dilution factors; a 10^-4 dilution means 1 part sample in 10 000 parts total, and concentration is multiplied by that factor back.

Potometers measure transpiration rate as distance moved per unit time; control temperature, humidity, light and airflow between trials.

Enzyme practicals control substrate concentration, pH and temperature; measure initial rate over the linear early phase before substrate depletion flattens the curve.

Record raw data in tables with units and repeat measurements; calculate means and graph processed data rather than substituting calculated values for raw observations.