# Science 9 reference sheet

## Inquiry and evidence
- Separate observation, inference, model, claim, evidence, uncertainty, implication, and source context.
- Multiple hypotheses should make predictions that evidence can distinguish.
- Graphs can support interpolation within a measured range; extrapolation requires stronger caution.

## Cell reproduction
- Cell theory: new cells arise from pre-existing cells.
- Mitosis preserves chromosome number in daughter cells after DNA replication.
- Meiosis: one DNA replication followed by two divisions; diploid → haploid gametes.
- Human model: 23+23rightarrow46 chromosomes at fertilization.
- Mitotic index: MI=fractextcells in mitosistextcells counted.

## Atoms and compounds
- Atomic number: Z=#p; mass number: A=#p+#n.
- Ion charge: q=#p-#e.
- Periodic-table position and valence-electron patterns help predict chemical behaviour.
- Ionic formulas must be electrically neutral, e.g. mathrmMg^2++2mathrmCl^-rightarrowmathrmMgCl_2.
- Covalent compounds share electrons; molecular formulas preserve atom counts, e.g. mathrmCO_2.

## Electricity
- Current: I=fracDelta QDelta t.
- Ohm’s law: V=IR, I=fracVR, R=fracVI.
- Series = one main path; parallel = multiple branches.
- Never use mains electricity for course investigations.

## Earth systems
- Solar radiation drives most biological productivity, winds, ocean circulation, and evaporation.
- Matter cycles; energy flows and is degraded in usable form through transfers.
- Track reservoirs, fluxes, sources, sinks, feedbacks, and time scales.
- Bioaccumulation occurs within organisms; biomagnification compares concentrations across trophic levels.
- First Peoples knowledge must retain Nation/community, place, source, and protocol context.
