ICAS Science Paper F — Year 8

Full-syllabus recall set for ICAS Science, 17 August. Weighted to Earth and Space (rocks, Moon and eclipses, tides, atmosphere, albedo) plus unfamiliar instruments — the 50% accuracy area worth about four marks. Also covers variables, multi-statement rules, accuracy vs precision, circuits, separation methods, ecology and energy.

Igneous rock — how it forms

Cooled magma or lava

Igneous — slow cooling underground

Large visible crystals (granite)

Igneous — fast cooling at surface

Fine grain, sometimes gas bubbles (basalt, pumice)

Sedimentary rock — how it forms

Sediment compacted and cemented together

Sedimentary — what you see

Visible layers, rounded grains, may contain fossils

Metamorphic rock — how it forms

Existing rock changed by heat and pressure, without melting

Metamorphic — what you see

Bands or stripes of aligned crystals, often folded

Photo shows layers

Sedimentary

Photo shows interlocking crystals, no layers

Igneous

Photo shows squashed stripes or folding

Metamorphic

Sedimentary examples

Sandstone, limestone, shale

Metamorphic examples

Slate (from shale), marble (from limestone), gneiss, schist

Rock cycle — the rule they test

ANY rock type can become ANY other type. No fixed order

Only route back to igneous

Melting and re-cooling

Any rock can become sediment via

Weathering and erosion

Moon phase order

New, waxing crescent, first quarter, waxing gibbous, full, waning gibbous, last quarter, waning crescent

Full moon cycle length

About 29.5 days

Waxing moon in Australia is lit on the

LEFT (opposite of overseas textbook diagrams)

Waning moon in Australia is lit on the

RIGHT

Solar eclipse — geometry

Moon between Sun and Earth. Only at NEW moon

Lunar eclipse — geometry

Earth between Sun and Moon. Only at FULL moon

Why eclipses don't happen monthly

Moon's orbit is tilted ~5°, so the shadow usually misses

Why solar and lunar eclipse can't share a day

They need the Moon at OPPOSITE points in its orbit

Two cycles must line up (comets, meteor showers)

Lowest common multiple of the two periods

Tides per day

Two high and two low in about 24 h 50 min

Gap between successive high tides

About 12 h 25 min

Tide times each day

Shift about 50 minutes LATER

Spring tides (biggest range)

Sun, Earth, Moon in a straight line — at new and full moon

Neap tides (smallest range)

At first and last quarter moon

Atmosphere layers, ground up

Troposphere, stratosphere, mesosphere, thermosphere, exosphere

Temperature pattern going up

Falls, rises, falls, rises

Troposphere

Weather happens here

Stratosphere

Ozone absorbs UV, so temperature RISES

Mesosphere

Meteors burn up here

Thermosphere

Aurora and the ISS

Albedo — high

Pale surfaces: ice, snow, cloud. Reflect sunlight

Albedo — low

Dark surfaces: ocean, soil, forest. Absorb sunlight

Ice melts to open ocean

Albedo drops, more energy absorbed, warming reinforces itself

Tree rings — one ring equals

One year

Tree rings — wide vs narrow

Wide = good growing conditions. Narrow = drought or stress

Tree rings — which way to count

INWARDS from the bark. Bark edge is the most recent year

Ternary plot

Three components that must total 100%

Ternary plot — find the third value

100 minus the other two

Secchi disc

Lowered until it disappears. Measures water clarity / light penetration

Deeper Secchi reading means

Clearer water, light penetrates further (NOT that the lake is deeper)

Unfamiliar instrument in a question

Read the caption twice — that IS the theory you need

Independent variable

The one you deliberately change

Dependent variable

The one you measure

Controlled variables

Everything kept the same

Fair test fails when

A second variable differs between groups, so effects can't be separated

Two variables differ between groups

Confounded — you can't attribute the result to either one

"Which statements are supported?"

Cover the options. Mark each statement T / F / not-stated, THEN look

Statement is reasonable but not in the stimulus

NOT SUPPORTED. Not stated ≠ false, but it's still not the answer

Any option containing one false statement

Dead. Eliminate it whatever else it says

"Increases with" vs "directly proportional"

Proportional means a straight line THROUGH THE ORIGIN. Check the zero value

Extrapolating past the data

Not supported — especially when the trend is levelling off

Data shows X then Y

Supports the ORDER only, never the cause

Accurate

Close to the TRUE value

Precise

Repeats agree closely with EACH OTHER

Tightly grouped but all off by the same amount

Precise, not accurate — instrument fault or fixed method error

Scattered but averaging near the true value

Accurate on average, imprecise

Series circuit

One path. Break it anywhere and everything goes out

Parallel circuit

Multiple paths. Remove one branch and the others still work

Remove a globe from a parallel pair

Total resistance RISES, current falls, series globe dims — but the surviving parallel globe BRIGHTENS

Density column

Density increases downwards

Object resting at a boundary between two liquids

Denser than the one above, less dense than the one below

Separating sand, salt and iron filings

Magnet first (dry), then dissolve, filter out sand, evaporate to recover salt

Filtering separates

Undissolved solid from liquid

Evaporation recovers

The dissolved solid from the solution

Chromatography separates

Dissolved substances by how far they travel

Distillation separates

Liquids by different boiling points

Remove a predator from a food web

Its prey increases, and what the prey eats decreases

Food web question

Follow the chain TWO steps, not one

"The whole ecosystem collapses"

Almost never the supported answer — too extreme

Energy transformation — solar torch

Light → electrical → chemical (battery) → electrical → light and heat

Every energy transformation also produces

Heat. An answer ending in light alone is usually incomplete

Mass vs weight in lower gravity

Mass unchanged. Weight decreases

Photosynthesis needs

Light, water, carbon dioxide. Produces glucose and oxygen

Rate levels off as one factor increases

Something else has become the limiting factor

Reaction rate increases with

Higher temperature, smaller particles (more surface area), higher concentration

Estimating distance to lightning

Count seconds after the flash, divide by 3 for km (sound ≈ 330 m/s)

Conclusion must always

Use the actual data values and units, and stay within the conditions tested