Practice

Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition.

Kingdom, Phylum, Class, Order, Family, Genus, Species.

Animalia, Plantae, Fungi, Protista, Monera (Bacteria).

Homo sapiens (genus capitalised, species lowercase, both italicised).

Two organisms in the same family — family is a narrower group than class, so members are more closely related.

A tool for identifying organisms by answering a series of either-or questions about observable features.

(a) A mushroom, yeast or bread mould. (b) An amoeba, paramecium or algae.

Colour varies with age, sex, season, and lighting, and is often subjective — so different users classify the same organism differently.

Genus: Felis. Species name: catus.

No. A flame releases energy and moves but does not grow (in the biological sense), reproduce, excrete waste, or sense its environment. It fails most of MRS GREN.

Kingdom Protista — single-celled eukaryotes (nucleus present) that cannot photosynthesise fit the protist description best.

No. The standard biological species definition requires that members can interbreed and produce fertile offspring. Looking identical is not enough.

Whales have fur (at least as embryos), produce milk, breathe air through lungs, and give birth to live young — all mammal features. Fish have gills, scales and lay eggs.

(i) Genus must be capitalised: Homo. (ii) Both words must be italicised (or underlined when handwritten).

Viruses reproduce but only inside a host, and they cannot respire, grow, take in nutrition or excrete on their own. They fail most MRS GREN tests, so most biologists classify them as non-living.

Either-or keeps each step unambiguous — there is exactly one correct branch. Three-way splits often overlap and confuse the user.

Example key. Step 1: lives entirely in water? Yes → goldfish. No → step 2. Step 2: has feathers? Yes → sparrow. No → step 3. Step 3: has fur? Yes → wombat. No → frog.

Kingdom Animalia — only animals have feathers (specifically birds).

Officers check: number of legs, wings, antennae, body segmentation, mouthparts, size. Correct identification decides whether the insect is a biosecurity threat (e.g. a fruit fly vs a harmless native), whether the cargo is destroyed or released, and the cost to agriculture.

Accept any correct table where each organism has a unique combination of the three feature values. Example features: "has feathers", "lives in water", "larger than 50 cm".

Science changes its mind when better evidence arrives — this self-correcting property is what makes it reliable over time. Classifications based on DNA reflect true evolutionary relationships more accurately than guesses from appearance.

Before the platypus, "mammal = gives birth to live young" was assumed. The platypus showed that milk production is the better defining feature. It is still a mammal because it has fur, a four-chambered heart, and produces milk; monotremes are a group of egg-laying mammals.

Example key. Step 1: lives entirely in water? Yes → crocodile or clownfish. No → step 2. Step 2 (for aquatic): scales and fins? Yes → clownfish. No → saltwater crocodile. Step 2 (for land): feathers? Yes → emu. No → step 3. Step 3: has a pouch and hops? Yes → red kangaroo. No → step 4. Step 4: has spines? Yes → echidna. No → koala.

No nucleus → Monera (Bacteria). Photosynthesises → specifically a cyanobacterium. Critical features: absence of a nucleus and presence of chlorophyll.

Habitat: where an organism lives. Population: all individuals of one species in an area. Community: all populations living together. Ecosystem: community plus abiotic environment.

Biotic (pond): fish, algae, frogs, insects. Abiotic: water, temperature, light, dissolved oxygen, pH.

A producer makes its own food from sunlight or chemicals. Examples: grass, algae, gum tree.

Decomposers break down dead organic matter and return nutrients to the soil. Examples: fungi, bacteria, earthworms.

Producer: grass. Primary consumer: rabbit. Secondary consumer: fox.

The arrow shows the direction energy flows — from the food to the feeder (prey to predator).

About 10% of the energy at one trophic level is transferred to the next; 90% is lost mostly as heat.

Energy decreases by roughly 90% each link, so after 4 or 5 steps there is not enough to support another level.

Biotic: trees, birds, insects. Abiotic: sunlight, rainfall, temperature, soil type.

Examples: cane toads, rabbits, foxes, European carp, lantana.

Grasshoppers: $500$ kg. Lizards: $50$ kg. Eagles: $5$ kg.

Because only about 10% of energy transfers up each level, the total biomass shrinks by 90% per step. Top predators have very little energy to share.

Birds lose insect food → population drops. Pesticide may also accumulate in birds' bodies through the insects they do eat, causing further harm (bioaccumulation).

Arrows represent energy flow from prey to predator. Reversed arrows would say the predator feeds the prey, which is biologically false and would mislead anyone trying to predict effects of change.

Short droughts stress organisms but do not remove species. A keystone species — one whose role disproportionately affects the web — removes many connections at once, so recovery may be impossible without reintroduction.

They recycle nutrients (carbon, nitrogen, phosphorus) locked in dead matter back into the soil for producers. Without them, dead material would pile up, nutrients would be trapped, and producers would starve.

Accept any web with at least 6 organisms and arrows pointing prey → predator. Example: grass → cricket → magpie → cat; grass → snail → magpie; leaves → possum.

Abiotic: warmer water holds less dissolved oxygen; evaporation increases. Biotic: cold-water fish die or migrate; algae grow faster, possibly causing blooms.

Short term: rabbit population surges. Mid term: grass overgrazed, soil erosion, eagles switch to other prey. Long term: grass dies back, rabbits crash from starvation, whole system destabilised.

90% of energy is lost at each trophic step. Feeding grain to cattle first loses that 90% before it reaches humans, so only a small fraction of the original grain's energy becomes beef.

Fertiliser runoff → algal bloom → algae die and are decomposed → bacteria using the dead algae consume dissolved oxygen → oxygen level in water crashes → fish suffocate. Extra food at the bottom does not help if decomposition strips the oxygen fish need.

IV: presence/absence of introduced fish. DV: native fish population (count per week). Controlled: pond size, water temperature, food added, predators excluded, duration. Use replicate ponds with and without the introduced species; compare native numbers over time.

Each link transfers only about 10% of the energy (producing the pyramid), but toxins like mercury are not broken down — they are stored in body tissue. A predator eats many prey, so it collects all their mercury, multiplying the concentration even as the energy thins.

After 1 year: dead plant and animal matter accumulates, nutrient cycling stops, soil becomes impoverished. After 10 years: producers decline from lack of nutrients, herbivores starve, chains collapse upward. After 100 years: the forest is gone, replaced at best by pioneer species that can tolerate nutrient-poor soil; long term, some decomposition may restart from airborne microbes.

(i) All matter is made of tiny particles. (ii) Particles are in constant motion. (iii) Particles have forces of attraction between them. (iv) Particles have spaces between them. (v) Higher temperature means faster motion.

Solid: particles touching, arranged regularly, vibrating on the spot. Liquid: particles touching, disordered, sliding past. Gas: particles far apart, moving fast and randomly.

(a) Melting. (b) Condensation. (c) Sublimation.

Density is mass per unit volume. Formula: $\rho = m/V$.

$\rho = 120/40 = 3.0$ g/cm$^3$.

Float — it is less dense than water.

Diffusion is the spreading of particles from high to low concentration. Example: the smell of perfume spreading through a room.

Cooling slows the gas particles, reducing collisions with the wall. Outside pressure pushes the balloon inward until the pressures balance.

Expansion joints allow the bridge materials to expand in heat and contract in cold without cracking.

Evaporation.

Gases have large spaces between particles that can be squeezed closer. Liquid particles are already touching, so there is almost no space left to compress.

During melting, the heat energy goes into breaking the forces holding the solid lattice, rearranging particles rather than speeding them up. Speed — and therefore temperature — stays constant.

Dye particles collide randomly with water particles, gradually spreading from the crowded area into less crowded water until evenly distributed.

Heated air particles move faster and spread apart, so hot air has lower density than the cooler air around it. Denser cool air sinks beneath, pushing hot air up.

Atoms do not change size. Heating makes them vibrate more, increasing the average spacing between them, which makes the whole object larger.

Gas particles move fast with large spaces and negligible attractive forces, so they spread to fill any container. Liquid particles still attract each other, so they stay together at the bottom while taking the container's shape.

Volume = $3^3 = 27$ cm$^3$. Density = $216/27 = 8.0$ g/cm$^3$. Close to iron ($7.9$ g/cm$^3$), not aluminium.

Density = $500/625 = 0.8$ g/cm$^3$. Less dense than water, so it floats.

The car's interior heats the trapped air. Particles move faster and hit the bottle walls harder and more often, raising pressure. If the pressure exceeds the bottle's strength, it bursts.

Warming $100$ g of water by $10$°C transfers energy into faster motion. Melting $100$ g of ice transfers energy into breaking all the solid-lattice bonds. Melting requires considerably more energy because bond-breaking is "expensive" — this is why ice is so effective for cooling drinks.

Liquid water particles have weak but flexible bonds. When freezing, water molecules form a hexagonal crystal with more empty space than in the liquid — so ice is less dense. Consequence: lakes freeze from the top down, insulating water below and allowing fish to survive winter.

A sealed pressure cooker traps steam, raising the gas pressure above the water. Higher external pressure makes it harder for water particles to escape as vapour, so water must reach a higher temperature before it boils — around $120$°C. Hotter water cooks food faster.

Hydrogen particles have smaller mass than helium, so at the same temperature they move faster (same kinetic energy, lower mass means higher speed). The hydrogen balloon has lower density than helium and rises faster. (Hydrogen is also flammable — one reason helium is used in practice.)

At depth, high water pressure dissolves more nitrogen from the breathing air into the blood. Surfacing drops the pressure rapidly; dissolved nitrogen comes out of solution as bubbles in blood vessels, blocking flow. Slow ascents allow nitrogen to be exhaled gradually.

Pure: one kind of particle. Mixture: two or more substances not chemically joined. Solution: homogeneous mixture (solute dissolved in solvent). Suspension: heterogeneous mixture with undissolved solid particles.

(a) Heterogeneous — milk under a microscope shows fat droplets. (b) Homogeneous. (c) Heterogeneous. (d) Homogeneous. (e) Heterogeneous.

Filtration: particle size. Distillation: boiling point.

(a) Magnetic separation. (b) Evaporation or crystallisation. (c) Chromatography. (d) Distillation.

Residue is the solid trapped in the filter paper; filtrate is the liquid that passes through.

Total mass $= 15 + 85 = 100$ g. Concentration $= 15/100 \times 100 = 15\%$.

Filtration: tea strainer, coffee filter. Evaporation: drying wet clothes, salt from salt pans.

Heating turns the solvent to vapour; cooling (condenser) turns the vapour back to liquid so it can be collected separately.

Evaporation just removes the solvent (keeps the solid behind). Distillation collects both the solid residue and the pure solvent.

Muesli, salad, fruit cocktail, a bowl of soup with chunks, oil-and-vinegar dressing.

Sugar is dissolved — its particles are separated into individual molecules among the water molecules, small enough to pass through the filter paper along with the water.

At least some pigments must dissolve in the solvent so they can be carried up the paper. Otherwise nothing moves and no separation occurs.

Not safe. Filtration removes undissolved solids but not dissolved chemicals, viruses, or most bacteria. Boiling or chemical treatment is still required.

(i) Add water to dissolve the salt. (ii) Use a magnet to remove iron filings. (iii) Filter to separate sand (residue) from salt solution (filtrate). (iv) Evaporate the filtrate to recover salt.

A pure substance has only one type of particle, so chromatography shows one spot. A mixture contains several pigments, each travelling a different distance — producing several spots.

Ethanol collects first because it has the lower boiling point ($78$°C); it vaporises and condenses before water does.

(i) Filter the mixture — insoluble pill solids stay as residue. (ii) Evaporate the filtrate — water leaves, dissolved sugar and colouring remain as solid. (iii) If pure sugar is needed, further chromatography or recrystallisation could separate the dye from the sugar.

$3.5\%$ of $2.0$ kg $= 0.035 \times 2000 = 70$ g.

Spot each suspect pen and the stain on a single chromatography sheet. Run in a solvent and compare the patterns. A suspect pen matching the stain's distances and colours is a likely source; any pen whose pattern differs can be eliminated.

Crude oil is heated and rises through a tall column. Lighter hydrocarbons with low boiling points rise highest before condensing; heavier ones condense at lower levels. Each fraction is collected where it condenses, separating the mixture by boiling point.

A solar still has a shallow tray of sea water with a sloped transparent cover. Sunlight heats the water, some evaporates, condenses on the cool cover, and runs down into a separate collection channel. The process is evaporation + condensation — the core steps of distillation — powered by solar energy instead of a flame.

(i) Magnet → remove iron filings. (ii) Add water → dissolve salt, leave sand + sawdust. (iii) Sawdust floats; pour off water with sawdust (decantation) and filter sawdust. (iv) Filter remaining mixture to separate sand (residue) from salt water (filtrate). (v) Evaporate filtrate to recover salt.

At low temperature, gas particles slow; nitrogen and oxygen condense at different points ($-196$°C and $-183$°C). Fractional distillation separates them by their different boiling points. At room temperature, both are gases mixed together — no difference in state to exploit.

Blood cells are roughly the same size as plasma particles at filter scales and can clog paper, but they are denser than plasma. Centrifugation spins the sample; denser red and white cells settle to the bottom, plasma stays at the top. It exploits density rather than particle size.

$24$ hours to rotate; about $365.25$ days to orbit the Sun.

Earth rotates on its axis; at any moment half faces the Sun (day) and half faces away (night).

Earth's axis is tilted $23.5°$, so each hemisphere gets more direct sunlight and longer days during its summer.

$23.5°$.

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

About $29.5$ days.

Sun, Moon, Earth in a line (Moon between Sun and Earth). Happens at New Moon.

Sun, Earth, Moon in a line (Earth between Sun and Moon). Happens at Full Moon.

Two high tides (and two low tides) per day.

A tide with a larger than usual range, occurring at New or Full Moon when Sun and Moon are aligned.

The hemisphere tilted towards the Sun sees the Sun rise earlier and set later because more of its latitudes are on the sunlit side of the Earth during rotation.

The ground and oceans take weeks to heat up, so peak temperature lags the peak of sunlight. This is called seasonal lag.

The Moon's orbit is tilted about $5°$ from Earth's orbit around the Sun, so at most New Moons the Moon passes above or below the Earth-Sun line, missing the alignment needed for an eclipse.

(a) Full Moon: Sun - Earth - Moon in a line (Earth between). (b) First quarter: Sun, Earth and Moon form a right angle at Earth.

Earth's atmosphere bends (refracts) red sunlight around into the shadow. Blue light is scattered away, leaving the Moon lit by deep red light — hence "blood Moon".

Tidal bulges require large bodies of water stretched across distances where the Moon's pull differs enough to matter. Lakes are too small for significant differential pull, so their tidal change is millimetres.

With zero tilt: (i) no seasons — each latitude's weather would be roughly the same all year. (ii) Equal day and night everywhere year-round. Agriculture, migration, and biodiversity would all change.

Yes — the Sun's gravity produces solar tides too, roughly half the size of Moon tides. Without a moon, tides would still exist but would be smaller and only driven by the Sun.

New Moon or Full Moon — spring tides occur then, giving the biggest range between high and low.

Martian seasons last about $2\times$ as long as Earth's because a Mars "year" is nearly twice as long. The temperature pattern is similar (tilted-towards hemisphere has summer) but the orbit is more elliptical, so seasons have unequal length in different hemispheres.

(a) As the Moon recedes, tidal friction slows Earth's rotation — days get longer. (b) Weaker pull at greater distance means the tidal bulges shrink, so tides become smaller.

A calendar month is $28$-$31$ days, slightly longer than the $29.5$-day lunar cycle. Occasionally two Full Moons fit in the same month — the second is called a blue Moon. Happens roughly every $2.7$ years.

Every New Moon — about once every $29.5$ days. Because the orbit is tilted, the Moon usually misses the alignment; if the tilt were zero the alignment would happen every lunar cycle.

Stand in a dark room. Hold a small ball (Moon) at arm's length and slowly orbit around a student (Earth) while a torch (Sun) shines from one side. Observer sees different lit portions as the Moon orbits. Limitation: the scale is wrong — in reality the Moon is far smaller and much further away than this model suggests, and the model cannot demonstrate why eclipses are rare.

Igneous, sedimentary, metamorphic.

From the cooling and solidification of molten rock (magma or lava).

Sediment is deposited in layers, compacted and cemented together into rock.

An existing rock is heated and/or pressed without melting, changing its minerals and texture.

Igneous: granite or basalt. Sedimentary: sandstone or limestone. Metamorphic: slate or marble.

Large crystals mean slow cooling (underground); small crystals mean rapid cooling (on the surface).

Sedimentary rock. It forms at low temperatures that do not destroy plant or animal remains, and sediment often buries them before decay is complete.

Sedimentary layers form from sediment settling (bedding). Metamorphic layers form from pressure alignment (foliation).

Coal.

Granite is hard, weather-resistant and takes a polish — durable and attractive for benchtops.

Basalt forms from lava on the surface that cools in days or weeks — crystals have no time to grow large. Granite forms underground where magma cools over thousands of years, allowing large interlocking crystals.

Coal forms from plant material compressed in layers over millions of years — a sedimentary process. It is not formed from molten rock.

Likely contains calcium carbonate. Could be limestone (sedimentary) or marble (metamorphic version of limestone).

The rock cycle is a loop, not a one-way path. Any rock type can transform into any other given the right conditions — including melting sedimentary back to igneous, or weathering igneous to sediment.

The rock was once a marine sedimentary layer. Tectonic forces pushed the layer upwards as plates collided, eventually raising it to mountain heights. The fossil is evidence that the rock formed underwater.

Metamorphism requires high temperature and/or pressure. These conditions exist at depth (buried by kilometres of rock) or near plate boundaries — not at the surface.

Slate. It is a metamorphic rock that splits cleanly along flat planes (foliation), making it ideal for waterproof roofing tiles.

Likely igneous (granite or similar) — visible interlocking crystals with no layering suggest slow cooling underground.

Example: granite weathers → quartz grains → deposited in river → compacted as sandstone (sedimentary) → buried and metamorphosed to quartzite → deeper still, melted to magma → cools as granite again.

$2$ m = $2000$ mm. At $0.5$ mm/year: $2000/0.5 = 4000$ years. The sediment may have been deposited in a stable lake or ocean environment, possibly during a long period of steady erosion upstream.

Zircon is a very hard mineral that can survive multiple trips through the rock cycle. A crystal can be released when its parent rock weathers, then redeposited in a new rock. The crystal's age is measured by radioactive decay and reflects when it first crystallised, not when its current rock formed.

Without plate tectonics: weathering, erosion, deposition and compaction (sedimentary formation) still work because they depend on water, wind and gravity. Metamorphism largely stops — there would be no mountain-building or subduction, so pressure-heating of deep rock is minimal. Igneous activity would also be reduced; most volcanism is plate-boundary related.

Both are carbon. Charcoal is light, crumbly carbon formed at the surface from burnt wood. Diamond forms $150+$ km deep under immense pressure and heat, arranging carbon atoms into a hard, transparent crystal. The rock-cycle context — the depth, pressure and slow growth — turns the same element into vastly different materials.

Fish fossils in the lower layer indicate an aquatic environment (lake or sea) at that time. Desert dune patterns above indicate later dry, windy conditions. The absence of mixing suggests a rapid environmental change. Order: water environment first, then drying, then desert conditions, all preserved in the sequence of layers.

A push or pull, measured in newtons (N).

Contact: friction, normal, tension, applied, air resistance. Non-contact: gravity, magnetic, electrostatic.

The single force that has the same effect as all the individual forces on an object combined.

Mass is how much matter is in an object (kg) — it does not change. Weight is the gravitational force on that mass (N) — it depends on gravity.

$25 - 10 = 15$ N to the right.

$m = W/g = 200/10 = 20$ kg.

A diagram showing every force acting on an object as an arrow from a single point, with correct direction and relative size.

Net force $= 50 - 50 = 0$ N. The rope does not accelerate; it stays at rest (or moves at constant speed if already moving).

It continues at constant speed in a straight line forever (no friction, no other forces).

$W = 60 \times 10 = 600$ N.

Gravity pulls the book down; the table pushes it up with an equal normal force. The two forces cancel, giving zero net force — so the book's motion does not change.

Balanced. Constant velocity in a straight line means zero net force; the driving force equals air resistance + rolling friction.

Forces: gravity (weight) downward, air resistance equal and upward. Net force $= 0$, so the skydiver falls at constant (terminal) speed.

From $F = ma$, for the same acceleration, a larger mass requires a proportionally larger force.

Mass is the amount of matter — unchanged by location. Gravity on the Moon is about $1/6$ of Earth's, so the gravitational force (weight) is $1/6$ — but the amount of matter is identical.

No. Although speed is constant, direction is changing (circular motion). A change in direction means the velocity changes, which requires a net force — gravity, pulling toward Earth.

$F_{\text{net}} = 5000 - 4000 = 1000$ N upward. The rocket accelerates upward.

$a = F/m = 12/3 = 4$ m/s$^2$.

(a) On jumping: gravity much greater than air resistance → large net force down → accelerates down. (b) As speed grows, air resistance grows → net downward force shrinks → acceleration decreases. (c) At terminal velocity: air resistance = weight → net force zero → constant speed.

The post is pulled at an angle between north and east. The pull is stronger toward north (80 N > 60 N), so the direction is closer to north than to east — roughly north-north-east.

$a = \Delta v/\Delta t = 20/10 = 2$ m/s$^2$. $F = ma = 1200 \times 2 = 2400$ N. This force is generated by friction between the drive wheels and the road (the engine spins the wheels; the ground pushes the car forward).

When a lift accelerates upward, the floor must push harder than gravity to both support the person and accelerate them upward — so the normal force is greater than weight, making you feel heavier. Going down: floor pushes less than gravity briefly, so you feel lighter.

Mass: $W/g = 50/10 = 5$ kg, unchanged. On the new planet: $W = 5 \times 30 = 150$ N. The astronaut feels three times heavier — walking, lifting and standing all become very tiring.

By Newton's third law the forces are equal and opposite. By $F = ma$ the skater with less mass ($40$ kg) has greater acceleration and moves faster ($60$ kg skater moves slower). Ratio of speeds: $60:40 = 3:2$.

Lever, inclined plane, wedge, screw, pulley, wheel and axle.

$F_L d_L = F_E d_E$.

Fulcrum: the wheel at the front. Effort: handles (lifted by person). Load: weight of material in tray. Class 2 (load between fulcrum and effort).

The ratio of the load force to the effort force — how many times the machine multiplies your effort.

$\text{MA} = 200/50 = 4$.

$300 \times 0.5 = F_E \times 1.5 \Rightarrow F_E = 150/1.5 = 100$ N.

$100 \times 1 = F_E \times 4 \Rightarrow F_E = 25$ N.

Tweezers, fishing rod, human forearm lifting a weight, a broom.

Direction only.

An inclined plane.

A ramp lets you apply a smaller force over a longer distance. The work done (force × distance) is about the same either way, but the smaller force is achievable by one person.

The lever rule $F_L d_L = F_E d_E$ can be rearranged to $F_E = F_L \times d_L/d_E$. For $F_E < F_L$ (that is, MA > 1), the denominator must be larger, so $d_E > d_L$.

MA = 3 means the effort is $1/3$ of the load. In return, the rope pulled is $3$ times the distance the load moves.

The lever rule requires $F_L d_L = F_E d_E$. If the weights are fixed, a heavier load must sit at a shorter distance from the fulcrum to balance the lighter person at a longer distance.

Friction at the fulcrum, along ramps, and in pulley bearings converts some of the input work to heat. Real MA is always slightly less than ideal MA.

The nail is the load, the hammer's head is the fulcrum, and your hand on the handle applies the effort. The long handle and short claw give a large effort arm : load arm ratio — high MA.

Weights: $60 \times 10 = 600$ N and $40 \times 10 = 400$ N. Let $d$ be distance for the $40$ kg child. $600 \times 2 = 400 \times d \Rightarrow d = 3$ m. But the see-saw is only $4$ m long with the fulcrum in the middle — $2$ m each side. So balance is impossible unless the fulcrum is moved. (Good — forces students to notice infeasibility.)

Ideal: work in = work out. $500 \times 1.2 = 150 \times L \Rightarrow L = 600/150 = 4$ m.

Effort: $600/4 = 150$ N. Rope pulled: $4 \times 2 = 8$ m.

Class 2 lever — the load (nut) is between the fulcrum (hinge) and the effort (hands).

Low gear (small front ring + large rear ring) gives a high MA: your pedal force at the chain is multiplied at the wheel, so climbing a hill needs less effort per pedal stroke, but you pedal more times for each wheel turn. High gear is the reverse: less force multiplication but the wheel turns further per pedal stroke — useful at speed on flat roads.

Yes — balance depends only on torque ratio, not absolute distances. $50 \times 0.2 = 50 \times 0.2$. It still balances.

Ideal effort: $400 \times 1 / 4 = 100$ N. With $20\%$ loss, work in = $400$ J / $0.8 = 500$ J. Actual effort $= 500/4 = 125$ N. Efficiency = $400/500 = 80\%$.

Pulley systems scale well with large MA in a small footprint and are safer than levers for tall buildings. Crane levers require long rigid arms and huge counterweights. Pulleys also allow workers to stand safely away from the load. Trade-offs: pulleys can jam, need strong ropes, and have more friction; cranes lift faster.

Investigable question: one answerable by measurement. Hypothesis: a testable prediction linking cause to effect. IV: what the experimenter changes. DV: what is measured. CV: anything else kept the same.

Example: "If the ramp is raised higher, the car will roll a greater distance after leaving the ramp, because the car starts with more gravitational potential energy converted to kinetic energy."

IV: ramp height. DV: distance rolled. CVs: same car, same surface, same starting point on ramp, same release (no pushing), same ramp material.

To reduce random error and identify anomalies by taking the mean of several readings.

(a) Line graph. (b) Bar graph. (c) Scatter plot.

A data point that does not fit the overall pattern of the results.

A list of possible hazards and how to control them, done before the experiment to keep the experimenter, others, and the environment safe.

Random: parallax when reading a meniscus. Systematic: a measuring cylinder miscalibrated so it reads $1$ mL too high.

A group treated exactly like the experimental groups except for the IV. It shows what happens without the "treatment" for comparison.

Larger samples average out random variation, making results more reliable and any real effect easier to detect.

An observation is what you directly see or measure (the leaf is yellow). An inference is an explanation you infer from the observation (the plant lacks nitrogen).

If several variables change at once, you cannot tell which caused the effect. Controlling variables isolates the IV as the only possible cause.

Writing it first prevents you from unconsciously shaping the design or interpretation to match the data — this is called confirmation bias.

Selecting "best" data misrepresents the experiment. Science requires honest reporting of all data, including outliers and disagreements with the hypothesis.

With more data, random variation cancels out more completely and any real pattern stands out more clearly from chance fluctuations.

Correlation without causation — both rise in summer because hot weather drives both independently. One does not cause the other.

IV: bottle colour (e.g. black, white, blue, red). DV: water temperature after $1$ hour. CVs: same bottle material and volume, same starting water temperature, same position in sun, same weather conditions, same thermometer, same time of day. Replicates: at least $3$ per colour.

Anomaly: $28$. Possible causes: typo for $13$ or $14$; wrong shoot measured (a different species); a genetic variant in that plant; measurement taken at a different date.

Temperature vs time (time on x-axis, temperature on y-axis). Roughly flat at $0$°C while the ice melts, then rising as the water warms. A line graph with a flat region then a rise.

IV: paper-towel brand. DV: mass of water absorbed (g). CVs: same piece size, same water volume, same dipping time, same squeezing. Replicates: $3$ strips per brand.

No. Alternative explanations: (i) students who eat breakfast may also sleep more or live in wealthier homes, and those factors drive both behaviours. (ii) students feeling good study more regularly and eat breakfast more regularly. A controlled experiment (randomly assigning students to eat or skip breakfast, with other conditions matched) would isolate the cause.

$102$ looks anomalous — pure water boils at $100$°C at normal pressure. Mean with it: $(99+101+100+100+102)/5 = 100.4$. Mean without: $(99+101+100+100)/4 = 100.0$. The $100.0$ value is a better estimate if we suspect $102$ was a misreading or a calibration fault.

Without a control, you cannot tell if changes in the plants are due to the fertiliser or to other changes over time (weather, age, light). Some growth would happen anyway. A control group receiving no fertiliser lets you separate the fertiliser's effect from natural growth.

IV: length of pendulum. DV: time for $10$ complete swings (divide by $10$ for period). CVs: same mass, same release angle, same location, same stopwatch. Procedure: tie string of known length, release from small angle, time $10$ swings, repeat $3$ times, calculate mean period. Vary length (e.g. $20, 40, 60, 80, 100$ cm). Graph: period increases with length, as a curve (square-root relationship).