Practice

(i) All living things are made of cells; (ii) the cell is the basic unit of structure and function; (iii) all cells come from pre-existing cells.

(a) Nucleus, (b) mitochondrion, (c) chloroplast.

Cell wall, chloroplasts, large central vacuole.

Controls what enters and leaves the cell; separates the cell from its surroundings.

The jelly-like fluid inside the cell where organelles sit and most chemical reactions happen.

Unicellular: bacterium, yeast, Amoeba. Multicellular: human, tree, mushroom.

No — their DNA floats freely in the cytoplasm.

Eukaryotes (typically 10-100 $\mu$m vs 1-10 $\mu$m for prokaryotes).

Bacteria (e.g. E. coli), archaea.

Animals, plants, fungi (also protists).

Prokaryotes still carry DNA; it is simply not enclosed in a membrane-bound nucleus.

$8$ mm $= 8000$ $\mu$m. $M = 8000 / 40 = \times 200$.

Image $= 60 \times 500 = 30\,000$ $\mu$m $= 30$ mm.

$24$ mm $= 24\,000$ $\mu$m. Real $= 24\,000 / 300 = 80$ $\mu$m.

$0.2$ mm $= 200$ $\mu$m; $4500$ $\mu$m $= 4.5$ mm.

Cell division needs DNA to be copied. Without a nucleus, a red blood cell has no DNA, so it cannot make new cells.

Specialisation lets different cells do different jobs well (e.g. muscle contracts, nerves signal). This is more efficient than every cell trying to do everything.

Without light, chloroplasts cannot photosynthesise. Chlorophyll may break down over time and the leaf may turn pale/yellow.

Cell theory states all living things are made of cells. Bacteria are cells, so they are alive, even though they lack a nucleus. Having a nucleus is not a requirement for life.

Real size $= 30$ mm $/ 1000 = 0.03$ mm $= 30$ $\mu$m.

$1$ mm $= 1000$ $\mu$m. $1000 / 5 = 200$ cells.

Two of: plant cell has a cell wall (rigid, rectangular shape); plant cell has chloroplasts (green); plant cell has a large central vacuole.

All cells come from pre-existing cells (cell theory, point 3). Surgical tools can carry bacterial cells that would reproduce inside a patient and cause infection. Sterilising destroys those cells.

(i) Mitochondria and chloroplasts are about the size of bacteria (prokaryotes). (ii) They have their own circular DNA, like prokaryotes. (iii) They divide by splitting in two, like bacteria.

A fungal cell (has wall, no chloroplasts) or a bacterial cell (has wall, no chloroplasts). Check for a nucleus: fungi are eukaryotic and have one; bacteria do not.

Volume of $1$ cm$^3$ = $10^{12}$ $\mu$m$^3$. Volume per cell $= 20^3 = 8000$ $\mu$m$^3$. Number of cells $\approx 10^{12} / 8000 = 1.25 \times 10^8$, i.e. about 125 million cells.

A unicellular organism must carry out every life process in one cell — limiting its maximum size because surface area must keep up with internal volume. Cells inside a multicellular organism can be supplied by blood and specialise, so they can be larger or have extreme shapes (e.g. long nerve cells).

cell $\to$ tissue $\to$ organ $\to$ organ system $\to$ organism.

(a) Heart; pumps blood to transport oxygen, nutrients and waste. (b) Lungs; take in oxygen and remove carbon dioxide. (c) Kidneys; filter liquid waste out of the blood.

The liver.

The nervous system.

Any two of: mouth, oesophagus, stomach, small intestine, large intestine, liver, pancreas.

Thin walls (short diffusion distance), large surface area (many gas molecules cross at once), rich blood supply (keeps a steep concentration gradient so gases move quickly).

Villi greatly increase surface area for absorbing digested nutrients into the blood.

The diaphragm pulls down to enlarge the chest cavity (drawing air in), and relaxes to push air out.

The heart pumps against pressure all around the body; thick muscular walls generate enough force.

Without a nucleus, there is more room for haemoglobin, so the cell can carry more oxygen.

The digestive system breaks down food in the small intestine, where glucose is absorbed into the blood. The circulatory system then pumps the glucose-rich blood to muscle cells, where it is used for energy.

Two of: build-up of toxic waste in the blood; imbalance of water/salts; high blood pressure; tiredness; changes in urine output.

The brain sends signals through the spinal cord to the legs. If the spinal cord is damaged, those signals cannot reach the leg muscles, so they cannot contract even if the muscles themselves are fine.

Hollow bones are still strong in the directions that matter (long-axis loading), but much lighter. Less mass to move means more efficient movement.

Faster heart rate delivers oxygen and glucose more quickly to muscles. Faster breathing brings more oxygen in and removes CO$_2$. Sweating prevents overheating as muscles release heat.

Circulatory system (platelets clot the blood), immune system (white blood cells attack any bacteria entering the wound), skin/integumentary system (skin seals the wound as it heals).

High blood sugar is detected by the pancreas, which releases insulin. Insulin signals cells (especially liver and muscle) to take glucose out of the blood. Blood sugar falls back toward normal.

Muscles need a continuous supply of oxygen during hard running. If the lungs cannot take in enough oxygen, muscles run out of fuel (energy) even if they are strong, so performance drops.

Flattened villi reduce surface area. Less nutrient absorption happens per length of intestine, so the person may become malnourished even with a normal diet (this is the case in coeliac disease).

In a single loop, blood goes heart $\to$ gills $\to$ body $\to$ heart — losing pressure at the gills. In a double loop, blood returns to the heart to be re-pumped at high pressure to the body, delivering oxygen more rapidly. This supports higher metabolic and activity levels.

In type 1 diabetes the pancreas cannot produce insulin. After a meal, blood sugar rises but cells do not take it up. High blood glucose damages vessels and organs; cells run short of fuel, causing tiredness. The feedback loop has broken at the "effector" step.

Nervous system: pulling a hand from a hot stove (reflex, milliseconds). Endocrine system: growth during puberty (years). Fast responses are needed for threats; slow hormonal changes coordinate long-term processes like growth and digestion.

(a) Element, (b) compound, (c) mixture, (d) element, (e) mixture, (f) compound.

H, O, C, Na, Cl, Fe.

(a) Gold, (b) copper, (c) silver, (d) potassium, (e) iron.

(a) 3, (b) 3, (c) 4.

4.

$2\text{H}_2\text{O}$ has $2 \times 1 = 2$ oxygen atoms.

$\text{Ca(OH)}_2$: 1 Ca, 2 O, 2 H.

$3\text{CO}_2 = 6$ O atoms; $2\text{SO}_3 = 6$ O atoms. Equal.

$\text{H}_2\text{S}$.

There are 3 hydrogen atoms per ammonia molecule.

Water is a compound — hydrogen and oxygen are chemically bonded in a fixed 2:1 ratio with entirely new properties. Sea water is a mixture — salt is simply dissolved in water and can be recovered by evaporating the water.

Both diamond and graphite are made of only carbon atoms (one kind of atom), so they are both the element carbon. They look different because the same atoms are arranged in different patterns.

A mixture — filtering is a physical separation method, which only works when substances are not chemically bonded.

Symbols are case-sensitive. Co = cobalt (one element). CO = carbon monoxide (a compound of carbon and oxygen). The capitalisation tells you whether you are reading one symbol or two.

Na: 1, H: 1, C: 1, O: 3. Total atoms = 6.

An element.

Wood contains carbon, hydrogen and oxygen atoms. Burning rearranges them into carbon dioxide and water vapour, which escape as gas. No atoms are lost — they just move into the air, which is why the wood "seems" to disappear.

Argon is in Group 18 (noble gases), which are very unreactive because their atoms are already stable. So argon reacts very little with other elements.

Each formula unit has 2 X and 3 Y. Four formula units: $4 \times 2 = 8$ X atoms and $4 \times 3 = 12$ Y atoms.

A mixture (of elements). Real example: the air we breathe is mostly N$_2$, O$_2$ and argon.

The core idea of atomic theory is that atoms of an element behave the same way chemically. Isotopes have the same number of protons and so react the same way; they just differ in mass. Atomic theory still holds — it just became more detailed.

Mendeleev's gaps let him predict the properties of elements that had not yet been discovered (such as gallium and germanium). When those elements were later found with matching properties, it was strong evidence that his table was a real pattern in nature, not an arbitrary sorting.

(a) P, (b) C, (c) C, (d) P, (e) C, (f) P.

Colour change, gas produced, precipitate formed, temperature change, light/sound emitted.

(a) Any reasonable physical change, e.g. melting butter, dissolving sugar, cutting vegetables. (b) Any reasonable chemical change, e.g. baking a cake, frying an egg, browning toast.

False — mass is conserved in a sealed container.

Each pigment is still the same substance after mixing; you could in principle separate them again. No new substance has formed, so the change is physical.

Oxygen ($\text{O}_2$).

Carbon dioxide ($\text{CO}_2$).

A lit splint at the mouth of the tube gives a squeaky pop.

Not hydrogen (no pop). Could be nitrogen, which gives no response to any of those tests.

Calcium hydroxide, $\text{Ca(OH)}_2$ — it reacts with CO$_2$ to form calcium carbonate, a white solid that clouds the water.

In a chemical change, atoms are rearranged into new groupings (new molecules), which have new properties. In a physical change the atoms stay in the same molecules — only their arrangement or state changes.

Rusting adds oxygen atoms from the air to the iron atoms, forming iron oxide. Total mass of iron + oxygen before equals mass of rust after. Mass was not lost — the rust is heavier than the iron was.

Endothermic reactions absorb energy from the surroundings, so the reaction mixture feels cold. Whether heat is taken in or given out, a new substance has formed, so it is still a chemical reaction.

Bubble the gas through limewater. If it turns cloudy/milky, the gas is CO$_2$.

Evidence: bright white light given off; new white powder formed (was silvery metal). Word equation: magnesium + oxygen $\to$ magnesium oxide.

Less than 200 g. Carbon dioxide escaped as gas, taking some mass with it.

Chemical change. A precipitate (the yellow solid, lead iodide) has formed — a new substance.

Different gases can sometimes come from similar-looking reactions, and some reactions produce a mixture. Testing confirms which gas you actually have and avoids wrong conclusions.

The extra $6.6$ g came from oxygen atoms in the air that combined with the magnesium to form magnesium oxide. Total mass (Mg + O + crucible) is still conserved; it just was not all on the scales at the start.

The gas does not react with limewater (rules out CO$_2$) but re-lights a glowing splint — so it is oxygen. Example lab preparation: decomposition of hydrogen peroxide using a catalyst (manganese dioxide): hydrogen peroxide $\to$ water + oxygen.

Combustion is a fuel reacting rapidly with oxygen to give out heat and light. It is exothermic because it releases energy. Everyday example: a gas stove burning natural gas.

carbonic acid $\to$ water + carbon dioxide. The CO$_2$ leaves as a gas, so the liquid volume shrinks — it looks like something has "been lost," but in a sealed container the total mass is unchanged.

(a) Renewable, (b) non-renewable, (c) non-renewable, (d) renewable, (e) renewable (managed), (f) non-renewable.

Any two of: coal, oil, natural gas.

Coal: Latrobe Valley (VIC) or Hunter Valley (NSW). Iron ore: Pilbara (WA). Solar: Bungala (SA), Gannawarra (VIC) — any reasonable example.

Carbon dioxide (CO$_2$).

Metals are not regrown like plants; they are extracted once, but they can be melted and used again many times.

Coal: open-cut or underground mining. Iron ore: open-cut mining. Natural gas: drilling (onshore or offshore).

Benefit: large energy output with very low CO$_2$ emissions at the power plant. Risk: radioactive waste lasting thousands of years (or: rare but severe accident risk).

Their output depends on weather (wind speed, sunlight), so production changes through the day and year and cannot be dialled up on demand.

Water held in a high dam flows down through turbines. The moving water spins the turbines, which turn generators to produce electricity.

Any two of: habitat destruction, dust pollution, water pollution, visual impact, disturbed wildlife.

Fossil fuels take hundreds of millions of years to form from buried organic matter. We use them far faster than they are replaced, so on any human timescale the total amount is effectively fixed.

Partly true: nuclear produces almost no CO$_2$ or smoke during power generation. But it does create radioactive waste that stays hazardous for thousands of years, and uranium mining has its own environmental impacts. "Clean" is more complicated than "no smoke".

Replanting keeps the total forest biomass growing, so future timber supply is maintained, and keeps the forest's role in absorbing CO$_2$, protecting soil, and sheltering wildlife.

Coal: high CO$_2$, cheap fuel, very reliable. Solar: zero CO$_2$ at the plant, free fuel, variable (depends on sun).

On paper yes: 7000 kWh produced vs 6500 kWh used. But production is highest in the day and lowest at night, while the family also uses power at night. Storage (battery) or feeding excess into the grid is needed to match supply to demand.

Any two of: river pollution from dust or runoff; habitat loss along the river; noise and vibration; water use for processing; impact on fish and riverside vegetation.

Any three of: What is the cost? What are the lifetime CO$_2$ emissions? How reliable is the power? What jobs does each option provide? What is the visual/noise impact? How do we dispose of waste?

Making new aluminium from bauxite takes large amounts of energy and mining. Recycling cans lets the aluminium re-enter the supply chain using far less energy and no new mining — closing the loop on an otherwise finite resource.

Example policies: (i) subsidies for rooftop solar — cost to taxpayers; (ii) retire coal plants early — risk of blackouts unless storage/gas cover the gap; (iii) mandate renewables in new builds — increases up-front cost of housing. Any reasonable suggestions with a real trade-off accepted.

Pumping water faster than rain recharges lowers the water table permanently, can cause the ground to sink (subsidence), and lets salty water intrude into coastal aquifers. The damage may be impossible to reverse even if rainfall continues.

Manufacturing an electric car creates more emissions than making a petrol car, mainly because of the battery. Ignoring manufacturing makes the EV look better than it really is. A full lifecycle shows EVs are still lower over their lifetime, but the gap is smaller than running-emissions alone suggest.

Uranium is spread through the crust, but extracting it economically only works in rare concentrated ores. Those ores cannot regrow within a human timescale, so they run out, and replacing them with lower-grade sources becomes increasingly costly and energy-intensive.

Crust, mantle, outer core, inner core.

The crust plus the rigid upper part of the mantle.

A few centimetres per year (roughly 2-10 cm/year).

Any two of: Pacific, Eurasian, North American, South American, African, Indo-Australian, Antarctic, Nazca.

Continents (up to $\sim 70$ km); oceanic crust is only $\sim 5$-10 km thick.

Divergent, convergent, transform.

Divergent.

Transform.

A mountain range (e.g. the Himalayas).

Subduction is when one plate (usually a denser oceanic plate) dives beneath another plate into the mantle at a convergent boundary.

At boundaries the plates either push into, pull away from, or slide past each other. All three movements generate stress in the rocks or let magma reach the surface, causing earthquakes and/or volcanic eruptions. Mid-plate regions are relatively stable.

Australia is near the middle of the Indo-Australian Plate, far from the grinding boundaries. New Zealand sits directly on the boundary between the Pacific and Indo-Australian plates, so it gets frequent earthquakes and volcanic activity.

A hotspot is a fixed column of hot mantle that pokes through the moving plate above. As the plate drifts, the hotspot punches new volcanoes through it in a line, leaving older volcanoes behind as a chain.

New seafloor forms at the Mid-Atlantic Ridge (a divergent boundary). As new crust forms and spreads, the ocean floor either side gets pushed apart, widening the Atlantic by $\sim 2$ cm/year.

$10$ cm/year $\times 10^6$ years $= 10^7$ cm $= 10^5$ m $= 100$ km.

Frequent earthquakes (plate grinding), tsunamis (seafloor earthquakes displace water), and explosive volcanoes (magma rising from the subducting plate).

Active volcanoes, hot springs, geysers, frequent small earthquakes, and new land forming as lava cools.

The species could not cross today's Atlantic Ocean, so the two continents must have been joined 200 million years ago and have since drifted apart — direct evidence of continental drift.

In the 1950s and 60s, mapping of the ocean floor revealed mid-ocean ridges, and palaeomagnetic stripes showed symmetric patterns of reversed/normal magnetism on either side of the ridges. This new evidence only made sense if the seafloor was forming and spreading. Science progresses when decisive new data arrive — theories are revised or accepted when the evidence is strong enough, not just because the idea is old.

Transform boundaries involve plates sliding past each other close to the surface, so fault movement (and the earthquakes it causes) occurs at shallow depth. Convergent boundaries involve one plate diving deep into the mantle, so earthquakes along the subducting slab can be hundreds of km deep.

The oceanic Nazca Plate subducts beneath the South American Plate. As the plate dives, water and minerals in it release, melting the mantle above. Magma rises and breaks through the crust well inland from the trench, forming the volcanoes of the Andes.

The Pacific Plate will continue moving northwest, carrying the Big Island away from the hotspot. The Big Island's volcanoes will go extinct and erosion will shrink it, while a new volcano rising over the hotspot (Loihi, already building south-east) will eventually breach the surface as a new island.

(a) Chemical, (b) elastic potential, (c) kinetic, (d) gravitational potential, (e) nuclear.

(a) Kinetic, (b) potential (elastic), (c) potential (gravitational), (d) kinetic.

Any four of: electrical, chemical, thermal, light, sound, kinetic.

Radiant (light / electromagnetic) energy.

Sound: a speaker. Light: a lamp. Chemical: food or a battery.

(a) Conduction, (b) convection, (c) radiation.

Radiation.

Plastic is a poor conductor (insulator), so the handle stays cool enough to hold while the metal stays hot in the food.

The water at the bottom heats first, expands and becomes less dense, so it rises. Cooler water sinks to the bottom to take its place. This cycle repeats, creating a convection current that spreads heat through the pot.

Black — it absorbs more radiant energy (while white reflects more).

Chemical (battery) $\to$ electrical $\to$ light + heat.

Chemical (petrol) $\to$ heat (combustion) $\to$ kinetic (moving pistons/wheels) + sound + heat.

Torch: waste heat (bulb warms). Car: waste heat in engine and exhaust, plus sound.

Energy cannot be created or destroyed, only transferred or transformed from one form to another.

Friction (at the pivot) and air resistance continuously transform kinetic energy into heat. The swing's motion decreases until it stops.

$\eta = 4/10 \times 100\% = 40\%$.

$\eta = 950/1000 \times 100\% = 95\%$.

Useful energy $= 25\% \times 2000 = 500$ J.

Into waste heat (mostly), sound, and vibration.

Lost energy $= 600 - 540 = 60$ J. It became heat (friction between wheels and ramp, and air resistance) and a small amount of sound.

Chemical (in muscles from food) $\to$ kinetic (running) $\to$ elastic potential (bending pole) $\to$ gravitational potential (height) $\to$ kinetic (falling back down).

$\eta = 400/2000 \times 100\% = 20\%$.

Double glazing traps a layer of air between two panes of glass. Air is a poor conductor, so less heat escapes in winter (or enters in summer). Lower heat loss means heaters and coolers run less, saving energy.

Real pendulums constantly transfer kinetic energy into heat (friction at the pivot, air resistance) and eventually stop. To run forever they would need a new energy source — which violates conservation of energy because no net energy can appear from nothing.

The $200\,000$ J becomes heat in the brake discs and tyres (they get very hot) and a small amount of sound (screeching). Energy has not disappeared — it has spread out as thermal energy.

Useful energy retained $= 280$ kJ out of $300$ kJ, so the insulation kept $\sim 93\%$ of the thermal energy over 10 hours. The remaining $\sim 7\%$ (20 kJ) leaked out via conduction through the walls and radiation from the surface.

Useful electrical $= 35\% \times 1000 = 350$ MJ. The remaining $650$ MJ is lost mostly as waste heat at the boiler and turbine (typically carried away by cooling water or cooling towers), with smaller losses in the generator and transmission.

(a) $0.8$ kW, (b) $2400$ W, (c) $1.5$ kW.

$0.1 \times 10 = 1$ kWh.

$2 \times 3 = 6$ kWh.

$0.05 \times 8 = 0.4$ kWh.

$1.5 \times 2 \times 0.30 = 0.90$ dollars.

$10\,859 - 10\,234 = 625$ kWh.

$720 \times 0.28 = 201.60$ dollars.

$91 \times 1.10 = 100.10$ dollars.

$440 \times 1.10 = 484.00$ dollars.

Any three of: meter readings (start and end), kWh used, tariff/price per kWh, supply charge, total cost, GST, billing period.

A: $400 \times 0.30 = 120$ dollars/yr. B: $500 \times 0.30 = 150$ dollars/yr.

The 4-star fridge — more stars means more efficient, so less energy per year.

Watts only tell you power; "kWh per year" builds in how much and how often the appliance actually runs, which is what you actually pay for.

Difference $= 300$ kWh/yr. Annual saving $= 300 \times 0.30 = 90$ dollars. Over $5$ years, total saving $= 450$ dollars.

Replace or reduce use of the heater. It draws $\sim 33\times$ more power than the LED and probably runs for hours each winter night, so it dominates the bill. LED lights are already low power.

Many appliances use several watts continuously, 24 hours a day. Across a whole home, standby can add up to 50-100 kWh/year — not huge individually, but meaningful and easy to cut.

Estimate the annual energy saved (lower heating/cooling kWh), multiply by the electricity tariff, then compare to the insulation cost. Payback time = cost / annual saving. If less than the life of the house, it is worthwhile.

Heating a large amount of water from cold to $\sim 60$°C takes a lot of energy, and hot water is used every day year-round. Compared with a fridge (small steady draw) or lighting, hot water typically dominates.

$0.2$ kW $\times 12$ h $= 2.4$ kWh/night. $\times 200 = 480$ kWh/yr. Cost $= 480 \times 0.30 = 144$ dollars/yr.

$3.5 \times 5 \times 60 = 1050$ kWh. Cost $= 1050 \times 0.30 = 315$ dollars.

$5000 \times 0.30 = 1500$ dollars avoided in year 1 (if all solar output replaces grid energy).

Winter is higher because of heating (and often hot water usage). Two effective actions: improve insulation/draughtproofing; replace old resistive heaters with a reverse-cycle heat pump, or add solar panels to offset grid use.

Daily energy $= 3.6 \times 3 = 10.8$ kWh. Annual $= 10.8 \times 365 = 3942$ kWh. Cost $\approx 1183$ dollars/yr. Cheaper alternative: a heat-pump hot water system (roughly $3\times$ more efficient) or solar hot water — could cut the bill by $60$-$80\%$.

Any three of: better insulation; smaller or more efficient appliances; fewer people or hours at home; use of renewable energy (solar); lower thermostat settings; more natural light; turning off standby.

Total annual saving $= (400 + 1800) \times 0.30 = 660$ dollars/yr. Payback $= 6000 / 660 \approx 9.1$ years.

An audit targets the biggest energy users and waste. Replacing or switching them off cuts kWh, which lowers bills directly and, because grid electricity in Australia still includes a large share of fossil fuels, also cuts CO$_2$ emitted at power stations. If done across many homes, the total emission reduction is significant.

(a) Ampere (A), (b) volt (V), (c) ohm ($\Omega$).

(a) Ammeter, (b) voltmeter.

Ammeter: in series (in line with the component, so current flows through it). Voltmeter: in parallel (across the component).

A cell is one unit; a battery is two or more cells joined together.

Any two of: bulb (light + heat), resistor (heat), motor (movement), buzzer/speaker (sound), heater element (heat).

$I = 12/3 = 4$ A.

$V = 0.5 \times 20 = 10$ V.

$R = 9/0.3 = 30$ $\Omega$.

$R = 240/10 = 24$ $\Omega$.

$R = 1.5/0.1 = 15$ $\Omega$.

$9/3 = 3$ V across each.

$12$ V across each branch.

The circuit is broken; all other bulbs go out.

The others keep working (each branch is still complete).

Appliances need the same full voltage, and if one device turns off or breaks, others must keep working.

High resistance means almost no current flows through the voltmeter itself, so it measures the voltage across the component without changing the circuit.

Ammeters have near-zero resistance. Connecting directly across a battery gives a huge current (short circuit) that can overheat wires and damage the ammeter.

In series, each bulb only gets a share of the voltage, so less current flows through both bulbs and each is dimmer. In parallel each bulb still sees the full voltage, so it glows at full brightness.

A simple loop: cell (positive terminal) $\to$ switch $\to$ ammeter $\to$ bulb $\to$ back to negative terminal. All components in a single series loop.

$R = V/I = 5/2 = 2.5$ $\Omega$.

$R = 240/0.25 = 960$ $\Omega$. Power $P = VI = 240 \times 0.25 = 60$ W.

(a) Each bulb: $I = 12/4 = 3$ A. (b) Total: $3 + 3 = 6$ A.

The Christmas lights are on their own circuit; the smoke alarm is on a different parallel branch (usually battery-powered). A fault in one parallel branch does not affect another.

(a) $R_{\text{total}} = 2 + 3 + 4 = 9$ $\Omega$. (b) $I = 9/9 = 1$ A. (c) $V_4 = IR = 1 \times 4 = 4$ V.

$R = 12/5 = 2.4$ $\Omega$ per headlight. In parallel, each still draws $5$ A, so total current $= 10$ A.

A short circuit has near-zero resistance. By $I = V/R$, a tiny resistance gives a huge current. The wire then heats rapidly ($P = VI$ is large), can melt insulation, and start a fire.

Put bulbs 1 and 2 in parallel with each other, controlled together by a first switch. Put bulb 3 on its own branch (also parallel to the rest) controlled by a second switch. Because every branch is in parallel with the battery, each branch operates independently at full voltage.

Scientific knowledge changes when new evidence appears, better instruments allow new observations, or improved ideas explain data better. Theories are revised or replaced as understanding grows.

Any valid example, e.g. continental drift $\to$ plate tectonics; geocentric $\to$ heliocentric model; phlogiston $\to$ oxygen theory of combustion; stress $\to$ bacterial cause of ulcers.

Research that draws on several different fields of expertise to answer a question no single field could answer alone.

Any three of: physics, chemistry, biology, geology, mathematics/statistics, computer science.

Cultural burning / fire management practices are now used alongside modern bushfire science to reduce fuel loads and protect biodiversity.

An issue where science informs a decision but other factors (ethical, economic, social, environmental) also matter. Examples: climate policy, vaccine mandates, GM crops, nuclear power.

Example (nuclear power): ethical — waste for future generations; environmental — low CO$_2$ but radioactive waste; social — public trust, local community impact; economic — high up-front cost but low fuel cost.

Different groups weigh risks, costs, and ethical values differently; they may also have different access to information or different things to lose. The science can be the same but the decision still varies.

Any valid example, e.g. banning leaded petrol (after research showed lead harm), restricting CFCs (after ozone-layer research), tobacco regulation, asbestos bans.

Any three of: How many dentists were surveyed? Were they paid or sponsored by the company? What exactly did they recommend — this brand, or "any fluoride toothpaste"? Was the claim peer-reviewed? Is the study repeatable?

Advantage: reaches large audiences quickly; lets scientists communicate directly. Risk: misinformation spreads as fast as accurate information; algorithms favour emotional content over evidence.

Honestly: acknowledges that measurements and models always have uncertainty, and new evidence can refine conclusions. Dishonestly: used to pretend weak evidence exists on both sides to delay action (e.g. tobacco, climate change).

In favour (science): at low concentrations fluoride reduces tooth decay across a population. Against (ethics): mass medication removes individual consent — people cannot easily opt out of the water supply.

Virologists/microbiologists, immunologists, chemists (formulating the vaccine), statisticians (trial design), medical doctors (clinical trials), manufacturing engineers, public health officials, ethicists. Any four.

Benefit: cheap large-scale electricity, local employment. Cost: CO$_2$ and particulate emissions, mining impacts. Third factor: social/ethical — climate impact on future generations, or job security for the workforce if the plant is closed.

Individual: only use antibiotics as prescribed; finish the course; avoid demanding antibiotics for viral illnesses. Policy: restrict routine antibiotic use in livestock; fund new antibiotic development; national surveillance of resistant strains.

The noble gases slotted neatly into a new column (Group 18) that had not been known before, without requiring changes elsewhere. A good classification should be able to absorb new data — the fact that it did was evidence the table reflected a real underlying pattern.

Marshall and Warren were initially dismissed because their claim contradicted the consensus. But they gathered strong evidence (including Marshall deliberately infecting himself) and eventually won the argument on evidence alone. Science needs room for challenging the majority view — provided the evidence is tested rigorously. Consensus should not be protected from new data.

Both tobacco and climate-change responses show a pattern: industries funded research designed to emphasise uncertainty, attacked inconvenient studies, and lobbied policy-makers to delay regulation. In both cases, the overwhelming scientific evidence eventually led to public-health and environmental policy, but decades of delay caused real harm.

Science is decided by the weight of evidence, not public opinion. The theory of evolution is supported by genetics, fossils, comparative anatomy, and direct observation of evolution in microbes. Polling shows cultural beliefs, not scientific soundness. Scientists should communicate better, but not adjust their confidence to public mood.

Answers will vary; a complete answer should (a) summarise the key evidence, (b) describe at least two competing stakeholders (e.g. fossil-fuel industry vs climate-impacted communities), (c) take a clear position with reasons, and (d) specify the evidence that would change the writer's mind — the last point is the most important test of scientific thinking.