IS2 - Water systems and quality

QUESTION 1 8 marks Criterion A

Medium

Scientific understanding: Water cycle, states and thermal processes

A solar still produces freshwater from salty water. Use integrated scientific understanding to explain the situation.

a. Give a scientifically accurate explanation of the central claim.

[4]

b. Show the relationship that could be used to quantify the claim.

[2]

c. Relate the explanation to another science discipline.

[2]

Show complete worked solution

(a)

Solar radiation heats water, evaporation separates it from non-volatile solutes, and condensation releases thermal energy to form liquid freshwater.

A transparent cover allows radiation in and provides a cooler surface for condensation.

(b)

\[Q=mc\Delta T\]

(c)

Physics describes heating, chemistry explains separation, and biology establishes the need for safe water.

QUESTION 2 11 marks Criterion B

Hard

Inquiry design: Water cycle, states and thermal processes

Determine how absorber color affects the rate of water collection in identical solar stills.

a. Identify the independent and dependent variables and state a scientific hypothesis.

[3]

b. Describe the sampling or experimental procedure.

[4]

c. Explain how repetition and processing improve the evidence.

[2]

d. State the controls and one risk-control measure.

[2]

Show complete worked solution

(a)

Independent variable: absorber color.

Dependent variable: mass of distilled water collected per hour.

Hypothesis: Collected mass rises almost linearly after the first hour.

(b)

Compare every named condition of absorber color with a matched baseline or control, using randomized or alternated trial order where possible. Measure mass of distilled water collected per hour with a calibrated method at fixed intervals or a defined endpoint. Repeat every condition at least three times.

(c)

Calculate a mean for each condition, show variation with a range or another suitable spread measure, and plot the dependent variable against the independent variable with units.

(d)

Keep constant salt concentration, water depth, cover angle, exposed area and solar irradiance.

Prevent tasting laboratory water and protect skin during prolonged outdoor work.

QUESTION 3 9 marks Criterion C

Medium

Evidence analysis: Water cycle, states and thermal processes

The graph shows results from a focused investigation of water cycle, states and thermal processes.

a. Calculate the mean collection rate from 1 h to 4 h.

[3]

b. Describe the overall relationship and explain its scientific meaning.

[3]

c. Evaluate one limitation and state a targeted improvement.

[3]

Show complete worked solution

(a)

\[r=\frac{92-18}{4-1}=\boxed{24.7\ \mathrm{g\,h^{-1}}}\]

(b)

Collected mass rises almost linearly after the first hour.

(c)

Changing sunlight and wind can alter the rate, so simultaneous replicates are needed.

Increase replication and resolution around important changes, check calibration, and measure the named confounding variables.

QUESTION 4 8 marks Criterion D

Medium

Science in context: Water cycle, states and thermal processes

A camp proposes solar stills as its only dry-season drinking-water source.

a. Compare the scientific advantages and disadvantages of the proposal.

[4]

b. State the further evidence needed for a defensible decision.

[2]

c. Give a reasoned conclusion that acknowledges uncertainty.

[2]

Show complete worked solution

(a)

They require no fuel and remove dissolved salts.

However, the output per area is low, weather-dependent and may not remove volatile contaminants.

(b)

Measure daily safe-water yield through the dry season, test water quality and compare demand, storage and alternative treatment.

(c)

The proposal is conditionally supportable if monitoring confirms the expected benefit and agreed thresholds control the risks. The conclusion is provisional because performance and impacts vary with place and time.

QUESTION 1 8 marks Criterion A

Hard

Scientific understanding: Solutions, concentration, pH and salinity

A freshwater fish farm experiences a rise in salinity. Use integrated scientific understanding to explain the situation.

a. Explain the central scientific process or relationship in this context.

[3]

b. Explain the observed or expected outcome.

[3]

c. Explain why an integrated-sciences explanation is stronger than a single-discipline description.

[2]

Show complete worked solution

(a)

Concentration describes solute amount per solution volume. Osmosis moves water across partially permeable membranes from higher to lower water potential.

(b)

A sudden external salinity change disrupts water and ion balance in fish cells.

(c)

Chemistry quantifies salinity while biology explains osmoregulation and organism response.

QUESTION 2 11 marks Criterion B

Hard

Inquiry design: Solutions, concentration, pH and salinity

Test how salt concentration affects mass change in equal potato cylinders as a model of osmosis.

a. State a directional hypothesis and the scientific reason for it.

[3]

b. Design a fair method, including a suitable range and measurement plan.

[5]

c. Explain how reliability, presentation and safety will be addressed.

[3]

Show complete worked solution

(a)

Hypothesis: Mass gain decreases as salinity rises and becomes a mass loss above the isotonic concentration.

The prediction follows from this scientific principle: Concentration describes solute amount per solution volume. Osmosis moves water across partially permeable membranes from higher to lower water potential.

(b)

Test at least five scientifically justified values of sodium chloride concentration across a safe range, including a baseline or control where possible. Measure percentage change in potato mass with a calibrated method at fixed intervals or a defined endpoint. Repeat every condition at least three times.

Keep constant cylinder size and source, solution volume, time and temperature.

(c)

Calculate a mean for each condition, show variation with a range or another suitable spread measure, and plot the dependent variable against the independent variable with units.

Use clean equipment, wipe spills and do not consume laboratory samples.

QUESTION 3 10 marks Criterion C

Hard

Evidence analysis: Solutions, concentration, pH and salinity

The graph shows results from a focused investigation of solutions, concentration, ph and salinity.

a. Estimate the isotonic concentration by linear interpolation between 10 and 15 g dm?³.

[3]

b. Compare the early and later parts of the dataset and interpret the change.

[3]

c. Explain how one feature of the method limits validity.

[2]

d. Specify one additional measurement or design change that would test the interpretation.

[2]

Show complete worked solution

(a)

\[c=10+\frac{1}{1+5}(5)=\boxed{10.8\ \mathrm{g\,dm^{-3}}}\]

(b)

Mass gain decreases as salinity rises and becomes a mass loss above the isotonic concentration.

(c)

Potato tissue is not a fish gill, so the model does not include active ion regulation.

(d)

Increase replication and resolution around important changes, check calibration, and measure the named confounding variables.

QUESTION 4 8 marks Criterion D

Hard

Science in context: Solutions, concentration, pH and salinity

Managers can dilute the pond rapidly or move fish gradually to lower-salinity tanks.

a. State the strongest scientific argument supporting the action.

[2]

b. State the strongest scientific argument for caution.

[2]

c. Construct a balanced decision rule rather than an unconditional answer.

[4]

Show complete worked solution

(a)

Gradual transfer allows physiological adjustment and reduces osmotic shock.

(b)

Delay leaves fish exposed to unsuitable water and moving them causes handling stress.

(c)

Set measurable performance and safety thresholds before implementation. Use species tolerance ranges, rate-of-change trials, dissolved oxygen, mortality and recovery data. Adopt the action in stages, monitor outcomes, and pause or revise it if thresholds are not met.

QUESTION 1 8 marks Criterion A

Medium

Scientific understanding: Aquatic ecosystems and eutrophication

Fertilizer runoff enters a shallow lake. Use integrated scientific understanding to explain the situation.

a. Give a scientifically accurate explanation of the central claim.

[4]

b. Show the relationship that could be used to quantify the claim.

[2]

c. Relate the explanation to another science discipline.

[2]

Show complete worked solution

(a)

Nitrate and phosphate can increase algal growth. Decomposition of dead biomass raises microbial respiration and lowers dissolved oxygen.

Low oxygen can kill fish even though algal photosynthesis produced oxygen during daylight.

(b)

\[\mathrm{glucose+oxygen\rightarrow carbon\ dioxide+water+energy}\]

(c)

Chemistry measures nutrients and oxygen, while biology explains population change and food-web effects.

QUESTION 2 11 marks Criterion B

Medium

Inquiry design: Aquatic ecosystems and eutrophication

Investigate how nitrate concentration affects algal population growth under controlled light.

a. Formulate a focused research question and a testable prediction.

[3]

b. Give a reproducible method and explain how the results will be processed.

[5]

c. Identify the main controls and manage the significant risk.

[3]

Show complete worked solution

(a)

Research question: How does nitrate concentration affect change in algal turbidity or cell count per day under the stated conditions?

Prediction: Algal density rises strongly up to 8 mg dm?³ and then plateaus, suggesting another factor becomes limiting.

(b)

Test at least five scientifically justified values of nitrate concentration across a safe range, including a baseline or control where possible. Measure change in algal turbidity or cell count per day with a calibrated method at fixed intervals or a defined endpoint. Repeat every condition at least three times.

Calculate a mean for each condition, show variation with a range or another suitable spread measure, and plot the dependent variable against the independent variable with units.

(c)

Keep constant algal inoculum, phosphate, light, temperature, volume and pH.

Use non-pathogenic cultures, closed vessels and disinfect waste before disposal.

QUESTION 3 9 marks Criterion C

Medium

Evidence analysis: Aquatic ecosystems and eutrophication

The graph shows results from a focused investigation of aquatic ecosystems and eutrophication.

a. Calculate the percentage increase in algal density from 0 to 8 mg dm?³ nitrate.

[3]

b. Describe the overall relationship and explain its scientific meaning.

[3]

c. Evaluate one limitation and state a targeted improvement.

[3]

Show complete worked solution

(a)

\[\frac{72-12}{12}\times100=\boxed{500\%}\]

(b)

Algal density rises strongly up to 8 mg dm?³ and then plateaus, suggesting another factor becomes limiting.

(c)

Turbidity can include dead cells or other particles and may not equal living population size.

Increase replication and resolution around important changes, check calibration, and measure the named confounding variables.

QUESTION 4 8 marks Criterion D

Hard

Science in context: Aquatic ecosystems and eutrophication

Farmers are asked to establish vegetated buffer strips beside streams.

a. Compare the scientific advantages and disadvantages of the proposal.

[4]

b. State the further evidence needed for a defensible decision.

[2]

c. Give a reasoned conclusion that acknowledges uncertainty.

[2]

Show complete worked solution

(a)

Buffers can trap sediment and absorb nutrients before they reach water.

However, they reduce cultivable land and performance varies with slope, vegetation and storm intensity.

(b)

Compare nutrient loads before and after buffers across seasons and include crop yield, maintenance and aquatic oxygen recovery.

(c)

The proposal is conditionally supportable if monitoring confirms the expected benefit and agreed thresholds control the risks. The conclusion is provisional because performance and impacts vary with place and time.

QUESTION 1 8 marks Criterion A

Medium

Scientific understanding: Water treatment, separation and analysis

A treatment plant receives muddy, microbe-contaminated river water. Use integrated scientific understanding to explain the situation.

a. Explain the central scientific process or relationship in this context.

[3]

b. Explain the observed or expected outcome.

[3]

c. Explain why an integrated-sciences explanation is stronger than a single-discipline description.

[2]

Show complete worked solution

(a)

Treatment combines physical separation with chemical or physical disinfection. Filtration removes particles; disinfection inactivates pathogens but does not remove all dissolved substances.

(b)

A clear sample can still be unsafe if microorganisms or dissolved toxins remain.

(c)

Physics and chemistry provide separation methods; biology determines health risks from pathogens.

QUESTION 2 11 marks Criterion B

Hard

Inquiry design: Water treatment, separation and analysis

Compare sand-filter depth and turbidity removal using identical columns.

a. Write the research question and justify a control or baseline condition.

[3]

b. Describe how the variables will be changed, measured and controlled.

[5]

c. State the prediction, data treatment and safety provision.

[3]

Show complete worked solution

(a)

How does sand-filter depth affect percentage turbidity removal under the stated conditions?

A baseline or control shows the response without the tested change, so an observed difference can be attributed more confidently to sand-filter depth.

(b)

Test at least five scientifically justified values of sand-filter depth across a safe range, including a baseline or control where possible. Measure percentage turbidity removal with a calibrated method at fixed intervals or a defined endpoint. Repeat every condition at least three times.

Keep constant influent turbidity and volume, sand grain size, column diameter and flow rate.

(c)

Prediction: Removal improves with depth, but the additional gain becomes smaller at greater depth.

Calculate a mean for each condition, show variation with a range or another suitable spread measure, and plot the dependent variable against the independent variable with units.

Use simulated muddy water or treat all samples as contaminated; wear eye protection and gloves.

QUESTION 3 10 marks Criterion C

Hard

Evidence analysis: Water treatment, separation and analysis

The graph shows results from a focused investigation of water treatment, separation and analysis.

a. Calculate the percentage-point improvement from 10 cm to 30 cm.

[3]

b. Compare the early and later parts of the dataset and interpret the change.

[3]

c. Explain how one feature of the method limits validity.

[2]

d. Specify one additional measurement or design change that would test the interpretation.

[2]

Show complete worked solution

(a)

\[91-61=\boxed{30\text{ percentage points}}\]

(b)

Removal improves with depth, but the additional gain becomes smaller at greater depth.

(c)

The test measures turbidity, not pathogen removal or flow capacity.

(d)

Increase replication and resolution around important changes, check calibration, and measure the named confounding variables.

QUESTION 4 8 marks Criterion D

Hard

Science in context: Water treatment, separation and analysis

A village can install centralized chlorination or distribute household ceramic filters.

a. State the strongest scientific argument supporting the action.

[2]

b. State the strongest scientific argument for caution.

[2]

c. Construct a balanced decision rule rather than an unconditional answer.

[4]

Show complete worked solution

(a)

Central chlorination can protect a large supply and leave a residual disinfectant.

(b)

Dose control, by-products, taste, maintenance and household recontamination must be considered.

(c)

Set measurable performance and safety thresholds before implementation. Test microbial counts at source and point of use, operator reliability, residual chlorine, user adoption and full cost. Adopt the action in stages, monitor outcomes, and pause or revise it if thresholds are not met.

QUESTION 1 8 marks Criterion A

Hard

Scientific understanding: Water resources, access and sustainability

A dry city considers desalination and wastewater recycling. Use integrated scientific understanding to explain the situation.

a. Give a scientifically accurate explanation of the central claim.

[4]

b. Show the relationship that could be used to quantify the claim.

[2]

c. Relate the explanation to another science discipline.

[2]

Show complete worked solution

(a)

Desalination separates salts but requires energy; recycling treats water to a quality matched to its intended use. A water balance compares inflows, use, reuse and losses.

Reducing leakage can provide water without the energy and infrastructure needed to produce an equal new volume.

(b)

\[V_{net}=V_{supply}+V_{reuse}-V_{demand}-V_{loss}\]

(c)

Chemistry addresses water quality, physics addresses energy, biology addresses health, and environmental science addresses ecosystems.

QUESTION 2 11 marks Criterion B

Hard

Inquiry design: Water resources, access and sustainability

Audit daily water losses in two school buildings before and after leak repair.

a. Convert the aim into a focused research question with named variables.

[3]

b. Propose a sequence that collects enough valid evidence.

[5]

c. State the expected pattern and how it will be tested against the results.

[2]

d. Give the essential safety or ethical precaution.

[1]

Show complete worked solution

(a)

How does repair status affect night-time water flow or daily unexplained consumption under the stated conditions?

The independent variable is repair status; the dependent variable is night-time water flow or daily unexplained consumption.

(b)

Compare every named condition of repair status with a matched baseline or control, using randomized or alternated trial order where possible. Measure night-time water flow or daily unexplained consumption with a calibrated method at fixed intervals or a defined endpoint. Repeat every condition at least three times.

Keep constant occupancy, observation period, meter calibration and scheduled water uses.

(c)

Expected pattern: Use falls after the intervention and remains lower, consistent with a substantial leak reduction.

Calculate a mean for each condition, show variation with a range or another suitable spread measure, and plot the dependent variable against the independent variable with units.

(d)

Do not open pressurized plumbing; use authorized maintenance staff.

QUESTION 3 9 marks Criterion C

Hard

Evidence analysis: Water resources, access and sustainability

The graph shows results from a focused investigation of water resources, access and sustainability.

a. Calculate the percentage reduction from week 1 to week 4.

[3]

b. Describe the overall relationship and explain its scientific meaning.

[3]

c. Evaluate one limitation and state a targeted improvement.

[3]

Show complete worked solution

(a)

\[\frac{42-30}{42}\times100=\boxed{28.6\%}\]

(b)

Use falls after the intervention and remains lower, consistent with a substantial leak reduction.

(c)

Weather, attendance or behavior may also have changed between weeks.

Increase replication and resolution around important changes, check calibration, and measure the named confounding variables.

QUESTION 4 8 marks Criterion D

Hard

Science in context: Water resources, access and sustainability

The city must prioritize leak repair, recycling, or a coastal desalination plant.

a. Compare the scientific advantages and disadvantages of the proposal.

[4]

b. State the further evidence needed for a defensible decision.

[2]

c. Give a reasoned conclusion that acknowledges uncertainty.

[2]

Show complete worked solution

(a)

A mixed strategy can reduce demand and create a drought-resistant supply.

However, desalination is energy-intensive and produces brine; recycling requires trust, controls and fit-for-purpose pipelines.

(b)

Use leakage surveys, marginal cost per cubic metre, energy source, brine ecology, health monitoring and drought projections.

(c)

The proposal is conditionally supportable if monitoring confirms the expected benefit and agreed thresholds control the risks. The conclusion is provisional because performance and impacts vary with place and time.

IS2 - Water systems and quality

IS2.1 - Water cycle, states and thermal processes 4 questions

IS2.2 - Solutions, concentration, pH and salinity 4 questions

IS2.3 - Aquatic ecosystems and eutrophication 4 questions

IS2.4 - Water treatment, separation and analysis 4 questions

IS2.5 - Water resources, access and sustainability 4 questions