Original open focus revision; complete specification coverage remains unfinished.
1 · Environmental systems, feedback and perspectives
stock · flow
ib_environmental_systems_sl:ess_systems:open:1 · 2 marks
What makes a reservoir budget incomplete?
- An unmeasured outflow
- Consistent units
- An explicit boundary
Answer and reasoning · 答案与解析
An unmeasured outflow
- Separate physical evidence from value judgements. A stock is an amount at a time; a flow is an amount per time. Sustainability decisions require ecological, social and economic evidence and a stated scale.
ib_environmental_systems_sl:ess_systems:open:2 · 4 marks
A stock starts at 600, receives 80 and loses 110. Find final stock.
Answer and reasoning · 答案与解析
570
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
A balance that closes mathematically can still omit a real process if terms were estimated to fit. Positive feedback does not mean a socially desirable result.
2 · Sampling populations without choosing the answer
quadrat · population
ib_environmental_systems_sl:ecology:open:1 · 2 marks
Which method investigates change from a path into woodland?
- Choose only large plants
- Use a transect with fixed sampling distances
- Take one convenient sample
Answer and reasoning · 答案与解析
Use a transect with fixed sampling distances
- Estimate total abundance by multiplying mean density by area, with consistent units. This assumes sampled areas represent the habitat. Patchiness and too few samples widen uncertainty.
ib_environmental_systems_sl:ecology:open:2 · 4 marks
Mean count is 6 in a 0.5 square metre quadrat. Find density per square metre.
Answer and reasoning · 答案与解析
12
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Quadrats suit organisms that do not move quickly. A food chain arrow shows the direction of energy transfer, not the direction a predator travels.
3 · Biodiversity, conservation and sampling evidence
species richness · evenness
ib_environmental_systems_sl:ess_biodiversity:open:1 · 2 marks
Two sites have three species each. Which can still differ?
- Their evenness
- The definition of a species must change
- They must have identical conservation value
Answer and reasoning · 答案与解析
Their evenness
- Compare surveys with similar area, effort, season and identification rules. A diversity index is meaningful only with its formula and conventions specified. Habitat fragmentation can affect movement and gene flow even when total area changes little.
ib_environmental_systems_sl:ess_biodiversity:open:2 · 4 marks
A survey records 6, 5, 3 and 2 individuals in four species. Find species richness.
Answer and reasoning · 答案与解析
4 species
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
An index cannot by itself explain the cause of a difference. A newly recorded species may reflect improved observation rather than a recent ecological arrival.
4 · Water, pollution and management trade-offs
eutrophication · pollutant load
ib_environmental_systems_sl:ess_water:open:1 · 2 marks
Which can occur after dilution without pollutant removal?
- Concentration decreases but pollutant mass remains
- All pollutant disappears
- The water becomes automatically safe
Answer and reasoning · 答案与解析
Concentration decreases but pollutant mass remains
- Distinguish concentration from total pollutant load. Dilution can reduce concentration without removing the pollutant mass. A management plan should consider upstream causes, users and effects on other parts of the catchment.
ib_environmental_systems_sl:ess_water:open:2 · 4 marks
Concentration is 3 mg/L and flow 200 L/min. Find load in mg/min.
Answer and reasoning · 答案与解析
600 mg/min
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Clear water is not necessarily safe water. Nutrient enrichment does not directly use up oxygen; the pathway includes biological activity and decomposition.
5 · Land, food and resource decisions
erosion · resource
ib_environmental_systems_sl:ess_land:open:1 · 2 marks
Which comparison measures land productivity?
- Total harvest without land area
- Harvest divided by cultivated area
- Only fertilizer price
Answer and reasoning · 答案与解析
Harvest divided by cultivated area
- Distinguish total yield from yield per area and energy input. Sustainable management must consider regeneration rates and impacts beyond the farm boundary. Different stakeholders may rank food security, biodiversity and income differently.
ib_environmental_systems_sl:ess_land:open:2 · 4 marks
A farm harvests 28 tonnes from 7 hectares. Find yield per hectare.
Answer and reasoning · 答案与解析
4 t/ha
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
A high yield is not proof of long-term soil health. Renewable resources can be depleted when use exceeds regeneration.
6 · Climate evidence, energy budgets and policy
mitigation · adaptation
ib_environmental_systems_sl:ess_climate:open:1 · 2 marks
Which action is adaptation to flood risk?
- Raising vulnerable electrical equipment above expected flood level
- Only measuring global CO2
- Pretending the risk is zero
Answer and reasoning · 答案与解析
Raising vulnerable electrical equipment above expected flood level
- Distinguish mitigation, which addresses drivers, from adaptation, which reduces harm from impacts. A policy assessment needs evidence about effectiveness, cost, equity and uncertainty; one criterion is not the entire decision.
ib_environmental_systems_sl:ess_climate:open:2 · 4 marks
Incoming energy is 240 units and reflected energy 72. Find reflected percentage.
Answer and reasoning · 答案与解析
30 %
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
The greenhouse effect is not the same process as ozone depletion. A carbon footprint estimate depends on its system boundary.
7 · Population, urban systems and indicators
immigration · indicator
ib_environmental_systems_sl:ess_population:open:1 · 2 marks
Which contributes positively to population change?
- Emigration
- Immigration
- Deaths
Answer and reasoning · 答案与解析
Immigration
- Compare rates with a common denominator and interval. An average can hide unequal access to services. At HL, evaluate how economic incentives, legal responsibilities and ethical priorities change an urban management proposal.
ib_environmental_systems_sl:ess_population:open:2 · 4 marks
A population of 2,000 grows by 40 in a year. Find percentage growth.
Answer and reasoning · 答案与解析
2 %
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
A projected population is conditional on assumptions. Urban growth does not automatically mean improved health, income or environmental quality for every resident.
8 · Uncertainty, gradients and model testing
uncertainty · systematic error
ib_environmental_systems_sl:uncertainty:open:1 · 2 marks
Which is most likely a systematic error?
- A balance reads 0.20 g when empty
- Repeated values fluctuate either side of the mean
- Random differences in reaction time
Answer and reasoning · 答案与解析
A balance reads 0.20 g when empty
- For a product or quotient, adding fractional uncertainties is a common maximum-uncertainty approximation. For a difference, add absolute uncertainties. A nonzero intercept can reveal an offset or an incomplete model.
ib_environmental_systems_sl:uncertainty:open:2 · 4 marks
A 40 cm reading has an absolute uncertainty of 1 cm. Find percentage uncertainty.
Answer and reasoning · 答案与解析
2.5 %
- Appropriate relation; consistent substitution; correct result; meaningful unit and interpretation.
Repeating readings reduces random uncertainty in a mean but does not automatically remove a zero error. Do not quote more decimal places than your measurement can support.