IB Environmental Systems and Societies practice questions.

In a systems model of an environmental value system (EVS), which of the following is best classified as an input?

• A decision to install solar panels on a house
• A choice to join a campaign against a new airport
• A school lesson on the causes of ocean acidification
• A letter written to a newspaper about local air quality

Answer: A school lesson on the causes of ocean acidification

An EVS is modelled as a system: education, cultural and religious teaching, media coverage and personal experience are the inputs, while the perspectives, decisions and actions that come out of it are the outputs. Installing panels, campaigning and writing letters are all behavioural outputs, not inputs.

A red fox in a woodland hunts at night, dens in a hollow log and feeds mainly on small rodents. This full description of what the fox does and how it interacts with other organisms is its

• habitat, because it describes where the fox is found
• population, because it describes a group of the same species
• niche, because it describes its role and interactions
• community, because it describes interacting species

Answer: niche, because it describes its role and interactions

The niche is the role a species plays, including its feeding, timing and interactions; the habitat is only the physical address where it lives. Students who answer habitat are describing where, not how.

Two woodland sites each contain 100 beetles belonging to four species. At site A the individuals are spread evenly across the four species; at site B a single species accounts for 91 of them. Compared with site A, the Simpson reciprocal index for site B will be

• higher, because one species is clearly dominant
• the same, because both sites contain exactly four species and 100 individuals
• lower, because the individuals are unevenly distributed among the species
• impossible to calculate without knowing the total area sampled

Answer: lower, because the individuals are unevenly distributed among the species

The reciprocal index combines richness with evenness; richness is identical at the two sites, so the strong dominance at site B enlarges the sum of n(n-1) and drives D down, from about 4.1 to about 1.2.

A catchment is progressively covered with tarmac and roofs during a period of rapid urban growth. Compared with before, the storm hydrograph of its river will show

• a longer lag time and a reduced peak discharge
• a longer lag time and an increased peak discharge
• a shorter lag time and a higher peak discharge
• a shorter lag time and a reduced peak discharge

Answer: a shorter lag time and a higher peak discharge

Impermeable surfaces block infiltration, so rainfall leaves as surface runoff through drains instead of percolating into soil and groundwater storage. Water reaches the channel sooner (shorter lag time) and in greater volume per unit time (higher peak discharge).

Nitrate dissolved in percolating rainwater is carried down below the rooting zone and into the groundwater. Within the soil system this movement is best described as

• an output that crosses the soil system boundary
• a transformation within the soil organic storage
• an input to the soil system from the parent material
• a transfer between two organisms in the soil

Answer: an output that crosses the soil system boundary

Leaching carries the nutrient across the system boundary and out of the soil altogether, so it is an output rather than an internal transfer; weathering of parent rock and the fall of litter are the corresponding inputs.

Which set of values best describes the composition of dry air in the troposphere by volume?

• nitrogen 21 %, oxygen 78 %, argon 0.93 %, carbon dioxide about 0.04 %
• nitrogen 78 %, oxygen 21 %, argon 0.93 %, carbon dioxide about 0.04 %
• nitrogen 78 %, oxygen 21 %, carbon dioxide 0.93 %, argon about 0.04 %
• nitrogen 65 %, oxygen 21 %, water vapour 13 %, carbon dioxide about 0.9 %

Answer: nitrogen 78 %, oxygen 21 %, argon 0.93 %, carbon dioxide about 0.04 %

Dry air is overwhelmingly nitrogen and oxygen, argon is the third most abundant gas, and carbon dioxide is a trace gas despite its climatic importance. Water vapour is excluded from these figures because it varies from almost nothing to about 4 % of the air.