Biological Oxygen Demand (BOD) is a standard criterion for

Explicitly mentions 'biological oxygen demand (BOD)' as a measured parameter for river water quality and gives a numeric comparison to a 'normal' safe value.

A student can use this example to infer that BOD is used as a standard metric in aquatic (river) pollution assessment and then ask whether the same metric is applied to terrestrial/forest air.

Describes eutrophication in aquatic systems where algal blooms and decomposition deplete oxygen in water, linking biological decomposition to oxygen consumption.

From this process, a student can infer that measuring oxygen demand (like BOD) is meaningful in water bodies where microbial decomposition drives oxygen changes.

Explains that oxygen in aquatic ecosystems is 'dissolved in water' and that its concentration varies due to inputs and outputs, highlighting a focus on dissolved oxygen monitoring in water.

A student could extend this to note that metrics designed for dissolved oxygen dynamics (such as BOD) are tailored to aquatic environments rather than open-air terrestrial ecosystems like forests.

Gives an explicit terrestrial/forest fact: a mature tree produces oxygen and human daily oxygen needs, emphasizing oxygen exchange in air around forests.

A student can contrast oxygen production and atmospheric oxygen usage in forests with dissolved-oxygen dynamics in water, suggesting different measurement approaches for forests versus aquatic systems.

Describes forest ecosystems (biotic communities, soil, climate) and their terrestrial nature, implicitly indicating forests are land-based systems where atmospheric gas exchange matters.

A student might use this to reason that standard water-quality metrics (like BOD) may not directly apply to terrestrial ecosystem oxygen accounting and that terrestrial metrics could differ.

Explicitly shows BOD is used as a numeric water-quality parameter (mg per liter) for rivers and bathing safety.

A student can infer BOD is an aquatic pollution/oxygen-consumption metric and so ask whether BOD is intended to measure atmospheric oxygen at altitude (likely not) or only water bodies.

Describes dissolved oxygen in aquatic ecosystems and that oxygen concentration in water differs greatly from oxygen in air.

Use the distinction to reason that BOD (which concerns oxygen in water) does not directly quantify atmospheric oxygen available to humans/animals at high altitude.

States that high altitudes have rarified air, low pressure and shortage of oxygen that impede agriculture and livestock.

Combine this with the aquatic focus of BOD to question applicability: to assess oxygen stress at altitude one would typically measure atmospheric oxygen/pressure rather than BOD.

Explains that reduced atmospheric pressure at high altitudes leads to less oxygen inhaled by humans, causing physiological effects.

A student could extend this to note that standard criteria for altitude oxygen assessment are atmospheric pressure/partial pressure of O2 or blood oxygenation, not BOD.

Notes that birds can fly at high altitudes where oxygen levels are low, implying biological/physiological measures are relevant for altitude oxygen assessment.

This suggests altitude oxygen issues are about air-breathing physiology (respiratory adaptations or air O2 measures), further indicating BOD (a water metric) is not the standard criterion for atmospheric oxygen at altitude.