In AP Environmental Science, mold is a fungal growth classified as a natural-source indoor air pollutant (EK STB-2.E.4). It grows in damp, poorly ventilated spaces and can trigger respiratory issues.
Mold is a fungus that grows indoors wherever there's moisture and not enough airflow. The College Board puts it in a specific bucket: a natural-source indoor air pollutant (EK STB-2.E.4), grouped right alongside radon and dust. "Natural source" just means it comes from a living organism or the environment, not from a factory-made product like paint or carpet glue.
The key thing to remember is the recipe for mold: moisture plus poor ventilation. A bathroom with a leaky shower and no fan, a basement that floods, a humid classroom corner. Those are mold factories. Because it's a biological pollutant, mold spores float in indoor air and get breathed in, which is why it's tied to respiratory problems rather than poisoning or cancer the way some other pollutants are.
Mold lives in Unit 7: Atmospheric Pollution, specifically Topic 7.5 (Indoor Air Pollutants). It supports two learning objectives: [AP Enviro 7.5.A], which asks you to identify indoor air pollutants and sort them by source, and [AP Enviro 7.5.B], which asks you to describe their effects. The exam loves to test whether you can categorize a pollutant correctly, so knowing that mold is natural-source (not human-made, not combustion-based) is the whole point. It's an easy way to lose a point if you lump it in with VOCs or formaldehyde, which are human-made.
Keep studying AP® Environmental Science Unit 7
Radon (Unit 7)
Radon is mold's closest cousin in the CED. Both are natural-source indoor air pollutants listed together in EK STB-2.E.4, but their health effects differ. Radon causes lung cancer, while mold triggers respiratory irritation, so don't swap their effects.
Volatile Organic Compounds (VOCs) (Unit 7)
VOCs are the human-made counterpart to mold. Both pollute indoor air, but VOCs come from manufactured stuff like furniture, paint, and carpets, while mold grows on its own from moisture. This is the natural-versus-human-made split the exam tests.
Carbon Monoxide (Unit 7)
Carbon monoxide rounds out the indoor air pollutant family as a combustion-source asphyxiant. Comparing CO, mold, and VOCs side by side is exactly how MCQs check whether you can match each pollutant to its source category.
Mold shows up most often in multiple-choice questions that hand you a scenario and ask you to identify or categorize the pollutant. A classic stem describes a bathroom or building with persistent moisture and poor ventilation and asks which natural pollutant is likely to develop. The answer is mold. Other stems group mold with dust mites and ask which category of indoor air pollutant is present. For FRQs on indoor air pollution (like the 2018 SAQ on household air pollution from biomass burning), you'll describe sources and health effects, so be ready to name mold as a natural source and connect it to respiratory problems caused by moisture and poor airflow.
Both pollute indoor air, but the source is the dividing line. Mold is a natural-source pollutant that grows from moisture, while VOCs are human-made, off-gassing from furniture, paneling, carpets, and paint. If a question stresses moisture and ventilation, think mold; if it stresses new furniture or renovations, think VOCs.
Mold is a fungal growth classified as a natural-source indoor air pollutant under EK STB-2.E.4, grouped with radon and dust.
The two ingredients for mold are moisture and poor ventilation, which is why bathrooms, basements, and humid rooms are common spots.
Mold's health effect is respiratory irritation, not lung cancer (that's radon) and not asphyxiation (that's carbon monoxide).
On the exam, the safest move is to correctly sort mold as natural-source rather than human-made or combustion-based.
Improving ventilation and controlling moisture is the practical fix for mold, which connects to indoor air quality questions.
Mold is a fungal growth that the CED classifies as a natural-source indoor air pollutant (EK STB-2.E.4). It grows in damp, poorly ventilated indoor spaces and can trigger respiratory issues.
Natural-source. The CED lists mold alongside radon and dust as natural-source indoor air pollutants. Human-made pollutants are things like VOCs from furniture and formaldehyde from building materials.
Source is the difference. Mold is natural and grows from moisture, while VOCs are human-made and off-gas from furniture, carpets, and paint. A scenario mentioning moisture and ventilation points to mold; one mentioning new renovations or furniture points to VOCs.
Moisture plus poor ventilation. A bathroom with no exhaust fan, a damp basement, or a humid room with little airflow are textbook conditions where mold develops.
No. Radon causes radon-induced lung cancer, the second leading cause of lung cancer in America. Mold instead causes respiratory irritation and breathing problems, so keep their effects separate on the exam.
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