4.11.6Additional lessons
The Effects of Pollution — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 97 of 101
Part 1 of 5Types of Pollutant
Pollution is the release of substances that harm living things or damage the environment.
Plastics
- These are slow to break down;
- animals may swallow or become tangled in them, and microplastics enter food chains.
Persistent organic pollutants
- Pesticides and industrial chemicals resist breakdown and dissolve in fats, so they remain in body tissues.
Heavy metals
- Mercury and lead from industry accumulate in organisms and damage the nervous system.
Oil
- Spills coat feathers and fur and poison marine life, reducing the insulation of birds and mammals.
| Term | Meaning |
|---|---|
| Bioaccumulation | Build-up of a substance in an organism over its lifetime |
| Biomagnification | Increase in concentration at each higher trophic level |
| Persistence | Time a pollutant stays in the environment before breaking down |
Part 2 of 5How Biomagnification Occurs
1
A fat-soluble, non-biodegradable pollutant enters the base of the food chain, taken up by producers or plankton.
2
Each primary consumer eats many producers, and the pollutant accumulates in its fat rather than being excreted.
3
Secondary consumers eat many primary consumers, so the concentration in their tissues is higher still.
4
Top predators receive the highest dose, and may show reproductive failure, as with eggshell thinning in some birds of prey.
Part 3 of 5Reducing the Impact
Reducing the Impact
Regulation
- Banning the most persistent chemicals and controlling discharge limits reduces the pollutant entering the environment.
Treatment
- Waste water treatment and filtration remove many contaminants before release.
Reduction
- Using less single-use plastic and improving recycling prevents plastic reaching rivers and oceans.
Monitoring
- Measuring indicator species and chemical concentrations shows whether controls are working.
Indicator organisms
- Changes in lichens, mayfly larvae and other sensitive species show the level of air or water pollution in a habitat.
Part 4 of 5Worked Example
Question
- In a hypothetical food chain, a pollutant is 0.5 µg kg⁻¹ in producers, 4 µg kg⁻¹ in herbivores, 30 µg kg⁻¹ in small carnivores and 250 µg kg⁻¹ in top carnivores.
- Calculate the magnification factor from producer to top carnivore.
- Factor = concentration in top carnivore ÷ concentration in producer.
- 250 ÷ 0.5 = 500.
Answer 500-fold increase
Part 5 of 5Exam Checklist & Tips
4.11.6 – Key Points for the Exam
- Pollution Harmful substances added to the environment by human activity.
- Bioaccumulation Gradual build-up of a pollutant within an organism.
- Biomagnification Rising concentration of a pollutant at successive trophic levels.
- Microplastic Plastic particles smaller than five millimetres.
- Non-biodegradable Not broken down by decomposers.
Common Mistakes
- Using bioaccumulation and biomagnification as if they were the same.
- Forgetting that the pollutant must be persistent and fat soluble for biomagnification.
- Explaining biomagnification by energy loss only, when the key is that the substance is not excreted.
- Stating that plastics are harmful only because they are unsightly.
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