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All 14 Flashcards — Impacts of water pollution
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Question
What is bioaccumulation?
Answer
Bioaccumulation is the build-up of a substance in an organism over time, faster than it can be broken down or excreted.
💡 Hint
Build-up in one organism.
Question
What is a seasonal dead zone (hypoxia)?
Answer
A seasonal dead zone is an area of water where dissolved oxygen becomes very low during certain months (often summer), so many organisms die or move away.
💡 Hint
Low oxygen, certain months.
Question
What is biomagnification?
Answer
Biomagnification is the increase in concentration of a substance at higher trophic levels in a food chain.
💡 Hint
Higher level = higher concentration.
Question
Why are dead zones often worse in summer?
Answer
Warm water holds less dissolved oxygen, and summer conditions can intensify algal blooms and decomposition, increasing hypoxia.
💡 Hint
Warm water holds less O2.
Question
Give a simple food-chain example showing biomagnification.
Answer
Plankton absorb a toxin → small fish eat many plankton → larger fish eat many small fish → top predators accumulate the highest toxin concentration.
💡 Hint
Many prey → higher dose.
Question
Which organisms receive the highest toxin concentrations in biomagnification?
Answer
Top predators (including humans) receive the highest concentrations because toxins accumulate up the food chain.
💡 Hint
Top predators.
Question
What is the typical dissolved oxygen threshold used to define hypoxia?
Answer
Hypoxia is commonly defined as dissolved oxygen below about 2 mg/L.
💡 Hint
2 mg/L.
Question
Why are humans at risk from biomagnification?
Answer
Humans can be top consumers in marine food webs, so toxins such as mercury and POPs can reach high concentrations in seafood and then in people.
💡 Hint
We are top consumers.
Question
Name three pollutant groups that often biomagnify.
Answer
Heavy metals (for example mercury), persistent organic pollutants (POPs such as DDT/PCBs), and microplastics that can carry absorbed toxins.
💡 Hint
Metals + POPs + plastics.
Question
Dead zone mechanism: why does decomposition reduce oxygen?
Answer
Decomposers respire as they break down organic matter, using dissolved oxygen and lowering oxygen levels in the water.
💡 Hint
Bacteria use O2.
Question
Why do some toxins persist in ecosystems for a long time?
Answer
Some pollutants are chemically stable and not easily degraded, so they remain in water/sediments and in organisms for long periods.
💡 Hint
Hard to break down.
Question
Why do fat-soluble, persistent pollutants biomagnify so strongly?
Answer
They are not easily broken down or excreted and can be stored in body fat, so they remain in organisms and increase in concentration as predators eat many contaminated prey.
💡 Hint
Persistent + stored in fat.
Question
Exam technique: what must you do to earn full marks on bioaccumulation/biomagnification questions?
Answer
Define the term clearly and apply it to a food-chain example, explaining why concentration is highest at the top.
💡 Hint
Define + apply.
Question
What is one likely food-web effect of hypoxia?
Answer
Fish and benthic organisms die or leave the area, reducing prey for higher trophic levels and disrupting the food web.
💡 Hint
Loss of organisms.
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