Toxins in Food Chains and Organisms Changing Habitats
Explain bioaccumulation within organisms, biomagnification of some pollutants through food chains, and ways organisms change their habitats
What a learner can do afterwards
- Distinguishes bioaccumulation within an organism from biomagnification, an increase in pollutant concentration across feeding levels
- Gives a real example of pollutant build-up, such as DDT-related effects in peregrine falcons or mercury in predatory fish
- Explains how organisms can change their habitat (e.g. earthworms aerating soil, beavers creating wetlands)
- Explains why top predators can receive high concentrations of pollutants that persist and biomagnify, while recognizing that harm also depends on sensitivity
1 · Read
Food webs connect organisms through feeding. Harmful substances can enter a body from food, water or other surroundings. Bioaccumulation is build-up within an organism over time when a substance enters faster than the organism removes it. Some pollutants remain in bodies for a long time. Others break down or leave quickly, so taking in a substance does not always mean it accumulates.
Biomagnification means a pollutant's concentration increases across feeding levels. Concentration is the amount per gram of tissue. Predators eat contaminated prey and may retain substances that leave slowly. Some persistent pollutants can reach high concentrations in top predators. This does not happen with every substance. Rapid breakdown or removal can prevent build-up. Harm also depends on an organism's sensitivity.
DDT was used as a pesticide. It reached peregrine falcons through contaminated birds they ate. DDT and its breakdown product DDE could build up in the falcons. DDE disrupted eggshell formation, producing thinner shells. More eggs broke during nesting, so fewer chicks hatched. This contributed to peregrine population declines. Peregrines mainly eat birds, not fish.
Total amount is different from concentration. A large animal can contain more toxin in total without having more per gram of tissue. For a model calculation, state the starting amount and how much is retained. A fish starting with zero units and keeping all the toxin from 3 prey with 8 units each gains 3 × 8 = 24 units. Real animals may remove some of a substance.
Organisms also change habitats. Earthworm tunnels can help air and water move through soil. Beaver dams slow flowing water and can flood nearby land, creating ponds and wetlands. Some wetland species gain suitable habitat, while species needing the flooded land may lose habitat. The same physical change can therefore have different effects on different organisms.
Build-up depends on intake, breakdown and removal. Rapid removal can prevent build-up despite repeated meals. Sensitivity means how strongly an organism is affected by a substance. A lower concentration can harm a more sensitive organism more than a higher concentration harms a less sensitive one. Feeding level or concentration alone cannot show which species suffers most.
Bioaccumulation is build-up within an organism. Some pollutants biomagnify across feeding levels. Organisms also change habitats, with different effects on different species.
Lesson revisions, questions and flashcard revisions written for this dataset. Numerical charts and complete-retention calculations are teaching models, not measured food-chain data.
The three readings were written for this dataset. Biomagnification and the Trouble with Toxins is a video by Amoeba Sisters. Rights in the video remain with its creators.
More to read
Build-up within bodies and between feeding levels
A substance can enter an organism through its food or surroundings. When intake is faster than removal, the amount stored can increase over time. This process within an organism is bioaccumulation.
Biomagnification compares pollutant concentrations across feeding levels. Concentration means the amount per gram of tissue. A large fish may contain more pollutant in total than a small fish without having a greater amount in each gram.
Some persistent pollutants leave bodies slowly. Predators can retain them from contaminated meals, and their concentrations can increase higher in a food chain. Other substances break down or leave quickly. Feeding position alone does not tell us how much will remain or how much harm an organism will suffer.
Contaminated meals and classroom models
A fish encounters mercury when it eats contaminated prey. It does not need to swim through a chemical spill to take mercury into its body. Build-up depends on intake and removal over time.
A classroom calculation may assume that every toxin unit from a meal remains in the predator. State that assumption and the predator's starting amount before calculating a final total. Complete retention is a model condition, not a rule for every animal and pollutant. A total still does not give a concentration unless tissue mass is considered.
Contaminated bird prey exposed peregrine falcons to DDT. Its breakdown product DDE disrupted eggshell formation. Thin shells broke more often during nesting, reducing successful hatching. This links pollution passing through food with an effect on reproduction.
Habitat changes have different effects
Organisms can alter the physical conditions around them. Earthworms make tunnels through soil, helping air and water move through it. Their surroundings are changed by their activity.
A beaver dam can slow a stream and raise the water level. Flooded ground may become pond or wetland habitat. Some organisms can use those new conditions, while others need the land that was flooded.
When explaining an organism's effect on habitat, separate the action from its consequences. First name what the organism does. Then describe the change to soil, water or another physical condition. Finally, consider which species could gain or lose suitable habitat. A new wetland is not automatically better or worse for every species.
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