Biological Magnification worksheet - Free Printable

Here are the correct answers with step-by-step explanations for each question.

1. Which organism in the food web shown to the right would contain the highest concentration of chemical pollutants?
* Reasoning: This process is called "biological magnification." As you move up the food chain, predators eat many prey animals. If those prey have a little bit of poison in them, the predator gets all that poison combined in its own body. Therefore, the animal at the very top of the food chain ends up with the most toxins. In this diagram, the hawk (Tertiary consumer) is at the top.
* Answer: D Tertiary consumers

2. Which organism in the food web shown to the right would contain the lowest concentration of chemical pollutants?
* Reasoning: Since toxins build up as they go up the food chain, the organisms at the bottom have the least amount. Producers (plants/algae) get their energy from the sun and absorb small amounts directly from the environment, but they do not eat other contaminated animals.
* Answer: A Producers

3. Which type of tissue that is found in greater amounts in top predators accounts most for the accumulation of chemical toxins?
* Reasoning: Many dangerous chemicals (like pesticides such as DDT) are "lipophilic," which means they dissolve in fat rather than water. Because these chemicals stick to fat cells, they stay inside the animal's body instead of being washed out. Top predators usually have significant fat stores where these toxins hide.
* Answer: B fat tissue

4. The accumulation of heavy metals or other pollutants causes a decline in the population of predatory birds because –
* Reasoning: One of the most famous effects of biological magnification (specifically with the pesticide DDT) is that it makes bird eggshells very thin and fragile. When the parent birds sit on the eggs to keep them warm, the shells break easily. This prevents the baby birds from hatching, causing the population to drop.
* Answer: C the pollutants interfere with bird reproduction

5. Chemical pesticides tend to be used in terrestrial ecosystems... How do these pesticides end up in these aquatic ecosystems?
* Reasoning: When farmers spray crops or people spray lawns, the chemicals don't just disappear. When it rains, the water flows over the land and carries these chemicals into nearby streams, rivers, and lakes. This flowing water is called "runoff."
* Answer: C Pesticides are carried to water sources by freshwater runoff.

6. What human activity is most responsible for the eutrophication that leads to algal blooms?
* Reasoning: Algae need nutrients like nitrogen and phosphorus to grow fast. Humans use fertilizers on farms and lawns that are full of these nutrients. Just like with pesticides, rain washes this fertilizer into the water. The extra food causes the algae to grow out of control.
* Answer: C Fertilizer food crops

7. The rapid growth of algae... can lead to the formation of dead zones... mainly because the algal bloom lowers the amount of –
* Reasoning: When the huge amount of algae eventually dies, bacteria come to decompose (eat) the dead algae. These bacteria use up almost all the oxygen in the water while they work. Fish and other animals need oxygen to breathe; when it runs out, they suffocate and die, creating a "dead zone."
* Answer: C dissolved oxygen

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Final Answer:
1. D
2. A
3. B
4. C
5. C
6. C
7. C