Use the web below for every question.
graph BT ALGAE["Algae"] --> ZOO["Zooplankton"] ALGAE --> SNAIL["Snails"] ZOO --> MINNOW["Minnows"] SNAIL --> CRAY["Crayfish"] MINNOW --> BASS["Bass"] CRAY --> BASS MINNOW --> HERON["Heron"] BASS --> HERON BASS --> DECOMP["Decomposers"] HERON --> DECOMP
1. Name every producer.
Answer
Algae, and only algae. It is the one organism here with no arrow pointing into it — nothing eats its way into existence; it makes its own food.
2. Write one food chain with four links.
Answer
Algae → zooplankton → minnows → bass. Algae → snails → crayfish → bass also works. Any unbroken path following the arrows is fine.
3. What trophic level are crayfish at? Explain why the answer is not simple.
Answer
Third: algae (1) → snails (2) → crayfish (3).
It is not simple because trophic level depends on the path you trace. Many organisms eat at several levels, so “level” is an average rather than an address. Bass are the clearest case here — reached by two different-length paths.
4. A pesticide kills the zooplankton. Trace the effect on every other population.
Answer
- Algae — rise at first; a grazer has been removed.
- Minnows — fall; they lose a food source.
- Bass and heron — fall; fewer minnows to eat.
- Snails — may rise; less competition for algae.
- Crayfish — may rise with the snails.
- Decomposers — a brief rise as die-off arrives, then a fall.
The point: something that never touched the heron can still reduce the heron.
5. Which organism would cause the most disruption if removed?
Answer
Algae. Every other organism traces back to it, so removing it collapses the whole web. Among the animals, minnows are the strongest answer — they sit on the most paths between the bottom and the top.
6. Arrows point from the eaten to the eater. Why is that the sensible direction?
Answer
Because the arrow follows the energy, not the appetite. Energy moves out of the algae and into the zooplankton, so the arrow does too.
Extension: bioaccumulation
A toxin becomes more concentrated at each level. Using the ten percent rule from Energy Flow in Ecosystems, explain why the heron is most at risk.
It takes roughly ten units of prey to build one unit of predator, and the toxin does not break down on the way. Every level multiplies the concentration by about ten, so the animal at the top carries the load of everything beneath it.