Ecology Practice Question 1

Attempt the question first before looking at the answer scheme below.

Read the following passage carefully before attempting this question.

An industrial chemical that pollutes groundwater can be neutralized by an obscure microbe that researchers have discovered in the bottom mud of the Hudson River.

In a study in the Science journal, researchers at Michigan State University reported that a previously unknown bacteria is able to turn trichloroethane, an industrial chemical that is difficult to clear from ground water, into a more benign compound.

Benjamin M. Griffin, a Michigan State researcher and a co-author of the study, said the microbe reduces trichloroethane through respiration to chloroethane, a compound that is more easily cleared from groundwater.

"This microbe thrives in the presence of TCA (trichloroethane)," Griffin said. In laboratory experiments, he said, the microbe is grown by adding TCA to its culture medium.

The microbe lives in the absence of oxygen and it can be useful for cleaning TCA from polluted groundwater containing TCA. TCA is present in 696 of 1430 cleanup priority sites identified by the Environmental Protection Agency.

"TCA was one of the remaining groundwater pollutants for which biodegradation has not been resolved," James Tiedje, the senior author of the study, said in a statement. "Until the discovery of the microbe from the Hudson River, there was no solution for the problem."

The diagram below shows a possible food web found in the Hudson River.


(a) Construct a complete food chain consisting of only 3 trophic levels from the food web given. [1]

(b) Explain why food chains in the above food web are usually limited to 4 trophic levels? [2]

(c) Trichloroethane is a industrial chemical pollutant which was previously nonbiodegradable before this novel bacteria was discovered. Which animal in the food web will be affected the most by tricholoethane pollution? Explain your answer. [2]



Answer Scheme
a) Seaweed --> Limpet --> Sea Gull /Lobster;

(b) Food chains are usually short as the energy stored in each trophic level is lost through processes like excretion, egestion and heat;
Thus this means that there is lesser energy available for the next level, and the food chain cannot support more than 4 links as there would be too little energy to sustain a 5th level;

(c) The sea gull will be most affected by trichloroethane as it is at the highest trophic level;
Since the chemical is non-biodegradable, it accumulates in the bodies of the organisms in each level and is not excreted, the animals in highest trophic level will have the highest level of toxicity which may eventually kill them;