about ecosystem.choose the best answer and please explain?

The answer is B, Humans. This is because as with most toxic chemicals in trace amounts the organism at the top of the food chain is more likely to ingest in higher quantities.

The crab eats the algae (which has lead in it) this gives an increase in lead in the crab, as the crab eats more algae the amount of lead in the crab increases. Now, the crocodile eats the crab and gets all the lead that was in the crab (an increased amount because of the lead in the crab from the algae it was eating). If the crocodile eats more crabs its levels of Lead go up again. Now if a man eats that crocodile its lead levels will be the highest, and so man will ingest the most lead because of a build up of lead through the system.

I'm the type who just answers the question without embellishing on the circumstances of why the situation arose to cause the person to answer that question or giving my own personal reasons for answering or telling my life storyabout how I came to know the answer to that question or going through in incredible detail the reasons I have for answering this or any other question.

The human will have the highest concentration of lead. It has to eat lots of crocodile which has to eat lots of crabs which has to eat lots of algae.

So... B.

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In ecology, the word 'ecosystem' is an abbreviation of the term, ecological system. Some consider this the basic unit in ecology. Ecosystems are not to be confused with biomes because they are smaller than biomes. They can be as big as the Sahara Desert, but as small as a pond. The term microecosystem may be used to describe a very small (often closed)ecosystem.

In general terms an ecological system can be thought of as an assemblage of organisms (plant, animal and other living organisms—also referred to as a biotic community or biocoenosis) living together with their environment (or biotope), functioning as a loose unit. That is, a dynamic and complex whole, interacting as an "ecological unit."

Early conceptions of this unit were as a structured functional unit in equilibrium. This equilibrium was characterized by energy and matter flows between its constituent elements. Others considered this vision limited, and preferred to understand an ecosystem in terms of cybernetics. From this view an ecological system is not a structured functional unit in equilibrium, but a functional organisation at dynamic equilibrium, or what was also called steady state. The branch of ecology that gave rise to this view has become known as Systems Ecology. Steady state is understood as the phase of an ecological systems evolution when the organisms are "balanced" with each other and their environment. This balance is achieved through various types of interactions, such as predation, parasitism, mutualism, commensalism, competition, and amensalism. Introduction of new elements, whether abiotic or biotic, into an ecosystem tend to have a disruptive effect. In some cases, this can lead to ecological collapse and the death of many native species. The abstract notion of ecological health attempts to measure the robustness and recovery capacity for an ecosystem. That is, how far the ecosystem is away from steady state.

The size and scale of an ecosystem can vary widely. It may be a whole forest, as well as a small pond, or even the geobiosphere itself. Different ecosystems are often separated by geographical barriers, like deserts, mountains or oceans, or are isolated otherwise, like lakes or rivers. As these borders are never rigid, ecosystems tend to blend into each other. As a result, the whole earth can be seen as a single ecosystem, or a lake can be divided into several ecosystems, depending on the scale used.