Why does matter follow a circular pathway, and energy a linear pathway?

Question

Stuck in science, the question is "in the biosphere, matter follows a circular pathway while energy follows a linear pathway, explain."

Answer 1

Fascinating question.

I think the answer is that matter cycles are a natural product of evolution.  If one type of life form consumes one kind of matter and produces another (e.g. plants breathing CO2 and breathing out O2) then this produces an abundance of the second kind of matter, which is a great opportunity for another life form to thrive that consumes it and produces another kind of matter (e.g. animals breating O2 and breathing out CO2).  So in the biosphere, cycles get more and more complex as new life forms evolve that consume the abundant waste products of others (including a life form that consumes all of the abundant carbon deposits left from billions of years of life, and burns it back into the atmosphere).

But with energy, all pathways ultimately start with one essentially unlimited energy source (the sun) and end with unusable energy (because of the second law of thermodynamics).  I.e. once plants have fixed energy from the sun into sugars, that energy is extracted at every level in the biosphere, and only lost, never added.   E.g. the biosphere never gives energy back to the sun.

I *love* this question!

Answer 2

It's loose talk, but I think what is intended is this:

In the biosphere, matter is recycled as living things are eaten by other living things, etc. Energy follows a one-way path beginning with sunlight, and is not recycled.

Answer 3

energy pathway is not like biosphere because energy exchange from one shape to another shape it is the characteristic of energy