The Living World: Ecosystems

Living systems run on cycles and energy, and this unit claims that understanding those two mechanics explains almost everything else in the course. Matter moves in loops: carbon, nitrogen, phosphorus, and water cycle through organisms, soil, atmosphere, and water in predictable pathways that humans interrupt in predictable ways. Energy does not loop. It flows in one direction through trophic levels and loses roughly 90% at each transfer. That single asymmetry between matter and energy is the architecture behind food webs, ecosystem productivity, and every pollution problem you will study later.

6–8% of exam