GED and HiSET science — ecosystems

Ecology questions are a staple of the life-science part of the GED and HiSET science tests. They usually describe a real place — a lake with an algae problem, a farm field left to grow wild, a forest that has lost its wolves — and ask you to predict what happens next or to explain why it happened. This material builds the ideas those questions rely on, with scenarios from farming, fishing, park management and lake associations.

The quiz covers how matter cycles: which processes take carbon dioxide out of the air (photosynthesis) and which put it back (respiration, decay and burning fuels), and why farmers plant beans or clover, whose root bacteria turn nitrogen gas into a form plants can use. It then works through food webs: naming the trophic level of an organism in a lake web, predicting how the loss of wolves ripples down to elk and the plants they eat, and explaining why mercury ends up most concentrated in ospreys at the top of a food chain. It classifies interactions between species — mutualism, parasitism and commensalism, and competition for a shared food — and follows how communities change over time, from primary succession on bare volcanic rock to secondary succession on an abandoned field, where grasses give way to shrubs and then trees. It ends with three forces that reshape ecosystems: invasive species such as kudzu that spread without their natural enemies, fertilizer runoff that sets off an algal bloom and an oxygen crash that kills fish, and keystone species such as sea otters, whose loss lets sea urchins strip a kelp forest.

The flashcards review the carbon and nitrogen cycles, biomagnification, the three kinds of symbiosis, primary and secondary succession, eutrophication, keystone species and invasive species.

The written work asks you to trace a cycle or a chain of cause and effect in a few sentences: what happens to a lake after heavy fertilizer runoff, how removing a predator affects two levels below it, why a new invasive species outcompetes native ones and what a community can do about it. In the oral exam an examiner describes ecosystems one at a time, asks you to predict and explain changes, and gives brief feedback at the end.

This is independent practice material based on the publicly described content of the two tests; it is not produced or endorsed by GED Testing Service or by ETS.

• Trace carbon and nitrogen through an ecosystem and explain the role of legumes
• Identify trophic levels and predict the effects of removing a predator
• Explain biomagnification and who is most at risk
• Classify mutualism, commensalism, parasitism and competition
• Distinguish primary from secondary succession and describe the usual order of change
• Explain how invasive species, nutrient runoff and the loss of a keystone species change ecosystems

Practice material written by Zestly, based on the published descriptions of the GED Science test (ged.com) and the HiSET Science subtest (hiset.org: life science — ecosystems and interactions).