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QLDMarine ScienceQuick questions
Unit 3: Marine systems - connections and change
Quick questions on Energy flow and nutrient cycling in marine ecosystems (QCE Marine Science Unit 3)
3short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.
What are marine producers?Show answer
Marine producers fix energy into organic molecules.
What is the marine carbon cycle?Show answer
Carbon dioxide dissolves into surface water and is fixed by producers during photosynthesis. It passes up the food web as organic carbon and is returned to the water through respiration and decomposition. A key marine process is the biological carbon pump: dead plankton, faecal pellets and other matter sink from the surface into the deep ocean, carrying carbon down and storing it for centuries. Carbon is also locked into the calcium carbonate skeletons of corals and shells, some of which becomes limestone over geological time.
What is the marine nitrogen cycle?Show answer
Nitrogen is often the limiting nutrient for marine producers. Nitrogen-fixing cyanobacteria (such as _Trichodesmium_, which forms blooms in the Coral Sea) convert dissolved nitrogen gas into ammonium. Bacteria then convert ammonium to nitrite and nitrate (nitrification), which producers take up. Decomposers release nitrogen from dead matter (ammonification), and denitrifying bacteria return nitrogen gas to the water and atmosphere.
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