Final answer:
The largest ecosystem in the world is the marine ecosystem, where about two-thirds of all species live, including biodiverse coral reefs and deep ocean habitats. Tropical rainforests are also highly diverse and essential ecosystems under threat from human activities.
Step-by-step explanation:
The largest ecosystem in the world is the marine ecosystem, where about two-thirds of all species live. Marine ecosystems cover 75 percent of Earth's surface and are comprised of three basic types: shallow ocean, which includes incredibly biodiverse coral reef ecosystems, deep ocean water, and the deep ocean bottom. The shallow ocean ecosystems are known for their high levels of biodiversity, hosting a myriad array of life forms, including the coral reefs that are home to a substantial percentage of marine species. Marine phytoplankton, small photosynthetic organisms, are responsible for 40 percent of all photosynthesis on our planet, underscoring the critical role of marine systems in the Earth's ecology.
On land, tropical rainforests, such as those in the Amazon Basin, represent another critical and immensely diverse ecosystem. Despite covering a smaller portion of the Earth's surface, they house an enormous variety of species. However, these ecosystems face significant threats from human activities like deforestation, compromising biodiversity and the many environmental services it provides, including food production, water purification, and the development of new medicines.