Final answer:
Species that are multi-celled, have nuclei, and perform photosynthesis exist in freshwater, marine, and terrestrial ecosystems, and can adapt to various environments including Arctic conditions.
Step-by-step explanation:
Species that are multi-celled, have nuclei, and photosynthesize can be found in all ecosystems mentioned including freshwater, marine, and terrestrial ecosystems. They are not exclusively found in any single type of ecosystem. For example, aquatic plants and algae are common in both freshwater and marine ecosystems, and land plants are representative of terrestrial ecosystems.
Freshwater ecosystems, although the least common, support a rich diversity including photosynthetic organisms such as algae and aquatic plants. Marine ecosystems cover the majority of Earth's surface and contain a variety of photosynthetic life, including phytoplankton and coral reefs, which are highly productive and crucial for global photosynthesis. Terrestrial ecosystems, comprising various land habitats, are home to a wide range of photosynthesizing organisms, such as trees, shrubs, and grasses. Notably, even in extreme environments like the Arctic, photosynthetic life forms, such as certain algae and lichens, can be found.