Final answer:
Euglena obtains nutrients either through photosynthesis using chloroplasts to convert light into energy, or through heterotrophic methods like phagocytosis or absorption when light is not available. They store carbohydrates in a unique glucose polymer and contribute to their ecosystems in various trophic roles.
Step-by-step explanation:
Euglena are intriguing unicellular organisms that can obtain nutrients through various methods, reflecting their capacity as versatile mixotrophs. They can harness matter and energy through photosynthesis when light is available, using chloroplasts they have acquired through secondary endosymbiosis from green algae. During this process, they convert carbon dioxide into carbohydrates using sunlight, which then serve as an energy source. They store these carbohydrates in a form of glucose polymer linked differently from typical starch. However, in the absence of light, Euglena act as heterotrophs, where they may ingest prey by phagocytosis or absorb nutrients directly from their aquatic environment, efficiently contributing to the ecosystems as both primary producers and decomposers.