A learner makes a note: euglena survives in light by photosynthesis but can also absorb nutrients in darkness. The missing scientific idea is:

Euglena is mixotrophic because it can combine autotrophic and heterotrophic nutrition. Chloroplasts allow photosynthesis, while absorption of dissolved organic substances helps when light is unavailable. This MCQ belongs to the Euglena topic in Animal Diversity-I and is written to test concept understanding rather than memorized wording.