Practice question

Euglenoids within Euglenozoa predominantly perform photoautotrophy using secondary plastids surrounded by three membranes containing chlorophyll a and b plus paramylon storage polysaccharide as beta-1,3-glucan granules. Genera like Euglena possess photoreceptive eyespot and flagellum for phototaxis, enabling light-directed movement toward optimal irradiance for photosynthesis. While capable of osmotrophy and phagotrophy when light limited, natural freshwater populations are chiefly photosynthetic in euphotic zone. Parasitic, saprophytic or obligate heterotrophic lifestyles remain minor compared to dominant autotrophic nutrition supported by functional chloroplasts. Flagellar arrangement with phototactic eyespot enables vertical migration optimizing light capture and avoiding photooxidative damage near surface.