2. Algae is a primitive and ancient lower organism. Algae have simple structure, no differentiation of roots, stems and leaves, and most of them are single cells, colonies or multicellular phyllodes. For example, Chlorella is a single cell, Volvariella volvacea belongs to a group, and kelp is a thallus.
3. Algae contain photosynthetic pigments such as chlorophyll, which can carry out photosynthesis and belong to autotrophs.