Answer:
The fossils that are found in the present day includes both heterotrophs and autotrophs. Those organism that can prepare their own food in the presence of sunlight, water and carbon dioxide, by the process of photosynthesis are considered as the autotrophs
Probably mutualism, maybe commensalism. need more detail about the effects this interaction has for algae.
Answer:
The cell wall provides protection/strength and structure to the cell