Algae and plants are similar organisms because both are autotrophic organisms which are able to produce their own food by the process of photosynthesis. The main difference between the two is the level of complexity. Algae are comparatively simple organisms, their structure ranges from single celled to multi-cellular organisms. They do not exhibit true roots, stems and leaves like plants. The plants exhibit complex specialized structure for transport of water, nutrients and to perform reproduction. The smallest to largest plant will exhibit roots, stems and leaves.
