Ferns are part of Plantae and flatform and humans lie under Animalia kingdom. The major difference is photosynthesis. Ferns are autotrophs and can synthesize their own food, whereas animals can't because they are heterotrophs. Also, the cells of the plants contain cell wall which is absent in animals. This is because animals are mobile, so they can protect themselves from harsh environmental conditions. But plants are immobile, so the cells need to be more rigid for the adverse conditions.