The cell is the smallest unit capable of performing life’s function. They form the building blocks of an organism. They possess many organelles of various structure and function:
Animals and plant cells organelles have some variation, example: animals have no cell wall or chloroplast but plants do.
Cell size is limited because of surface to volume ratio, which decreases as cell size increases. Thus cells cannot get too large or too small because there might be enough DNA to support life, with the exception being viruses.
Prokaryotes are single celled organisms with no true nucleus, example: bacteria
Eukaryotes are multi or single celled organisms. They possess a true nucleus. Example: Protista, animals and plants.
These also have many similarities and differences in terms of structure.