* Constantly changing: New species are being discovered all the time, and our understanding of existing organisms is continually evolving.
* Difficult to classify: Determining what constitutes a distinct species can be challenging, especially for microscopic organisms.
* Focus on Kingdoms: While there are many different types of eukaryotic organisms, it's often easier to categorize them into the major eukaryotic Kingdoms:
* Protista: Single-celled eukaryotes like algae and protozoa.
* Fungi: Multicellular organisms like mushrooms, yeasts, and molds.
* Plantae: Multicellular photosynthetic organisms like trees, flowers, and ferns.
* Animalia: Multicellular organisms that obtain food by eating other organisms.
So, instead of a precise number, think of it this way:
* All multicellular organisms: Every plant, animal, and fungus is made up of eukaryotic cells.
* Many single-celled organisms: A vast diversity of protists are eukaryotic, adding significantly to the number of organisms with eukaryotic cells.
It's safe to say that millions of species on Earth are eukaryotic, making it the most abundant type of cell on the planet.
