Eukaryotes are cells that contain all traditional cell parts and are highly organized to perform very specialized tasks. These types of cells are in almost every single, living thing on Earth. Without eukaryotes, we would not be alive.
Unlike prokaryotes, eukaryotes contain an organized, membrane-bound nucleus and cell organelles. The nucleus contains DNA and basically directs the cell on what it is supposed to do. You can think of the nucleus as the brain of the cell and does all directing to the other organelles. Organelles are specialized parts of the cell that performs unique and essential functions. There are many different organelles and but not all eukaryotic cells contain them all. The majority of eukaryotes will contain a mitochondria, chloroplast, and endoplasmic reticulum.
Although most eukaryotes are very small, they are still over a hundred times bigger than prokaryotes. They vary in size because of the amount of organelles they contain. Because eukaryotes have a nucleus, they can produce many, different organelles. There are some forms of eukaryotes that are made up of just one cell yet they are really big in size. These cells contain many nuclei.