Eukaryotic cells have complex internal structures that allow them to be larger and more specialized than prokaryotic cells. They have a nucleus that contains their DNA and organelles like the endoplasmic reticulum, Golgi apparatus, mitochondria, and chloroplasts that perform specialized functions. Eukaryotic cells also have cytoskeletons and can develop external structures like flagella and cilia. This complex internal organization allows eukaryotic cells to form multicellular organisms and carry out complex processes like photosynthesis.