Here's why:
* Mature red blood cells lose their nuclei during development. This allows them to carry more oxygen. The lack of a nucleus makes them biconcave discs, increasing their surface area for gas exchange.
* Other human cells, including muscle cells, nerve cells, skin cells, and all other cell types, contain nuclei. The nucleus holds the cell's DNA, which is essential for all cellular functions.
Let me know if you have any other questions!
