The structure present in both plant and yeast cells but not bacterial cells is a nucleus.

Here's why:

* Plant and yeast cells are eukaryotes. This means they have a true nucleus that houses their DNA.

* Bacterial cells are prokaryotes. They lack a true nucleus and their DNA is located in a region called the nucleoid, which is not enclosed by a membrane.

Let me know if you'd like to learn more about any of these cell types!