Fluid-filled sacs surrounded by a membrane almost identical to the cell membrane of human cells are called lysosomes.

Here's why:

* Lysosomes are membrane-bound organelles found in animal cells. They contain a variety of hydrolytic enzymes that break down cellular waste products, worn-out organelles, and engulfed materials.

* The lysosomal membrane is indeed similar to the cell membrane, but with additional adaptations to protect the cell from the destructive enzymes within.

While other organelles like vacuoles are fluid-filled, they don't have the same membrane structure or function as lysosomes.