A mitochondrion is described as a cell within a cell mainly because it:

1. The claim rests on the mitochondrion having the machinery a cell needs to run itself. 2. It carries its own circular DNA and its own ribosomes, so it makes some of its own proteins. 3. It is bounded by a double membrane, matching a cell's own boundary. 4. It has no nucleus, no Golgi apparatus and no cytoplasm — those belong to the cell around it. 5. Naming a nucleus or cytoplasm is the common slip, and drawing three layers instead of two is the matching drawing error. _Source: NECTA ACSEE 2023 Biology 133/1, Question 1: Cytology_