Q.Mitochondria are described as 'semi-autonomous organelles' mainly because they:

The mitochondrion is a double-membraned organelle whose inner membrane folds into cristae to maximise surface area for ATP synthesis, enclosing a matrix that carries its own DNA and ribosomes.

(This answer describes and labels the structure in words, since a hand-drawn figure cannot be rendered here.)

Outer membrane: a smooth, continuous membrane that forms the outer boundary of the organelle and is freely permeable to small molecules and ions.

Inner membrane: located just inside the outer membrane, it is highly folded into finger-like or shelf-like projections called CRISTAE, which extend into the matrix. This folding greatly increases the inner membrane's surface area. The inner membrane bears numerous small, stalked particles on its matrix-facing surface called OXYSOMES (F0-F1 particles/ATP synthase complexes), the actual sites of ATP synthesis during oxidative phosphorylation. The inner membrane is selectively permeable and houses the electron transport chain.

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