Q.What are the Semi-autonomous organelles in a cell? Give a very brief account of any such organelle you know.

Mitochondria and plastids are semi-autonomous organelles because each has its own DNA and ribosomes but still depends on the nucleus for most of its proteins.

Semi-autonomous organelles are organelles that contain their own genetic material (DNA) and protein-synthesising apparatus (ribosomes), which allows them to independently synthesise some of their own structural and enzymatic proteins and to divide/replicate somewhat independently of the cell cycle. They are called only 'semi'-autonomous (not fully autonomous) because the bulk of their proteins are still coded for by nuclear genes and imported from the cytoplasm.

Example — Mitochondrion:

• Double membrane-bound organelle; the outer membrane is smooth, the inner membrane is folded into finger-like cristae that increase surface area for oxidative phosphorylation.
• Called the 'powerhouse of the cell' as it is the site of aerobic respiration and ATP synthesis.
• Contains its own circular, naked (histone-free) DNA, along with 70S ribosomes (similar to prokaryotic ribosomes) and the RNA needed to synthesise a small set of its own proteins. …