You can click to find out more about protein synthesis . Mitochondria Mitochondria are large organelles which are shaped a bit like fat sausages. Most cells contain many mitochondria. Mitochondria are sometimes called the 'power stations' of the cell because they burn up food molecules, in the presence of oxygen, to release energy in a process called aerobic respiration . The inner membrane of the mitochondria is folded into cristae which give a large surface area for attachment of some of the enzymes involved in respiration.
All eukaryotic cells contain endoplasmic reticulum.
The ER of a cell often takes up more than a tenth of the total cell volume. The membrane structure of both are identical, but rough ER has lots of attached ribosomes and so looks 'spotty'. Smooth ER has no attached ribosomes and so looks 'smooth'. Rough ER takes in the proteins made on the ribosomes so that they cannot escape into the cytoplasm. Small vesicles containing newly-synthesised proteins pinch off from the ends of the rough ER and either fuse with the Golgi complex or pass directly to the outer cell membrane.