Liver cell. Coloured high resolution scanning electron micrograph of a liver cell (hepatocyte). At centre is the nucleus with its chromatin fibres (spongy). The chromatin contains the chromosomes which hold the genetic instructions. Mitochondria (red saw-toothed) are the sites of energy production. The high number here indicates a metabolically active cell. The stacked membranes (yellow) are endoplasmic reticulum (ER). On some ER ribosomes give the membranes a granular appearance. This rough" ER is involved in protein synthesis. "Smooth" ER (without ribosomes) is involved in fat metabolism. Magnification unknown."