An organelle is a specialized cellular structure in eukaryotic cells analogous to an organ in the body. Organelles are discrete structures within the cell that perform a specialized function. Most are surrounded by internal membranes and can be seen in the light or the electron microscope. Organelles increase the efficiency of cellular processes by concentrating the factors necessary to carry out specific biochemical reactions separate from the rest of the cell. Bacterial cells do not contain organelles or intracellular membrane-bound structures. Examples of organelles are lysosomes, nucleus , mitochondria , and the endoplasmic reticulum .
Stephen A. Adam