An organelle is a unit found inside a cell that performs a specific function. The name alludes to the way organs in your body have specific functions. Examples of organelles are the nucleus, mitochondria and chloroplasts. More on Wikipedia.
Li and colleagues combined the use of transmission electron microscopy, x-ray microtomography, and transcriptome methods to characterize the major anatomical and molecular changes that occur during the development and death of velamen radicum cells of Cymbidium tracyanum, a typical epiphytic orchid.