Image from Wikipedia.org under the item ‘Bacteial conjugation’

Sometimes a bacterium transfer its DNA duplication to another one by a bacterial conjugation (that is a tube-like protrusion from its membrane which injects into another bacterium) for mysterious purpose. Rosemary J. Redfield called this one form of sex that bacteria have. In this form a bacterium should first create the protrusion, or pilus, which can analogously called an ‘erection’. This process involves the spontaneous deformation of the bi-layer membrane of the cell, which, along with other membrane-directed cellular behaviors, have been a hot topic of biophysics for quite a long time. Recently, scientists from Jilin University of China experimentally observed a similar process in a kind of well-defined synthetic vesicles which protrude with time multiple tubular structures from the original spherical shape. Although the real mechanism of this process is not assured, The researchers believe that this finding maybe helpful for the understanding of the dynamics of the vesicle evolution in cellular events.

Image from Wikipedia.org under the item ‘Aerial refueling’

Similar scenes are there in aerial refueling.