All eukaryotic cells have within them a variety of different structures called organelles. Organelles are small and function much like organs function in a large organism. Some organelles are responsible for gathering cell energy, others for controlling cell activities.Note-although this organelle is also found animal cells, the vacuoles from plant cells are drastically bigger and play a much more important role in the processes of the cell.
HIV crossed from chimps to humans in the 1920's in what is now the Democratic Republic of Congo. This was probably as a result of chimps carrying the Simian Immunodeficiency Virus (SIV), a virus closely related to HIV, being hunted and eaten by people living in the area.
There are two types of HIV; they are HIV-1 and HIV-2 and they have many subtypes. HIV-1 is the cause of the current worldwide pandemic while HIV-2 is found in west Africa but rarely elsewhere. HIV-2, which is transmitted in the same ways as HIV-1, causes AIDS much more slowly than HIV-1. HIV-1 resulted from human infection by SIVcpz that infects chimpanzees and HIV-2 resulted from infection by SIVsmm harbored by sooty mangabeys. HIV-2 is closely related to the SIV found in west Africa.