The primary producers of the deep-sea hydrothermal vent ecosystem are Archaebacteria, they have a chemosynthetic mode of nutrition. In most of the animals, the metabolic reactions or entire physiological functions proceed optimally in a narrow temperature range. In humans, it occurs at 37^oC temperature. However, there are microbes like Archaebacteria that flourish in hot springs and deep-sea hydrothermal vents where temperatures far exceed 100^oC. Archaebacteria sustain their life under extremes of temperature and pH. The cell membrane contains branched-chain lipids (phytanyl side chains) which decrease membrane fluidity. This chemical composition of the cell membrane enables these organisms to withstand extremes of temperature and pH.