University of Agricultural Sciences, Bangalore

The proteins that gather light for photosynthesis are embedded within cell membrances. The simplest way these are arranged is in photosynthetic bacteria, where these proteins are held within the plasma membrane. However, this membrane may be tightly folded into cylindrical sheets called thylkoids, or bunched up into round vesicles called intracytoplasmic membrances. These structures can fill most of the interior of a cell giving membrance a very large surface area and therefore increasing the amount of light that the bacteria can absorb. # The cell wal is the tought, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and proteiction, and also as a filtering mechanism. A major functiono of the cell walll is to act as a pressure vessel, preventing over-expansion when water enters the cell. They are found in plants, bacteria, fungi, algae, and some archaea. Animals and protozoa do not have cell walls. The cell membrance plays host to a large amount of protin that is responsible for its various activities. The amount of protein differs between species and according to function, however the typical amount in a cellm embrance is 50%. Thesse proteins are undoubtedly important to a cell: Approximately a third of the genes in yeast code specifically for them, and this number is even higher in multicellular organisms.