GASES

• There are 4 gases in the protoplasm which remain dissolved in its free water.
• These 4 gases are follows-

                 CO₂    >  O₂ > N₂  > H₂

• CO₂ is used in biosynthesis of urea.
• CO₂ helps in the dissociation of oxyhaemoglobin.
• In green cells of protists, algae and plants, CO₂ is used in photosynthesis as a raw material for glucose formation.
• O₂ is used in oxidation of substances.
• O₂ is a reactive gas. It release energy by oxidation of food, and is vital for life.
• H₂ is used in ETS.
• N₂ is an inert gas, and takes no part in cell reactions.
• Certain organism can make atmospheric nitrogen a component of organic compounds. This process is called nitrogen fixation and the organism capable of this are termed nitrogen fixing organisms, e.g. Azotobacter, Nostoc, Rhizobium.
• NH₃ is a toxic compound because of a potentially high pH after reaction with water.
• In lower animals, it leaves the cell by diffusion.
• In higher animals, it is changed into urea for elimination by special excretory organs.
• Nitrosomonas can oxidase NH₃ to NO^- and Nitrobacter and Penicillium, oxidase NO^- to NO^-. This process is called nitrification. The organism capable of this process are called nitrifying organism.