Question

Nitrogen fixation is inhibited by oxygen. However, in aerobic nitrogen fixing bacteria, nitrogen is fixed in presence of oxygen. Nitrogenase in such organisms is protected by which one of the following mechanisms:
(A) Channelizing oxygen to form ozone
(B) Removal of oxygen by metabolic activity
(C) Utilizing oxygen for membrane remodeling
(D) Utilizing oxygen for synthesis of pentapeptide chains in peptidoglycan.

Answer 1

Hint:Nitrogen fixation is a process in which nitrogen is converted to ammonia. The nitrogen fixation process is carried out in soil naturally by nitrogen fixing bacteria such as Azotobacter. There are some nitrogen fixing bacteria present which have a symbiotic relationship with other plant groups such as legumes.

Complete answer: The process of nitrogen fixation is carried out by nitrogenase which is present in microbes. The symbiotic nitrogen fixing bacteria invades the root hairs of host plants. Over there they get multiplied and the stimulation of root nodules and the enlargement of the plant cells and bacteria in intimate association occur. The bacteria convert the free nitrogen to ammonia within the nodules itself. This is used by the host plant for its development. This conversion of free nitrogen to ammonia is not only expensive but also sensitive to oxygen. The two proteins which make the nitrogenase irreversibly undergo denaturation due to the presence of oxygen. The system which supports nitrogenase has evolved mechanisms so that low oxygen temperature is maintained at the site of nitrogen fixation. The oxygen gas is removed by organisms by various metabolic pathways.

 So,the correct option for this answer is option (B).

Note:The soil fertility is increased by nitrogen fixing bacteria, as the plant root leaves some biologically available nitrogen there. The nitrogen fixing bacteria also helps in nitrogen cycle as at the time of organism decomposition the nitrogen in soil is transferred in the nitrogen cycle. Nitrogen fixing bacteria is important because plants cannot use free nitrogen and being an essential part of survival they convert it into ammonia for protein synthesis and other vital functions.