Bacteria do not decompose non-biodegradable wastes.

Female Aedes mosquito acts as a carrier of dengue.

Carrier organisms are the organisms which carry disease-causing microorganisms to spread them from an infected person to a healthy person. All the communicable/infectious diseases are transmitted from a diseased to a healthy person through some source. Malaria is the disease for which the carrier organism is female Anopheles mosquito.

Preservatives are substances that prevent attack and growth of micro organisms in food and prevent its spoilage. So, to keep food for longer duration, preservatives are added. 

 Communicable diseases may spread from a diseased to a healthy person through air, water or food. When we sneeze, we release micro organisms into air. If they are disease-causing, they will infect the other person also. 

 Preservatives are substances that prevent attack and growth of micro organisms on food and prevent its spoilage. So, to preserve food for longer duration, preservatives are added. Jams, Jellies and squashes are sweet substances. Sugar also acts as a preservative and is added to these to store them longer. 

 High temperature prevents growth of microbes but providing high temperature for longer duration than the required time can even spoil the food. So, optimally, heating the food substance at 70^oC for 15-30 seconds, helps prevent growth of microorganisms. 

Nitrogen is a gas that cannot be directly used by plants. Rhizobium is bacteria present in root nodules of leguminous plants that converts the atmospheric nitrogen into nitrogen salts to be used in soluble form.

 Symbiotic relationship is the relationship between two groups of organisms both of which are benefited from each other in a mutual manner. Rhizobium is the bacterium, which lives in root nodules of leguminous plants. It gets its shelter from the plant and in reverse it fixes the atmospheric nitrogen to make it available to the plant. 

 Deep freezing involves keeping food  at low temperature to prevent growth of micro organisms. Canning involves preservation through cutting off atmospheric contact with food. Pasteurization is a method of preserving milk by boiling and cooling it immediately. Thereafter, immunization refers to the protection against diseases by vaccination and is thus not a method of preservation. 

Female mosquitoes contain particular enzymes that can cause malaria. These enzymes are not secreated by male mosquitoes.

 Putrefying bacteria is the bacterial form, which converts organic form of nitrogen into ammonia. This process is known as ammonification. Nitrobacterium converts nitrites into nitrates. Nitrosomonas converts nitrogen into nitrites and Rhizobium fixes atmospheric nitrogen. 

 Nitrobacterium is the bacterial form, which converts the already formed nitrites into more soluble andmore easily absorbable nitrogen salts i.e. the nitrates. 

 Nitrogen fixation is the process, which converts atmospheric nitrogen into nitrogen salts, ammonification refers to formation of ammonia from organic nitrogen, and denitrification refers to the conversion of nitrogen salts into atmospheric nitrogen back. To keep the percentage of nitrogen constant in the atmosphere, all these processes along with some other go simultaneously and the process in known as nitrogen cycle. 

 Rust of wheat is a plant disease caused by bacteria. Yellow vein mosaic of bhindi is again a plant disease but caused by a virus. Foot and mouth disease is a viral disease, which affects cattle.Citrus canker is the disease for which the causal organism is fungi. 

 Any nutrient, which is to be absorbed by the plant is absorbed in the soluble form in water and this function is performed by the roots of plants. 

Plants and animals contain nitrogen as a major constituent of their body in form of proteins in major. The percentage of atmospheric nitrogen i.e. N₂ gas is very high but it cannot be directly used and utilized by living organisms. Nitrogen does not exist in elemental form as N so can not be used also. The gaseous N¬2 from the atmospheric is first converted into such compounds, which are readily used by plants and animals and thus is the correct option