The nitrogen cycle could no exist without bactria. bacteria that lived inside the ground, catch the nitrogen that has been fixed and covert it into nitrate.
Answer - B
Fish and reptiles both are ectothermic but fish have gills and reptiles have lungs. Ectothermic organisms do not have an internal mechanism of regulating their body temperature and are dependent on their atmosphere for temperature regulation. Fish, reptiles and invertebrates are examples of ectothermic organisms.