They use the process of respiration
The cation that is likely to be found in place of Fe(ii) in the square planar binding domain of hemoglobin is the Cobalt ions (Co2+)
Cobalt ion is closely related to Iron (ii) ions as a transition metal and can support a square planar coordination environment.
CO2 i think if you understand so mark me as brainliest please.
Gold fold experiment replaced the plum pudding model