The primary function of a is to build and repair body tissues and structures.

The primary function of a protein is to build and repair body tissues and structures. Hemoglobin is the protein molecule found in the red blood cells or erythrocytes that carries oxygen fom the lungs to the body’s tissues and returns carbon dioxide from the tissues back to the lungs. The protein molecule in hemoglobin contains iron containing compound that is vital in transporting oxygen and carbon dioxide in the blood. It has no attraction for carbon monoxide. The cells that would need a large number of mitochondria to function and survive are the eukaryotes. They need this in order for protein to be consumed and converted to energy. 

Other organisms can change their behavior to take the place of the plants in the ecosystem.