colour of blood red????

In all human beings and vertebrates ,the colour of blood is always red????

Yes, its amazing that all the vertebrates,including humans, have red colour of blood (vertebrates means, any creature having the vertebral bones,or backbone).

This is due to presence of a protein pigment, called Haemoglobin, that imparts red colour to the blood. This protein present in the blood inside red blood cells,carries iron, and due to this iron the colour of blood is red. In other animals this iron is not present and their blood is not red. Some animals contain copper instead of iron & their blood is blue e.g. many arthopods.

ALL THE HUMAN BEINGS BLOOD IS RED.ALL CONTAIN THE SAME HAEMOGLOBIN, THE SAME IRON ATOM IN THE BLOOD,"STILL WE HUMAN BEINGS ARE DIFFERENTIATED ON THE BASIS OF ORIGIN,SKIN,CASTE & CREED, SOCIOECONOMIC STATUS ETC".

????????????????????????????????? WHY?