Answer very briefly, Red Blood cells have no nucleus, then why do we call them cells?
RBC are formed in the liver and spleen when the organisjn is foetus. After birth these are formed in the red bone marrow. At the time of formation of RBC’s they have nucleus but later on they loose nucleus. Those enucleated cells perform all the functions of a cell so these are called cells.
RBC’s are surrounded by semipermeable plasma membrane. It contains homogenous cytoplasm and it is without the nucleus, endoplasmic reticulum, mitochondria, ribosomes and centrioles. RBC’s get advantage due to this condition. Corpuscles have more space to hold haemoglobin. It can as well give more oxygen by the haemoglobin to the tissue cells. So the enucleated condition is more useful to the tissue cells. The necessity of work has made them without nucleus and perform all the functions of the cells so they are called cells.