Why Do Red Blood Cells Not Have A Nucleus?

One of the often recited rules in Biology is that all living things possess a nucleus. This is generally true but the red blood cell is a significant exception to this rule. It develops from progenitor cells with nuclei but as red blood cells mature, they lose their nucleus completely.

This is all part of the red blood cell's adaptations for its function of carrying oxygen around the body. Each cell is packed with a protein called haemoglobin, which attracts oxygen very strongly when blood flows through the lungs. The oxygen passes from the air in the alveoli and into the blood through the alveoli and capillary wall. Because the red blood cell has no nucleus (which would be a large spherical structure in the middle of the cell) it can use all of its volume for haemoglobin, so can carry as much oxygen as possible.

Its other adaptation to its function is that it has a biconcave shape – this enables it to have a large surface area for picking up oxygen in the first place.

Red blood cells does not have a nucleus as, they need space for oxygen to go in. It's only because the ONLY job that the red blood cell's going to do is to transfer oxygen to other parts of your body. The red blood cells cannot do cell division, that's why some people have leukemia, where the white blood cells overtook the number of the red cells. Hope you like my information.

Because that way there is more space for it to carry more oxygen around.

so they have more room to hold haemoglibin

Because a nucleus decreases the amount of space that a RBC has to transport oxygen to the body and CO2 from the body.

Having a nucleus is reducing the surface area that the production of oxygen can act on, and so decreasing the rate of oxygen production, thus the rate of respiration decreases too.

This is so that the cells can carry as much oxygen as possible however, if there is a nucleus the red blood cell would only be able to carry a small amount of oxygen, due to that fact that a nucleus is quite big.
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Rbc are mad so they do not contain nucleus