4. when do the sister chromatids separate?

Are separated from each other during mitosis or the second division of mitosis

The two sister chromatids are separated from each other into two different cells during mitosis or during the second division of meiosis.

Explanation:

Immune system comprises of all the cells and processes responsible for the defense system in vertebrates. Skin form the first line of defense system that does not allow the penetration of pathogens inside the body. Inside the body there are certain cells called lymphocytes that play role in the defense mechanism. B lymphocytes form the antibodies against the antigens or foreign objects. Similarly T lymphocytes also helps in killing and recognizing the foreign particles.

An antigen is a foreign object that are targeted by antibodies. Antigens are recognized by antibodies present in the body.Antibodies get bind to the antigens at specific sites and triger the process of defense system.