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Q.
The cells that lack nucleus are
Cell : The Unit of Life
Solution:
Erythrocytes of many mammals and tube cells of vascular plants lack nucleus, so as to carry out specialised functions. Absence of nucleus in human $RBCs$ help them to transport maximum amount of $O _{2}$ and $CO _{2}$ across body tissues. Absence of nucleus in tube cells of vascular plants allow maximum movement of food (mostly sugar). Lymphocytes of mammals are nucleated cells.