In unicellular organisms, waste products are expelled directly through the surface of the cell, as opposed to mammals, which expel urine through the urethra, which is a component of the excretory system.
Mammals are the living species included human that have war blood, with hairs on their body with backbones are all mammals.
Like other living species, female mammal produce milk in so that their newborn or young baby can be nourished and pampered.
Thus, In unicellular organisms, waste products are expelled directly through the surface of the cell
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