Endosomes are membrane-bound compartments within cells that play a crucial role in transporting and sorting materials. They form when the cell membrane engulfs external substances, creating a pocket that pinches off to become an endosome. These structures help in processing nutrients, recycling cellular components, and regulating the delivery of proteins and lipids to their proper destinations. There are different types of endosomes, including early endosomes and late endosomes, which have distinct functions. Early endosomes are involved in the initial sorting of internalized materials, while late endosomes are more mature and often lead to degradation or recycling of these substances. Cell biology studies the functions and mechanisms of endosomes in greater detail.