Unicellular organisms lack the systems that help multicellular organisms function. For example: they do NOT have excretory or digestive systems. How do these
organisms use food for energy and then get rid of its wastes? Think CELLS and
ORGANELLES!

We are all familiar with many of the organ systems that comprise the body of ... Later chapters will focus on animals, such as sponges that have no organs at all, and other organisms that lack many of the organ systems we take for granted. ... into and out of the cell by regulation of the cell membrane and its functioning.

Explanation:

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