The oxygen atom shares its two electrons with the hydrogen t…

The oxygen atom shares its two electrons with the hydrogen to form H2O through a [covalent] bond, like they are having a potluck party.  On the other hand, table salt NaCl is formed through an [ionic] bond where sodium gives one of its electrons to the chloride, like it never gets it back. 

Cells are small enough to facilitate all the basic functions…

Cells are small enough to facilitate all the basic functions of living organisms, including maintaining cell structure, regulating materials in and out, reproducing and removing wastes, and more.  Explain why the cell has to be small enough to function efficiently and what the advantages of reducing its size are, as you see in the picture comparing one large cell to eight small cells in the same volume.