I believe that the basic unit of structure and function in protists and monerans is the cell. This is because cells are basic unit of structure and function of all living things. A cell is the smallest unit of life, it is the basic membrane-bound unit that contains the fundamental molecules of life and of which all living things are composed.
They survive without water by entering a special mode, otherwise called as shriveling. They can lose even 95% of water in their body and still live, even though they would look like dead plants, they would actually be alive. In the absence of water, tardigrades use a sugar called trehalose, which becomes their source of life until they find some water.
Hemoglobin has tetrahedral structure containing four heme groups that surround a globin group.
Heme is ringlike organic compound also known as a porphyrin to which an iron atom is attached. There are four iron atoms that bind four oxygen atoms and transport them to tissues.