Approximately 75% of the Earth's surface is covered in water. Why is water considered such a precious resource?

The skeletal system performs a variety of functions that are crucial to maintaining life processes. what function is performed in the bone marrow, but not in the ossified bones of the skeleton? a oxygen transportation c mineral storage b. muscle attachment d red blood cell production

Can someone i have no idea of how to do this.

Which of these parts of the membrane large moecules pass through it ?