The valence electrons an element has in its outer shell, the easier it is to complete. The electron shells an element has, the easier it is to fill its outermost shell. Reactivity in nonmetals as you go from left to right in a group, and as you go from top to bottom.

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1) clean up you lab area2) dispose of the chemicals as instructed by your teacher3) put everything back where it belongs unless your teacher tells you otherwise4) dispose of gloves5) wash hands with soap and water

Mitochondria produce atp, a high energy compound. atp is used for all sorts of enzyme-mediated reactions, such as making proteins/nucleotides/etc, certain compounds cross the cell membrane, muscles move, etc.  without this source of energy, a cell will die. it will not be able to repair itself, defend against pathogens, etc.