How do valence electrons affect living organisms?
Wow - in lots of ways! This is a very open ended question.
Valence electrons are what determine how atoms bond to each other. The molecules of water in our bodies are held together by covalent bonds because of the valence electrons which are shared between hydrogen and oxygen atoms.
The valence electrons of molecules give those molecules many of their properties. For example, valence electrons are shared pretty evenly in non-polar molecules like fats and oils but are shared unevenly between atoms of polar molecules like sugar. These interactions determine which substances can and which ones can't dissolve in water.
The molecules that make up your cells are held together by covalent bonds.
Breaking old chemical bonds and forming new bonds involves energy. This means that metabolic processes will either use energy or release energy, and valence electrons are involved!
You can even get static shocks because of valence electrons.
p.s. If this is for a homework assignment or a take home exam, you should base your work off of this response and other research that you do to find out more information, but not submit this summary as your individual work.