Unlike ionic bonds, covalent bonds involve the
a. gain of one or more electrons by one atom from another.
b. development of positively and negatively charged ions.
c. sharing of electrons between atoms.
d. loss of one or more electrons from one atom to another.

organ system-an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.

photosynthesis makes the glucose that is used in cellular respiration to make atp. the glucose is then turned back into carbon dioxide, which is used in photosynthesis. while water is broken down to form oxygen during photosynthesis, in cellular respiration oxygen is combined with hydrogen to form water.