C4 photosynthesis

​Photosynthesis in all plant species involves multiple steps with many enzymes that can be divided into two main steps occurring in the membranes making up most of the content of chloroplasts. 
 
Light energy is used to split H2O molecules into its hydrogen and oxygen atom components freeing up electrons. These electrons allow provide the energy to unite the oxygen and carbon form the glucose molecule (C6H12O6), releasing the excess O2 molecules that eventually escape through the stomata. Electrons binding the components of glucose later are released in the respiration processes within the cells, providing energy for synthesis of proteins for growth in plants plus movement in animals.
 
This photosynthesis process is present in most plant species.  The release of oxygen through stomates is dependent upon open stomates and therefore is dependent of light being absorbed by the stomate guard cells and sufficient water transported from the roots to maintain those cells to swell.  Thus, at night and during droughts most plants no longer can absorb the CO2 needed for more glucose synthesis and the excess oxygen is consumed in nighttime metabolism.  This is a character of most plants with C3 photosynthesis processes.
 
Some species, including corn, have evolved a system to avoid this wasteful system.  Chloroplasts in the corn leaves make normal photosynthesis process but then break down the C3 molecules, have them transfer them to the specialized, vascular bundle cells surrounding the vascular system that are loaded with special chloroplast for C4 molecules.  These molecules are then enzymatically combined to make sugar which is moved elsewhere in the leaves and other parts of the plant.  This system occurs in species that are native to dry, hot environments such as that of corn’s central America origin.  The ultimate advantage is that corn can continue to produce carbohydrates despite environments that cause stomates to close.  Whereas most C3 plants such as soybeans, wheat and rice do not utilize light intensity greater than 3000 foot-candles, corn photosynthesis rate keeps increasing with light intensities to our maximum sun brightness of 10000 foot-candles.  Those few cells surrounding the xylem and phloem of a corn leaf vein have a special role in allowing the photosynthetic efficiency of maize.
 
This type of photosynthesis drives the rapid growth of a corn plant and ability to store excess glucose as starch in the grain.