Cells in both plants and animals use cellular respiration as a means of converting stored energy into a chemical that individual cells consume. Adenosine triphosphate (ATP) is a chemical food that all cells use. Plants first create a simple sugar through photosynthesis. Individual cells then break down that sugar through cellular respiration.
The reason plants create glucose is that it is an excellent means of storing the sun’s energy for later use by the plant. Dissolved in water, glucose is easy for the plant to move into all its components -- roots, leaves, stems, fruit, or flowers. The plant uses glucose as the energy source to carry on all its metabolic functions. It is at the cellular level that everything changes.
Overall Chemical Reactions
Chemically, photosynthesis and cellular respiration are total opposites, even though both must occur for plant survival. During photosynthesis, the plant builds glucose from sunlight, water and carbon dioxide. The plant releases oxygen as a byproduct during photosynthesis. As cells tear apart glucose molecules and create ATP, they expel water and carbon dioxide as byproducts of cellular respiration. The plant recaptures some of the carbon dioxide and water expelled by the cells and recycles them for glucose production.
The Process of Glycosis
As with photosynthesis, the actual chemical reactions that take place during cellular respiration are complex, and they must take place every time the cells have the need to consume ATP. The first steps in cellular respiration reactions are called glycosis, and they take place in the absence of oxygen. This process occurs in the cell’s cytoplasm, which is a gel material contained inside the plant’s individual cells. The cell makes a tiny amount of ATP during glycosis, but the primary reason for this step is the creation of intermediary chemical substances from glucose. In all, ten chemical processes occur during glycosis.
The second phase of cellular respiration and ATP creation is even more complicated than glycosis, involving another series of chemical reactions. This phase is termed aerobic respiration, and it must occur in the presence of oxygen. Floating inside the cell’s cytoplasm are tiny organelles called mitochondria. These organelles perform the function necessary for the occurrence of aerobic respiration. Mitochondria use enzymes as a means of breaking down those chemical substances created during glycosis. The cell then reassembles the resulting atoms into ATP molecules. The cell makes a net of two ATP molecules from each molecule of glucose. The gain is net because cellular respiration itself uses up some of the cell’s ATP.