Animals obtain energy for their cells by feeding on photosynthetic organisms such as plants and algae or other organisms. All energy comes from the sun and some of this energy is stored in the organic molecules of food. The process which generates oxygen as well as organic molecules that are used by eukaryotes in their mitochondria for cellular respiration is photosynthesis.
The chemical elements that are essential to life are recycled as the waste products of cellular respiration, carbon dioxide and water, are the key materials for photosynthesis, which takes place in the chloroplasts of plant cells.There are two general types of metabolic pathways, catabolic pathways and anabolic pathways. Cellular respiration is an example of a catabolic pathway. These pathways release energy while breaking down organic molecules into simpler molecules. Organic compounds possess potential energy due to the arrangement of their electrons in the bonds of the atoms. These compounds go through exergonic reactions, a chemical reaction that releases energy as the bonds between atoms are broken, and degrades complex organic compounds into simpler waste products with less potential energy.
The most efficient catabolic pathway is aerobic respiration, in which oxygen is consumed along with the organic fuel. For example, as a person jogs outside, the food he ate earlier would be used as fuel along with an increase breathing rate bringing more oxygen into his lungs to be exchanged in the blood. As he jogs, his muscles demand more oxygen to burn more fuel as energy in his cells. His body’s arteries supply his muscles with organic molecules and oxygen. In cellular respiration, energy stored as fuel is converted to ATP, adenosine triphosphate, inside a cells mitochondria. ATP is the source of energy in the cell and powers the work of a cell, such as contractions of the jogger’s leg muscles.
