Answer: every living thing in this food web uses oxygen gas and releases carbon dioxide back into the environment.
Explanation:
Breathing is the process by which living beings exchange gases with the external environment. It consists of the entrance of oxygen to the body of a living being and the exit of carbon dioxide from it. It is indispensable for the life of aerobic organisms. Depending on the type of organ in charge of the process, breathing can be pulmonary as in mammals, tracheal in arthropods, gill in fish or cutaneous in annelids. The exchange can occur with atmospheric air as in birds and mammals or take place in the aquatic environment which also contains oxygen and dissolved carbon dioxide.
Oxygen is needed to perform a process called cellular respiration. This concept of cellular breathing or cellular respiration is different. It is the set of biochemical reactions by which certain organic compounds are completely degraded inside the cell, by oxidation. This metabolic process needs oxygen and provides usable energy for the cell (mainly in the form of ATP). In aerobic breathing, oxygen is required which acts as the ultimate acceptor of electrons. <u>Oxygen plays a key role in increasing ATP production from 4 molecules per glucose molecule to approximately 30 molecules of ATP per glucose molecule</u>.
In other words,<u> cellular respiration involves a metabolic process by which cells reduce oxygen and produce energy and water and carbon dioxide as a waste product. And this is done to metabolize glucose which is the main source of energy.</u>
So, we need oxygen to get energy from the food we eat. This oxygen is breathed in from the environment. And carbon dioxide is released which is a waste product of that process in which energy is obtained from food.
