Respiration
Adrian Whyte and Joanna Johnson, Contributor

Lower sixth-form science student, Toshiro Russell, explains the structure of the DNA nuecleotype during biology class at Herbert Morrison Technical High School, in Montego Bay, recently. - Claudine Housen Photo

MANY PEOPLE confuse the terms respiration, breathing and gaseous exchange thinking that they are one and the same, but this is not so.

Breathing is the mechanism in animal which brings oxygen to a respiratory surface.

Gaseous exchange is the exchange of gases at a respiratory surface.

Respiration is a series of reaction which releases energy from foods in all living cells. The energy that is released is stored in a chemical called Adenosine triphosphate or ATP for short.

There are two types of respiration:

Aerobic respiration and anaerobic respiration

Aerobic respiration occurs in the mitochondria of cell. Here, glucose is oxidised (combined with oxygen) to produce carbon dioxide, water and energy.

Glucose + oxygen carbon dioxide + water + energy

* Although glucose is the most popular sugar to be used in this process, it is not the only one that can be used; actually any sugar can be broken down to give energy.

* Fats can also be used in the process of respiration.

* Also note that aerobic respiration is actually a burning process! The food is actually being burnt to give off the energy! Amazing!? Let's take a closer look at the formula.

* Glucose in the presence of oxygen gives of energy and Carbon dioxide. This is a classic case of combustion where heat is normally the energy given off. By the way, heat is also given off during respiration. Hence you usual warm feeling.

* The difference between usual combustion and aerobic respiration is a controlled process that uses enzymes to release the energy in a very controlled manner. Thus we do not burn up from the process.

* A next difference is that the energy released is not all heat; some of it is chemical in nature (ATP).

* Note here that this equation is very similar to a photosynthesis equation ­ but in reverse.

Anaerobic respiration occurs in the cytoplasm of cells. Here cells carry out respiration without the use of oxygen. In anaerobic respiration glucose is not completely broken down therefore less energy is released than from aerobic respiration. Anaerobic respiration occurs in many types of organisms, and only the end products usually variy:

* Anaerobic respiration in yeast cells involves the breaking down sugars into ethanol (alcohol) and carbon dioxide,

glucose ethanol + carbon dioxide + energy

a process known as fermentation. Fermentation in yeast cells is also utilised commercially in such processes as baking bread, making wine and beers. Anaerobic respiration in muscle cells occurs when oxygen is not enough. Oxygen available to oxidise the glucose molecules, so what happens is that the glucose is now broken down into a substance called lactic acid. In this case carbon dioxide is not given off.

Lactic acid is a mild poison which causes muscle cramps if allowed to build up in the blood stream. So an individual has to rest in order to break it down into carbon dioxide and water. This now require oxygen. The amount of oxygen that is needed to oxidise the lactic acid that is built-up during anaerobic respiration is known as an oxygen debt.

Why would it be necessary for muscle cells to respire anaerobically?

Under normal conditions muscle cell respire aerobically. However, there are times when these do not get sufficient oxygen, such as during strenuous exercise, so they are then forced to respire anaerobically so that they can be able to provide energy for the muscles to carry out their functions until enough oxygen is present again to respire aerobically.

Q: Why does anaerobic respiration produce less energy than aerobic respiration?

* Adrian Whyte and Joanna Johnson teach Biology at Ardenne High School
masterbio@gmail.com.