Respiration: Definition, Mechanism and Its Types

As we all know, food is the “Fuel” for cell energy production. Most living organisms require oxygen from the air to get energy from their food. This oxygen reacts with the food molecules, like glucose, inside their cells, and slowly burns them to release energy. The released energy is stored in the form of ATP molecules in the cells, and the body can use this stored energy whenever needed. The process by which organisms take in oxygen from the air and release carbon dioxide is known as breathing. Respiration is a more complex process, as it includes breathing as well as the oxidation of food in the cells of organisms to release energy. The average breathing rate in an adult is about 15 to 18 times per minute.

What is Respiration?

“Respiration” is the unique process of releasing energy from food. It is vital for life because it provides the energy needed to carry out all the essential life processes that keep organisms alive. The process of respiration which releases energy and takes place inside the cells of the body is known as Cellular Respiration which provides energy to the cell. Cellular respiration is ordinary in all living organisms. Cellular respiration has two by-products: Carbon dioxide and water. Out of which only CO₂ is considered the real waste product of respiration because its accumulation is harmful to the body. The water released during respiration is considered a beneficial product.

Respiration is a unique biochemical process that occurs in stages and involves many enzymes. Its main purpose is to release energy by oxidizing simple food molecules like glucose. Respiration is just the opposite of photosynthesis. Photosynthesis is responsible for producing food (like glucose) using carbon dioxide, water, and sunlight energy while releasing oxygen. In contrast, respiration breaks down food (like glucose) by using oxygen and releases carbon dioxide, water, and energy.

Types of Respiration

As we have studied that respiration takes place in the presence of Oxygen. Most living beings carry out aerobic respiration for example humans, animals, birds, snakes, frogs, and insects. Respiration can happen in the absence of Oxygen, though it is very rare. That means oxidation of food can occur in the presence as well as in the lack of oxygen. There are two types of respiration in Biology which are Aerobic Respiration and Anaerobic Respiration:

1. Aerobic Respiration 
2. Anaerobic Respiration

Now let us briefly describe these two types of respirations.

Aerobic Respiration

 The respiration which uses oxygen is known as Aerobic Respiration. In aerobic respiration, the food (glucose) is completely broken down into carbon dioxide and water by oxidation. Aerobic respiration forms a considerable amount of energy which gets stored in the ATP molecules. The process of aerobic respiration can be represented as:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP (Energy)

The chemical equation of Aerobic respiration can be explained as Glucose (1 molecule) with the help of glycolysis in the cytoplasm gives Pyruvate(2 molecules of Pyruvic acid). This pyruvate or pyruvic acid enters the mitochondria, where with the help of oxygen gives 6CO₂, 6H₂O, and 38ATP.

Organisms that use aerobic respiration need oxygen to live. The aerobic respiration process occurs in the mitochondria of the cells.

Anaerobic Respiration

The respiration which takes place in the absence of oxygen is called anaerobic respiration. The anaerobic respiration produces a very less amount of energy. Microscopic organisms, such as yeast and certain bacteria, get their energy through anaerobic respiration, also known as Fermentation. During this process, these microorganisms, like yeasts, break down glucose into ethanol and carbon dioxide, releasing energy. The breaking down of food by anaerobic respiration can be represented as:

C₆H₁₂O₆ → 2C₃H₆O₃ + 2 ATP (Energy)

The chemical equation for anaerobic respiration can be explained as In yeasts, 1 molecule of glucose with the help of glycolysis in the cytoplasm gives 2 molecules of Pyruvate (pyruvic acid). This Pyruvate gives 2C₂H₅OH, 2CO₂, and 2ATP in the absence of oxygen. 

We (human beings) obtain energy by aerobic respiration, but sometimes anaerobic respiration also occurs in our muscles. For example, When we do vigorous exercise, our muscles perform anaerobic respiration because oxygen gets used up quickly in the muscle cells. In humans, lactic acid is formed by the breakdown of glucose at the time of Anaerobic respiration. This lactic acid gets accumulated in the muscles and causes muscle cramps. To ease muscle cramps, you can try taking a warm bath or getting a gentle massage.

Mechanism of Respiration

When oxygen burns the food in our body’s cells to release energy, it produces waste products like carbon dioxide and water. These waste products need to be eliminated from the body. The primary function of respiration is the exchange of gases. The process of respiration involves taking in Oxygen (air) into the cells, using it for releasing energy by burning food, and then eliminating the waste products (carbon dioxide and water) from the body. The process of respiration can be written as:

Food + Oxygen →  Carbon dioxide + Water + Energy

The mechanism of respiration includes two main processes: Inhalation and exhalation.

Inhalation (Inspiration)

1. Inhalation is the first step of respiration, in which air is taken into the lungs. During Inhalation, the diaphragm (a dome-shaped muscle that is present at the base of the lungs) contracts and moves downwards.
2. Accordingly, the intercostal muscles, which are present in between the ribs get contracted, elevating the ribcage and expanding the chest cavity.
3. Because of all these actions, the volume of the chest cavity increases, and the lungs get expanded. This expansion decreases the pressure inside the lungs as compared to the atmospheric pressure outside.
4. Due to this pressure difference, the air is drawn into the respiratory tract through the nose or mouth and travels down the trachea or windpipe and into the bronchial tubes, eventually reaching the alveoli. Alveoli are tiny air sacs in the lungs.
5. The actual gas exchange occurs in the alveoli. The oxygen from inhaled air diffuses across the alveolar walls and binds the hemoglobin in red blood cells.
6. Then, these oxygen-rich blood cells get circulated to the rest of the body.

Exhalation (Expiration)

1. After complete oxygen exchange occurs, the body needs to get rid of the unwanted waste gas, Carbon dioxide (CO₂ ).
2. Exhalation is the process in which the lungs release carbon dioxide-rich air out of the body.
3. At the time of exhalation, the diaphragm and intercostal muscles relax and decrease the volume of the chest cavity.
4. The lungs recoil and return to their original size, this reduces the space within the lungs. Which increases the air pressure inside the lungs, and this air pressure is higher than the atmospheric pressure outside.
5. Due to this, the air containing carbon dioxide is forced out of the lungs and released from the body through the mouth or nose.

This Inhalation and Exhalation process continues continuously so that there is a constant supply of oxygen to the body’s cells and the removal of carbon dioxide, and maintains a proper balance in the bloodstream. The respiratory system works in coordination with the cardiovascular system(which involves the heart and blood vessels) to transport gases and sustain cellular respiration, which is very important for the body to function properly.

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