RESPIRATION: Meaning, Stages, Conditions Required, Characteristics

Respiration can be defined as biochemical activity of the cell, in which glucose is broken down by a series of reactions, controlled by enzymes, to release energy.


[Photo credit: Regis Frey]


Respiration is characterized by the breathing in of oxygen and breathing out of carbon dioxide. Oxygen breaks down the food substances (glucose) to release energy. The energy released by this process is used in various life processes.

Stages of Respiration
The process of respiration is in two stages: External Respiration and Internal(tissue) Respiration.

1. External Respiration: This is the exchange of gases between the environment and the respiratory organs of an organism. The process of breathing in oxygen is known as inspiration or inhalation while the process of breathing out carbon dioxide is known as expiration or exhalation.

2. Internal(Tissue or Cellular) Respiration: This is the process by which food substances are oxidized within the cells to release energy, carbon dioxide and water. It only takes place when inhalation occurs, i.e when oxygen is breathed in. The oxygen breathed in is used to oxidize the food substances. Carbon dioxide, water and energy are the products of this process.

It can be represented by the equation:

C₆H₁₂O₆ + 6O_{2 ------>} 6H₂0 + 6C0₂ + Energy

Condition Required for Respiration

For efficient respiration to take place, the following conditions are required:

1. Respiratory organ: Respiratory organ refers to the organ through which oxygen is taken into the body and carbon dioxide, water vapor, are given off. In other words, respiratory organ is the organ through which gaseous exchange takes place. e.g lungs in mammals and gills in fish
2. Respiratory medium: By respiratory medium, we refer to the surroundings, from which an organism obtains oxygen. e.g air and water
3. Transport medium: Transport system refer to the system which moves the dissolved gases, e.g oxygen, around the body to all cells and eliminates gases, e.g carbon dioxide, out of the body. An example of this is blood.
4. Ventilation: Ventilation is the movement of air or water, in one direction over the respiratory surface. It helps to renew the air or water near a respiratory surface with fresh ones. It increases the rate of gaseous exchange.
5. Respiratory surface: This refers to the surface of a respiratory organ e.g lungs.

Features of Respiratory Surfaces

The following are the features of the respiratory surfaces of living thing (plants and animals):

1. They are moist.
2. They are permeable to allow the movement of gases in and out.
3. They are highly vascularized - equiped with capillaries or similar network to transport diffused gases.
4. They have adequate supply of transport medium.
5. They are thin-walled to shorten diffusion distance and make diffusion easier and faster.
6. They have a large surface area to aid easy diffusion of gases.

Differences Between Respiration And Photosynthesis

Respiration	Photosynthesis
It takes place in all living cells	It takes place in plants only
It takes place at all times	It takes place in the presence of sunlight only
Food substances are broken down	Food substances are built up
It releases energy	It makes use of energy
It results in a decrease in weight	It results in increase in weight
oxygen is used	Oxygen is released
Carbon dioxide and water are released	Carbon dioxide and water are used

Read also: Respiratory system in unicellular organisms, insects, fish and frog

Categories: Biology, Respiration, Respiratory System