Respiration as one of the characteristics of living things can be defined as the ability of a living thing to respire or exchange gases between itself/himself and its/his own non-living environment. Living things exchange gases with their immediate environment. For instance, all animals breathe in oxygen (Inspiration/inhalation) and expel carbon dioxide (Exhalation/Expiration). The main purpose of respiration in living organisms is energy production with the intake of oxygen which helps in the breaking down of complex organic substances into carbon dioxide, water and energy in the form of Adenosine Triphosphate (ATP) during a complete oxidation. It can be divided into two major groups: internal respiration and external respiration. These two major shall be discussed in details as follows:
1. Internal respiration- This type of respiration occurs in the cells that is why it is referred to as cellular respiration. The two gases mentioned early on (Carbon dioxide and Oxygen) are exchanged within the cells. The respiratory organs that are involved in this type of gaseous exchange include the following: nose, pharynx, larynx, trachea, bronchi and lungs.
2. External respiration- This is the exchange of gases between the external environment and a distributing system of the living-thing e.g. lungs of higher vertebrates, tracheal tubes of insects, stomata of plants etc.
Respiration can also be defined with respect to the presence or absence of oxygen in the energy production during respiration. The type of respiration that occurs in the presence of oxygen is called Aerobic respiration. It takes place in the mitochondria and requires oxygen and glucose thereby producing carbon dioxide, water and energy.
Furthermore, any type of respiration that occurs in the absence of oxygen is referred to as anaerobic respiration. This takes place in the cell cytoplasm and produces lactic acid.
CONDITIONS NECESSARY FOR RESPIRATION
1. Respiration medium: It refers to the surroundings of the organisms from which it obtains oxygen which include air and water.
2. Respiratory organ: This is the organ through which oxygen is taken in to the body and carbon dioxide and water vapour are given out e.g. lungs in mammals, gills in fish etc.
3. Transport medium: This is the system which moves the dissolved gases e.g. oxygen around the body to all the cells and collects the gases e.g. carbon dioxide which needs to be eliminated from the body e.g. blood in mammals.
4. Ventilation: The movement of water or air in one direction over the respiratory surface is called ventilation.
5. Respiratory surface: It refers to the definite surface of the body where gaseous exchange takes place e.g. the surface of lungs or a gill.
Characteristics of Respiratory Surfaces
1. Respiratory surfaces must be moist
2. It must be permeable to allow gases to pass in and out of it
3. It must be thin-walled to shorten diffusion distance making it easier.
4. It must have adequate supply of transport medium e.g. blood
5. Respiratory areas must be highly vascularized, i.e. equipped with capillaries.
Interdependence of Animals and Plants during respiration
Animals and plants are largely interdependent as far as respiration is concerned. Animals breathe in oxygen and expel carbon dioxide while plants take in the carbon dioxide and expel oxygen during the day. During the night, plants consume oxygen but they don't release any. One of the byproducts of animal respiration, carbon dioxide is used up by plants during photosynthesis while oxygen that is released during photosynthesis as a byproduct is used up by animals during respiration. What follows after respiration from the acronym MR NIGER CAD is "N" which stands for nutrition!
