Respiration

• Respiration is defined as the catabolic biochemical process during which organic compounds break down in order to release energy
• The organic compounds that are broken down are called the substrates. Glucose is the most common substrate.
• The general equation for respiration is C₆H₁₂O₆ +6O₂6CO₂+6H₂O+ 38ATP
• Breathing provides the mechanism necessary to take in oxygen and give out carbon dioxide that is a waste gas. It is a physical process and part of respiration. Respiration is a biochemical and physical process.

Respiration takes place in the following three stages:

External Respiration

The exchange of gases between the environment and the body is called external respiration or gaseous exchange.

Internal Respiration

The exchange of gases between the body spaces or fluids and the cells is called internal respiration or tissue respiration. The area over which this exchange takes place is called the respiratory surface.

Cellular Respiration

It takes places within the cells of an organism. biochemical processes involved in respiration break down the substate to release energy in the tissues within the cells of the organism. Thus it is called cellular respiration.

• Gaseous exchange in plants takes place through the stomata in the leaves, lenticels in the stem and general surface of the roots
  
  
• Gaseous exchange in earthworm takes place through its skin. The skin always remains moist and is in close contact with the blood vessels so that gaseous exchange can take place.
  
  
• Gaseous exchange in fish takes place through specialised structures called the gills. The fish utilises the oxygen present in water and the carbon dioxide liberated is also dissolved in the surrounding water. The gills are constructed so as to draw maximum amount of oxygen from the water which flows through them.
  
  
• Gaseous exchange in grasshopper takes place through the spiracles, the pores on the body wall. The pores open into a interconnected air tube system that directly takes the oxygen to the tissues and brings the carbon dioxide from them to the outside.
  
  
• Gaseous exchange in humans takes place with the help of a pair of lungs. The lungs are situated in the thoracic cavity next to the heart and are connected to the outside with the help of bronchi and trachea.
  
  
• Air is drawn into the lungs by the process of inspiration and expelled by expiration. These are called the breathing movements.
  
  
• The breathing movements are carried out with the movement of the rib cage and the diaphragm along with the help of muscles. Inspiration involves outer intercostal and abdominal muscles whereas expiration involves inner intercostal and abdominal muscles.
  
  
• Lung volume and other respiratory volumes can be measured by spirometer
• The respiratory tract consists of nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles and the alveoli. Alveoli are the units of the lungs.
  
  
• Alveoli form the respiratory surface where the gases are exchanged with the blood coming from the heart. The purified blood goes back to the heart.
  
  
• The oxygen is transported to the different parts of the body through the circulatory system. The red blood cells in the blood have pigments called haemoglobin which transport oxygen to the tissues. From the tissues, most of the carbon dioxide is transported as bicarbonate ions in the plasma (outside red blood cells) of the blood.
  
  
• During cellular respiration glucose undergoes glycolysis forming pyruvic acid. The pyruvic acid then enters into the Kreb's cycle. The products of Kreb's cycle enter into the electron transport system which liberates energy. The total energy produced during respiration is stored in 38 ATP molecules.
  
  
• There are two types of respiration based on the availability of oxygen. Aerobic respiration makes use of oxygen and produces carbon dioxide, water and 38 molecules of ATP. Anaerobic respiration takes place in the absence of oxygen. The products formed may be ethanol (alcohol) and carbon dioxide or only lactic acid. In both the cases, the energy released during anaerobic respiration is only 2 ATPs.
  
  
• Anaerobic respiration is a commercially important process
• Respiration along with photosynthesis helps to maintain the delicate oxygen-carbon dioxide balance of nature