Those diseases or disorders that effect human respiration are called respiratory disorders. Following are some respiratory disorders found in humans.

1. Acute Bronchitis

It occurs most commonly as a result of viral infection. It may also occur due to exposure in gases such as ammonia, chlorine and Sulphur dioxide.

2. Emphysema

Lungs affected by emphysema suffer from loss or degeneration of alveoli. It is most commonly associated with cigarette smoking and bronchitis.

3. Coronary Heart Diseases

This disease is caused due to an inadequate supply of oxygen rich blood to the heart muscles because of blocking of a coronary artery by fatty and fibrous tissue.

Test Your Understanding and Answer These Questions:

1. Name two diseases found in lungs of human beings.
2. Explain some respiratory disorders found in human beings.

The process of respiration takes place in two phases:

    1. Inspiration and
    2. Expiration

1. Inspiration

Inspiration may be defined as the process of drawing in air into the lungs. It occurs with the help of diaphragm muscles. The muscles of diaphragm contract due to which diaphragm moves in the downward direction. Due to this, the volume of chest cavity increases and it results in decrease of air pressure inside the chest cavity. Now, the oxygenated air present outside the body being at high pressure flow rapidly into the lungs by passing through nasal cavity, pharynx, larynx, trachea, bronchi and bronchioles.

Exchange of Gases

In the lungs, oxygenated air finally reaches the tiny air sacs (alveoli) by passing through bronchioles. Now, each alveoli is thin walled and surrounded by a network of very fine blood capillaries. The oxygen gas present in the air passes through the walls of the alveoli into the blood present in blood capillaries. This blood is returned to the heart to be supplied to all the tissues of the body. In the tissues oxygen is used for oxidation of food and is converted into carbon dioxide. From the tissues, carbon dioxide is absorbed by blood and carried to the alveoli of lungs for expiration.

2. Expiration

Expiration may be defined as the process of expelling out foul air from lungs. This happens when the muscles of diaphragm relax and come back to their original position. This decreases the volume of chest cavity, due to which our chest cavity contracts and pushes out carbon dioxide containing foul air through bronchi, trachea, larynx, pharynx, nasal cavity and nostrils.

Test Your Understanding and Answer These Questions:

1. Give differences between inspiration and expiration.
2. Describe the mechanism of breathing in human beings.
3. Explain exchange of respiratory gases in lungs of human beings.
4. What happens to the carbon dioxide which collects in human tissues?
5. Explain the mechanism of gaseous exchange between tissues and blood.
6. What is the normal rate of breathing in human beings under normal conditions?

The human respiratory system is made up of many organs such as nose, nasal cavity, pharynx, larynx, trachea, bronchi and a pair of lungs. But, lungs are the main respiratory organs where exchange of gases takes place. Following is the detail of human respiratory system.

1. Nasal cavity

In human beings air containing oxygen enter the body through nose. There are present two holes in our nose called nostrils. The nostrils opens behind in the nasal cavity. The nasal cavity lies above the buccal cavity. The function of nasal cavity is to moisten, warm and trap dust particles present in the air coming in it through nostrils. The nasal cavity opens behind in the pharynx.

2. Pharynx

Pharynx is a common passage for both the respiratory and digestive system. It leads into the larynx (voice box).

3. Larynx

It is also known as voice box. It lies at the top of trachea. The pharynx opens into the larynx through a slit like opening called glottis. The glottis is protected by a leaf shaped flap of cartilage called epiglottis. Epiglottis covers the mouth of glottis when we swallow food, so that food may not enter the trachea.

There is present a pair of vocal cords inside the larynx. When air passes through the larynx, vibrations are produced in the vocal cords and it results in production of sound.

4. Trachea

It is also known as wind pipe. It is 10-12 cm. long tube with a diameter of 2-3 cm. trachea is supported by 15-20 cartilaginous rings. These rings prevent trachea from collapsing when no air is present in it and also provides flexibility and strength.

At its lowerend the trachea divides into two smaller tubes called bronchi (singular bronchus)which enters the right and left lungs. The walls of bronchi are also supported by cartilaginous rings. In the lungs, each bronchus further divides into still smaller tubes called bronchioles. At the ends of each bronchiole there is present a cluster of tiny and thin walled sacs called alveoli. Each alveoli is surrounded by a network of very fine blood capillaries.

5. Lungs

In humans, a pair of lungs is present in the thoracic cavity, one on each side of the heart. These are called right lung and left lung respectively. The right lung is larger than the left lung. The right lung has three lobes and two fissures. While, the left lung has two lobes and only one fissure. Both the lungs are covered by two membranes called pleura. The fluid present in between these two membranes is called pleural fluid. It protects the lungs from mechanical injuries.

Test Your Understanding and Answer These Questions:

1. State the functions of epiglottis.
2. Name the membranes covering the lungs.
3. What is the function of air sacs in lungs?
4. What are vocal cords? What is their function?
5. Draw the respiratory system of human beings.
6. Which is the main respiratory organ in human beings?
7. Why do the walls of trachea not collapse when there is less air in it?
8. Out of right and left lung found in human which is larger in size?
9. Give differences between right lung and left lung of human beings.

In aquatic animals such as fish respiration takes place through special respiratory organs called gills, however lung fish respiration takes place through lungs. Gills are present on both the sides of the head of fish. The gills are covered by gill covers also called operculum. When the fish open its mouth, water is drawn into the buccal cavity and passed through the gills. The gills contain special type of cells that absorb the oxygen present in water. The absorbed oxygen is then supplied to all the cells of body through blood. In the cells, oxygen is converted into carbon dioxide and returned back to gills through blood. Ultimately, the gills release the carbon dioxide in water passing through them. 

The gills of fish are very efficient; it is estimated gills can extract about 80% oxygen dissolved in water. In addition to the respiratory organs, the gills have an important role in maintaining the right balance of salts in the body.

Test Your Understanding and Answer These Questions:

1. Name the respiratory organ of fish.
2. Describe the mode of respiration in fish.

Earthworms are found in the soil. In the soil they eat dead and decaying organic matter along with soil. In return, they help in aeration of soil by digging holes in it and enhance fertility of soil. In earthworms there is no specialized organ to do respiration. So, in earthworms respiration process takes place through its moist, thin and highly vascular skin. The oxygen gas absorbed by the skin diffuses into the blood and transported to all the cells of the body. In the cells, oxygen is used up for oxidation of food. During this process, carbon dioxide is produced. Then, this carbon dioxide mixes in the blood and diffused out of the body through its moist skin.

Test Your Understanding and Answer These Questions:

1. Name the respiratory system of earthworm.
2. Explain the process of respiration in earthworm.

The process of breathing in insects such as grasshopper and cockroach is very slow. Insects do not breathe like human beings. Insects do not have lungs to do respiration. In insects respiration takes place through tracheae. Tracheae are tube like structures that open on the sides of their body through tiny holes called spiracles. Each trachea is further divided into fine tubules called tracheoles which reach all the parts of the body. During respiration, the oxygen rich air enter in the body of these insects through spiracles and reach all the cells of the body by passing through network of trachea and tracheoles. Thus, every cell gets oxygen directly. In the cells oxygen gas is used up to break the food particles. During breaking up of food a large amount of carbon dioxide gas and energy is produced. The carbon dioxide produced during respiration is released out of the body through the same network of trachea and tracheoles.

Test Your Understanding and Answer These Questions:

1. Name the respiratory organ of an insect.
2. How does air reach every cell of an insect?
3. How air reaches directly inside the body of insects?
4. Describe the mode of respiration in an insect with a diagram.

Different animals have different types of respiratory organs which uptakes oxygen and removes carbon dioxide out of body. For example, in unicellular organisms such as amoeba and paramecium exchange of gases takes place through plasma membrane by simple diffusion. In earthworm, leech and frogs exchange of gases takes place through their moist skin. In insects such as grasshopper and cockroach respiration is done through spiracles and trachea. In aquatic animals such as fish respiration takes place through special respiratory organs called gills. While in all the land animals such as birds, dog, cat, cow and humans respiration takes place through special respiratory organs called lungs. Now, we shall discuss respiration in amoeba, insects, earthworm, fish and human beings in detail.

Respiration in Amoeba

We know that amoeba is a unicellular organism which lives in fresh water. This organism does not have a specialized organ to do the process of respiration. So in amoeba respiration takes place through its cell membrane also called plasma membrane. Amoeba gets oxygen gas dissolved in surrounding water through its plasma membrane by the process of diffusion. The oxygen gas diffused inside the body is used up by amoeba. In the body the oxygen gas absorbed is used to break down the complex food material into simple molecules. During these metabolic reactions in the body of amoeba the oxygen gas is converted into carbon dioxide gas. The carbon dioxide gas is also liberated in the surrounding water through the same process of diffusion.

Test Your Understanding and Answer These Questions:

1. In which animal gills are found?
2. Explain the process of respiration in amoeba.
3. From where do Prawn and Rat take in oxygen?
4. Write the names of three animals which respire through skin.
5. Write the names of two animals which respire through plasma membrane.
6. Name the respiratory organs of 1. Fish 2. Mosquito 3. Earthworm and 4. Dog. 

 In order to carry on respiration, plant cells need oxygen and a means of disposing of carbon dioxide just as animal cells do. Unlike animals, plants have no specialized organs for gas exchange (with the few inevitable exceptions!). Each part of the plant such as leaves, stems and roots perform their own respiration. In plants respiration takes place at much slower rate as compared to animals. Also, there is very less transportation of respiratory gases from one part of the plant to another.

Respiration in leaves

In leaves the exchange of respiratory gases takes place through very small pores called stomata (singular stoma). The stomata are present in large number on the lower surface of leaves of plant. Each stoma has a pore at its centre which is surrounded and controlled by two kidney shaped cells called guard cells. When the stoma opens the exchange of gases takes place between the atmosphere and interior of the leaf by the process of diffusion.

Respiration in stems

In the plants having hard and woody stems and mature roots the exchange of gases takes place through lenticels. Lenticels are actually loosely packed dead cells which are present as small pores on the bark of woody plants or old roots. These enable oxygen to reach the intercellular spaces of the interior tissues and carbon dioxide to be released to the atmosphere by the process of diffusion.

Respiration in roots

In plants respiration also takes place through roots. In soil oxygenated air is present in air spaces between soil particles. This oxygen is absorbed into the roots by root hair present on the roots. In fact, a root hair is a lateral tubular outgrowth of the outer epidermal cells of a root. The oxygen present in between the soil particles diffuse into the root hairs. From root hairs, oxygen is supplied to all the parts of roots for respiration. During respiration, oxygen is converted into carbon dioxide gas which is diffused out of the roots by the same root hairs.

Test Your Understanding and Answer These Questions:

1. Explain respiration in plants.
2. Write a brief note on stomata.
3. What are stomata and lenticels? What is their role in respiration?
4. Which part of roots is involved in exchange of respiratory gases?

Food alone cannot provide energy for living organisms to survive. The energy has to be released from the food. it is done by combining food with oxygen. During this process carbon dioxide is released as a by-product. This process is called respiration.

Respiration may be defined as an oxidative process which involves the breaking up of food substances in the cells to form carbon dioxide, water and energy.The process of respiration can be represented by a chemical equation as given below:

Food + oxygen → carbon dioxide + water + energy

Breathing and respiration

Breathing may be defined as the process of taking in oxygen from the environment and giving out carbon dioxide So, breathing is just a physical process in which no energy is released. On the other hand, the process of respiration is more complex. It involves the inhalation of air, absorption and transport of oxygen to various cells of the body, oxidation of food in the cells and elimination of carbon dioxide from the body. Thus, respiration is a biochemical process. During the process of respiration energy is released which is used for performing various biological activities and maintenance of life.

What happens to the rate of breathing during vigorous exercise and why?

In a healthy person the normal rate of breathing is 18 times per minute. But during vigorous physical exercise the rate of breathing increases to 20-25 times per minute. This is due to the reason that during vigorous physical exercise our body needs more energy. This requirement of more energy can be met only by supplying more oxygen gas. So, in order to meet the requirement of high energy during vigorous physical exercise, breathing becomes fast so that more oxygen gas can be supplied to body cells.

Differences between Breathing and Respiration

Test Your Understanding and Answer These Questions:

1. Define respiration.
2. What is breathing?
3. How is respiration different from breathing?

The process of respiration can take place in the presence as well as absence of oxygen. Hence, respiration is of two types:

        1. Aerobic respiration and
        2. Anaerobic respiration

Aerobic respiration

The respiration which takes place in the presence of oxygen is called aerobic respiration. In aerobic respiration food (glucose) is completely broken down into carbon dioxide and water by oxidation of food. This result in the production of a large amount of energy which is stored in the form of ATP (Adenosine TriPhosphate) molecules. It should be noted that 1 molecule of glucose produces 38 high energy molecules of ATP during aerobic respiration takes place both in cytoplasm and in the mitochondria of a cell. Aerobic respiration can be written in the form of chemical equation as:

C₆H₁₂O₆   +   6O₂  →   6CO₂   +   6H₂O   +   Energy

During aerobic respiration 1 mole of Glucose produces 2830 Kilojoules of energy.

Anaerobic respiration

The respiration which takes place in the absence of oxygen is called anaerobic respiration. This type of respiration is found commonly in microorganisms such as yeast and bacteria. In microorganisms the term fermentation is more commonly used in place of anaerobic respiration. Fermentation may be defined as the anaerobic breakdown of carbohydrates and other organic compounds into ethyl alcohol, carbon dioxide or lactic acid. For example, fermentation of sugar is done by yeast. Actually yeast produces two enzymes called invertase and zymase which break down carbohydrates anaerobicaly in ethyl alcohol and carbon dioxide. The chemical equation for this can be written as:

C₆H₁₂O₆    →    2C₂H₅OH    +    2CO₂    +    Energy

During anaerobic respiration only 2 ATP molecules are produced thus anaerobic respiration produces less energy as compared to aerobic respiration. 1 mole of glucose produce 118 Kilojoules of energy during anaerobic respiration.

Anaerobic respiration also takes place in our muscles during vigorous exercise, because they do not get as much oxygen as is used up. During this process, muscles produce lactic acid from glucose. This results in pain in muscles. The breaking down of glucose in lactic acid during anaerobic respiration can be represented as follow:

Glucose    →    Lactic acid    +    Energy

Test Your Understanding and Answer These Questions:

1. What is ATP? What is its function?
2. What are different types of respiration?
3. What is aerobic and anaerobic respiration?
4. What are the end products of aerobic respiration?
5. What are the end products of anaerobic respiration?
6. In which kind of respiration more energy is produced.
7. Give differences between aerobic and anaerobic respiration.
8. Write names two microorganisms which respire anaerobicaly.
9. What is fermentation? What is the role of yeast in fermentation?
10. Give differences between anaerobic respiration and fermentation.
11. Which gas is taken in and released out during the process of respiration?
12. How much energy is produced from 1 mole of glucose in aerobic respiration?
13. How much energy is produced from 1 mole of glucose in anaerobic respiration?