Competitive Exams: Respiration

Respiration is a chemical reaction catalysed by enzymes. It takes place in each and every mitochondria of the cells. Respiration is done to obtain energy needed by the body. For vital functions to take place, the body needs energy. It also needs energy to keep a constant body temperature and to transport chemical messages.

Plants need energy for active transport to take place.

Differences between respiration and breathing:

Respiration is carried out in all cells to obtain energy.

Breathing is the exchange of gases, in case of humans and other organisms, the removal of carbon dioxide and obtaining oxygen.

In large organisms such as mammals, respiratory surfaces are required for gas exchange (breathing, not respiration) to take place efficiently. In humans, like all mammals, lungs are used for this purpose.

There are two types of respiration: Aerobic (oxygen involved) and anaerobic (no oxygen involved).

Anaerobic Respiration

Anaerobic means without oxygen, and thus this type of chemical reaction involves only sugars (obtained from digestion of food). Energy is released by the chemical breaking of bonds in organic molecules (containing carbon) present in sugars and other carbohydrates, obtained from digestion. There is more than one type of anaerobic respiration; it depends on the organism.

One very common type of anaerobic respiration is alcohol fermentation represented in this equation below:

This type of reaction (alcohol fermentation) is done by yeast. As it produces alcohol, it is important for world economy for the production of beer, wine and other alcoholic drinks. Yeast's most important function is surely in the production of bread. Anaerobic respiration is also important for the economy as certain reactions, anaerobic bacteria produce lactic acid, which is used to make butter, yoghurt cheese and other dairy products. Some other types of bacteria produce methane gas (CH4), a flammable gas used for cooking and fuelling machinery, lighting, and used in the production of hydrogen, hydrogen cyanide, ammonia, ethyne, and formaldehyde.

Anaerobic respiration takes place in humans as well. During strenuous exercise, blood vessels cannot provide enough oxygen for muscle cells to do proper aerobic respiration; in this case, anaerobic respiration takes place in the muscles. In these reactions, lactic acid (slightly poisonous) is produced and can cause cramps. After the exercise, the lactic acid is converted into carbon dioxide and water by oxygen. This whole process is known as oxygen debt.

Aerobic respiration

Aerobic respiration is the respiration, which involves oxygen. The enzymes catalyze the oxidation of glucose to form carbon dioxide and water. 2830kJ of energy are released by oxidizing 180 grams of glucose. Energy is stored in the body as ATP (adenosine triphosphate), because glucose alone does not provide energy. As enzymes catalyse this reaction, it is controlled also by temperature, so when the body temperature rises above 40oC, respiration slows down because heat denatures enzymes.

The lungs

The lungs are the respiratory surface of mammals, birds, reptiles and some amphibians.

The Air Passage

The air passes through a number of passages before it goes to the bloodstream to be used up. First the air passes through the nose and through the trachea, which is surrounded by rings of cartilage to stay stiff. The nose and trachea have special cells on their walls. There are some cells with cilia; hair-like structures that are continuously beating up and down. These trap germs as well as dust from the air. Another type of special cells in the epithelium of the nose and trachea are the mucus-secreting cells. These have a hole in them from where mucus is secreted. After the trachea, the air passes through the bronchi, bronchioles and finally to the air sacks, or alveoli.

Oxygen and carbon dioxide are exchange in the alveoli by diffusion. Numerous alveoli create a large surface area for gas exchange. Oxygen is carried in the red blood cells (rbc) while carbon dioxide is carried in the plasma as Hydrogen Carbonate (HCO3-) ions.

The alveoli are adapted for gas exchange by a number of factors:

  1. They have a thin film of water to ensure good and fast gas exchange by diffusion surrounds the alveoli. In fact, some of this water evaporates and there is always some water vapour in our exhaled breath.

  2. Alveoli are surrounded by a lot of blood capillaries

  3. Blood capillaries are very thin to allow diffusion.

  4. There are many air sacks for a large surface area.

Breathing Process

While breathing in, the rib cage moves upwards and outwards, the diaphragm flattens and the volume in the chest increases. Since the volume increases the pressure decreases and the air is drawn into the lungs.

While you exhale, the rib cage moves inwards and downwards, the diaphragm relaxes (dome shaped) and the volume in the chest decreases. Since the volume decreases pressure increases and the air is expelled out of the lungs.

Smoking and its Negative Effects

Cigarettes contain 3 harmful chemicals:

  • Tar
  • nicotine and while it is burning it produces
  • carbon monoxide

Apart from these, the cigarettes contain many other chemicals. Some of these are irritants. Irritants and chemicals that annoy the lungs. Other chemicals are carcinogens; may cause cancer. The smoke produced by the cigarettes is very harmful, it affects the epithelium in two ways: It irritates the goblet cells, making them produce more mucus.

Secondly, it slows down, or even stops the beating of the cilia, so that they can no longer sweep out the mucus. Coughing can only clear the build up of mucus in the lungs. This is known as smoker's cough.

Some diseases caused by cigarettes are bronchitis, emphysema and lung cancer.

Bronchitis: This disease results as much of the epithelium is damaged and destroyed by the cigarettes'smoke and irritants. Germs and irritants penetrate deeper into the lung tissue and so the body's defence cell move into attack. Their remains, along with the mucus make up phlegm, which must be coughed and spat everyday. Bronchitis causes more than a 1000 deaths every year and it is a disease, which mostly causes loss of workdays.

Emphysema: Emphysema causes the walls between alveoli become torn and broken, while the others left become thicker. This causes the lungs to have a smaller surface area for gas exchange. The sufferer coughs and wheezes and struggles for breath. This illness can cause permanent disability and eventually death.

Lung Cancer: Carcinogenic chemicals (chemicals which can cause cancer) cause lung tissue to divide in an uncontrolled manner. This growth is called a tumour or cancer. The tumour spreads through the lung destroying other healthy tissue. Cancerous cells may go into the bloodstream and secondary tumour may arise. This disease, although it can be treated if detected in the early stages, it is usually found too late and the victim dies.

Other Lungs diseases

Pneumonia: Certain bacteria and viruses cause this illness. These cause the alveoli to get filled with fluid and cell debris. Oxygen starvation results since a much of the alveoli block gas exchange.

Tuberculosis (TB): It is cause by a bacillus (pathogenic bacteria). This disease can be treated and cured nowadays. The germs doesn't do much harm but sometimes, the bacillus may spread out through the lungs causing sever damage. Dust Diseases: These diseases are caused when large amounts of dust are breath during work. Stonecutters, miners and asbestos workers may catch illnesses such as silicosis, pneumoconiosis and asbestosis respectfully. Special precautions must be taken because once caught, these diseases are incurable.

Air Pollution

The air is polluted by mainly 5 different gases: Carbon dioxide, carbon monoxide, sulphur dioxide, nitrogen dioxide and ozone. 4 of them are poisonous for the human body, namely carbon monoxide CO, sulphur dioxide SO2, nitrogen dioxide NO2 and ozone O3.

Carbon dioxide CO2 is not a toxic gas in moderate concentrations, but it contributes to global warming, thus it is a greenhouse gas (traps the sun's heat, causing global temperature to rise, changing climate and endangering animal and plant species). CFC's (chlorofluorocarbons) although not considered pollutants, convert ozone in the protective ozone (O3) layer back into oxygen (O2), thus it makes a hole in this layer, letting harmful ultraviolet rays from the sun penetrate the atmosphere, causing skin cancer.

Sulphur Dioxide and Nitrogen Dioxide rise from industrial effluent and car exhaust. They are both toxic gases and in order to block nitrogen dioxide from escaping into the air, cars should be equipped with catalytic converters. These devices convert nitrogen oxides and carbon monoxide into carbon dioxide, harmless nitrogen and water, with the help of rare catalysts.

Carbon monoxide is also produced by cars and other burning sources that are not properly ventilated such as gas heaters and fire places in enclosed rooms. It is a harmful gas because it combines with the blood, preventing it from absorbing oxygen. Even in small concentrations it may be fatal.

Certain electrical machinery and photocopiers produce ozone (O3) gas. Although ozone is useful in the ozone layer, which is 20 − 50 km above sea level, it is highly poisonous and can contribute to acid rain.