There are two types of respiration
1) Aerobic respirarion
Aerobic respiration is the release of energy from glucose or another organic substrate in the presence of Oxygen. Strictly speaking aerobic means in air, but it is the Oxygen in the air which is necessary for aerobic respiration. Anaerobic respiration is in the absence of air.
Here is a molecular model of a glucose molecule. You do not need to memorise the diagram for you GCSE exam, but it should help you to understand that a molecule of glucose contains six atoms of Carbon (shown in blue), twelve atoms of Hydrogen (shown in green), and six atoms of Oxygen (shown in red).
In our tissues glucose can be broken down to release energy. The energy is used to make a substance called Adenosine Tri-Phosphate or ATP as it is usually called. ATP can provide energy for other processes such as muscle contractions.
Here is a balanced chemical equation for the process of aerobic respiration. You only need to memorise this for the Higher Tier GCSE paper, however I am sure that you really want a grade "A" so why not memorise it.
You should be able to see six carbon atoms on each side of the equation; one molecule of glucose contains six atoms of Carbon and six molecules of Carbon Dioxide each contain one atom of Carbon.
You should also be able to see that the Hydrogen is balanced. One molecule of Glucose contains twelve atoms of Hydrogen and six molecules of water each contain two atoms of Oxygen.
Now look at the Oxygen. To make six molecules of Carbon Dioxide we need twelve atoms of Oxygen and to make six molecules of water we need another six atoms of Oxygen. That makes a total of eighteen atoms of Oxygen. The glucose already contains six atoms of Oxygen so the cell will need a further six molecules of Oxygen from the air.
The basic minimum knowledge for GCSE biology is the word equation given below. Even if you don't understand it you can memorise it like a parrot.
Glucose + Oxygen = Carbon Dioxide + Water + Energy
Aerobic respiration takes place in almost all living things. It is easy to get rid of the Carbon Dioxide and excess water; this is excretion (the removal of the toxic waste products of metabolism), and maximum energy is released from the glucose.
Some organisms can respire in the absence of air: this is anaerobic respiration. This does not release so much energy and it produces much more toxic waste products. However, if Oxygen is not available, anaerobic respiration is better than nothing. When this happens in our muscles we produce lactic acid which gives you cramp. The bacteria in milk produce the same chemical when they turn it sour. "Lactic" means "of milk". So lactic acid is the acid in sour milk. Yeasts produce alcohol which is also toxic. Eventually there will be so much alcohol that the yeast cannot survive.
Anaerobic Respiration
When oxygen is not available to serve as the final electron acceptor, the electron transport system is unable to function. Electrons are not passed down the cytochrome system, and both FADH2 and NADH are unable to release electrons. If the carrier molecules cannot be returned to their oxidized state, they are unable to accept new electrons. The entire aerobic pathway will shut down.
The cell does have an alternative system which will allow glycolysis to continue despite the lack of oxygen. Anaerobic fermentation will remove hydrogens and electrons from NADH and will remove the end product pyruvate. Together, these actions will allow glycolysis to continue.
Two different anaerobic fermentation pathways are known. Alcoholic fermentation is common in bacteria and yeast cells. In alcoholic fermentation, pyruvate is first decarboxylated to yield a 2-carbon substance acetaldehyde. Acetaldehyde is then reduced as hydrogens are transferred from NADH to acetaldehyde to produce ethyl alcohol.
Once the NAD has been oxidized, glycolysis can continue.
The same result is reached by animal cells through the process of lactic acid fermentation. Here pyruvate is used as the direct acceptor of the hydrogens removed from NADH. The end product is a molecule of lactic acid. Lactic acid [or lactate] is a common by-product of anaerobic respiration in muscle cells.
The steps of anaerobic fermentation do not themselves produce any additional ATP. Their sole value is that, by permitting the continuedglycolytic activity, they allow at least some energy to be recovered in the absence of oxygen.
Some bacteria are obligate anaerobes. They are entirely dependent on anaerobic pathways. Most other organisms are aerobic, but some organisms, and some tissues are able to function in a facultative anaerobic state. That is, they are able to manufacture enough ATP through anaerobic processes to sustain themselves when oxygen is not sufficiently available for aerobic events.
Animal Respiration
In complex animals, where the cells of internal organs are distant from the external environment, respiratory systems facilitate the passage of gases to and from internal tissues. In such systems, when there is a difference in pressure of a particular gas on opposite sides of a membrane, the gas diffuses from the side of greater pressure to the side of lesser pressure, and each gas is transported independently of other gases. For example, in tissues where carbon dioxide concentration is high and oxygen concentration is low as a result of active metabolism, oxygen diffuses into the tissue and carbon dioxide diffuses out.
In lower animals, gas diffusion takes place through a moist surface membrane, as in flatworms; through the thin body wall, as in earthworms; through air ducts, or tracheae, as in insects; or through specialized tracheal gills, as in aquatic insect larvae. In the gills of fish the blood vessels are exposed directly to the external (aquatic) environment. Oxygen–carbon dioxide exchange occurs between the surrounding water and the blood within the vessels; the blood carries gases to and from tissues.
In other vertebrates, including humans, gas exchange takes place in the lungs. Breathing is the mechanical procedure in which air reaches the lungs. During inhalation muscular action lowers the diaphragm and raises the ribs; atmospheric pressure forces air into the enlarged chest cavity. In exhalation the muscles relax and the air is expelled. This combined rhythmic action takes place about 12–16 times per minute when the body is at rest. The rate of breathing is controlled mainly by a respiratory center in the brain stem that responds to changes in the level of hydrogen ion and carbon dioxide in the blood, as well as to other factors such as stress, temperature changes, and motor activities. Some residual air always remains in the lungs, but with each breath an additional quantity of fresh air, called tidal air, is inhaled. Artificial respiration is used for respiratory failure.
In higher vertebrates, oxygen-poor, carbon dioxide–rich blood from the right side of the heart is pumped into the lungs and flows through the net of capillaries surrounding the alveoli, the cup-shaped air sacs of the lungs; oxygen diffuses across the capillary membranes into the blood, and carbon dioxide diffuses in the opposite direction. The oxygen combines with the protein hemoglobin in red blood cells as the blood returns to the left side of the heart, is pumped throughout the body, and is released into tissue cells (see circulatory system). Carbon dioxide passes in the opposite direction, from the cells of the tissues to the red blood cells. In the blood, carbon dioxide exists in three forms: as bicarbonate ion, in which form it serves as a buffer, keeping blood acidity fairly constant; combined with hemoglobin; and as the dissolved free gas. Of these, only free carbon dioxide gas is available for diffusion from the blood into the lungs.
The Human Respiratory System
This system includes the lungs, pathways connecting them to the outside environment, and structures in the chest involved with moving air in and out of the lungs.
The human respiratory system.
Air enters the body through the nose, is warmed, filtered, and passed through the nasal cavity. Air passes the pharynx (which has the epiglottis that prevents food from entering the trachea).The upper part of the trachea contains the larynx. The vocal cords are two bands of tissue that extend across the opening of the larynx. After passing the larynx, the air moves into the bronchi that carry air in and out of the lungs.
The lungs and alveoli and their relationship to the diaphragm and capillaries.
Bronchi are reinforced to prevent their collapse and are lined with ciliated epithelium and mucus-producing cells. Bronchi branch into smaller and smaller tubes known as bronchioles. Bronchioles terminate in grape-like sac clusters known as alveoli. Alveoli are surrounded by a network of thin-walled capillaries. Only about 0.2 µm separate the alveoli from the capillaries due to the extremely thin walls of both structures.
Gas exchange across capillary and alveolus walls
The lungs are large, lobed, paired organs in the chest (also known as the thoracic cavity). Thin sheets of epithelium (pleura) separate the inside of the chest cavity from the outer surface of the lungs. The bottom of the thoracic cavity is formed by the diaphragm.
Ventilation is the mechanics of breathing in and out. When you inhale, muscles in the chest wall contract, lifting the ribs and pulling them, outward. The diaphragm at this time moves downward enlarging the chest cavity. Reduced air pressure in the lungs causes air to enter the lungs. Exhaling reverses theses steps.
Inhalation and exhalation
Diseases of the Respiratory System
The condition of the airways and the pressure difference between the lungs and atmosphere are important factors in the flow of air in and out of lungs. Many diseases affect the condition of the airways.
- Asthma narrows the airways by causing an allergy-induced spasms of surrounding muscles or by clogging the airways with mucus.
- Bronchitis is an inflammatory response that reduces airflow and is caused by long-term exposure to irritants such as cigarette smoke, air pollutants, or allergens.
- Cystic fibrosis is a genetic defect that causes excessive mucus production that clogs the airways.
The Alveoli and Gas Exchange
Diffusion is the movement of materials from a higher to a lower concentration. The differences between oxygen and carbon dioxide concentrations are measured by partial pressures. The greater the difference in partial pressure the greater the rate of diffusion.
Respiratory pigments increase the oxygen-carrying capacity of the blood. Humans have the red-colored pigment hemoglobin as their respiratory pigment. Hemoglobin increases the oxygen-carrying capacity of the blood between 65 and 70 times. Each red blood cell has about 250 million hemoglobin molecules, and each milliliter of blood contains 1.25 X 1015 hemoglobin molecules. Oxygen concentration in cells is low (when leaving the lungs blood is 97% saturated with oxygen), so oxygen diffuses from the blood to the cells when it reaches the capillaries.
Effectiveness of various oxygen carrying molecules
Carbon dioxide concentration in metabolically active cells is much greater than in capillaries, so carbon dioxide diffuses from the cells into the capillaries. Water in the blood combines with carbon dioxide to form bicarbonate. This removes the carbon dioxide from the blood so diffusion of even more carbon dioxide from the cells into the capillaries continues yet still manages to "package" the carbon dioxide for eventual passage out of the body.
Details of gas exchange.
In the alveoli capillaries, bicarbonate combines with a hydrogen ion (proton) to form carbonic acid, which breaks down into carbon dioxide and water. The carbon dioxide then diffuses into the alveoli and out of the body with the next exhalation.
Control of Respiration
Muscular contraction and relaxation controls the rate of expansion and constriction of the lungs. These muscles are stimulated by nerves that carry messages from the part of the brain that controls breathing, the medulla. Two systems control breathing: an automatic response and a voluntary response. Both are involved in holding your breath.
Although the automatic breathing regulation system allows you to breathe while you sleep, it sometimes malfunctions. Apnea involves stoppage of breathing for as long as 10 seconds, in some individuals as often as 300 times per night. This failure to respond to elevated blood levels of carbon dioxide may result from viral infections of the brain, tumors, or it may develop spontaneously. A malfunction of the breathing centers in newborns may result in SIDS (sudden infant death syndrome).
As altitude increases, atmospheric pressure decreases. Above 10,000 feet decreased oxygen pressures causes loading of oxygen into hemoglobin to drop off, leading to lowered oxygen levels in the blood. The result can be mountain sickness (nausea and loss of appetite). Mountain sickness does not result from oxygen starvation but rather from the loss of carbon dioxide due to increased breathing in order to obtain more oxygen.
Editorial Team, Mindfiesta |
Respiration
