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Overview of the Human Respiratory Syste

Paper Type: Free Essay Subject: Biology
Wordcount: 3186 words Published: 23rd Sep 2019

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Respiration is an example of an exothermic reaction. It releases energy from glucose molecules for use by the body. Organisms need this energy for chemical reactions to build larger molecules, for movement and to keep warm. Respiration in cells can be aerobic (with oxygen) or anaerobic (without oxygen).

Aerobic respiration takes place in the mitochondria and requires oxygen and glucose to do so. Glucose is a substance which is essential to life. It breaks down into ATP for the energy for respiration in all living things. However, glucose and its transfers are particularly key to human life, it provides us with all our energy and is transported through diffusion. Diffusion I a passive process – this is the rapid and random movement of particles from a high concentration of solutes to a low concentration of solutes-which in this case is glucose.

For example, one of the most common processes of aerobic respiration is where it occurs in the muscle

This type of respiration produces carbon dioxide, water and energy.  The chemical equation for aerobic respiration is…

C6H12O6+6O2 will produce 6CO2+6H2O(+38ATP)

The faster the rate of respiration, the greater the rate of oxygen use and the greater the rate of carbon dioxide release.


Stage 1-Aerobic glycolysis is the same process as Anaerobic glycolysis except that the presence of oxygen inhibits the accumulation of lactic acid by diverting pyruvic acid further into the aerobic system. Pyruvic acid combines with coenzyme A to form Acetyl CoA.

Stage 2- Krebs Cycle- The Acetyl CoA from stage 1 combines with oxaloacetic acid to form citric acid. Then complex reactions within the matrix of mitochondria take place:

  1. Carbon dioxide is produced and removed by the lungs
  2. Hydrogen atoms are removed (oxidation)
  3. Energy is produced to resynthesize 2 molecules of ATP
  4. Oxaloacetic acid is regenerated

Stage 3- Electron transport chain- The hydrogen atoms combine with the coenzymes NAD and FAD to form NADH and FADH. These are carried down the electron transport chain where hydrogen is split into H+ and e-. This takes place when the cristae folds of the mitochondria, where 3 important things take place:

  1. The hydrogen electron splits from hydrogen atom and passes down the ETC.
  2. This provides sufficient energy to resynthesize 34 ATP.
  3. The hydrogen ion combines with oxygen to form water.

The total energy produced by this system is 38 ATP.

•        2 ATP from Aerobic glycolysis

•        2 ATP from Krebs cycle

•        34 ATP from ETC

Anaerobic respiration also produces energy and uses glucose; however, it produces less energy and does not require oxygen. This is useful in tissues that have a high energy demand such as in working muscles, in which there is not enough oxygen to produce all the energy needed by using anaerobic respiration alone. Anaerobic respiration takes place in the cell cytoplasm and produces lactic acid. The chemical equation for anaerobic respiration is…

C6H12O6 will produce 2C3H6O3(+2ATP)

The lactic acid is toxic and needs to be oxidised to carbon dioxide and water to prevent it from building up. This process requires oxygen and therefore following anaerobic respiration there is oxygen debt in the cell, as oxygen is needed to break down the lactic acid. The waste product, lactic acid, builds up in the muscles causing pain and tiredness. Anaerobic respiration releases much less energy per glucose molecule than aerobic respiration does. Muscle fatigue is the result of anaerobic respiration in the musclecells.


Fermentation is a metabolic process that consumes sugar in the absence of oxygen. The products of fermentation are organic acids, gases, or alcohol. Fermentation takes place in yeast and bacteria and also in oxygen starved muscle cells as in the case of lactic acid fermentation. In micro-organisms fermentation is the primary way of producing ATP by the degradation of organic nutrients anaerobically. The chemical and word equations for fermentation are…

Glucose will produce ethanol+ carbon dioxide

C6H12O6 will produce 2C2H5OH+2CO2

Ways of checking respiration in humans:

There are different ways to check the respiration in humans, with different tests to see how much respiration a person is capable of.

One method is to measure Peak Flow. This is a person’s maximum speed of expiration. This is measured with a Peak Flow Meter. This measures the airflow through the bronchi and the extent of potential obstruction in the airways. Peak Flow is generally measured in units of litres per minute(L/min). Peak Flow readings are higher when you are well and lower when the airways are constricted. However due to the wide range of ‘normal’ results and high amount of variability, peak flow is not recommended to test whether somebody has asthma.

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Blood Pressure is also another way to check. When the heart beats, it pumps blood around the body to give it the energy and oxygen it needs. As the blood moves, it pushes against the sides of the blood vessels. The strength of this pushing is your blood pressure. If your blood pressure is too high it puts an extra strain on your heart and arteries and could lead to heart attacks and strokes.

Blood pressure readings have two numbers, for example 140/90mmHg. The top number is your systolic blood pressure (the highest pressure when your heart beats and pushes blood around the body). The bottom number is your diastolic blood pressure (the lowest pressure when your heart relaxes between beats).


Factors affecting the respiratory system in humans:

One factor affecting the respiratory system is asthma. Asthma is a condition whereby the airways of the respiratory system become restricted. Asthma makes the bands around the airways tighten so air cannot move freely in or out of the body phlegm can also narrow the airway further. Exercise can induce an asthma attack. Asthma reduces our respiration rate as it restricts oxygen getting to the working muscles. However exercise can benefit someone with asthma as it can reduce the effects by increasing respiratory muscles, vital capacity and the oxygen and carbon dioxide diffusion rate.

Another factor is partial pressure/altitude. Partial pressure tells us how much of a particular gas is present. Oxygen moves from high pressure (alveoli) to low pressure (capillaries) until the pressures are equal. The greater the differences in these gases, the quicker the rate of diffusion. At altitude there is less oxygen reducing the partial pressure, because there is less oxygen available you have to work harder. This can cause: shortness of breath, dizziness and difficulties in concentration. Due to the lack of oxygen altitude can lead to hypoxia which causes an increase in breathing rate and depth. Over a period of time at altitude your respiratory will adapt to the conditions. Athletes will train at altitude so their body adapts, adaptations include an increasing in red blood cells and capillaries which will allow more oxygen to be carried and diffused to the working muscles.

Another factor affecting respiration is temperature. At very high temperatures the rate of respiration decreases with time. At low temperatures the respiration rate is insignificant. The optimum temperature of respiration is between 20 to 30°C. Also if there is an increase in water then there will be an increase in respiration rate. When you increase the temperature you will give the particles more kinetic energy. This means that there will be more frequent collisions between the particles as there is an increase in movement of the particles. However too much heatmeans that the rate of reaction will decrease. This same concept applies to non-human organisms!

Another factor affecting respiration rate is exercise. During exercise the body needs more energy, so the rate of respiration increases. The heart rate, breathing rate and breath volume all increase to supply the muscles with more oxygen and glucose for the increase in aerobic respiration. During periods of intense activity, the muscles may not get supplied with enough oxygen, so anaerobic respiration starts to take place in the muscle cells. This causes a build up of lactic acid and creates an oxygen debt. The lactic acid causes the muscles to hurt and stops them contracting efficiently. Lactic acid is a poison, so needs to be got rid of quickly. Once exercise is finished, the oxygen debt must be repaid. Also after exercise blood flowing through the muscles transports the lactic acid to the liver where it is broken down. The oxygen debt is the amount of extra oxygen the body needs after exercise to react with the lactic acid and remove it from the cells.





One factor affecting respiration rate in non humans is the oxygen content of the atmosphere. The percentage of oxygen in the atmosphere has a great impact on the rate of respiration. When there is a decrease in oxygen to about 10% in the atmosphere then there is a decrease in respiration. At 5% of oxygen in the atmosphere there is definite retardation of respiration.

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Another factor affecting respiration rates in non-humans is temperature. When you increase the temperature you will give the particles more kinetic energy. This means that there will be more frequent collisions between the particles as there is an increase in movement of the particles. However too much heat can cause tissue deterioration. The respiration rates of certain fruits can be controlled by storing them in cool, dry places as lower temperatures are able to slow the respiration rate and prevent the fruit from ripening.


Basal metabolic rate is the number of calories your organs need to function while you perform no activity whatsoever. Since your BMR is based largely on involuntary functions like breathing and pumping blood, changes in your day to day activity don’t do much to raise or lower this number.

BMR calculation for men BMR = 66.5 + ( 13.75 × weight in kg ) + ( 5.003 × height in cm ) – ( 6.755 × age in years ) 

BMR calculation for women BMR = 655.1 + ( 9.563 × weight in kg ) + ( 1.850 × height in cm ) – ( 4.676 × age in years )

Things that affect BMR:

Body weight, Gender, Activity Levels, Temperature, Age, Muscle Mass, Body Fat Percentage.

Men tend to have higher BMRs than women because women tend to have less muscle mass than men. Also men tend to be larger in size, this means that more energy is required to perform basic functions as the body is larger. Women also tend to have a higher body fat percentage. This means that less energy will be required due to the fat acting as an insulator.

Direct calorimetry- Measurement of heat actually produced by the organism which is confined in a sealed chamber or calorimeter. This process is accurate. However, the person has to be isolated for a long time (at least 24 hours)

Indirect calorimetry- Estimates the heat production by measuring gas exchange. This process is really quick as it only takes 10 minutes and it can also be done at home. You also have to fast for 12 hours before it.

Fermentation experiment:

This experiment is performed to test the rate of respiration of yeast, a single celled kind of fungus. And given food and air it will grow and multiply. And to test which environment is best you make up a series of sugar solutions. You use different temperatures of water in each sugar solution and then add the yeast to the solution. Once the yeast has been added you quickly close the bung and time it. Each minute you record how much gas has been produced by the yeast respiring and make a note of it. You should find that as the time increases so does the amount of gas produced by the yeast. We repeated the experiment 3 times to be able to get valid and reproducible results and also to get a mean volume of gas produced by the yeast undergoing fermentation.

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