Biology Notes Form 2 Topic 5: Gaseous Exchange And Respiration

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Gaseous Exchange And Respiration

Gaseous Exchange







The Concept of Gaseous Exchange

Organs Responsible for Gaseous Exchange in Living Organisms

Organs responsible for gaseous exchange in living organisms include the following:

Amoeba Cell membrane
Insects Tracheal system
Spider Book lung
Fish Gills
Plants Leaves, stems, roots
Amphibians Skin, gills and lungs
Mammals Lungs
Birds Lungs
reptiles Lungs

Features of Respiratory Surface

  1. They are thin to reduce diffusion distance
  2. They are moist to dissolve gaseous so that they dissolve and diffuse in solution form
  3. They are highly braced, folded or flattened in order to increase the surface area for gaseous exchange
  4. They are close to efficient transport and exchange easily by the cells
  5. They are well ventilated so that gaseous passes easily

The Concept of Gaseous Exchange

Gaseous exchange refers to the movement of oxygen and carbon dioxide across the respiratory surface. Is the process through which respiratory gaseous are passed through the respiratory surface. Respiratory surface are specialized organs for gaseous exchange. Gaseous exchange takes place through a process of diffusion.

Gaseous Exchange in Mammals

Parts of the Respiratory System

The gaseous exchange in mammals takes place in the lungs.

 Gaseous Exchange

The Features of Different Parts of the Respiratory System and their Adaptive Features

The Features of Different Parts of the Respiratory System include the following:

  • Nose and nasal cavity: It has mucus and hair which trap dust and microorganisms
  • Glottis: It is situated in the epiglottis which closes the trachea during swallowing to prevent food from entering the respiratory system
  • Trachea, Bronchus, and Bronchioles: They have blood vessel which have ring cartilage and mucus which warm hair and prevent collapse of respiratory track also they trap and fitter dust and micro organisms
  • Lungs:They are sponge with air space (alveoli) which is the main organ of mammalian gaseous exchange
  • Ribs: They are made up of hard bone tissues which protect the lungs from injury.
  • Intercostal muscles: They more antagonistically to allow expansion and relaxation of the thoraic cavity
  • Diaphragm: is the muscular sheet of tissue which separate thorax from abdomen
  • Alveoli: they are numerous in number; they are moist and thin membranes

Functions of alveolus

  • Provide surface area for gaseous exchange
  • Reduce distance for diffusion of gaseous
  • Enable gaseous to dissolve into solution before diffusing
  • Transport oxygen from the alveoli to the tissues and carbon dioxide to the alveoli
  • Maintain the shape and avoid collapsing

The Mechanism of Gaseous Exchange in Mammals

Gaseous exchange in mammals happens as a result of inhalation and exhalation. Inhalation is breathing in air in to the lungs. Exhalation is the breathing out of air from the lungs. During inhalation the muscle of the diaphragm contract pulling the diaphragm downwards. As this happens, the external inter costal muscle contract and pull the rib cage upward and outwards. This increase volume and decreases pressure in the thorax. This makes air rush in the lungs.

During exhalation the muscles of the diaphragm resumes its dome shape. The external intercostal muscles relax pulling the rib cage inwards and downwards. This decreases volume and increases pressure. This forces air out through the bronchioles, trachea and nostrils

Gaseous Exchange Across the Alveolus

The actual exchange of oxygen and carbon dioxide takes place in the alveoli. One mammalian lung has millions of alveoli. When we breathe air in it accumulates in the alveoli. There is higher concentration of oxygen in the alveoli than in the blood stream. The oxygen combines with hemoglobin to form oxy hemoglobin. Oxygen is then transported to the tissues

The tissue use oxygen and release carbon dioxide which diffuses in blood capillaries and combine with hemoglobin to form carbon hemoglobin. Capillaries transform this form to alveoli as it is then transported through the bronchioles trachea, glottis, pharynx, and finally nostrils into the atmosphere.

Gaseous Exchange

Factors Affecting Gaseous Exchange in Mammals

Factors affecting gaseous exchange in mammals include the following:

  • Exercise or physical activities
  • Age
  • Emotions
  • Temperature
  • Health
  • Carbon dioxide concentration
  • Hemoglobin concentration
  • Altitude

Gaseous Exchange in Plants

In plants gaseous exchange takes place through the stomata on the leaves and lenticels on the stem. But some plants such as mangrove also carry out gaseous exchange through breathing roots.

Parts of Plant Responsible for Gaseous Exchange

In plants gaseous exchange takes place through the stomata on the leaves and lenticels on the stem. But some plants such as mangrove also carry out gaseous exchange through breathing roots.

The Process of Gaseous Exchange in Plants

Gaseous exchange in leaves: Through stomata, atmospheric air moves in and out of the leaf. Gaseous exchange mostly takes place in the air spaces in the spongy mesophyll.

 Gaseous Exchange

During the day, green plants carry out photosynthesis to produce glucose and this takes place within the guard cells that surround the stomata then the cell sap of the guard cells becomes hypertonic and draws in water from the neighboring cells by osmosis.

The guard cells become turgid and the stomata open whereby the air from the atmosphere such as carbon dioxide enters into the air spaces in the spongy mesophyll.

In this case carbon dioxide (CO2) is more in the air within the air space but oxygen is less. Then the carbon dioxide and oxygen diffuse in opposite direction depending on their concentration gradients (such as oxygen out and carbon dioxide in). The carbon dioxide diffuses into neighboring cells until it reaches the site for photosynthesis and oxygen moves out through the open stomata to the atmosphere.

During the night there is no light so that photosynthesis ceases and there is no production of glucose. Therefore the guard cells do not absorb water by osmosis hence the stomata remain partially closed.

However respiration process takes place at night in plants. The partially open stomata allow small amount of air to enter and accumulate in the air spaces. In this case there is more oxygen and less carbon dioxide in the air spaces compared to plant cells.

Oxygen moves into the plant cells while carbon dioxide moves into the air spaces and eventually into the atmosphere through the partially open stomata. This explains why green plants produce carbon dioxide at night and oxygen during the day.

Importance of Gaseous Exchange in Plants

Importance of Gaseous Exchange in Plants include the following:

  1. It enables the plants to eliminate excess carbon dioxide at night of which if left will harm the plants
  2. It enables plants to obtain carbon dioxide which is one of the raw materials necessary for photosynthesis
  3. Plants obtain oxygen which is necessary for production of energy which is produced during respiration through gaseous exchange


The concept of Respiration

Respiration: Is the metabolic activity or reaction in which complex food substances are broken down step by step to release energy within a cell.

Cellular Respiration:Is a set of metabolic reaction and process that takes place in the cell of organisms to convert biochemical energy from nutrients into ATP.

NB: The reaction involved is catabolic reaction, which breaks larger molecules into smaller ones to release energy. Cellular respiration is considered as exothermic reaction. Exothermic reaction is the process whereby energy is released out.

Types of Respiration

There are two types of respiration

  1. Aerobic Respiration
  2. Anaerobic Respiration

Aerobic Respiration

The Concept of Aerobic Respiration

This is the combustion reaction. This means that oxygen is required in order to generate ATP. The simplified reaction of respiration of carbohydrates is C6H12O6.

Aerobic respiration – In the presence of oxygen glucose molecules are broken down into carbon dioxide water and energy

Equation of Aerobic respiration

C6H12O6 + 6O→ 6CO2 + 6H2O + Energy (38ATP)

The Mechanism of Aerobic Respiration

Respiration starts with glucose (usually). In aerobic and anaerobic respiration initial reactions are common as a result of which pyruvic acid is formed by breakdown of glucose.

The process is called Glycolysis or EMP Pathway (Embden-Meyerhof-Parnas Pathway). This process does not require O2although this can take place in the presence of oxygen. After this stage, the fate of pyruvic acid is different depending upon the presence or absence of oxygen.

If oxygen is present there is complete oxidation of pyruvic acid into H2O and CO2and chemical reactions through which this occurs is called Tri-Carboxylic Acid cycle (TCA Cycle) or Krebs Cycle. This cycle occurs in mitochondria. If oxygen is absent, pyruvic acid forms ethyl alcohol (C2H5OH) and CO2without the help of any cell organelle. This process is called anaerobic respiration.

Experiments on Aerobic Respiration

Respiration by living organisms can be investigated by carrying out experiments to show the production of carbon dioxide and heat.

Investigating carbon dioxide production

Limewater turns milky in the presence of carbon dioxide. It can be used to show that exhaled air contains more carbon dioxide than inhaled air.

Carbon dioxide dissolves in water to form a weakly acidic solution. Hydrogen carbonate indicator is used to show the presence of carbon dioxide in solution. It is:

  • red at neutralpH (no carbon dioxide)
  • yellow at low pH (carbon dioxide present)

Investigating heat production

The release of heat can be shown by carrying out an experiment using germinating seeds. Two vacuum flasks are used:

  • one containing living plant material
  • one containing dead plant material (the control)
Contents Start temp (°C) End temp (°C) Temp change (°C)
Living plant material 21 29 8
Dead plant material 21 21 0

Factors which Affect the Rate of Respiration

The rate of respiration in organisms is rarely constant. There are several factors in that affect rate of respiration. These apply equally to aerobic and anaerobic respiration although the examples given here refer to aerobic respiration

  1. Temperature: Respiration is a chemical process therefore its rate increases with increasing body temperature as an increasing in temperature increases the rate of chemical change.
  2. Activity: All body activity requires energy. When an organism becomes active it requires more energy than when it’s inactive. Since respiration provides energy required for the activity the rate of respiration will correspondingly increase.
  3. Body Size: Small organisms have high surface area to volume ratio. Heat loss occurs at the surface; therefore small organisms tend to lose heat more rapidly than larger ones. Small animals e.g. shrews, have to maintain higher rate of respiration than larger ones to maintain their body temperature.
  4. Age: Young organisms are growing and as a result require more energy than older mature individual whose growth may slow down or stopped. Younger individual tend to be more physically active also. Both of these rate factors lead to increased rates of respiration in younger organism

An Aerobic Respiration

The Concept of Anaerobic Respiration

This is the process whereby energy is released in absence of oxygen although the energy outcome in anaerobic respiration is much less than aerobic respiration. Anaerobic respiration differs in plant and animal.

  1. Anaerobic Alcoholic fermentation in plant cell and yeast
  2. Anaerobic lactic fermentation

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The Mechanism of Anaerobic Respiration

Anaerobic respiration differs in plant and animal.

  1. Anaerobic Alcoholic fermentation in plant cell and yeast
  2. Anaerobic lactic fermentation

Anaerobic Alcoholic fermentation in plant and yeast

In the presence of Alcoholic fermentation glucose molecule is broken down into ethanol and carbon dioxide and energy.

  • Glucose → Ethanol + Carbon dioxide + Energy
  • C6H12O6 → 2C2H5OH + 2CO2 + 2 ATP
  • Raw Material → End Product

Anaerobic Lactic Fermentation

If there is lack of oxygen carbohydrate molecule is broken down to lactic acid and energy outcome only 2ATP.

  • C6H12O6 (Glucose)→ C3H6O3 + 2ATP Energy (Lactic Acid)
  • Raw Material → End Product

A more common occurrence of lactic acid fermentation is in muscles; during exercise. During this period the respiratory surface is incapable of supplying oxygen to the molecule, which is requirement. Hence due to this lactic acid is produced. Accumulation of lactic acid will cause muscle cramp and so prevent muscles from operating.

The End Products of Anaerobic Respiration

The following are the End Product of Anaerobic Respiration:

In plants

  1. Ethanol
  2. Carbon dioxide
  3. Energy

In Animals

  1. Lactic Acid
  2. Energy (2ATP)

Importance of Anaerobic Respiration

  • This process brings about fermentation. Fermentation occurs when simple sugar (glucose) is broken down by bacterial in absence of oxygen
  • Bacteria break down milk sugar to reduce lactic acid
  • Production of composite manure

Oxygen debt

During heavy exercise, oxygen supply is less than what is required by the body. As a result of anaerobic respiration taking place and lactic acid accumulates. This creates oxygen deficit.

Oxygen debt refers to the amount of oxygen required to convert lactic acid into carbon dioxide, water and energy.


An Experiment to Demonstrate the Application of Anaerobic Respiration

Application of Anaerobic respiration in industry and home

  • Alcohol brewing e.g. making beer and wine
  • Production of acetic acid and other acid such as citric acid
  • Production of biogas from cooking and lighting
  • Bread making process
  • Production of composite manure

The Difference Between Aerobic Respiration and Anaerobic Respiration

Differences between Aerobic Respiration and Anaerobic Respiration include the following

Aerobic Respiration Anaerobic Respiration
Oxygen is used up Oxygen is not used
Larger amount of energy is released Less amount of energy is released
Water molecules are produced Water molecules are not produced
Takes place in mitochondria Takes place in cytoplasm
Products produced are not harmful Products produced are harmful example lactic acid

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Infection and Diseases of the Respiratory System

Common Airborne Infections and Diseases which Affect the Respiratory System

There are several airborne infections, which affect the human respiratory system. The common ones are influenza, pneumonia, common cold and tuberculosis.

Most of the airborne infections are a result of close contact with an infected person. When the sick person breathes out, coughs or sneezes, the pathogens are released into the air.

Airborne infections can be controlled by isolation of the infected patients, proper disposal of infected secretion such as sputum, living in a well-ventilated house and avoiding overcrowding especially in bedrooms.


The Causes, Symptoms, Effects and Control Measures of Common Infections and Diseases of the Respiratory System

Airborne infections can be controlled by isolation of the infected patients, proper disposal of infected secretion such as sputum, living in a well-ventilated house and avoiding overcrowding especially in bedrooms.

Disorders of the Respiratory System

Disorders of the Respiratory System

Disorders of the Respiratory System include the following:


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Causes, Symptoms and Effects of the Disorders of the Respiratory System


Pneumonia is inflammation of the lung. It is caused by bacteria, viruses, fungi or by inhaling chemical toxins or irritants. Pneumonia is normally followed by other illnesses such as cold or flu.


  • Fever
  • Chills
  • Shortness of breath associated with pain
  • Increase of mucus production
  • Cough


  • Staying warm
  • Avoiding overcrowded areas
  • Avoiding cold food and drinks, hot drinks are preferred more as they loosen secretions
  • Get treatment as early as possible since it is curable by antibiotics


Bacteria, viruses and inhaling of irritating substances can cause the lining of the respiratory system to become inflamed. This causes an infection called bronchitis. Bronchitis can be acute or chronic.


This is caused by whooping cough or recurrent attacks of influenza; smoking can also cause acute bronchitis.


  • Pain in the chest
  • Rapid breathing
  • Fever
  • Coughing
  • Headache


Heavy smoking and recurrent acute bronchitis cause chronic Bronchitis.


  • Coughing with the production of thick sputum
  • Breathing difficulties


  • Avoiding smoking
  • Avoid very smoky or dusty areas
  • Live in a well-ventilated house
  • Keep your body warm
  • Seek medical help


Asthma is characterized by inflamed and constricted airways. The narrowing of the airways restricts the flow of air into the lungs.

Asthma can be caused by:

  • Allergic reactions to dust, pollen, spores or animal fur
  • Herediroty diseases of the respiratory system
  • Extremely cold weather
  • Frequent viral or bacteria lung infection


  • Narrowing of bronchioles resulting in breathing difficulties and a wheezing or hissing sound when breathing
  • Coughing
  • Shortness of breath
  • Excessive production of mucus
  • Dilation of blood vessels leading to low blood pressure, low blood pressure can be fatal
  • Chest tightness


  • Avoid allergens (things that cause allergenic reaction)
  • Get treatment for respiratory infections as early as possible
  • Keep the body warm
  • Muscle relaxants in the form of sprays, pills and injections are used to prevent the narrowing of bronchitis


The main cause of lung cancer is smoking. The nicotine in cigarette smoke stops the cilia in the trachea from expelling foreign materials leading to respiratory infection.


  • Chest pain
  • Breathing difficulty
  • Weight Loss
  • Persistent Cough
  • Abnormal Production of Mucus


  • Stop smoking
  • There is no cure for cancer. However chemotherapy and physiotherapy are used to control the disease


This is a lung disease, which results from destruction of the structure supporting the alveoli leading to these collapse. This significantly reduces the surface area available for gaseous exchange.


  • Mainly cigarette smoke
  • Air pollution
  • Hereditary
  • Old age


  • Shortness of breath
  • Coughing
  • Obstructive lung disease
  • Difficulties when breathing especially during exercise
  • Wheezing during breathing


  • Avoid cigarette smoking and exposure to smoke
  • Lung surgery is usually done to relieve the symptoms
  • Use of medical drugs
  • In severe cases, lung transplant is necessary


Tuberculosis is highly infections disease. The causal organism for TB is one of the strains of bacteria belonging to the Mycobacterium tuberculosis. Tuberculosis can be spread from one person to another person, when the bacteria become airborne.


  • Cough
  • Fever
  • Weight Loss
  • Loss of appetite


Disorders of the Respiratory System and HIV/AIDS

Tuberculosis is the most common opportunistic infection associated with HIV worldwide. Tuberculosis is an infection by the tuberculosis bacterium that predominantly affects the lungs, but it can spread through the blood and lymph nodes to the rest of the body in people with HIV.

The disease can strike people with HIV no matter what the level of the CD4 count, which means that TB can often occur years before other problems associated with HIV develop.

Pneumocystis Carinii Pneumonia (PCP)

This is the most common opportunistic infection that occurs with AIDS the fungus that causes the PCP infection is spread through breathing or coughing. Symptoms include cough, fever, trouble breathing and loss of weight.

Cryptococci Meningitis

This is caused by fungus and it is the most common central nervous system infection associated with HIV. Meningitis is an inflammation of the membranes and fluid surrounding the brain and spinal cord.


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