GASEOUS EXCHANGE AND RESPIRATION 2

Oxygen is at a higher concentration in the atmosphere than in the root cells. Therefore, oxygen diffuses into the root cells through the epidermis.

During respiration, the plant uses oxygen and releases carbon dioxide. This causes the concentration of carbon dioxide in the root cells to be higher than in the atmosphere. Carbon dioxide diffuses from the root cells into the atmosphere through the epidermis.

Importance of gaseous exchange in plants

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

Respiration

Respiration is the process by which food substances are broken down to provide energy. It is controlled by enzymes. Enzymes are substances that affect the rate at which a reaction occurs but are not used up in the reaction themselves. Respiration takes place in the mitochondria of the plant cells.

There are two types of respiration: aerobic respiration and anaerobic respiration.

Aerobic respiration

This is a type of respiration whereby oxygen is used to break down glucose, releasing energy, carbon dioxide and water. The chemical reaction for aerobic respiration is:

The energy produced is in the form of ATP (adenosine triphosphate). Thirty-eight molecules of ATP are produced at the end of the aerobic respiration.

Aerobic respiration takes place in two stages: glycolysis and Kreb's cycle.

Glycolysis takes place in the cytoplasm. It does not require oxygen so it is a phase that is common for both aerobic and anaerobic respiration.

During glycolysis, enzymes break down glucose into a three carbon compound called pyruvic acid. Glycolysis produces 2 molecules of ATP per molecule of glucose.

The pyruvic acid can further be broken down in the presence or absence of oxygen. If there is oxygen, the pyruvic acid proceeds to the next stage of aerobic respiration, which is Kreb's cycle. If there is no oxygen, anaerobic respiration occurs.

Note that pyruvic acid passes through a stage where it is decarboxylated (one carbon dioxide molecule removed from it) before going through the Kreb's cycle.

Kreb's cycle is also called the citric acid cycle. It involves the formation of citric acid molecule (a six carbon) from the two carbon molecule by addition of a four carbon molecule, i.e. oxaloacetic acid in a cyclic process.

Kreb's cycle takes place inside the cristae of the mitochondria.

Anaerobic respiration

Anaerobic respiration takes place in the absence of [oxygen.

In plants, anaerobic respiration is also called fermentation. It involves the breaking down of glucose by bacteria or fungi to form alcohol, carbon dioxide and energy. This is represented by the following equation:

In animals anaerobic respiration takes place during strenuous activity, for example during sports. It leads to the accumulation of lactic acid in the muscles. Lactic acid is toxic.

Anaerobic respiration occurs when the body's oxygen supply does not meet the body's needs. Therefore, an oxygen debt or oxygen deficit occurs. This causes the animal to breathe fast and deeply in order to get enough oxygen to convert the lactic acid to carbon dioxide and water. Some of the lactic acid is converted to glucose. Breathing goes back to normal when the acid has been broken down.

Anaerobes are organisms that respire anaerobically. They include bacteria, yeast and fungi. There are two types of anaerobes:

Obligate anaerobes which can only live and respire in the absence of oxygen. They die in the presence of oxygen.

Facultative anaerobes; which respire both in the presence and in the absence of oxygen

   Differences between aerobic and anaerobic respiration

Aerobic respiration	Anaerobic respiration
1. Oxygen is used	1. Oxygen is not used
2. Large amounts of energy are produced	2. Small amount of energy are produced
3. Water molecules are produced	3. Water is not produced
4. Food substances are completely broken down	4.Food substances are not completely broken down
5. Takes place in the mitochondria and cell membrane	5.Takes place in the cytoplasm
6. Carbon dioxide and water are the end-products	6. Lactic acid is produced in animals and alcohol is produced in plants

Factors affecting the rate of respiration

The rate at which respiration takes place varies depending on the state of an organism. Hence, respiration is sometimes fast and at other times slow. The following factors affect the rate of respiration:

Temperature

Respiration is controlled by enzymes. The functioning of enzymes is affected by temperature. The rate of respiration is slow at low temperatures and increases with increase in temperature until the optimal temperature. Optimal temperature is the temperature at which the enzymes function best. If the temperature is raised above optimal temperature, the enzymes are denatured and the rate of respiration reduces.

Activity

When an organism is involved in a vigorous activity, it requires more energy than when it is at rest. For example, a human being requires less energy when sitting than when taking part in arace. Therefore, the rate of respiration changes to suit the needs of the organism’s physical activity.

Size

Small organisms lose heat faster than big organisms. This is because small organisms have a larger surface area to volume ratio. Heat is a form of energy. Therefore, small organisms need to respire faster than large organisms to replace the energy lost through heat.

Age

Generally, young organisms respire faster than older organisms. This is because they need energy to grow. In addition, young organisms are more active than old organisms.

Health

When we are sick, the rate of respiration increases so as to remove the toxic materials produced by the pathogens in our bodies.

Infections and diseases of 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 as 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. Hence, a person who is close by may catch the infection. Sometimes, droplets may infect bedding, clothes and surfaces used by the sick person.

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

Pneumonia

Pneumonia is inflammation of the lungs. 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.

Signs and symptoms of pneumonia

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

Prevention and treatment of pneumonia

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

Bronchitis

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.

Acute bronchitis

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

Signs and symptoms of acute bronchitis

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

Prevention and treatment of acute bronchitis

• Staying warm. Cold temperatures make the body more susceptible to bacterial infections
• Get treatment for all infections as fast as possible

Chronic bronchitis

Chronic bronchitis is caused by heavy smoking and recurrent acute bronchitis.

Signs and symptoms of chronic bronchitis

• Coughing, with the production of thick sputum
• Breathing difficulties

Prevention and treatment of chronic bronchitis

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

Asthma

Asthma can be caused by:

• Allergic reactions to dust, pollen, spores oranimal fur
• Hereditary diseases of the respiratory system
• Extremely cold weather
• Frequent viral or bacterial lung infections

Signs and symptoms of asthma

• Narrowing   of   bronchioles   resulting   in breathing difficulties and a wheezing or hissing sound when breathing
• Excessive production of mucus
• Dilation of blood vessels, leading to low bloodpressure. Low blood pressure can be fatal

Prevention and treatment of asthma

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

Lung cancer

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.

Signs and symptoms of lung cancer

• Chest pain
• Breathing difficulty
• Weight loss
• Persistent cough
• Abnormal production of mucus

Prevention and treatment of lung cancer

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

Emphysema

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

Causes of emphysema

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

Signs and symptoms of emphysema

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

Prevention and treatment of emphysema

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

Chapter Summary:

1.      Gaseous exchange is the exchange of oxygen and carbon dioxide through a respiratory surface.

2.       

§  thin membrane

§  large surface area

§  moist lining

§  Dense network of capillaries.Features of a gaseous exchange surface are:

3.      The structures involved in gaseous exchange in mammals are the nose, mouth, pharynx, glottis, trachea, lungs, bronchioles, alveoli, ribs, pleural membranes and diaphragm.

4.      Gaseous exchange is affected by the amount of haemoglobin in the blood and carbon dioxide concentration.

5.      In plants, gaseous exchange can take place through the stomata in the leaves, lenticels in woody stems or in breathing roots. 

6.      Respiration is the process by which food substances are broken down to release energy.

7.       Aerobic respiration takes place in the mitochondria in the presence of oxygen

8.      Aerobic respiration involves  two stages: glycolysis and Kreb's cycle.

9.      Anaerobic respiration takes place in the cytoplasm in the absence of oxygen. 

10.  Diseases and infections that affect the respiratory system include bronchitis, asthma, pneumonia, tuberculosis, and emphysema and j influenza.

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