(c) Gaseous exchange through the roots (Breathing roots)  
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Oxygen is at a higher concentration in the atmosphere than in the root cells.  
Therefore, oxygen diffuses into the root cells through the thin epidermis layer.  
During respiration, the plant uses oxygen and releases carbon dioxide. This causes  
higher concentration of carbon dioxide in the root cells than in the atmosphere.  
Therefore, carbon dioxide diffuses from the root cells into the atmosphere though  
the thin epidermis layer of the roots.  
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Importance of Gaseous Exchange in Plants  
(i) It enables plants to obtain carbon dioxide, which is one of the raw materials necessary  
for photosynthesis.  
(ii) It enables plants to obtain oxygen which is necessary for the production of energy.  
Energy is produced during respiration.  
(iii) It enables the plants to eliminate excess carbon dioxide at night. If not removed, the  
carbon dioxide would harm the plant.  
QUIZ  
1. Unlike animals, plants have no special organs for gaseous exchange. How then do  
they carry out gaseous exchange? Give three points.  
2. Which of the following is not a characteristic of respiratory surfaces?  
A. Thin walls to facilitate diffusion of gases  
B. Moist surface to allow gases to dissolve before diffusion  
C. Impermeable to prevent poisonous gases to move across them  
D. Large surface area for maximum exchange of gases  
E. Plentiful blood supply to facilitate transport of gases  
3. One of the following sets contains respiratory gases. Which one is that?  
A. Hydrogen and nitrogen  
B. Nitrogen and sulphur  
C. Sulphur and oxygen  
D. Oxygen and carbon dioxide  
E. Carbon dioxide and hydrogen  
6.2: RESPIRATION IN MAMMALS  
Respiration is the process of breaking down food substances to release energy. It takes  
place in the cytoplasm and mitochondria of a cell and is controlled by enzymes. This  
process occurs in all living cells hence called cellular respiration. There are two type of  
respiration which are aerobic respiration and anaerobic respiration.  
(a) Aerobic Respiration  
This is the type of respiration whereby oxygen is used to break food substances (glucose)  
to release energy, carbon dioxide and water. The energy released is in the form of ATP  
(Adenosine Triphosphate).  
Glucose + Oxygen  
C6H12O6 + 6O2  
Carbon dioxide + Water + Energy  
6CO2 + 6H2O + ATP  
The Mechanism of Aerobic Respiration  
Aerobic respiration takes place in three stages, namely; Glycolysis, Krebs (tricarboxylic  
acid) cycle and Electron transport chain. In this chapter, only two stages are discussed.  
(i) Glycolysis.  
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Glycolysis takes place in the cytoplasm of the cell and 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 and 2 molecules of ATP.  
In presence of oxygen the pyruvic acid proceeds to the next stage of aerobic  
respiration, which is Krebs cycle but in absence of oxygen, anaerobic respiration  
occurs.  
(ii) The Krebs Cycle.  
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The Krebs cycle occurs in the matrix of mitochondria and it involves series of  
reactions.  
In presence of oxygen, the two molecules of pyruvic acid from the glycolysis are  
broken down to produce carbon dioxide gas and water and ATP.  
Carbon dioxide produced is removed as a waste product.  
(b) Anaerobic Respiration  
Anaerobic respiration is the process whereby glucose is broken down in the absence of  
oxygen to release a relatively small amount of energy. Glucose is not completely broken  
down thus, less energy is released.  
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In plants and yeast, anaerobic respiration is called fermentation or alcoholic  
Fermentation. It involves the breaking down of glucose by bacteria or fungi to form  
alcohol, carbon dioxide and energy.  
Glucose  
C6H12O6  
Ethanol + Carbon dioxide + Energy  
2C2H5OH + 2CO2 + ATP  
In animals, anaerobic respiration leads to the formation of lactic acid and energy. It  
takes place during vigorous activity such as sports. It leads to the accumulation of  
lactic acid in the muscles.  
Glucose  
C6H12O6  
Lactic acid + Energy  
2C3H6O3 + ATP  
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Lactic acid is toxic, therefore, accumulation of lactic acid in the muscles prevents  
them from contracting and relaxing hence causing muscle pain.  
OXYGEN DEBT  
When the accumulation of lactic acid in the muscle occurs, oxygen is required to  
oxidize lactic acid into water and carbondioxide. The oxygen required to remove lactic  
acid in the muscle by converting it into water and carbondioxide is known oxygen debt.  
Oxygen debt causes the animal to breath rapidly and deeply in order to get enough  
oxygen required to convert lactic acid to carbondioxide and water. Breathing goes to  
normal when the acid has been broken down.  
NOTE:  
Organisms that respire anaerobically are called anaerobes. They include bacteria, yeast  
and fungi. There are two types of anaerobes, namely;  
(i) Obligate anaerobes: These are organisms which can only live and respire in absence  
of oxygen. They die in the presence of oxygen.  
(ii) Facultative anaerobes: These are organisms which respire and survive both in the  
presence and in the absence of oxygen. In that case, they respire in all environment.  
Application of Anaerobic Respiration in Industries and Homes  
(i)  
Alcohol brewing (brewery industries) e.g. making beer and wine.  
Production of vinegar (acetic acid) and other acids, such as citric acid.  
(ii)  
(iii) Production of biogas for cooking and lighting.  
(iv) In bakery industries or bread baking process in different industries and at home.  
(v)  
Production of composite manure.  
Table 6.5: Differences between aerobic respiration and anaerobic respiration  
Aerobic Respiration  
Anaerobic Respiration  
(a) It uses oxygen to oxidize glucose.  
(b) It produces large amounts of energy.  
(c) Water is produced.  
(a) It does not use oxygen.  
(b) It produces small amounts of energy.  
(c) Water is not produced.  
(d) Food substances are completely broken  
down.  
(d) Food substances are not completely  
broken down.  
(e) It starts in the cytoplasm and ends in  
the mitochondria.  
(e) It takes place in the cytoplasm.  
(f) Carbon dioxide and water are the end-  
products.  
(f) Lactic acid is produced in animals and  
alcohol is produced in plants.  
Factors Affecting the Rate of Respiration  
The rate respiration is sometimes fast and at other times slow. The following are factors  
in that affect the rate of respiration.  
(i)  
Temperature: Respiration is controlled by enzymes. The functioning of enzymes is  
affected by temperature. The rate of respiration slows down at low temperatures and  
increases with the increase in temperature to the optimal level. Temperature above  
optimal level, the enzymes are denatured and the rate of respiration is reduced.  
(ii) Body size: Small organisms loose heat faster than large organisms. Therefore, small  
organisms need to respire faster than large organisms to replace the energy lost  
through heat. For example; a mouse respires faster than an elephant.  
(iii) Activity: All body activity requires energy. When an organism is active, it requires  
more energy than when it is inactive (not working). The rate of respiration increases  
with the activity.  
(iv) Age: Generally, young organisms respires faster than older organisms. This is because  
they need more energy for growth and they are more active than older organisms.  
(v) Health status: During illness, breastfeeding, pregnancy or injury the rate of  
respiration is fast. For example; a sick person has higher rate of respiration than a  
healthy person because during illness the body works harder to fight infections.  
INFECTIONS AND DISEASES OF THE RESPIRATORY SYSTEM  
There are several airborne infections and diseases which affect the human respiratory  
system. The common ones are; Pneumonia, Bronchitis, Asthma, Lung cancer,  
Tuberculosis, Corona Virus Disease 2019 (COVID-19)  
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.  
1. Pneumonia  
Pneumonia is an 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  
(i)  
Fever.  
(ii) Chills.  
(iii) Shortness of breath associated with pain.  
(iv) Increased mucus production.  
(v) Cough.  
Prevention and Treatment of Pneumonia  
(i)  
Staying warm.  
(ii) Avoiding overcrowded areas.  
(iii) Avoiding cold food or drinks. Hot drinks are more preferred as they loosen  
secretions.  
(iv) Get treatment as early as possible since it is curable by antibiotics.  
2. Bronchitis  
This is an inflammation of the bronchial tubes (bronchi). It can be acute or chronic.  
(a) Acute Bronchitis: This is caused by viral infection and occasionally bacterial  
infections. It lasts for a few weeks following cold or respiratory infection.  
Signs and Symptoms of Acute Bronchitis  
(i)  
Pain in the chest  
(ii) Rapid breathing  
(iii) Fever  
(iv) Coughing  
(v) Headaches  
Prevention and Control of Acute bronchitis  
(i) Staying warm. Cold temperatures make the body more susceptible to bacterial  
infections.  
(ii) Get early treatment for all respiratory infections as fast as possible.  
(b) Chronic bronchitis  
Chronic bronchitis is caused by heavy smoking and recurrent acute bronchitis.  
Signs and Symptoms of Chronic Bronchitis  
(i) Coughing with the production of thick sputum.  
(ii) Breathing difficulties.  
Prevention and Control of Chronic bronchitis  
(i) Avoid smoking.  
(ii) Avoid very smoky or dust areas.  
(iii) Live in a well-ventilated house.  
(iv) Keep your body warm.  
(v) Seek medical help.  
3. Asthma  
Asthma can be caused by:  
(i) Allergic reactions to dust, pollen, spores or animal fur.  
(ii) Hereditary diseases of the respiratory system.  
(iii) Extremely cold weather.  
(iv) Frequent viral or bacterial lung infections.  
Signs and Symptoms of Asthma  
(i)  
Narrowing of bronchioles resulting in breathing difficulties and a wheezing or  
hissing sound when breathing.  
(ii)  
Excessive production of mucus.  
(iii) Dilation of blood vessels, leading to low blood pressure. Low blood pressure can  
be vital.  
Prevention and Control of Asthma  
(i) Get treatment for respiratory infections as early as possible.  
(ii) Avoid allergens.  
(iii) Keep the body warm.  
(iv) Muscle relaxants in the form of sprays, pills and injections are used to prevent  
the narrowing of the bronchioles.  
4. 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:  
(i) Chest pain  
(ii) Breathing difficulty  
(iii) Weight loss  
(iv) Highly persistent coughs  
(v) Abnormal production of mucus  
(vi) Blood in the sputum  
Prevention and Control of Lung Cancer:  
(i) Stop smoking.  
(ii) Maintain healthy life style like eating a balanced diet and exercising.  
5. Tuberculosis  
Tuberculosis is a disease which mainly affects the lungs. It is causes by a bacteria  
Mycobacterium tuberculosis. Tuberculosis can be spread by inhaling droplets from the  
coughs or sneezes of an infected person.  
Signs and Symptoms of Tuberculosis  
(i) Persistent cough for more than three weeks.  
(ii) Fever.  
(iii) Chest pain.  
(iv) Night sweats.  
(v) Coughing blood.  
(vi) Loss of appetite.  
(vii) Loss of weight.  
(viii) Fatigue (extreme tiredness).  
Prevention and Control of Tuberculosis  
(i) Tuberculosis is prevented by vaccination. The Bacilli Calmette-Guerin (BCG)  
vaccine is given to children to prevent tuberculosis.  
(ii) It can also be prevented by adhering to hygienic rules such as washing hands  
after coughing or sneezing and covering the mouth when coughing or sneezing.  
(iii) It can also be prevented by isolation.  
6. COVID-19 (Acute respiratory distress syndrome)  
This is a pandemic disease caused by the corona viruses that can trigger respiratory  
tract infection which may lead to severe acute respiratory syndrome. It normally affects  
the upper respiratory tract (sinuses, nose and throat) or lower respiratory tract  
(windpipe and lungs)  
Signs and Symptoms of COVID-19  
(i)  
Fever  
(viii) Sore throat  
(ii)  
Coughing  
(ix) Loss of sense of smell and taste  
(iii) Difficulty in breathing  
(iv) Fatigue  
(x)  
Nausea  
(xi) Diarrhoea  
(xii) Chest pain  
(xiii) Muscle ache  
(v)  
Chills  
(vi) Body aches  
(vii) Headaches  
Prevention and Control of COVID-19  
(i)  
Wash your hands often with soap and running water for at least twenty seconds  
or clean them with any alcohol-based sanitizer.  
(ii)  
Practice both social and physical distancing.  
(iii) Cover the nose and mouth in crowded environments with a face mask.  
(iv) Avoid touching the face particularly the nose, mouth and eyes.  
(v)  
Clean and disinfect the frequently touched surfaces with soap and water or  
alcohol-based sanitizer.  
(vi) Quarantine. Restriction on the movement of people to prevent the spread of the  
disease.  
(vii) Practice isolation if you are infected.