GASEOUS EXCHANGE AND RESPIRATION
Gaseous exchange
/Gaseous exchange is the movement of oxygen and carbon dioxide across a respiratory surface.
Unicellular organisms carry out gaseous exchange by diffusion across the cell membrane. Large organisms cannot carry out diffusion efficiently so they have developed specialized organs for gaseous exchange. These are called respiratory surfaces
.
Table below shows examples of respiratory surfaces in various organisms. Respiratory surfaces in various organisms
Characteristics of respiratory surfaces
1. They are thin to reduce the diffusion distance.
2. They are moist to dissolve gases so that they diffuse in solution form.
3. They are highly branched, folded or flattened in order to increase the surface area for gaseous exchange,
4. They are close to an efficient transport and exchange system so that gases can be taken to and from the cells easily.
5. They are well ventilated so that gases can pass through them easily
GASEOUS EXCHANGE IN INSECTS
Insects uses tracheal system.There is Spiracle as opening through which air enter tubes called tracheal tube
-tracheal tube run throughout the entire body and branched into finer tubes called tracheoles
GASEOUS EXCHANGE IN FISH
Gaseous exchange in most fish takes places through special organs called Gills
- Gills is made up a curved bone called the Gill bar to which the gill filaments are attached
- The gill filament is made up in double row on the outer facing curve of the gill filament
-Each gill filament is made of thin structure called Lamellae which increase surface area of the gill filament in order to maximize the gaseous exchange
-On the opposite side of gill bar there are projection called Gill rakers. Their role is to prevent of dirt or food that could clog up the filament and reduce the efficient of gaseous exchange
Mechanism of ventilation in fish
1. The mouth is opened and th opercula closed
2.The floor of the pharynx is lowered increasing its volume
3.The increase in volume lowers the pressure inside the pharynx
4Water flows into themouth and pharynx
5.The mouth is closed
6.The floor of the pharynx is raised, squeezing water out past the gill
GASEOUS EXCHANGE IN AMPHIBIAN
i.Gas exchange through the skin
-When frog is in water.its uses skin which is richly supplyied with bood capillaries as organ of gaseous exchange
-Cutaneous gaseous exchange is the exchange of gases between the surrounding water andthe blood capillaries by diffusion
ii.Gaseous exchange through the buccal cavity(mouth)
Buccal cavity in frog is large and its surface lining is richly supplies with blood capillaries
iii.Lung or pulmonary gaseous exchange
An adult frog has a pair of lung. but this type of gaseous exchange take place in the frog only when the need for oxygen is very great, normally cutaneous and buccal exchange
GASEOUS EXCHANGE IN MAMMALS
The components of the gaseous exchange system in mammals include the nostril, trachea, lungs, intercostals muscles, diaphragm and ribs.
The adaptations and functions of parts of the mammalian respiratory system
Part Adaptive features Functions Nose and nasal cavity Mucus lining and hairs (cilia) Trap dust and microorganisms Glottis
The mechanism of gaseous exchange in mammals
Gaseous exchange in mammals happens as a result of inhalation (or inspiration) and exhalation (or expiration).
Inhalation is breathing in air into the lungs.
Exhalation is breathing out air from the lungs
During inhalation the muscles of the diaphragm Contract, pulling the diaphragm downwards; As this happens, the external intercostal muscles contract and pull the ribcage upwards and outwards. The result of these movements is an increase in the volume and a decrease in the air pressure of the thorax. This makes air rush into the lungs through the nostrils, trachea and bronchioles.
During exhalation, the muscles of the diaphragm relax and the diaphragm resumes its dome shape. The external intercostal muscles relax, pulling the ribcage inwards and downwards. As a result, the volume of the thorax decreases and the pressure inside it increases. This forces air out through the bronchioles, trachea and nostrils
or
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. The alveoli are surrounded by network of capillaries.
Gas exchange across alveolus
When we breathe in, air accumulates in the alveoli. There is a higher concentration of oxygen in the air in the alveoli than in the bloodstream.
Therefore, oxygen diffuses out the alveoli into the blood in the capillaries. It combines with haemoglobin to form oxyhaemoglobin
The oxygen is then transported to the tissues. Once in the tissues, the oxyhaemoglobin breaks down to release oxygen and haemoglobin. The tissues use released oxygen and release carbon dioxide.
This causes the levels of carbon dioxide to become higher in the tissues than in the blood.
Carbon dioxide therefore diffuses into the blood in the capillaries and combines with haemoglobin to form carbaminohaemoglobin.
The capillaries transport carbon dioxide in this form to the alveoli.
The concentration of carbon dioxide is higher in lie blood in the capillaries than in the air in the
alveoli. Carbon dioxide therefore diffuses from the Capillaries into the alveoli. It is then transported through the bronchioles, trachea, glottis, pharynx and finally nostrils into the atmosphere
Composition of inspired and expired air
Inspired air Expired air
Oxygen gas
20.95% 16.40%
Carbon dioxide 0.03% 4.00%
Factors affecting the rate of gaseous exchange
1. Concentration of carbon dioxide
High concentration of carbon dioxide in the blood increases the rate of gaseous exchange. This provides the tissues with adequate amounts of oxygen and lower carbon dioxide concentration in the blood.
2. Concentration of haemoglobin
Haemoglobin is responsible for the transportation of gases from the lungs to the tissues and back. Efficient transportation of gases takes place when the body has adequate amounts of haemoglobin.
When a person is anaemic, the body has a low concentration of haemoglobin. Only small amounts of oxygen can be transported at a time. As a result, the rate of gaseous exchange has to increase so that the tissues get adequate amounts of oxygen.
3. Physical activity
A more active body requires more oxygen than a less active body. As a result, gaseous exchange takes place faster when there is increased body activity.
4. Health status of the body
Generally, the rate of gaseous exchange increases when somebody is sick. This is as a result of increased metabolism by the liver in order to remove the toxins released by disease-causing microorganisms or break down the drugs taken. Certain diseases also make the body weak and cause slowing down of the breathing process.
5. Altitude
Altitude is the height above sea level. At high altitudes, the concentration of oxygen is lower compared to low altitudes. Breathing is therefore faster at high altitudes. At high altitudes, there is also decreased atmospheric pressure. This makes breathing difficult. Organisms therefore have to breathe in faster in order to get enough oxygen.
6. Age
Young people are generally more active than old people. Also, a lot of growth processes take place in the bodies of young people. This increases the demand for oxygen and therefore increases the breathing rate.
Gaseous exchange in plants
In plants, gaseous exchange mostly takes place through the stomata on the leaves and lenticels on the stem. Some plants such as mangrove and ficus also carry out gaseous exchange through breathing roots.
Gaseous exchange in the leaves
Atmospheric air moves into and out of the leaf through the stomata. Gaseous exchange mostly takes place in the air spaces in the spongy mesophyll.
During the day, guard cells that surround the stomata absorb water by osmosis.As a result, the cell sap of guard cells becomes hypertonic and draws in water from the neighbouring cells by osmosis.
The guard cells become turgid and the stomata open. Air from the atmosphere enters into the air spaces in the spongy mesophyll.
The cells next to the air spaces have more oxygen (produced by the cells during photosynthesis) but less carbon dioxide (used up during photosynthesis).
On the other hand, carbon dioxide is more in the air within the air spaces but oxygen is less. Carbondioxide and oxygen diffuse in opposite directions depending on their concentration gradients. The carbon dioxide diffuses to neighbouring cells until it reaches the site for photosynthesis. Oxygen moves out through the open stomata into the atmosphere.
At night, there is no light, therefore photosynthesis ceases. No glucose is produced therefore the guard cells do not absorb water by osmosis. Hence, the stomata remain partially closed.
However, respiration takes place in plants at night. The partially open stomata allow in small amount of air which accumulate in the air spaces. There is more oxygen and less carbon dioxide in the air spaces compared to the 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 plants produce carbon dioxide at night and oxygen during the day.
Gaseous exchange through the lenticels
Lenticels made up of loosely packed cork cells located on the bark of woody stems and roots. They are small pores through which gaseous exchange occurs.
Gaseous exchange in the lenticels
The loose arrangement of the cells facilitates the movement of gases between them. The cells have a thin layer of moisture so that gases diffuse in and out while in solution form
At night, there is a higher concentration of oxygen in the air spaces between the cork cells than in the ells themselves. Oxygen therefore diffuses into the cells surrounding the lenticels. The cells use oxygen far respiration and release carbon dioxide in the process. Thus, the concentration of carbon dioxide in the cells becomes higher than in the air spaces. Carbon dioxide therefore diffuses out through the cells into the air spaces and then out through the lenticel. The opposite happens during the day.
Gaseous exchange through the roots
This occurs through breathing roots. Plants with breathing roots have a very thin epidermal layer which enables the root to carry out gaseous exchange.
Breathing roots
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.
TYPE OF RESPIRATION
There are two types of respiration: aerobic respiration and anaerobic respiration.
1.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:
i. glycolysis,
ii.Kreb's cycle.
iii. Electron transport chain
i.Glycolysis
Involves a series of reaction that convert glucose to two molecules of three-carbon acid called pyruvic acid
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.
ii.Kreb's cycle is also called the citric acid cycle.
It is series of reaction that removes carbon dioxide and hydrogen atoms from pyruvic acid
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.
iii.Electron transport chain
Is the series of reaction that involves in rmoving hydrogen
-At the end of the chain Oxygen is combines with hydrogen to form water.
2.Anaerobic respiration
It involves the breaking down of glucose by bacteria or fungi to form alcohol, carbon dioxide and energy in absence of Oxygen. :
In plants, anaerobic respiration is also called fermentation
In animals, anaerobic respiration leads to the formation of lactic acid and energy.
This is written as
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.
occurs when the body's oxygen supply does not meet the body's needs.
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.
1.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
Gaseous exchange
/Gaseous exchange is the movement of oxygen and carbon dioxide across a respiratory surface.
Unicellular organisms carry out gaseous exchange by diffusion across the cell membrane. Large organisms cannot carry out diffusion efficiently so they have developed specialized organs for gaseous exchange. These are called respiratory surfaces
.
Table below shows examples of respiratory surfaces in various organisms. Respiratory surfaces in various organisms
| Organism | respiratory surface |
| Amoeba | Cell membrane |
| Insects | Tracheal system |
| Spider | Booklung |
| Fish | Gills |
| Plants | Leaves,stems,Root |
| Amphibians | skin,gills.and lung |
| Mammals | lung |
| Birds | lung |
| Reptiles | lung |
Characteristics of respiratory surfaces
1. They are thin to reduce the diffusion distance.
2. They are moist to dissolve gases so that they diffuse in solution form.
3. They are highly branched, folded or flattened in order to increase the surface area for gaseous exchange,
4. They are close to an efficient transport and exchange system so that gases can be taken to and from the cells easily.
5. They are well ventilated so that gases can pass through them easily
GASEOUS EXCHANGE IN INSECTS
Insects uses tracheal system.There is Spiracle as opening through which air enter tubes called tracheal tube
-tracheal tube run throughout the entire body and branched into finer tubes called tracheoles
GASEOUS EXCHANGE IN FISH
Gaseous exchange in most fish takes places through special organs called Gills
- Gills is made up a curved bone called the Gill bar to which the gill filaments are attached
- The gill filament is made up in double row on the outer facing curve of the gill filament
-Each gill filament is made of thin structure called Lamellae which increase surface area of the gill filament in order to maximize the gaseous exchange
-On the opposite side of gill bar there are projection called Gill rakers. Their role is to prevent of dirt or food that could clog up the filament and reduce the efficient of gaseous exchange
Mechanism of ventilation in fish
1. The mouth is opened and th opercula closed
2.The floor of the pharynx is lowered increasing its volume
3.The increase in volume lowers the pressure inside the pharynx
4Water flows into themouth and pharynx
5.The mouth is closed
6.The floor of the pharynx is raised, squeezing water out past the gill
GASEOUS EXCHANGE IN AMPHIBIAN
i.Gas exchange through the skin
-When frog is in water.its uses skin which is richly supplyied with bood capillaries as organ of gaseous exchange
-Cutaneous gaseous exchange is the exchange of gases between the surrounding water andthe blood capillaries by diffusion
ii.Gaseous exchange through the buccal cavity(mouth)
Buccal cavity in frog is large and its surface lining is richly supplies with blood capillaries
iii.Lung or pulmonary gaseous exchange
An adult frog has a pair of lung. but this type of gaseous exchange take place in the frog only when the need for oxygen is very great, normally cutaneous and buccal exchange
GASEOUS EXCHANGE IN MAMMALS
The components of the gaseous exchange system in mammals include the nostril, trachea, lungs, intercostals muscles, diaphragm and ribs.
 |
| Fig mammalian respiratory system |
The adaptations and functions of parts of the mammalian respiratory system
Part Adaptive features Functions Nose and nasal cavity Mucus lining and hairs (cilia) Trap dust and microorganisms Glottis
| part | adaptive features | functions |
| Nose and nasal cavity | Mucus lining and hairs cilia | Trap dust and microorganism |
| Glottis | Presence of epiglottis | prevent food from entering |
| respiratory system | ||
| trachea, bronchusand | -blood vessels near the surface. | warm the air |
| bronchioles | -have rings of cartilaage tissue | prevent collapsed of tract |
| Mucus lining and hairs cilia | ||
| lungs | spongy with air space(alveoli) | organ for gaseous exchange |
| Alveoli | Numerous in number | Provide large surface area for g. exchange |
| Thin membranes | reduce distance for diffucion of gases | |
| Moist surface | enable gases to dissolve into solution | |
| Has dense network of capillaries | transport from the alveoli to tissue | |
| Constantly air | maintain shape to avoid collapsing. | |
| Pleural membrane | contain pleural fluid | lubricates the membrane |
| Ribs | are made of hard bone tissue | protect the lungs from inury |
| intercostal muscle | move antigonisticaly | allow expansion and contraction of cavity |
| Diagram | muscular sheet of tissue | separate abdomente the thorax from |
The mechanism of gaseous exchange in mammals
Gaseous exchange in mammals happens as a result of inhalation (or inspiration) and exhalation (or expiration).
Inhalation is breathing in air into the lungs.
Exhalation is breathing out air from the lungs
During inhalation the muscles of the diaphragm Contract, pulling the diaphragm downwards; As this happens, the external intercostal muscles contract and pull the ribcage upwards and outwards. The result of these movements is an increase in the volume and a decrease in the air pressure of the thorax. This makes air rush into the lungs through the nostrils, trachea and bronchioles.
During exhalation, the muscles of the diaphragm relax and the diaphragm resumes its dome shape. The external intercostal muscles relax, pulling the ribcage inwards and downwards. As a result, the volume of the thorax decreases and the pressure inside it increases. This forces air out through the bronchioles, trachea and nostrils
| Breathingin(inhalation | Breathingout(exhalation) |
| External intercostal muscle contract | The external intercosta muscle relax |
| Internal intercostal muscle relax | The internal intercosta muscle rcontrct |
| The ribcage is lifted upward and outward | The ribcage is move inward and downward |
| The diaphram contract and flattens | The diaghram relaxes and become domed shaped |
| The volume of thoracic cavity increase as | The volume of thoracic cavity decrease as |
| pressure decrease | pressure incresase |
| Air enter alveoli through nostril, pharynx, | Air leave alveoli to atmosphere through |
| epiglotis,trachea, broncheoles and finaly | broncheole, bronchus, pharynx ,epiglotis and nostril |
| alveoli |
or
No
|
Inhalation
|
No
|
Exhalation
|
1
|
Ribs and sternum raised by contraction of
intercostal muscles
|
1
|
Ribs and sternum lowered by relaxation of
intercostal muscles and gravity.
|
2
|
Diaphragm contracts and lowers, becoming
flatter
|
2
|
Diaphragm rexes and returns to normal done-
shaped position
|
3
|
Volume of thoracic cavity increases
|
3
|
Volume of thoracic cavity decreases.
|
4
|
Pressure in the thoracic cavity decreases
|
4
|
Pressure in thoracic cavity increases
|
5.
|
Air is sucked into the lungs to equalize the
pressure
|
5
|
Air is forced out of the lungs to equalize
the pressure
|
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. The alveoli are surrounded by network of capillaries.
Gas exchange across alveolus
When we breathe in, air accumulates in the alveoli. There is a higher concentration of oxygen in the air in the alveoli than in the bloodstream.
Therefore, oxygen diffuses out the alveoli into the blood in the capillaries. It combines with haemoglobin to form oxyhaemoglobin
The oxygen is then transported to the tissues. Once in the tissues, the oxyhaemoglobin breaks down to release oxygen and haemoglobin. The tissues use released oxygen and release carbon dioxide.
This causes the levels of carbon dioxide to become higher in the tissues than in the blood.
Carbon dioxide therefore diffuses into the blood in the capillaries and combines with haemoglobin to form carbaminohaemoglobin.
The capillaries transport carbon dioxide in this form to the alveoli.
The concentration of carbon dioxide is higher in lie blood in the capillaries than in the air in the
alveoli. Carbon dioxide therefore diffuses from the Capillaries into the alveoli. It is then transported through the bronchioles, trachea, glottis, pharynx and finally nostrils into the atmosphere
Composition of inspired and expired air
Inspired air Expired air
Oxygen gas
20.95% 16.40%
Carbon dioxide 0.03% 4.00%
Factors affecting the rate of gaseous exchange
1. Concentration of carbon dioxide
High concentration of carbon dioxide in the blood increases the rate of gaseous exchange. This provides the tissues with adequate amounts of oxygen and lower carbon dioxide concentration in the blood.
2. Concentration of haemoglobin
Haemoglobin is responsible for the transportation of gases from the lungs to the tissues and back. Efficient transportation of gases takes place when the body has adequate amounts of haemoglobin.
When a person is anaemic, the body has a low concentration of haemoglobin. Only small amounts of oxygen can be transported at a time. As a result, the rate of gaseous exchange has to increase so that the tissues get adequate amounts of oxygen.
3. Physical activity
A more active body requires more oxygen than a less active body. As a result, gaseous exchange takes place faster when there is increased body activity.
4. Health status of the body
Generally, the rate of gaseous exchange increases when somebody is sick. This is as a result of increased metabolism by the liver in order to remove the toxins released by disease-causing microorganisms or break down the drugs taken. Certain diseases also make the body weak and cause slowing down of the breathing process.
5. Altitude
Altitude is the height above sea level. At high altitudes, the concentration of oxygen is lower compared to low altitudes. Breathing is therefore faster at high altitudes. At high altitudes, there is also decreased atmospheric pressure. This makes breathing difficult. Organisms therefore have to breathe in faster in order to get enough oxygen.
6. Age
Young people are generally more active than old people. Also, a lot of growth processes take place in the bodies of young people. This increases the demand for oxygen and therefore increases the breathing rate.
Gaseous exchange in plants
In plants, gaseous exchange mostly takes place through the stomata on the leaves and lenticels on the stem. Some plants such as mangrove and ficus also carry out gaseous exchange through breathing roots.
Gaseous exchange in the leaves
Atmospheric air moves into and out of the leaf through the stomata. Gaseous exchange mostly takes place in the air spaces in the spongy mesophyll.
During the day, guard cells that surround the stomata absorb water by osmosis.As a result, the cell sap of guard cells becomes hypertonic and draws in water from the neighbouring cells by osmosis.
The guard cells become turgid and the stomata open. Air from the atmosphere enters into the air spaces in the spongy mesophyll.
The cells next to the air spaces have more oxygen (produced by the cells during photosynthesis) but less carbon dioxide (used up during photosynthesis).
On the other hand, carbon dioxide is more in the air within the air spaces but oxygen is less. Carbondioxide and oxygen diffuse in opposite directions depending on their concentration gradients. The carbon dioxide diffuses to neighbouring cells until it reaches the site for photosynthesis. Oxygen moves out through the open stomata into the atmosphere.
At night, there is no light, therefore photosynthesis ceases. No glucose is produced therefore the guard cells do not absorb water by osmosis. Hence, the stomata remain partially closed.
However, respiration takes place in plants at night. The partially open stomata allow in small amount of air which accumulate in the air spaces. There is more oxygen and less carbon dioxide in the air spaces compared to the 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 plants produce carbon dioxide at night and oxygen during the day.
Gaseous exchange through the lenticels
Lenticels made up of loosely packed cork cells located on the bark of woody stems and roots. They are small pores through which gaseous exchange occurs.
Gaseous exchange in the lenticels
The loose arrangement of the cells facilitates the movement of gases between them. The cells have a thin layer of moisture so that gases diffuse in and out while in solution form
At night, there is a higher concentration of oxygen in the air spaces between the cork cells than in the ells themselves. Oxygen therefore diffuses into the cells surrounding the lenticels. The cells use oxygen far respiration and release carbon dioxide in the process. Thus, the concentration of carbon dioxide in the cells becomes higher than in the air spaces. Carbon dioxide therefore diffuses out through the cells into the air spaces and then out through the lenticel. The opposite happens during the day.
Gaseous exchange through the roots
This occurs through breathing roots. Plants with breathing roots have a very thin epidermal layer which enables the root to carry out gaseous exchange.
Breathing roots
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
Is the step-by-step chemical breakdown of glucose (mainly) within
living cells to release energy
or.
Once the digested food substances are absorbed into the cells of a
living organism they may be subjected to the following.
- They can be rebuilt into larger molecules
which can be stored in the body and build it.
- They can
further be broken down to inorganic substance eg. Glucose is converted to glycogen which is
stored in the liver and muscle cells. Amino acids can be broken down into carbondioxide.
Respiration takes place in the mitochondria of the plant cells.
TYPE OF RESPIRATION
There are two types of respiration: aerobic respiration and anaerobic respiration.
1.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:
i. glycolysis,
ii.Kreb's cycle.
iii. Electron transport chain
i.Glycolysis
Involves a series of reaction that convert glucose to two molecules of three-carbon acid called pyruvic acid
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.
ii.Kreb's cycle is also called the citric acid cycle.
It is series of reaction that removes carbon dioxide and hydrogen atoms from pyruvic acid
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.
iii.Electron transport chain
Is the series of reaction that involves in rmoving hydrogen
-At the end of the chain Oxygen is combines with hydrogen to form water.
2.Anaerobic respiration
It involves the breaking down of glucose by bacteria or fungi to form alcohol, carbon dioxide and energy in absence of Oxygen. :
In plants, anaerobic respiration is also called fermentation
In animals, anaerobic respiration leads to the formation of lactic acid and energy.
This is written as
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.
occurs when the body's oxygen supply does not meet the body's needs.
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.
1.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
2.common
cold and influenza
Are caused by viruses.
Symptoms
Sneezing
Runny nose caused by excess production of mucus in the nasal passages
Sore throat
Cough
•
Acute
bronchitis
- caused by whooping cough or
recurrent attack of influenza. Smoking can also cause acute bronchitis
Sign and Symptoms
•
Pain in the chest
•
Rapid
breathing
•
Fever
•
Coughing
•
Headache
Prevention and treatment
•
Staying warm
•
Get
treatment for all infections as fast as possible
•
Chronic
bronchitis
•
Is
caused by heavy smoking and recurrent acute bronchitis.
Sign and symptoms
•
Coughing
with the production of thick septum
•
Breathing
difficulties.
Prevention and treatment
•
Avoid
smoking
•
Avoid
very smoky or dust areas
•
Live in
a well-ventilated house
•
Keep
your body warm
•
Seek
medical help.
5Asthma
It is caused by
•
Allergic
reactions to dust, pollen spores or animal fur.
•
Hereditary
diseases of respiratory system
•
Extremely
cold weather
•
Frequent
viral or bacterial lung infection
Signs and symptoms of asthma
•
Narrowing
of Bronchioles resulting in breathing difficulties
•
Excessive
production of mucus
•
Dilation
of blood vessels; leading to blood pressure.
Prevention and Treatment
•
Avoid allergens (things that cause allergic
reaction)
•
Get
treatment for respiratory infection as early as possible
•
Keep the
body warm
•
Muscle relaxants in the farm sprays, pills and
injections.
Lung cancer:
•
Man cause is smoking
Sign and symptoms
•
Chest pain
•
Breathing
difficulty
•
Weight
loss
•
Persistent
cough
•
Abnormal
production of mucus.
Prevention and Treatment
•
Stop smoking
•
There is
no cure of cancer.