TOPIC 1.CLASSIFICATION KINGDOM FUNGI
During the guard cells that surround
the stomata. 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.
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.
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
- It Enables plants to obtain carbon dioxide, which is one of the raw materials necessary for photosynthesis.
- Plants obtain oxygen which is necessary for the production of energy. Energy is produced during respiration.
- 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 leads to the formation of lactic acid and
energy. This is written as
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.