Transcript Gaseous Exchange in Plants and Animals

Gaseous Exchange in Plants and
Animals
Contents
Exchange of materials
Gaseous exchange in
Flowering Plants
Adaptations of leaf for rapid
diffusion of gasses
Gaseous exchange in Humans
Functions of the various parts
Pathway of the air
An efficient respiratory
surface
How do we breathe?
Inspiration
Expiration
Gaseous Exchange in the
Alveoli
How does the blood carry
O2?
How does the blood carry
CO2?
Composition of inhaled and
exhaled air
Asthma
Chronic Bronchitis
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Other Respiratory Disorders
Exchange of materials
Necessary between the cells of an organism
and its environment.
Oxygen, carbon dioxide, nutrients, wastes and
ATP all move by diffusion.
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Exchange of materials is
necessary
• To allow oxygen combine with food to
release energy (ATP) = respiration.
• To ensure that the fluid balance of cells (=
homeostasis) and their temperature is kept
constant.
• To remove waste materials produced in
cells = excretion.
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Gaseous exchange in
Flowering Plants
• O2 and CO2 exchanged through stomata.
• Stomata are tiny openings in the upper or
lower epidermis of a leaf through which
gases pass - surrounded by two guard cells.
• In woody stems gaseous exchange occurs
through lenticels.
• Lenticels are raised openings (pores) in the
bark of a woody stem formed by loosely
arranged cells with air spaces between them
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to facilitate gaseous exchange
Lenticel
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During the day
• CO2 diffuses into the leaf through the
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stomata
Moves to the chloroplasts
Used in photosynthesis to make glucose
O2 produced as waste
Diffuses out of leaf through stomata
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Adaptations of leaf for rapid
diffusion of gases
1.
2.
3.
4.
are flattened
have stomata
have air spaces between the cells
mesophyll cells (ground tissue) are
loosely arranged and their surfaces are
moist
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T.S. of leaf
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Gaseous exchange in Humans
• Occurs at a special site called the
respiratory surface = the lungs.
• The lungs are part of the breathing system.
• They lie in the thoracic (chest) cavity above
the diaphragm.
• Enclosed and protected by the rib cage.
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The parts of the human
breathing system
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Functions of the various parts
Part
(1/2)
Function
Nostrils
Allow air to enter the nose
Nose
Warms, filters and moistens air
Pharynx (throat)
Connects nose and mouth to
larynx
Glottis
Opening to the larynx
Epiglottis
Prevents food passing into the
windpipe when you swallow
Larynx (voice box) Makes sounds
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Functions of the various parts
Part
(2/2)
Function
Trachea (windpipe) Allows air to pass to lungs
Cartilage
Bronchus
Keeps trachea and bronchi
open
Transports air into lung
Bronchiole
Transports air into alveoli
Alveoli (air sacs)
Site of gas exchange
Pleural membranes Allow friction-free movement
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of lungs
Pathway of the air
Air enters the nostrils and passes through the
nose, nasal passages, pharynx, larynx,
bronchi, bronchioles and finally reaches the
alveoli.
Some air enters through the mouth, buccal
cavity, pharynx, larynx … alveoli.
Gaseous exchange occurs in the alveoli.
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An efficient respiratory surface
(1/2)
Must have the following:
• A large surface area
• It must be moist - O2 and CO2 can only
diffuse in solution
• It must be very thin – for rapid diffusion
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An efficient respiratory surface
(2/2)
• It must have a large blood capillary network
– to allow gaseous exchange between air
and blood stream – capillary walls only one
cell thick – increase rate of diffusion.
• It must receive a constant supply of air – the
breathing movements provide good
ventilation.
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How do we breathe?
Occurs in two stages: Inhaling (Inspiration) and
Exhaling (Expiration)
One breath = one inhalation + one exhalation
At rest approx 16 breaths per minute.
Breathing not under conscious control.
Controlled by brain.
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Inspiration - Active i.e. requires
energy
This is taking air into the lungs.
The intercostal muscles between the ribs
contract causing the ribs to move upwards
and outwards.
The circular muscles of the diaphragm
contract and cause it to flatten.
These actions result in an increased volume of
the thorax and a decrease in the air pressure
in the lungs - consequently air is drawn into
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the lungs.
Inhaling
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Expiration - Passive i.e. requires
no energy.
This is expelling air from the lungs.
The diaphragm and intercostal muscles relax
causing the ribs and diaphragm to return to
their original position.
These actions result in a decreased volume of
the thorax and an increase in the air
pressure in the lungs - consequently air is
expelled from the lungs
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Exhaling
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The bell jar model of the lungs
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Control of breathing
Breathing is controlled by the 'respiratory
centre' in the medulla oblongata
- connected by nerves to the diaphragm and
intercostal muscles.
A rise in the amount of carbon dioxide in the
blood passing through the respiratory centre
stimulates impulses to be sent to the
diaphragm and intercostal muscles, causing
an increase in the depth and rate of
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breathing.
Gaseous Exchange in Alveoli
Occurs by diffusion.
Air in alveoli is rich in O2
Blood in capillary is O2 poor
O2 diffuses from the alveoli into the blood
capillaries.
CO2 is plentiful in blood capillaries
CO2 low in the alveoli
 CO2 diffuses out of the capillaries into the
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alveoli
Rapid diffusion is possible
because
• There are millions of alveoli (350,000,000
per lung)
• Alveolus wall one cell thick and surrounded
by a thin layer of fluid
• Large blood capillary network surrounding
each alveolus
• Capillaries narrow and walls are only one
cell thick also
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Gas exchange at an alveolus
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How does the blood carry O2?
O2 dissolves in moist lining of alveolus.
Diffuses through walls of alveolus and capillary.
And into red blood cells.
Joins with haemoglobin to form oxyhaemoglobin.
Carried to every cell in the body.
O2 released and passes from the capillary into the
cells.
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How does the blood carry CO2?
(1/2)
CO2 produced by cells during respiration.
Diffuses from cells into the blood.
Some dissolves in blood plasma.
Most of it diffuses into the red blood cells.
Here an enzyme joins it to water to form
carbonic acid:
CO2 + H2O --> H2CO3
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How does the blood carry CO2?
(2/2)
The carbonic acid (H2CO3) is split into
hydrogen ions (H+) and bicarbonate ions
(HCO3-).
HCO3- ions diffuse out of red blood cells and
are transported in the plasma.
H+ ions remain in the red blood cells.
Removing CO2 from lungs ensures pH of
blood remains constant.
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Composition of inhaled and
exhaled air
Gas
Inhaled
Exhaled
Nitrogen (N2)
79%
79%
Oxygen (O2)
20.9%
16.4%
Carbon dioxide (CO2)
0.03%
4.1%
Variable
Saturated
Water vapour (H2O)
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One of the following
Breathing Disorders
1. Asthma
2. Chronic Bronchitis
Asthma
What is it?
Asthma results in the narrowing of the
bronchioles which prevents air reaching the
alveoli.
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Symptoms
• Breathlessness and wheezing
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Causes
Can be triggered by a number of different
things: • Pollen, house dust, vigorous exercise, cat
and dog dander (scaly pieces of skin),
infection, tobacco smoke and other air
pollutants.
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Prevention
If a specific cause is known to trigger the
asthma then steps can be taken to avoid it.
e.g. if pet dander is responsible, then the
person should not keep a pet or hold or play
with one if possible.
A person with asthma should not smoke.
A person without asthma should not smoke
either.
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Treatment
Inhaling a bronchodilator which widens the
bronchioles is common.
The inhalation technique is very important.
Inhalers should only be used on medical
advice.
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Chronic Bronchitis
What is it?
an inflammatory condition affecting the
bronchi causing them to become narrower.
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Symptoms
Persistent cough,
Breathlessness,
Production of a lot of mucus (phlegm).
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Causes
Smoking and other air pollutants.
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Prevention
Never smoke,
Why not?
When you smoke tiny particles get trapped on
the mucus lining the bronchi.
This is an irritant and causes more mucus to
be produced.
Excess mucus collects in the bronchi,
And causes the familiar ‘smoker’s cough’. 44
Treatment
A bronchodilator (e.g. ventilin) to open the
bronchi may be prescribed to relieve the
breathlessness.
In severe cases the patient may need to inhale
pure oxygen.
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Other Respiratory Disorders
Not examinable
for information only
Lung cancer
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Spread of lung cancer
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How smoking damages the lungs 1
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How smoking damages the lungs 2
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END
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