Biology Lesson Notes Chapter 8 Gas Exchange in Humans: The Human Breathing System
Biology Lesson Notes Chapter 8 Gas Exchange in Humans: The Human Breathing System
Biology Lesson Notes Chapter 8 Gas Exchange in Humans: The Human Breathing System
The exchange of respiratory gases between the cells of an organism and the environment is
called (1) (氣體交換).
Unicellular organisms are relatively small and have a large surface area to volume ratio.
Gas exchange takes place effectively by diffusion across their cell surfaces.
Multicellular organisms, such as humans, have a small surface area to volume ratio.
Diffusion over the body surface is inadequate for gas exchange. Humans have evolved a
(2) (呼吸系統) to move air into and out of the body for
effective gas exchange.
nostril
larynx
(4)
right lung
(6)
(5)
(7)
rib
pleural
intercostal muscle
cavity
(8) pleural
membranes
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Lesson Notes 8 Gas exchange in humans
Challenge yourself
Complete the flowchart below to show the path by which air enters the lungs:
in the lungs
Nostrils (鼻孔) are lined with (9) to filter out dust and other particles from
the air.
On the wall of the nasal cavity (鼻腔):
Pharynx (咽) is the common passageway for food and air. From the pharynx, air passes into
the larynx (喉) of the breathing system, while food and drink enter the oesophagus of the
digestive system.
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Lesson Notes 8 Gas exchange in humans
When we swallow, the larynx rises and the (13) (會厭) covers the glottis
(聲門). This prevents food and drinks from entering the trachea.
The trachea (氣管) branches into two (14) (支氣管) which divide further
into many smaller tubes called (15) (小支氣管) in the lungs.
The trachea is supported by (16) -shaped rings of cartilage. The bronchi are
supported by (17) rings of cartilage. Without the support of cartilage, the
trachea would collapse with the fall in air pressure when we breathe in.
oesophagus
C-shaped cartilage
lumen of the trachea
The inner walls of the trachea, bronchi and large bronchioles are lined with ciliated epithelial
cells and mucus-secreting cells.
The air sacs are surrounded by dense networks of blood capillaries. These capillaries are
supplied with blood from the (19) (肺動脈) and are
drained by the (20) (肺靜脈).
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Lesson Notes 8 Gas exchange in humans
A. How does gas exchange occur between air sacs and the capillaries?
The pulmonary arteries carry (30) blood from the heart to the capillaries
surrounding the air sacs. Oxygen and carbon dioxide then diffuse across the walls of air sacs
due to the concentration gradients between the blood and the air sacs.
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Lesson Notes 8 Gas exchange in humans
Feature Adaptation
Water film covering the inner surface Allows oxygen to dissolve in it and diffuse across
the walls of air sacs
Very thin (one-cell-thick) walls Provide a short distance for diffusion of gases
Surrounded by a dense network of Provides a rich blood supply that transports the
blood capillaries gases to and from the air sacs, maintaining a steep
(32) of gases
The walls of air sacs lie close to the Provide a short distance for diffusion of gases
walls of blood capillaries
Practical 8.4 Comparison of the oxygen content of inhaled air and exhaled air
Refer to Coursebook p.8-13 and SBA Practical Workbook p.8-9.
The candle burns for a longer period of time in (34) air than in
(35) air. This shows that the (36) air contains more oxygen than
(37) air.
Practical 8.5 Comparison of the carbon dioxide content of inhaled air and exhaled air
Refer to Coursebook p.8-14 and SBA Practical Workbook p.8-12.
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Lesson Notes 8 Gas exchange in humans
Inhaled air passes through the hydrogencarbonate indicator in flask X, while exhaled air passes
through the indicator solution in flask Y.
The major differences in composition between exhaled air and inhaled air:
Challenge yourself
Write ‘T’ for a true statement or ‘F’ for a false statement in each box provided.
Red blood cells have the following adaptations for carrying oxygen:
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Lesson Notes 8 Gas exchange in humans
Feature Adaptation
Key: Hb = haemoglobin
HbO2 = oxyhaemoglobin
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Lesson Notes 8 Gas exchange in humans
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Lesson Notes 8 Gas exchange in humans
Challenge yourself
Which of the following statements correctly describe the transport of oxygen and carbon dioxide
respectively in the human body? Write the suitable letters in the space provided.
Breathing is brought about mainly by the actions of (58) muscles and the
(59) .
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Lesson Notes 8 Gas exchange in humans
Inhalation Exhalation
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Lesson Notes 8 Gas exchange in humans
Inhalation occurs when the pressure in the lungs is lower than atmospheric pressure.
Exhalation occurs when the pressure in the lungs is higher than atmospheric pressure.
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