Gaseous exchange in animals

1. GASEOUS
EXCHANGE
A S BIOLOGY
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3. LUNG FUNCTION
• Humans need to get oxygen into the blood for respiration and get
rid of carbon dioxide made by respiring cells. This is where
breathing(or ventilation its sometimes called)and the lung.s come
in
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M.R.NJOROGE

4. Lungs are specialized organs for gaseous exchange
Fig 1.0 Lung structure
• As you breathe in the air enters
the trachea (wind pipe)
• The trachea splits into two
bronchi-one bronchus leading to
each lung.
• Each bronchus,then branches off
into smaller tubes called
bronchioles.
• The bronchioles end in small air
sacs called alveoli-this is where
gases are exchanged.
• The rib cage,intercostal muscles
and diaphragm all work together
to move air in and out.
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Identify the parts labeled A-G,below?

6. In humans gaseous exchange happens in the
alveoli
About alveolus
• Lungs contain millions of
alveoli-the gas exchange
surface.
• Each alveoli is made from a
single layer of thin ,flat cells
called alveolar epithelium.
• Alveoli are arranged in
bunches and the end of
bronchioles
• They are surrounded by
network of capillaries, giving
each alveolus its own blood
supply.
Structure of alveolus
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7. • Oxygen diffuses out of the alveoli,across the alveolar
epithelium and the capillary endothelium.(a type of
epithelium that forms the capillary wall),and into
haemoglobin in the blood.
• Carbon dioxide diffuses into the alveoli from the blood
,crossing the capillary endothelium then the alveolar
epithelium. After entering the alveolar space its breathed
out.
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Epithelial tissue is
pretty common in
the body. Its
usually found on
exchange
surfaces

8. ADAPTATIONS OF ALVEOLI TO GASEOUS
EXCHANGE
Alveolus have features that speeds up the rate of diffusion so gases
can be exchanged quickly.
• A thin exchange surface-the
alveolar epithelium is only
one cell thick. This means
there's is a short diffusion
distance.(which speeds up
diffusion)
• A large surface area –the
numerous alveoli means
there's large surface area for
gas exchange.
• Alveoli are highly
vascularised to increase the
rate of blood flow to and from
alveoli.
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9. Gaseous exchange has different parts with different
functions
The respiratory system has other parts that help it to exchange
gases efficiently.
• Goblet cells secrete mucus.
The mucus traps
microorganisms and dust
particles in the inhaled air
stopping them from reaching
the alveoli.
• Cilia on the surface of the
cells beat the mucus ,which
move it (plus trapped
microorganisms and dust)
upwards away from the
alveoli towrads the throat
,where its swalloowed.this
helps prevent lung infection.
• Elastic fibres in the walls of
the trachbronchi
,bronchioles and alveoli
help in the process of
breathing out.on breathing
in ,the klungs inflate and the
elastic fibres are strethed
,then the fibres recoilto help
push the air out when
exhaling.
• Smooth muscle
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10. Review question
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1. Fig. 6.1 is a section through lung tissue showing an alveolus and its blood
supply.
(a) (i) Name the type of epithelial cell shown by
label lines A and B.[1] squamous / pavement
(epithelial) ;
(ii) Describe how the elastic fibres of the alveoli
contribute to the healthy functioning of
the lungs.[2] )
stretch / expand, on inspiration and recoil on
expiration ;R contraction (stretch) to increases,
surface area / volume of air, for, diffusion / gas
exchange ;
(recoil) to help, expel air / force air out ;
A carbon dioxide A if destroyed then cannot expel
air
prevent alveoli, bursting / breaking / AW ;ref. to
emphysema if elastic fibres destroyed ; (b) The actual diameter of the alveolus along
the line X–Y is 220 micrometres (μm).
Calculate the magnification of Fig. 6.1.
Show your working and give your answer to the
nearest whole number.
answer × [2]
(c) Outline two features of a gas exchange surface
that are shown on Fig. 6.1.[2]

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b) award two marks if correct answer (anything in range 336–346)
allow +/– 1 mm in reading the line (74–76 mm)
75000 μm / 220 μm = 341 ;;if answer incorrect, award one mark for
correct measurement with unit and division by 220
award one mark if correct answer given to one or more decimal
places[2]
(c) look for two ideas – follow usual rules for marking numbered
answer lines
thin, alveolar wall / epithelial lining / AW ;
Ashort diffusion distance (between air in alveolus and blood in
capillary)
Asquamous cells are thin Rthin, membrane / cell membrane R large
surface area surrounded by, capillaries
/ capillary network ;A close contact with, capillaries / blood (vessels /
cells) A many capillaries A large area of alveolus in contact with,
capillaries / blood

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(d) max 3 if no ref. to diffusion
(named) gas(es), diffuse
down, pressure gradients / concentration gradient / AW ;
A from high(er) partial pressure to low(er) partial pressure
A high(er) concentration to low(er) concentration ignore
‘along a concentration gradient’
in the answers accept the following AWs
capillaries / haemoglobin for blood
lungs for alveoli body for tissues
lungs valid statement linking information in table below – 1 mark for each row
comparison in partial pressure may be ‘higher / lower’ not both or high and
low, but if not then figures have to be given

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(d) Fig. 6.2 is a simplified diagram of the circulatory system of a human, showing gas
exchange in the lungs and in respiring tissue. The partial pressures of oxygen
(pO2) and
carbon dioxide (pCO2) at four locations are also shown.
With reference to Fig. 6.2, explain
how the differences in pO2 and
pCO2 in the alveolus and in blood
enable gas exchange in the lungs
and respiring tissue……………………..[4]

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