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Gas exchange
1. Across the body surface of a single-celled
organism
2. In the tracheal system of an insect (tracheae
and spiracles)
3. Across the gills of a fish (gill lamellae and fi
laments including the countercurrent
principle)
4. By leaves of dicotyledonous plants
(mesophyll and stomata).
Unicellular organisms
Unicellular Organisms do not have specialised gas exchange
surfaces. Instead gases diffuse in through the cell membrane.
The smaller something is, the smaller the surface area is but, more
importantly, the bigger the surface area is compared to its
volume.
In other words, unicellular organisms have a large surface area to
volume ratio. They are therefore efficient when it comes to
exchanging gases through their membrane.
Also, all parts of the organism are supplied with oxygen because the
diffusion path is short.
Gas exchange in Insects
Insects have no transport system so
gases need to be transported directly
to the respiring tissues.
There are tiny holes called spiracles along
the side of the insect.
Insects
The spiracles are openings of small tubes running
into the insect's body, the larger ones being
called tracheae and the smaller ones being
called tracheoles.
The ends of these tubes, which are in contact
with individual cells, contain a small amount of
fluid in which the gases are dissolved. The fluid
is drawn into the muscle tissue during exercise.
This increases the surface area of air in contact
with the cells. Gases diffuse in through the
spiracles and down the tracheae and tracheoles.
Ventilation movements of the body during
exercise may help this diffusion.
The spiracles can be closed by valves and
may be surrounded by tiny hairs. These
help keep humidity around the opening,
ensure there is a lower concentration
gradient of water vapour, and so less is
lost from the insect by evaporation.
Gas exchange in Fish
A Bony Fish
Lamellae
Secondary Lamellae
Gill Plates
Counter Current Mechanism
http://www.kscience.co.uk/animations/anim_3.htm
Gas exchange
Similarities
Differences
Dissection
C.O.W!!
Match the correct letter with the correct part;
1.Operculum
2.Buccal cavity
3.Gill arch
4.Opercular cavity
In today’s lesson…
1. Identify the buccal cavity, opercular
cavity, operculum and gills on a fish.
2. Recall the benefits of countercurrent to
fish
3. Carry out a dissection
Fish head dissection
In pairs dissect the fish
head.
You must identify and
remove the;
Operculum
Gill arch
Identify the primary lamellae
Use a light microscope to
identify the secondary
lamellae
How would the pressure and
volume of the buccal cavity and
opercular cavity change as the fish
swims through the water?
Things to consider• Buccal cavity open and fills with water
•Buccal cavity closes and water is forced over gills into
opercular cavity
•Operculum opens and water is forced out
The graph shows the change in pressure in the mouth (buccal) cavity of
a fish during ventilation of the gills.
+0.1
Pressure /
0
kPa
–0.1
A
0.2
0.4
0.6
0.8
1.0
B
Time/s
) Calculate the rate of ventilation per minute. Show your working.
Rate per minute ........
(2)
(i
(ii) Explain what causes the fall in pressure between points A and B.
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(1)
The diagram shows the arrangement of the
respiratory surface in the lungs of birds.
Trachea
Blood capillaries
around bronchioles
Bronchi
Network of bronchioles
forming gas exchange
surface
Air sacs
Lungs
(i) Give one similarity and one difference between the gas exchange surface of a bird
and that of a mammal.
Similarity...........................................................................................................
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Difference..........................................................................................................
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(2)
The efficiency of diffusion is
increased if there is:
•
•
•
A large surface area over which
exchange can take place.
A concentration gradient without which
nothing will diffuse.
A thin surface across which gases
diffuse.
Fick’s law
Rate of diffusion α
Area of surface x Difference in conc
Thickness of surface
Qu.. What conditions maximise the rate of diffusion??
Gas exchange in plants
Ψ Cell
Ψ Cell = Movement?
Ψ Solute= Distilled water?
Ψ Pressure= Animal cells? Plant cells?
The diagram shows the potassium (K+) ion concentrations in the cells around an
open and closed stoma in Commelina. The concentrations are in arbitrary units.
(i) Explain how the movement of K+ ions accounts for the opening of the
stoma.
(ii) Explain how K+ ions are moved against a concentration gradient.
(i) K+ ions move into guard cells;
Water potential of guard cells becomes
more negative;
Water enters;
How uptake of water causes stoma to open;
(ii) Energy/respiration/ATP/active transport;
Intrinsic proteins/carriers/channels.