Gas exchange is the uptake of oxygen from the environment and release of carbon dioxide. It occurs across respiratory surfaces like the skin, gills, or lungs. Efficient gas exchange requires surfaces to be moist, large, and protected. Diffusion of gases down pressure gradients moves oxygen inward and carbon dioxide outward. As organisms grow larger, gas exchange becomes more difficult due to decreasing surface area to volume ratio, requiring adaptations like lungs. Ventilation improves gas exchange by moving air or water over respiratory surfaces using structures like gill covers or the diaphragm and rib cage. Respiratory pigments like hemoglobin increase the oxygen carrying capacity of blood.

1. Gas Exchange

2. What is gas exchange?
• Gas exchange is the uptake
of molecular oxygen from
the environment and the
discharge of carbon dioxide
to the environment.

3. • It is often called respiratory
exchange or respiration but it
should not be confused with
cellular respiration.
• Oxygen is needed in tissues
for aerobic cellular
respiration to occur and
extract ATP from food.

4. • Carbon dioxide must be
released to prevent
physiological pH in tissues from
being very acidic. In plants
however, the carbon dioxide
that is released as a by-product
of cellular respiration may again
be taken up for the process of
photosynthesis.

5. Basic principles
influencing gas
exchange:

6. 1. The respiratory surface or
organ is the part of an animal’s
body where gases are
exchanged with the
environment. To allow for gas
exchange, it must be moist,
large enough, and protected
from dessication.

7. 2. Respiratory
systems rely on the
diffusion of gases
down pressure
gradients.

8. 3.Surface-to-volume ratio
• As an animal grows, the surface
area increases at a lesser rate than
its volume, making diffusion of
gases into the interior more
difficult
• Animals must have a body design
that keeps internal cells close to
the surface (e.g. flatworms) or
must have a system to move the
gases inward.

9. 4. Ventilation
• It refers to the movement of the respiratory
medium (air or water) over the respiratory
surface.
• Bony fish moves the gill covers
(operculum) for water carrying
oxygen to flow across the gill.
• Humans move the muscles of the
thorax to expand and contract the
chest cavity and move air in and out of
the lungs.

10. 5. Respiratory Pigments or
Proteins
• is any molecule that
increases the oxygen
carrying capacity of
blood.

11. Structures for gas exchange in
plants:
1. Stomates in leaves
• Stomata are cell structures in
the epidermis of tree leaves and
needles that are involved in the
exchange of carbon dioxide and
water between plants and the
atmosphere

12. 2. Lenticels in stems
• Lenticels permit the exchange of
gases between the environment and
the internal tissue spaces of the
organs (stems and some fruits)
• They permit the entrance of oxygen
and simultaneously the output of
carbon dioxide and water vapor

14. 3. Root hairs in aerial roots

15. 4. Pneumatophores or the
lateral roots of mangroves

16. Respiratory surfaces or organs in
invertebrates:
1. Cell surface or cell membrane – especially
used in unicellular organisms

17. 2. Integumentary exchange – refers
to the general body surface or skin
used by animals with high surface-
to-volume ratio; e.g. flatworm and
earthworm. Amphibians also use
their skin in addition to lungs as
gas exchange surface

19. 3. External Gills – used by
invertebrates that live in aquatic
habitats; gills are highly folded,
thin- walled, vascularized
epidermis that project outward
from the body; e.g. crayfish,
lobster, sea star, nudibranch

21. 4. Tracheal system in
arthropods – utilizes fine air-
conducting tubules to provide
gaseous exchange at the
cellular level; it is not
dependent on a circulatory
system; e.g. insects, spiders.

23. Respiratory surfaces in vertebrates:
1. External Gills – thin, vascularized epidermis
that project from the body surface of a few
amphibians; e.g. larval salamander
2. Internal Gills – rows of slits or pockets in
adult fishes positioned at the back of the mouth
such that water that enters the mouth can flow
over them as it exits just behind the head.

25. 3. Lungs – internal respiratory surfaces
shaped as a cavity or sac; lungs provide
a membrane for gaseous exchange;
since they are not in direct contact with
all other parts of the body, lungs require
a circulatory system to transport gases
to the rest of the body; found in birds,
reptiles, and mammals

26. The human respiratory system:
• Air enters or leaves the respiratory
system through nasal cavities where air
is filtered by hair and cilia, warmed by
blood vessels, and moistened with
mucus.

27. These are the parts:
Nose.
Mouth.
Throat (pharynx)
Voice box (larynx)
Windpipe (trachea)
Large airways (bronchi)
Lungs.

28. Compare breathing mechanisms in
vertebrates:
• Amphibians ventilate their
lungs by positive pressure
breathing which forces air
down the trachea.

29. • Birds use a system of air
sacs as blower to keep air
flowing through the lungs
in one direction only,
preventing the mixing of
incoming and outgoing air.

30. • Mammals ventilate their lungs by
negative pressure breathing
which pulls air into the lungs
when the volume of the lungs
expands as the rib muscles and
diaphragm contract. However,
the incoming and outgoing air
mix, decreasing the efficiency of

31. The control of respiration in
vertebrates:
• The nervous system
controls oxygen and
carbon dioxide levels for
the entire body by
regulating the rate and
depth of breathing

32. • The brain monitors the pH of the
cerebrospinal fluid through sensors
(reflecting carbon dioxide concentration
in the blood).
• Secondary control is exerted by
sensors in the aorta and carotid
arteries that monitor blood levels of
oxygen as well as carbon dioxide
(via blood pH).

33. Some respiratory problems and
impact on public health:
• In a respiratory disorder like
asthma, the muscles around
bronchioles contract more than
usual, increasing resistance to
airflow.

34. • Emphysema is an abnormal condition of
the lungs marked by decreased
respiratory function; associated with
smoking or chronic bronchitis or old age
• Smoking tobacco products is one of
the leading global causes of death
and is strongly linked to cancer,
cardiovascular disease, stroke, and
emphysema.

35. • Pneumonia is an
infectious disease
involving inflammation
and fluid buildup in the
lungs.