Subjects: BIOLOGY RESPIRATORY SYSTEM

1. Week 3 lesson: Gas
Exchange

2. MELC: Compare and contrast the following
processes in plants and animals: reproduction,
development, nutrition, gas exchange,
transport/ circulation, regulation of body fluids,
chemical and nervous control, immune
systems, and sensory and motor mechanisms.
(STEM_BIO11/12-IVa-h-1)

3. LESSON OBJECTIVES:
1. state some basic principles in gas
exchange;
2. describe the structures for gas exchange
in plants and animals;
3. describe the organs in the human
respiratory system and their roles;

6. GAS EXCHANGE IN PLANTS
Plants obtain the gases they need through their
leaves. They require oxygen for respiration and
carbon dioxide for photosynthesis. The gases
diffuse into the intercellular spaces of the leaf
through pores, which are normally on the underside
of the leaf - stomata. From these spaces they will
diffuse into the cells that require them. Stomatal
opening and closing depend on changes in the
turgor of the guard cells.

9. When water flows into the guard cells by osmosis,
their turgor increases and they expand. Due to the
relatively inelastic inner wall, the guard cells bend
and draw away from each other, so the pore
opens. If the guard cells loose water the opposite
happens and the pore closes. The guard cells
lower their water potential to draw in water from
the surrounding epidermal cells, by actively
accumulating potassium ions. This requires
energy in the form of ATP which, is supplied by
the chloroplasts in the guard cells.
GAS EXCHANGE IN PLANTS

10. Respiration occurs throughout the day and night,
providing the plant with a supply of energy.
Photosynthesis can only occur during sunlight
hours so it stops at night. A product of respiration
is carbon dioxide. This can be used directly by the
plant in photosynthesis. However, during the day,
photosynthesis can be going 10 or even 20 times
faster than respiration (depending on light
intensity), so the stomata must stay open so that
the plant has enough carbon dioxide, most of
which diffuses in from the external atmosphere.
GAS EXCHANGE IN PLANTS

12. In animals, gas exchange follows the same general
pattern as in plants. Oxygen and carbon dioxide
move by diffusion across moist membranes. In
simple animals, the exchange occurs directly with
the environment. But with complex animals, such
as mammals, the exchange occurs between the
environment and the blood. The blood then carries
oxygen to deeply embedded cells and transports
carbon dioxide out to where it can be removed
from the body.
GAS EXCHANGE IN ANIMALS

13. Earthworms exchange oxygen and carbon dioxide
directly through their skin. The oxygen diffuses
into tiny blood vessels in the skin surface, where it
combines with the red pigment hemoglobin.
Hemoglobin binds loosely to oxygen and carries it
through the animal’s bloodstream. Carbon dioxide
is transported back to the skin by the hemoglobin.
GAS EXCHANGE IN ANIMALS

14. Terrestrial arthropods have a series of openings called
spiracles at the body surface. Spiracles open into
tiny air tubes called tracheae, which expand into fine
branches that extend into all parts of the arthropod
body. Fishes use outward extensions of their body
surface called gills for gas exchange. Gills are flaps
of tissue richly supplied with blood vessels. As a fish
swims, it draws water into its mouth and across the
gills. Oxygen diffuses out of the water into the blood
vessels of the gill, while carbon dioxide leaves the
blood vessels and enters the water passing by the
gills.
GAS EXCHANGE IN ANIMALS

15. Respiratory System
Gas exchange

16. Warning: terminology!
• “Respiration” is used several different ways:
• Cellular respiration is the aerobic breakdown
of glucose in the mitochondria to make ATP.
• Respiratory systems are the organs in
animals that exchange gases with the
environment.
• “Respiration” is an everyday term that is often
used to mean “breathing.”

17. Respiratory system function
• Respiratory systems allow animals to
move oxygen (needed for cellular
respiration) into body tissues and
remove carbon dioxide (waste product of
cellular respiration) from cells.

18. Gas exchange by Diffusion
• Some animals simply
allow gases to diffuse
through their skins.
• These animals have a
low metabolic rate.
Why?
• All of these are aquatic
animals. Why?

19. Specialized structures
• Structures
specialized for gas
exchange include:
• gills (aquatic
animals)
• spiracles
(terrestrial insects)
• lungs (most
terrestrial
vertebrates)

20. Fish Gills
• Fish increase gas
exchange efficiency
using countercurrent
exchange.
• Running blood through
the system in the
opposite direction to
water keeps a diffusion
gradient throughout the
entire exchange.

21. Gills exchange gases in fish. What is the
site of gas exchange in mammals?
1 2 3 4
25% 25%
25%
25%
1. Alveoli
2. Tracheids
3. Bronchi
4. Esophagus

22. Human respiratory system
• Nose
• Nasal/oral cavity
• Pharynx (throat)
• Epiglottis
• Larynx (voice box)
• Trachea (windpipe)
• Bronchi
• Bronchioles
• Alveoli (exchange of O2 from
alveoli and CO2 from
bloodstream)
O2
CO2

23. Moving air in and out
• During inspiration
(inhalation), the
diaphragm and
intercostal muscles
contract.
• During expiration
(exhalation), these
muscles relax. The
diaphragm domes
upwards.

24. Alveoli (air-sacs)
• The alveoli are
moist, thin-walled
pockets which are
the site of gas
exchange.
• A slightly oily
surfactant prevents
the alveolar walls
from collapsing and
sticking together.

25. What happens when you breathe
in?
1 2 3 4
25% 25%
25%
25%
1. The rib muscles
relax.
2. The diaphragm
contracts.
3. Air leaves the
alveoli.
4. Air moves between
the chest wall and
the lung.

26. In the alveolus

27. Gas exchange
• Air entering the lungs
contains more oxygen
and less carbon dioxide
than the blood that
flows in the pulmonary
capillaries.
• How do these
differences in
concentrations assist
gas exchange?

28. Oxygen transport
• Hemoglobin binds
to oxygen that
diffuses into the
blood stream.
• What are some
advantages to using
hemoglobin to
transport oxygen?

29. Carbon dioxide transport
• Carbon dioxide can
dissolve in plasma,
and about 70%
forms bicarbonate
ions.
• Some carbon
dioxide can bind to
hemoglobin for
transport.

30. At the cells
• Cells use up oxygen quickly for cellular
respiration. What does this do to the
diffusion gradient? How does this help
cells take up oxygen?
• Cells produced carbon dioxide during
cellular respiration as waste product, so
CO2 levels in the cell are higher than in
the blood coming to them.

31. In what specific part of our body
oxygen is needed?
1 2 3 4
25% 25%
25%
25%
1. In the heart.
2. In the lungs to help
us breathe.
3. In every cell or our
body as raw material
for cellular
respiration.
4. In our red blood cell
specifically,
hemoglobin.

32. TASK: Trace the pathway of O2 and CO2
by mentioning the parts shown in the picture
below:

33. Human respiratory system
• Nose
• Nasal/oral cavity
• Pharynx
• Epiglottis
• Larynx (voice box)
• Trachea (windpipe)
• Bronchi
• Bronchioles
• Alveoli (exchange of O2 from
alveoli and CO2 from
bloodstream)
O2
CO2