Biology 103 - Main points/Questions
1. How do your lungs work?
2. How do gasses get to your cells?
3. What gasses do plant cells need to
transport?
Remember Circulation …
• Plants and animals push extracellular fluids
– Plants generate flow w/o muscle tissue
– Animals generate flow with pumping muscles
• Fungi move intracellular fluids
– Use cytoplasmic streaming
– Proteins in the cell “stir” the cytoplasm moving
nutrients etc. to rapidly growing hyphae.
• Protists use diffusion & streaming
Why exchange gases?
Cellular respiration - summarized as:
• Glucose + oxygen  carbon dioxide + water
• Look! This consumes oxygen and gives off CO2
• And, of course, produces ATP!
• So - Gas exchange supplies oxygen for cellular
respiration and disposes of carbon dioxide
Gas Exchange
• All the complex multicellular critters use
oxygen to produce ATP in mitochondria
– So all cells need gas exchange for this
• Many plant cells also need a supply of
carbon dioxide for photosynthesis
• We look at animals first
Gas exchange
occurs between an
organism and the
environment, often
in specialized
respiratory organs.
In vertebrates
gases are
transferred via the
circulatory system!
Ultimately
exchange happens
between cells and
the interstitial fluid
that surrounds
them!
Types of Respiratory Systems
• The simplest animals obtain oxygen directly
from their environments through diffusion
Mouth
Gastrovascular
cavity
Exchange
Exchange
1.5 mm
Cnidarians
Diffusion works well
as long as distances
But
as organisms
are small
and
become
surfaces more
are
complex
they need
permeable
specialized exchange
organs
Mouth
Gastrovascular
cavity
Exchange
Exchange
1.5 mm
Cnidarians
Diffusion works well
as long as distances
All
areorganisms
small anduse
diffusion
the
surfacesatare
cellular
level but…
permeable
Types of Respiratory Systems
• As organisms get more complex they need
specialized organs to exchange gases with
the environment
• different phyla have different organs:
– Gills in fish, some arthropods, mollusks,
– Tracheae in insects,
– and lungs mostly in terrestrial chordates
Why do gases move?
Gases diffuse down pressure gradients in
the lungs and other organs
In the lungs and tissues, O2 and CO2 diffuse
from where their concentrations are higher
to where they are lower
Remember diffusion
• Movement from high concentration to low
– Doesn’t require any energy expenditure to make
happen
– Works very quickly over short distances
– Important transport mechanism of cellular
material
Factors controlling diffusion rate:
• Can you remember what some are?
Factors controlling diffusion rate:
• Temperature
• set by organism
• Size of molecule:
• set
• Concentration gradient: • constantly maintained
• Surface area:
• Increased as much as possible
• Distance:
• Decrease as much as possible
• Medium
• Gas as often as possible
Respiratory Medium
• Animals can use air or water as a source
of O2, or respiratory medium
• In a given volume, there is less O2
available in water than in air
• Obtaining O2 from water requires greater
efficiency than air breathing
Respiration in Aquatic Vertebrates
• Water moves past a fish’s gills in one direction
– this permits countercurrent flow
Respiration in Aquatic Vertebrates
• Countercurrent flow
– extremely efficient way of extracting oxygen
– blood flows through a gill filament in an opposite
direction to the movement of water
– the blood always encounters water with a higher
oxygen concentration (constant gradient for
diffusion)
Because the two
fluids flow in
opposite directions
blood can continue
to pick up oxygen
well past the 50%
mark.
Figure 30.3 Countercurrent flow
If blood flowed in
the same direction
as water the
system could
exchange at most
50% of the gas
dissolved.
Figure 30.3 Countercurrent flow
Terrestrial gas exchange
• For organisms on the land gas exchange
poses a new problem
• The exchange must happen on living
cells bathed in fluid – but fluid loss can be
a huge problem so…
• Gas exchange organs are moved into the
body & adaptations to prevent water loss
are common.
Tracheal Systems in Insects
• The tracheal system of insects consists
of tiny branching tubes that penetrate the
body
• The tracheal tubes supply O2 directly to
body cells
Fig. 30.1.c
Lungs
• Lungs - an infolding of the body surface
• The circulatory system transports gases
between the lungs and the body
• The size and complexity of lungs
correlate with an animal’s metabolic rate
In humans:
• A system of branching ducts conveys air
to the lungs
• Air inhaled through the nostrils passes
through the pharynx via the larynx,
trachea, bronchi, bronchioles, and
alveoli, where gas exchange occurs
• Exhaled air passes over the vocal cords
and can create sounds
Fig. 30.6
Fig. 30.4.c
How a Mammal Breathes
• Mammals ventilate their lungs by negative
pressure breathing, which pulls air into
the lungs
• Lung volume increases as the rib muscles
and diaphragm contract
Figure 30.7 How breathing works
• Blood arriving in the lungs has a low
amount of O2 and a high concentration of
CO2 relative to air in the alveoli
• In the alveoli, O2 diffuses into the blood
and CO2 diffuses into the air
• In tissue capillaries, gradients favor
diffusion of O2 into the interstitial fluids
and CO2 into the blood
Alveolus
Alveolus
PCO2 = 40 mm Hg
PO2 = 100 mm Hg
PCO2 = 46
PO2 = 40
PCO2 = 40
PO2 = 100
• Blood arriving in the lungs has a low O2 and a
Circulatory
Circulatory
high CO2 system
relative to air in the alveoli
system
• When it leaves this has reversed
P = 40
P = 100
P
= 40
P
= 46
• Then in body tissue the situation is the
opposite
O2
O2
PO2 ≤ 40 mm Hg
CO2
CO2
PCO2 ≥ 46 mm Hg
Body tissue
(a) Oxygen
Body tissue
(b) Carbon dioxide
Circulatory
system
PO2 = 40
Circulatory
system
PO2 = 100
PO2 ≤ 40 mm Hg
PCO2 = 46
PCO2 = 40
PCO2 ≥ 46 mm Hg
Body tissue
Body tissue
• In tissue capillaries, O2 moves out of the blood
and CO2 moves into the blood… why?
• To move more gas they are carried in several
ways
• hemoglobin molecules contain iron oxygen binds in a reversible way
Figure 30.8 The hemoglobin molecule
hemoglobin acts like little sponges for oxygen
• at high O2 levels (like in the lungs), most
hemoglobin carry a full load of O2
• in the tissues, the O2 levels are much lower
and hemoglobin gives up its bound oxygen
• The vast majority (> 90%) of oxygen you use
was carried to your cells on hemoglobin
• CO2 must also be transported by the blood
– about 8% simply dissolves in the plasma
– 20% is bound to hemoglobin
– rest is carried as HCO3- in blood cells & plasma
• This is highlighted on figure from your book…
Figure 30.9 How respiratory gas exchange works
CO2
O2
Light
H 2O
Sugar
O2
H2O
and
minerals
CO2
• What about
plants? Do they
transport gasses
in circulatory
system?
• No! – they rely
only on diffusion
• specialized
anatomy makes
this work…
Leaf cross section shows…
• Cells packed in top layer - photosynthesis
• Open “spongy” layer below for exchange
• But cuticle blocks gas exchange…
Plant leaf anatomy:
• Lots of open spaces inside but…
• Must open stomata (pores) to get gasses in
Opened
Closed
This causes leaf to lose water so…
• plants need to balance water loss and gas
exchange
• Guard cells control opening/closing
• How…?
• changes in the water pressure of guard cells
Figure 23.20 - guard cells open and close stomata
• When the guard
cells are plump and
swollen with water,
they are said to be
turgid and the
stoma is open
• When the guard
cells lose water, the
stoma closes
Controlling stomata opening:
• Most plants keep closed at night open during
the day. Why?
• Some specially adapted plants keep closed
during day & open at night… Why would you
do that?
• Hint:
➔