Principles of Biology
By
Frank H. Osborne, Ph. D.
Respiration
Respiration
•Breathing is generally called respiration. We use
respiration to distinguish breathing from cellular
respiration, which is the oxidation of glucose for
energy production. All higher organisms require
O2. Unless the O2 diffuses into the body, they must
have a mechanism and a system for bringing in O2
and eliminating the CO2 that results from cellular
respiration.
Respiration
•Plants and the lower members of the animal
kingdom can obtain their O2 and eliminate their
CO2 by diffusion. They do not require lungs or
gills. Higher animals, including humans, require
a breathing apparatus in order to exchange these
gases.
Unicellular Organisms
•In unicellular organisms, gases exchange with
the surrounding medium by diffusion across the
moist cell membrane of the cell. The membrane
must be moist. It is more difficult for gases to
diffuse across a dry membrane. Besides, a dried
out organism is usually dead. No special
breathing apparatus is required by these
organisms.
Green Plants
•Gases enter and exit
the air spaces of
leaves via the
stomates. The
openings of stomates
are controlled by
guard cells.
Green Plants
•Older stems are usually impermeable to gases.
Some trees have lenticels that let air into the
cambium. In many large trees, there are enough
cracks in the bark so that air is available for the
cambium and living phloem cells.
Green Plants
•Roots can exchange
gases with the soil.
This is done via the
moist cell membranes
of the cells in the lower
parts of the roots.
Coelenterates
Hydra does not have any specialized breathing
apparatus. It only has two cell layers and
therefore does not need one. Each cell layer is in
contact directly with the exterior aqueous
environment. Gas exchange is across the moist
cell membranes of the individual cells.
Coelenterates
Hydra.
With only two
body layers, no
special breathing
equipment is
required.
Higher Marine Animals
Gills are used by marine worms, molluscs
(clams), and fishes. The gill lamellae (layers)
have a large area for exchange of gases. The
gases are transported to the rest of the body by
the circulatory system. In the crustacea
(lobsters) and echinoderms (starfishes), different
systems are used.
Diagram of clam
Diagram of fish
Diagram of lobster
Diagram of starfish
Gill Function
•The afferent vessel carries blood toward the gill
(afferent and approach both begin with "a").
This blood is high in CO2 and low in O2.
•The blood in the gill exchanges gases with the
water. The CO2 leaves the gill and enters the
water while the O2 leaves the water and enters the
gill.
•Then, the efferent vessel carries blood away
from the gill (efferent and exit both begin with
"e"). This blood is high in O2 and low in CO2.
Gill
Function
Insects and Spiders
Each cell in the body of an insect or spider is in
contact or near a breathing tube known as a
trachiole. A group of trachioles will be combined
to form a larger breathing tube called a trachea.
These animals have numerous tracheas that exit
through holes on the side of the body called
spiracles. These spiracles are used for gas
exchange, the "spir" part is also found in the
word "respiration."
Grasshopper
Frog
•In the frog and other amphibians, about half of
the gas exchange takes place across the skin.
The other half of the respiration is done using
lungs. Frogs do not have a diaphragm so they
must force air into the lungs. This is called
positive pressure breathing. Humans have a
diaphragm so their breathing is by negative
pressure.
Frog
Birds
•Birds have a complicated respiratory system
consisting of lungs and air sacs in the bones. Air
is cycled through the air sacs in the hollow
spaces in the bones.
Birds
Human Respiration
•The human respiratory system consists of the
lungs, bronchi and trachea. The lungs are
located in the thoracic (chest) cavity, the area in
the chest above the diaphragm. The heart is also
located in the chest cavity.
Human
Lungs
Human Respiration
•In humans, the diaphragm contracts and makes
the chest cavity larger. This creates a partial
vacuum in the chest cavity. Air rushes in
because the pressure is lower in the chest cavity
when the diaphragm contracts.
•The air that enters the lungs from the outside is
high in O2 and low in CO2.
Human Respiration
•Inspiration is the term used for inhaling air.
When the diaphragm relaxes, the pressure in the
chest increases and forces the air out. The air
that leaves the lungs is low in O2 and high in
CO2.
•Expiration is the term used for exhaling air.
Breathing
Control of Breathing
•Control of breathing is done by the nervous
system. The brain stem has a CO2 sensor that
detects the concentration of CO2 in the blood.
When CO2 increases as a result of exercise, for
example, the breathing rate and heart rate
increase.
•When there is little CO2 in the blood, the
nervous system slows the breathing rate.
Gas Exchange in the Lungs
•Gases are exchanged in the air sacs (alveoli) of
the lungs. Air makes its way down to the air sacs
where O2 passes through the capillary walls by
diffusion, and into the blood stream where it
enters the red blood cells.
•Blood leaving the alveoli is high in O2
and low in CO2.
Gas Exchange in the Lungs
•Simultaneously, CO2 and some water leave the
blood stream and enter the alveoli of the lungs.
These respiratory gases pass up through the
respiratory system to the outside.
•All air exchange in the lungs is external
respiration and occurs through the moist
surfaces of the cell membranes of the air sacs of
the lungs and the capillaries of the blood stream.
Cellular respiration is internal respiration.
Gas
Exchange
in the
Lungs
The End
Principles of Biology
Respiration