the importance of a respiratory system - limestone...
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Why do we breathe? Aerobic organisms require every cell to obtain oxygen and
remove carbon dioxide to survive Gas Exchange
All organisms share two characteristics:
1. Large respiratory surface
2. Moist environment
3 factors that determine rate of exchange:
1. Area of cell membrane - larger area, more exchange.
2. Concentration difference - more oxygen in air then in lungs,
greater rate of diffusion.
3. Diffusion distance - a very slight increase in distance can greatly
reduce the rate at which a diffusing substance reaches its goal
(2s to travel 10um, 4s to travel 20um, 16s to travel 40um etc.)
Simple Gas Exchange
Single celled organisms rely on diffusion.
To fulfill the moist requirement these organisms must live
in wet, aquatic environments.
Either in the environment or in a host organism.
Some simple multicellular organisms also exchange gas in
this manner.
The key is that they are aquatic as well
Green algae, hydra and planarian worm
Specialized Breathing
The larger the organism the more difficult it is to get
oxygen to every cell in the organism.
1. Diffusion distance needs to be very small
2. As cells become differentiated for other purposes
the amount of surface area devoted to gas
exchange is reduced.
Adaptations have been developed to allow
increased complexity while maintaining gas
exchange at significant levels.
Specialized Breathing
Skin Respiration (p.283, fig.3a)
Phylum Annelida segmented worms
Skin must be kept moist to allow diffusion of oxygen to occur.
Skin is lined with capillaries which allow oxygen to enter the circulatory system and carbon dioxide to exit.
This is an advancement due to the fact that it is in this phylum that circulation starts to play a role in ensuring all cells respire properly.
Diffusion would simply not allow enough exchange of gases.
Specialized Breathing
Gills (p.283, fig.3b & 4)
Whole body is not available for gas exchange due to habitat in
which these organisms live.
Both as defense and maintaining internal environment.
Surface area to allow exchange of gases is decreased however this
is combated in two ways:
1. Where gas exchange does occur the surface area is increased.
2. A mechanism has evolved to allow the organism to ventilate this surface,
that is, to move the oxygen containing medium over the gills to gain fresh
oxygen.
Specialized Breathing
Gills
Feathery tissue in many aquatic species that allow gas exchange across thin gill membranes.
In some organisms (ex. tube worm) the gill is moved through the water while in other organisms (ex. fish and clams) water is ventilated over the gills in usually just one direction.
This reduces the amount of energy the animal must expend to move water over the gills.
Typical Movement
Water moves in through the mouth and over the gills.
Tiny capillaries absorb oxygen and release carbon dioxide.
Counter-current flow in fish
Water flow over gills in one direction
Saves energy since fish does not have to correct flow of
water
As water flows over the gills the most oxygen
depleted blood draws oxygen from the oxygen
depleted water.
Oxygen will diffuse into the blood
As blood flows out of the gill it becomes increasingly
oxygen rich due to the fact that it continues to meet
water that is increasingly oxygen rich.
Specialized Breathing
Out of the Water
Moisture retention becomes the main problem.
Breathing is the concept of ventilating a respiratory
surface with air and it relies on a simple law of physics:
Air will move from a region of high pressure to a region of
lower pressure until equilibrium is acquired.
Two main methods of terrestrial breathing have evolved
based on this principle:
Tracheal Respiratory System and Lungs
Specialized Breathing
Tracheal Respiratory System
Insects utilize a series of external pores called spiracles which each
lead to an internal series of tubes called tracheae.
Spiracles are controlled by valves to monitor water loss by the
organism and to facilitate the pressure differential.
Abdomen expands air pressure drops in tracheae 4 anterior paired spiracles
open air rushes into tracheae
Abdomen contracts 4 anterior paired spiracles stay closed but 6 posterior
spiracles open air pressure inside is now high and air flows out
Insects respiratory system and circulatory system are separate from
each other.
Specialized Breathing
The Lung
Characteristic of air-breathing vertebrates is the internal lung.
Internal respiratory surface connected to the air by means of internal passageways.
Main components of lungs:
1. Have a moist respiratory surface.
2. A means of forcibly bringing air into contact with the lung surface.
3. A circulatory system to move the gases around the body.
Frog uses a lung system in conjunction with skin respiration.
Birds
Migratory birds have developed a respiratory advantage to give them enough energy to migrate.
Utilize air sacs that ensure that residual air is never in contact with the lungs.
Air sacs do not allow gas exchange, simply a method of holding air to allow maximum efficiency.
Always an oxygen rich medium in contact with lungs
Birds also have a countercurrent exchange system with respect to their circulatory system
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