8.1 The Task of Respiration

The Respiratory System

• Respiration: The exchange of oxygen & carbon dioxide between an organism & its external environment.

• The respiratory system supplies oxygen to cells & removes carbon dioxide.

Cellular Respiration• The process that releases the energy

needed to drive all cell functions. Each cell requires a supply of oxygen and produces the waste product carbon dioxide. The basic function of the respiratory system is to provide a means of obtaining a supply of oxygen and a means to rid the body of CO2. This is known as gas exchange.

C6H12O6 = CO2 + H2O + ATP

Respiration in various organisms• Different organisms have different

respiratory systems. Regardless of the type of system, each shares two requirements.

1. The respiratory surface must be large enough for gas exchange to occur at a rate that will meet the organism’s metabolic needs.

2. Respiration must take place in a moist environment so that the gases are dissolved.

Simple Gas Exchange• Most single-celled organisms do not have a

distinct respiratory system and rely on diffusion to meet their gas exchange requirements. The respiratory surface is the cell membrane itself, which is moist.

• Limitations: • Diffusion is effective over a distance of a few cells

therefore organisms that are more than a few cells thick need a more specialized system

• Body parts become more differentiated in more complex organisms; therefore the body surface cannot be totally dedicated to gas exchange.

The Specialized Respiratory System

1. Skin respiration• The skin surface of earthworms is

lined with many tiny capillary vessels. • Gases diffuse in/out of these vessels

and are carried to other parts of the body by the circulatory system.

Earthworms

• Diffusion of gasses occurs through their thin, moist skin.

• Mucous & other body fluids are excreted onto skin. • Emerge only at night when the evaporating potential

of the air is low.• Light-sensitive tissues near their head enable it to

detect light, so they can avoid coming out in the sun.

Gills• Some organisms have protective coats that

decrease the surface area for gas exchange• Gills are feathery tissue structures that

consist of numerous branches. Gases are exchanged across the thing gill membranes

• In most gilled animals, water flows only one way over the gills, which reduces the amount of energy needed to move the water over the respiratory surface

• When an oxygen-containing medium is moved over the respiratory surface, it is called ventilation.

Fish• Water enters the mouth & passes over the

gills.• The water flows in an opposite direction to

the blood (countercurrent flow). • Oxygen diffuses from the water & into the

blood.

Animation of fish breathing cycle

2. The Tracheal Respiratory System

• It is harder to respire on land than in the water because it is more difficult to keep the respiratory surface moist.

• A series of external pores can resolve this problem. The spiracles lead to an internal network or tubes called tracheae.

• Gas is exchanged through these pores and moves through the network of tracheae. These tubes come into close contact with all the living cells to allow gas exchange by diffusion.

• This system does not require the use of the circulatory system.

Grasshoppers• Air enters tracheal tubes through spiracles.• The tracheae carries air directly to individual

cells where diffusion of gases occurs.• Contraction of abdominal muscles

compresses the air sacs & forces air out of the tracheae.

• As the muscles relax, the air sacs return to its normal volume & air is drawn in.

3. The Lung

• The lung is an internal respiratory system connected to the air by means of internal passageways

• All lung systems have three common characteristics:

1. Moist respiratory surface2. A means of forcibly bringing air into contact with

the lung surface3. A circulatory system to carry the gases between

the lungs and the other cells of the body

Air Pressure• At equilibrium, air pressure is equal in both

vessels• If the volume of one vessel increases, the air

pressure inside it decreases. Air flows from the vessel with the higher pressure into the vessel with the lower pressure.

• If the volume of one vessel decreases, the air pressure inside it increases. Air flows from the vessel with the higher pressure into the vessel with the lower pressure.

Frogs

Inner Lining of Mouth• Roof of mouth has rich supply of blood vessels.• Constant movements of throat brings air in through

the nose & into the mouth, where diffusion occurs.• The air is then released through the nose. • The passage to the

lungs is kept closed.

FrogsLungs• Inflate lungs in stages.• They block off their nose, pass the air from

the throat into their lungs, close their lungs off & bring in more air through their nose.

• This process is repeated until the lungs are inflated.

• Once the lungs are fully inflated, gas exchange occurs.

Frog Respiration

Frogs

Skin• Thin & moist.• Contains rich supply of blood vessels.• Gases diffuse between the blood vessels &

the outside environment. • Glands in their skin produce a mucus to keep

them moist.

BirdsInhalation• Both sacs expand at the same time.• Pressure decreases & air enters the trachea.• The posterior air sacs fill with fresh air.• The anterior sacs fill with stale air from the lungs.

Exhalation• Both sacs contract at the same time. • Air passes out of the anterior sacs & out via the trachea. • Fresh air moves from the posterior sacs & into the lungs.

* Air sacs act as a bellows to suck air into the body, then circulate it in a one-way flow through the lungs

Tutorial 48.1 Airflow in Birds

Humans