Comparing Respiratory Systems

Respiration

Respiration is a process involving the movement of oxygen gas into cells and carbon dioxide out of cells, (This better called “BREATHING”) in order to facilitate reactions such as cellular respiration (a chemical reaction in the mitochondria).

Oxygen gas moves into cells and carbon dioxide moves out by the process of DIFFUSION.

Respiration

Remember:

In order for diffusion to occur effectively, the surface across which the gas it to diffuse must be moist (gases must be DISSOLVED for diffusion to occur) and thin.

Also, the distance that the gas must diffuse must be small.

Bacteria – Unicellular Organisms

Bacteria are unicellular organisms (consist of only one cell). Because of this, their structure is simple.

In order to obtain the gases required for life, simple diffusion across the cell membrane is sufficient. (BECAUSE S.A./Vol. is huge because they are tiny)

Diffusion across a membrane

Bacteria – Unicellular Organisms

Bacterial cells must remain in a moist environment in order for diffusion to occur (maintains a moist surface on the cell).

Bacterial cells (and ALL cells) must have a large surface area to volume ratio to ensure there is enough surface for the gases to diffuse to meet the needs of the size of the cell.

Earthworm

Earthworms rely on skin diffusion obtain the gases that they need to survive.

Earthworms are simple animals. Their cells require oxygen to support cellular respiration, and must eliminate CO2 that is produced through this process.

Earthworm

In order to accommodate enough diffusion to survive, earthworms must live in moist environments (to help maintain a layer of moisture on their skin).

Also worms produce a mucous layer that aids in maintaining a layer of moisture on their surface.

Earthworm

Internally, directly beneath the skin, earthworms have an intricate network of small blood vessels (capillaries) that will pick up oxygen that diffuses inward and carry it to the cells deeper within the worm’s body.

This ensures that cells that are not close to the surface can receive adequate oxygen. Remember, diffusion cannot occur across far distances.

Earthworm

Fish

Fish are unable to obtain oxygen directly from the air. They use a gill respiratory system to remove dissolved oxygen from the water for use in their cells.

Because fish are aquatic organisms, they do not need to worry about maintaining a moist respiratory surface.

Fish

Fish

A fish’s gills contain a rich supply of blood to carry away dissolved O2 as it diffuses across the gill surface. The blood carries O2 to the body, and also delivers CO2 to the gills.

The fan structure of the gill helps to ensure that there is an adequate surface area:volume ratio across the respiratory structure to service the size of the fish.

Fish

Fish have an effective method for obtaining dissolved oxygen from the water around them. The process used is called counter-current gas exchange. This process will be discussed in a later section

Grasshoppers - Insects

Insects use a tracheal system for respiration. This system consists of a series of tubes that carry gases deep inside the body of the insect from a series of small pores on the insect’s abdomen. These pores are called spiracles.

Grasshoppers - Insects

As insects are terrestrial organisms, their respiratory system must be kept moist. As the tracheal tubes lead deep inside the insects body, internal fluids maintain humidity in the tubes.

The spiracles (openings) are able to open to allow gases to be exchanged, and close when no exchange is occurring – this keeps moisture inside.

Grasshoppers - Insects

Grasshoppers - Insects

Grasshoppers - Insects

Frog

Frogs spend part of their lives in water and part of their lives on land. Because of this, at different stages of their lives, they rely on different methods of breathing.

Frogs

As tadpoles, frogs are purely aquatic. Tadpoles have gills much like a fish, for obtaining dissolved oxygen from the water.

Tadpoles

Frog

As the tadpole transforms into a frog, it changes its habitat from a purely aquatic one, to a terrestrial one.

Adult frogs lose their tadpole gills and develop a set of hollow internal lungs.

Frog

Frog

An active adult frog has a high O2 requirement. Frogs swim under water, but rely on O2 from the air for respiration.

Frogs must surface and breathe air to maintain activity.

Frog

An adult frog will hibernate over winter. Often, they will burrow in the muddy beds of lakes or ponds.

Frog

Their bodies go into a sort of “suspended animation” where their hearts continue to beat and pump blood, but they are basically just maintaining life functions. Their O2 and food requirements are minimal as there is no movement.

Frog

During hibernation, a frog may obtain the amount of oxygen in requires to survive through skin diffusion across it’s thin skin, or through the lining of it’s mouth.

Human

We are large and complex animals. Our O2 requirements are large, as we are relatively active for many hours in a day. Our gas exchange system must be large enough to supply an adequate amount of O2 and remove CO2. Because we are terrestrial, it must also be kept moist.

Human

The surface area of a human lung is comparable to the size of a tennis court.

It is held within the body to keep it moist, and a layer of mucus in the upper respiratory system helps maintain moisture as well.

Human

Our lungs are found deep within our chest. It must supply O2 to, and remove CO2 from cells all around the body.

To deliver and remove gases to these cells, the body relies on our circulatory system and blood to do this. The lungs are supplied with a rich supply of blood.

Human

Human