Comparing Respiratory Systems

Bacteria – Unicellular Organisms Bacteria and amoeba 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

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

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.

counter-current gas exchange tutorial

Fish – Counter Current Blood flows through the gills in an opposite direction than the water that flows past the gill Oxygen in the water is always at a higher concentration than the oxygen concentration in the fish’s blood Oxygen diffusion between the watery environment and the fish’s blood will be continuous. Diffusion will not reach equilibrium.

Mammal - 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.

Mammals (human) lung system Mammals have a lung system directly linked to the circulatory system. Oxygen is carried by hemoglobin (a blood protein) and carbon dioxide is carried in blood plasma (liquid portion of blood) Gases are exchanged at single-celled structures called alveoli.

Human

Human