Which Type Of Animal Has The Most Efficient Respiratory System?

Learning Outcomes

Discuss the respiratory processes used by animals without lungs

The photo shows a round, green cell with a smooth, shiny surface. The cell resembles a balloon.

Figure ane. The cell of the unicellular alga Ventricaria ventricosa is i of the largest known, reaching one to five centimeters in diameter. Like all single-celled organisms, 5. ventricosa exchanges gases across the jail cell membrane.

All aerobic organisms require oxygen to carry out their metabolic functions. Along the evolutionary tree, unlike organisms accept devised different means of obtaining oxygen from the surrounding atmosphere. The environment in which the animal lives greatly determines how an animal respires. The complexity of the respiratory system is correlated with the size of the organism. Equally animal size increases, diffusion distances increment and the ratio of surface expanse to volume drops. In unicellular organisms, diffusion across the jail cell membrane is sufficient for supplying oxygen to the cell (Figure 1).

Diffusion is a ho-hum, passive ship procedure. In order for diffusion to be a feasible ways of providing oxygen to the prison cell, the rate of oxygen uptake must match the rate of diffusion across the membrane. In other words, if the cell were very large or thick, diffusion would not be able to provide oxygen rapidly enough to the within of the cell. Therefore, dependence on improvidence equally a means of obtaining oxygen and removing carbon dioxide remains viable simply for small-scale organisms or those with highly-flattened bodies, such equally many flatworms (Platyhelminthes). Larger organisms had to evolve specialized respiratory tissues, such every bit gills, lungs, and respiratory passages accompanied by a complex circulatory systems, to transport oxygen throughout their entire torso.

Direct Diffusion

The photo shows a worm with a flat, ribbon-like body, resting on sand. The worm is black with white spots.

Figure ii. This flatworm'southward procedure of respiration works by diffusion across the outer membrane. (credit: Stephen Childs)

For small multicellular organisms, diffusion across the outer membrane is sufficient to meet their oxygen needs. Gas exchange by straight improvidence across surface membranes is efficient for organisms less than 1 mm in diameter. In simple organisms, such every bit cnidarians and flatworms, every cell in the torso is shut to the external environs. Their cells are kept moist and gases diffuse chop-chop via straight improvidence. Flatworms are pocket-size, literally apartment worms, which "breathe" through diffusion beyond the outer membrane (Figure 2). The flat shape of these organisms increases the surface area for improvidence, ensuring that each cell inside the body is close to the outer membrane surface and has access to oxygen. If the flatworm had a cylindrical torso, then the cells in the centre would not be able to get oxygen.

Skin and Gills

Earthworms and amphibians employ their skin (integument) every bit a respiratory organ. A dense network of capillaries lies merely below the pare and facilitates gas exchange betwixt the external surround and the circulatory system. The respiratory surface must be kept moist in society for the gases to dissolve and diffuse beyond cell membranes.

The photo shows a carp with a wedge of skin at the back of the head cut away, revealing pink gills.

Effigy 3. This common carp, similar many other aquatic organisms, has gills that allow it to obtain oxygen from h2o. (credit: "Guitardude012″/Wikimedia Commons)

Organisms that live in water demand to obtain oxygen from the water. Oxygen dissolves in water but at a lower concentration than in the atmosphere. The temper has roughly 21 percent oxygen. In water, the oxygen concentration is much smaller than that. Fish and many other aquatic organisms accept evolved gills to take up the dissolved oxygen from water (Figure 3). Gills are thin tissue filaments that are highly branched and folded. When h2o passes over the gills, the dissolved oxygen in water rapidly diffuses beyond the gills into the bloodstream. The circulatory system tin can and then carry the oxygenated claret to the other parts of the body. In animals that incorporate coelomic fluid instead of claret, oxygen diffuses across the gill surfaces into the coelomic fluid. Gills are institute in mollusks, annelids, and crustaceans.

The folded surfaces of the gills provide a big surface area to ensure that the fish gets sufficient oxygen. Diffusion is a process in which cloth travels from regions of high concentration to depression concentration until equilibrium is reached. In this example, blood with a depression concentration of oxygen molecules circulates through the gills. The concentration of oxygen molecules in water is higher than the concentration of oxygen molecules in gills. As a result, oxygen molecules diffuse from water (loftier concentration) to blood (depression concentration), equally shown in Effigy 4. Similarly, carbon dioxide molecules in the blood diffuse from the blood (loftier concentration) to water (depression concentration).

Figure 4. Equally water flows over the gills, oxygen is transferred to blood via the veins. (credit "fish": modification of piece of work past Duane Raver, NOAA)

Tracheal Systems

The illustration shows the tracheal system of a bee. Openings called spiracles appear along the side of the body. Vertical tubes lead from the spiracles to a tube that runs along the top of the body from front to back.

Effigy 5. Insects perform respiration via a tracheal system.

Insect respiration is independent of its circulatory system; therefore, the blood does non play a direct role in oxygen transport. Insects have a highly specialized blazon of respiratory arrangement chosen the tracheal system, which consists of a network of minor tubes that carries oxygen to the unabridged body. The tracheal organisation is the most direct and efficient respiratory system in active animals. The tubes in the tracheal system are made of a polymeric material called chitin.

Insect bodies accept openings, called spiracles, along the thorax and abdomen. These openings connect to the tubular network, assuasive oxygen to laissez passer into the trunk (Figure54) and regulating the improvidence of CO₂ and water vapor. Air enters and leaves the tracheal system through the spiracles. Some insects tin ventilate the tracheal system with trunk movements.