Describe the Structural and Physiological Adaptations Shown by Invertebrates to Varying Oxygen Concentrations.

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Karen Baker

Biology Essay: Describe the Structural and Physiological Adaptations Shown by

Invertebrates to Varying Oxygen Concentrations.

For aquatic animals, changes in oxygen concentration are particularly important because many aquatic animals cannot survive when oxygen concentrations dip below a certain level.  Oxygen concentrations also determine the solubility of several important substances, notably phosphate, iron, and manganese.

One problem faced is that the oxygen concentration in water is a great deal less than that of air, as oxygen is soluble in water only to a limited extent, so the respiratory gases needed are much less available in water than they are in air.  Also, oxygen availability is temperature dependent.  The solubility of any gas in water depends on the temperature of medium: the warmer the medium, the lower the concentration of gas which can be dissolved in it:

Water viscosity is also much greater than air viscosity.  Viscosity is the tendency of the fluid to resist flow, and is important when it comes to respiration, because respiration requires the movement of fluid over a respiratory surface.  The more viscose the fluid, the more difficult that movement becomes.  Water viscosity makes it difficult to ventilate a respiratory surface sufficiently to get enough oxygen from the low concentration contained within it.  In some cases, this problem is overcome by providing a larger surface area over which the oxygen can be dissolved.  For example, oxygen may be obtained by diffusion over the entire body surface.

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Essentially, the problems faced by invertebrates when obtaining oxygen from water are solved by five methods of respiration:

  1. Passive diffusion

This is a reliance on movement of respiratory gases by diffusion across the body surface of the invertebrate.  It is only effective at high surface area to volume ratios, so where the concentration of oxygen inside the organism is lower than that of the surrounding water, a concentration gradient is formed, allowing diffusion of the oxygen.  This means on the whole it is only possible in invertebrates which are small or long and thin, and the rate ...

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