| Air provides lift and flotation support for organisms
| Water uses an upward force on an object and in it which allows flotation.
| Viscosity (resistance to movement)
| Air has a low viscosity. This makes it easier for organisms to move through it.
| Water has a high viscosity. This makes it more difficult for organisms to move through it
| Light can pass freely through air. Plenty of light is available to land organisms. Dense plant growth or topography may affect light penetration to some areas. The amount of light received is important for plant growth.
| Light falling on water may be reflected, scattered or absorbed. Light penetration in water decreases rapidly with depth. Also Light availability affects the distribution of organisms.
| Water availability may vary. The amount of rainfall and when it falls can affect plants. Obtaining water and preventing its loss may be a problem for all land organisms.
| Water availability is rarely a problem in aquatic environments, but the effects of fresh and salt water are important to organisms
| Oxygen availability
| Oxygen is freely available in air and diffusion is rapid. Air contains about 20% oxygen and 0.03% carbon dioxide. The remainder is mostly nitrogen
| Air availability in water is high and depends on the temperature. Diffusion is slower. More gases can be dissolved at lower temperatures. Oxygen Concentration also decreases with depth.
| Surface temperatures on land vary far more than in water. The highest recorded is 60°C, and the lowest is less than –80°C.
| Water heats up more slowly than air. Temperatures in the surface ocean layers vary from 30°C at the equator to freezing point in arctic regions.
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