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What adaptations are present in organisms that live in or around water?

Beavers
Animals like this beaver have streamlined bodies and specialized limbs to help them move quickly through the water.
Living organisms like plants and animals all need certain things to survive: food, water, a way to reproduce, and a place to live, to name a few. But surviving on land and in the water are two very different things, and they require different adaptations. Keep the terrestrial adaptations you just studied in mind as you click through these slides that show some common aquatic biome adaptations.


Water-Salt Balance

Seagull

One of the biggest obstacles to living in the water is, surprisingly, water balance. This is, in part, because water tends to move from areas of higher concentration (and low salt) to areas of lower concentration (and high salt) in a process called osmosis. Many freshwater aquatic organisms prevent problems caused by too much water entering their cells by excreting large quantities of urine. Some marine organisms have adaptations that allow them to excrete the excess salt that enters their bodies. (This gull has a salt gland that allows it to secrete salt through its beak.) Less salt means less influx of water into the body.

Reproduction

Tadpoles
Tadpoles on a lake.

For many marine organisms, sperm and egg are brought together by water. Simply laying eggs and releasing sperm in the water means fertilization (the joining of sperm and egg) is not controlled. Furthermore, newly formed organisms are a likely food source for consumers. In many cases, aquatic organisms create huge numbers of offspring to ensure that some survive. 

Movement and Body Shape

Dolphins

Whether they have fins, webbed feet, or streamlined bodies, aquatic animals have adaptations that allow them to move through water quickly and efficiently. While aquatic plants don't move through the water, many of them have structures that allow water to flow around and over their cells, bringing them nutrients and carrying waste away. 

Respiration

Sharks

Gas exchange in aquatic biomes is much different than in terrestrial biomes for one obvious reason: aquatic organisms must find a way to get molecules that are often in a gas form from a watery environment. To that end, many aquatic animals have gills. These specialized structures are able to extract oxygen from the water and release carbon dioxide. Gas exchange in aquatic plants occurs as oxygen and carbon dioxide pass directly in and out of cells.

Question

What terrestrial adaptation serves the same function in land animals as gills do in some aquatic animals?

Lungs in land animals perform the same function that gills do in aquatic animals.