Cryptobiosis
From Freepedia
Cryptobiosis is an ametabolic state of life entered by some lower organisms in response to adverse environmental conditions such as desiccation, freezing, and oxygen deficiency. In the cryptobiotic state, all metabolic procedures stop, preventing reproduction, development, and repair. An organism in a cryptobiotic state can essentially live indefinitely until environmental conditions return to being hospitable. When this occurs, the organism will return to its metabolic state of life as it was prior to the cryptobiosis.
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Anhydrobiosis
Anhydrobiosis is the most studied form of cryptobiosis and occurs in situations of extreme desiccation. The term anhydrobiosis derives from the Greek for "life without water" and is most commonly used for the desiccation tolerance observed in certain invertebrate animals such as bdelloid rotifers, tardigrades, brine shrimps and nematodes. However, other life forms, including resurrection plants, the majority of plant seeds, and many micro-organisms such as bakers' yeast, also exhibit desiccation tolerance. Invertebrates undergoing anhydrobiosis often contract into a smaller shape and some proceed to form a sugar called trehalose. Desiccation tolerance in plants is associated with the production of another sugar, sucrose. These sugars are thought to protect the organism from desiccation damage, and studies have shown that anhydrobiotic organisms can survive for decades in the dry state. In some creatures, such as bdelloid rotifers, no trehalose has been found, which has led scientists to propose other mechanisms of anhydrobiosis.
Cryobiosis
Cryobiosis is a form of cryptobiosis that takes place in reaction to decreased temperature. To initiate cryobiosis, the organism freezes all of the water within its cells. This allows the organism to endure the freezing temperatures until more hospitable conditions return. Studies have shown that the longer an organism remains in cryobiosis, the longer it takes for the organism to come out of cryobiosis. This is because the organism has to use its own energy to come out of cryobiosis, and the longer it stays in cryobiosis the less energy it has.
Osmobiosis
Osmobiosis is the least studied of the four types of cryptobiosis. Osmobiosis occurs in response to increased solute concentration in the solution the organism lives in. Not much is known for sure, other than that osmobiosis appears to involve a cessation of metabolism.
Anoxybiosis
Anoxybiosis isn't considered a form of cryptobiosis by some. It takes place in situations lacking oxygen, and involves the organism intaking water and becoming turgid and immobile. Studies have been done about survival rates of organisms during anoxybiosis, but have achieved conflicting results.
Examples
The most commonly known organism which undergoes cryptobiosis is the tardigrade, or water bear. It is the most studied as well, partially because it can undergo all four types of cryptobiosis. While in this state their metabolism lowers to less than 0.01% of what is normal and their water content can drop to 1% of normal. They can withstand extreme temperature, radiation, and pressure while in a cryptobiotic state.
