Reading: Matching Features: Question 1

Tardigrades, microscopic eight-legged animals known as water bears, can survive complete drying out by entering a motionless state called cryptobiosis, sometimes for years, before resuming normal activity within hours of rehydration. For most of the twentieth century the mechanism behind this was little more than speculation. Only in the last two decades have several independent research groups begun to explain how the animals actually achieve it.

Dr. Petra Lindqvist, of the Cryobiology Unit at the Tromsø Polar Institute, isolated a class of proteins, which she named vitrin proteins, that appear inside tardigrade cells only during drying and reorganise the cell's remaining water into a rigid, glass-like state that halts damaging chemical reactions. Using gene-silencing techniques, Lindqvist's team then blocked production of vitrin proteins in a laboratory population; when dried out, none of these modified specimens survived, compared with over 80 percent of an unmodified control group.

Professor Adebayo Okonjo, at the Kestrel Marine Station, compared how the speed of drying affects survival. His team dried genetically similar tardigrade populations either slowly, over 48 hours in a humidity-controlled chamber, or rapidly, within 90 minutes under a dry air stream. Specimens dried slowly survived at a rate of 91 percent, compared with just 28 percent among those dried rapidly, showing that the pace of water loss strongly influences an individual's chances of entering dormancy successfully.

Dr. Miriam Castellanos, of the Sierra Altiplano Research Station, used high-speed video microscopy to document the physical transformation the animals undergo before dormancy: as water is lost, the animals retract their legs and contract into a compact, barrel-like shape called a "tun", a process her footage showed unfolds gradually over several hours.

Dr. Henrik Sallman, of the Baltic Coastal Research Unit, tracked oxygen consumption after rehydration as a measure of metabolic activity. He found that specimens dormant for only a few days resumed measurable activity within about 30 minutes of rehydration, whereas specimens that had remained dried for over a year took closer to two hours, suggesting the length of dormancy affects how quickly normal function can restart.

The phenomenon itself was recorded long before any of this mechanistic work began: the Victorian naturalist Dr. Eleanor Fitzwilliam noted, in an 1878 paper on moss-dwelling invertebrates, that dried "water bears" could be revived simply by adding a drop of water, though without explaining the underlying mechanism. Her account is remembered today as the first written record of the effect, not as an analysis of its cause.

List of Researchers A. Dr. Petra Lindqvist B. Professor Adebayo Okonjo C. Dr. Miriam Castellanos D. Dr. Henrik Sallman E. Dr. Eleanor Fitzwilliam

The following statements describe findings about tardigrade cryptobiosis. Match each statement with the correct option, A–E. NB You may use any option more than once.

1. Identified a specific class of protective molecules that helps form a rigid, glass-like state inside cells during dehydration.
2. Found that experimentally blocking production of a particular protective molecule caused nearly all treated specimens to die when dried out.
3. Showed that the speed at which drying occurs significantly affects an individual's chances of survival.
4. Provided a specific numerical comparison between survival rates under a slow-drying and a rapid-drying regime.
5. Documented the gradual physical process by which the body contracts into a compact shape before full dormancy begins.
6. Established roughly how quickly metabolic activity resumes once a dormant specimen is rehydrated.
7. Found that the length of time a specimen had spent in dormancy affected how quickly it resumed normal activity after rehydration.