Tardigrade Physiology and Evolution

Tardigrades exhibit remarkable resilience to high doses of ionising radiation that would prove 1 to most multicellular organisms. This resistance relies heavily on a unique chromatin-associated protein known as Dsup, which physically binds to nucleosomes. By forming a protective molecular barrier, Dsup 2 DNA strands from hydroxyl radicals, thereby significantly reducing double-strand breaks without impeding normal gene 3.

• accelerates
• expression
• safeguards
• decay
• fragile
• lethal

Tardigrades possess a bilateral, cylindrical body divided into five distinct segments, including a head and four pairs of unjointed legs terminating in 1. Their outer surface is covered by a flexible chitinous cuticle that undergoes periodic 2 during growth. Internally, a tubular pharynx equipped with piercing stylets allows them to penetrate plant or fungal cells and 3 nutrient-rich fluids.

• extract
• claws
• fins
• inject
• fossilisation
• moulting

Exposure to sub-zero temperatures triggers cryobiosis, an adaptive survival response that prevents damaging ice formation within tardigrade tissues. As external fluids freeze, the organism synthesises ice-binding proteins and trehalose-like compounds to control crystallisation. These substances 1 ice crystal growth in extracellular spaces while maintaining the fluid viscosity necessary to 2 intracellular rupture, enabling rapid revival once environmental temperatures 3.

• promote
• plummet
• ignite
• stabilise
• prevent
• suppress

The evolutionary origin of tardigrades remains an intriguing subject within invertebrate palaeontology. Classified alongside arthropods and onychophorans in the clade Panarthropoda, their microscopic size has severely 1 the fossil record. Nonetheless, rare specimens preserved in Cretaceous amber 2 that their fundamental body plan has remained largely 3 over hundreds of millions of years.

• demonstrate
• expanded
• limited
• unchanged
• erratic
• deny