Evidence in Tables & Graphs Practice Test

Hydrogels are water-swollen, cross-linked polymeric networks used extensively in tissue engineering. The physical properties of a hydrogel can be tuned by altering its chemical structure. Introducing chemical cross-links creates a tightly bound three-dimensional mesh, as opposed to loose, linear chains. A polymer chemist hypothesized that while cross-linking a hydrogel would physically restrict its ability to absorb large volumes of water (lowering its swelling ratio), the resulting mesh network would yield a hydrogel capable of withstanding significantly greater compressive stress than a linear hydrogel.

Methanogens are microorganisms that produce methane as the primary metabolic product of hydrogen reduction. In astrobiology, deep-subsurface methanogens are studied as analogues for potential life on Mars, where surface conditions are inhospitable. Because deep-subsurface environments are severely nutrient-limited, a researcher theorized that subsurface strains would survive by dramatically slowing their metabolism, utilizing less hydrogen and producing less methane per day than surface-dwelling strains.