IELTS Mock Exam

AIn 1963, archaeologists excavating the fortress of Masada, near the Dead Sea, recovered a handful of date palm seeds from a storeroom that had lain undisturbed for two millennia. The seeds sat in a drawer for forty years. Then, in 2005, a research team in Israel planted three of them in a pot of ordinary soil. One germinated. Radiocarbon analysis of fragments of the seed coat placed the seed at roughly two thousand years old. The seedling, a male, was named Methuselah, and it is now a tree several metres tall.

BWhat makes such a resurrection possible is dormancy — the capacity of a seed to suspend almost all metabolic activity until conditions favour growth. Botanists distinguish between two broad mechanisms. In physical dormancy, a hard, water-resistant coat simply prevents moisture from reaching the embryo; the seed waits until fire, abrasion or the digestive tract of an animal breaks the seal. In physiological dormancy, the embryo is chemically inhibited, and germination begins only after a period of cold, of darkness, or of exposure to particular wavelengths of light. Many species combine the two, which is why gardeners are so often instructed to scratch, soak or refrigerate their seeds before sowing.

CMethuselah, remarkable as it is, is not the record holder. In 2012 a Russian team announced that they had regenerated flowering plants of Silene stenophylla from tissue found in fossilised squirrel burrows in the Siberian permafrost. The material was dated at approximately 32,000 years old — sixteen times the age of the Masada seed. Because the burrows had been sealed at a constant sub-zero temperature since the late Pleistocene, the tissue had escaped both the drying and the microbial decay that destroy most buried seed within a few decades.

DPermafrost, in other words, was a seed bank before anyone thought to build one. Modern gene banks copy its logic deliberately. At the Svalbard Global Seed Vault, dug into a mountainside on a Norwegian island, duplicate samples of the world's crop varieties are dried to a low moisture content and held at minus eighteen degrees Celsius. Under those conditions, so-called orthodox seeds — wheat, rice, beans, most vegetables — remain viable for decades and in some cases for centuries. The economics are unusually favourable: a single vault can hold several million samples, and the running cost per variety per year is a matter of pennies.

ENot every plant cooperates. The seeds of cocoa, oak, mango, rubber and coconut are recalcitrant: they cannot be dried below a certain moisture level without dying, and freezing them ruptures their cells. For these species, conservation means either cryopreserving excised embryos in liquid nitrogen, a delicate and expensive procedure, or maintaining living collections in the field, which are vulnerable to storm, disease and shifting budgets. Roughly a third of tropical tree species fall into this category, and it is precisely the tropics where habitat loss is fastest.

FThe case for all this effort rests on a simple observation: a crop variety that has vanished cannot be bred from. When a new fungus or a shifting climate threatens a staple, breeders look for resistance among old and wild relatives, and they can only look where samples survive. Critics of the vault model, however, argue that a frozen collection is a museum — a snapshot of diversity, cut off from the pests, droughts and farmers that produced it. They favour in-situ conservation: keeping traditional varieties in cultivation on working farms, where they continue to adapt. The argument is not really a contest. A frozen sample cannot evolve; a field crop cannot survive a bad decade. Most conservationists now speak of the two approaches as a single system with two halves, and worry less about which is superior than about how thinly both are funded.