Biggest thing alive

Sequoiadendron giganteum
(Giant sequoia)

The giant sequoia is the largest single organism in the world. While colonies of coral or stands of Aspen trees (that have a common root system) could be considered larger, no singular organism bests the might sequoia. The largest sequia on record was longer than a football field (almost 311 feet), and was over 56 feet in diameter. The bark surrounding a giant sequoia can be up to 3 feet thick.  For such a huge tree, its roots are surprisingly shallow, boring down only about 13 feet into the ground. But they do spread out wide: roots from on tree can fill an acre of land. These roots have to suck up huge amounts of water as sequoia trees transpire (a tree version of sweating) over 500 gallons of water a day.