The largest living organisms in the world are plants.
The Great Barrier Reef is coral system near Australia that's visible from space! There's a Honey Fungus in Oregon that's approximately 2400 years old and covers about 2200 acres. General Sherman is a Giant Sequoia in California that has enormous mass. Pando, is a "clonal colony" (many off-sprouting trees, all genetically identical) aspen tree growing in Utah.
But the largest animal, is our old friend, the Blue Whale. I remember seeing one at the Museum of Natural History when I was a child. And that wasn't even the largest one of the species! They can grow to be over 185 metric tons! Kid what!
So now I ask... why is it so hard for me to lose TEN measly pounds!