Is there a limit to how large a living organism can be?

Answer 1

This answer is more simple than it seems. The weight of an animal increases as the cube of its height, generally. In other words, as an animal gains in height, it also gains in width and depth, 3 dimensions.

The muscles needed to move gain strength in width and depth, not in length, or two dimensional. For example, take a weight lifter. His muscle strength increase in relation to the size of the muscle, measured in cross section, two dimensions.

So the size of an animal is limited by the strength of muscles. As an animal grows in 3 dimensions, its strength only grows in two. The large plant-eating dinosaurs were the largest land animals ever to exist, and they would have been slow-moving. The largest animal ever to exist is the blue whale, where the advantage of buoyancy requires less muscular exertion, hence they are larger than any land animal, and would not be able to move or even breathe if they were on dry land.