The characteristic of all living things that involves an increase in the amount of material in an organism is growth.

Here's why:

* Growth is a fundamental process of life: All living organisms grow and develop over time.

* Growth involves an increase in size and mass: This increase is due to the production of new cells and the accumulation of more biological material.

* Growth is essential for survival: Growth allows organisms to increase in size, complexity, and capabilities, which helps them survive and reproduce.

While other characteristics of life like reproduction, adaptation, and metabolism are also important, growth is a defining feature that sets living things apart from non-living matter.