Particle size can influence gross biodegradability of a material. Composting is a surface phenomenon since micro-organisms are active only on surfaces. They have no way to access, for example, the interior of a wood chip. As the overall surface area of a given mass of waste increases, the quantity of food available for the microbes will increase. Hence, the overall rate of conversion of biodegradable material into biologically stable compost will increase. While the biodegradability of a material at the molecular level may not vary appreciably with particle size because the rate of biochemical transformations and enzymatic reactions at a specific temperature are fixed, a smaller particle size does expand the surface area for the microbial attack. An expanded surface area enables the support of a larger number of organisms each of which contributes to the overall biodegradation of the material. As an example, shredded leaves have a larger surface area and break down more rapidly than unshredded leaves because a greater surface area is exposed for degradation.