The next time you grab a sheet of paper to do your homework, remember that the product you're writing on was once a tree. Most kids know this, but what you may not know is how a tree is turned into paper. Trees are made of cellulose fibers, organic compounds and a natural glue-like substance called lignin that holds everything together. Cellulose makes up about half of a tree and is used to make paper. But first you need to separate cellulose from other wood parts. Paper mills get their wood from two sources: small trees that are harvested for paper and scraps from larger trees that were sent to sawmills for lumber. The bark is stripped off, and trees are put through a chipper, which makes it easier to process. Once the wood has been chipped, it's converted to wood pulp. Pulping requires a combination of steam, pressure, chemicals, grinders and in some cases, bleach. Unbleached pulp becomes bags and boxes. Bleached pulp is turned into paper for writing or printing. (Bleached wood pulp is gooey and white _ like mashed potatoes, without the yummy taste.) When the pulp is finished, it's mixed with water and sprayed onto large, moving screens. The water drains through the screens, and that lets the cellulose fibers stick together to make paper. The paper moves at high speeds through a series of presses and driers. Additives strengthen the paper. Finally, the finished paper is wound on rolls and cut to size. Now that you know the basics of making paper, I have a question for you. True or false? You can buy paper that's made from elephant poop. True. Depending on the season, an elephant's diet consists of grass, leaves, twigs, bark, vines, roots, flowers and even fruit. However, since vegetation can be difficult to digest, lots of plant fiber comes out of the elephant's body without being broken down. By cleaning and removing the waste from undigested plant matter, you can harvest enough cellulose to make paper. Thanks to the enterprising minds of eco-friendly folks, you can buy paper made from the poop of pandas, kangaroos, sheep, bison and reindeer. Do you think any of your friends might like some as a birthday present? - - - Bennett is a Washington pediatrician and author of health-related books for kids. 