Biology, Answering the Big Questions of Life/Metabolism
What is energy?
In order to live, organisms need to get Energy. Energy is defined as the ability to do work. Animals like you and me get energy by eating food.
Both a wagon rolling down a hill, and a boy chasing after the wagon are using energy. This kind of energy is called kinetic energy. Kinetic energy is the energy of motion.
If the boy catches the wagon and sits it on top of the hill again, the wagon has what we call potential energy. Potential energy is stored energy. Just a little push and the wagon will roll down the hill again.
The food we eat also has potential energy. The energy is stored and just a little push will release that energy so that we can use it to power ourselves.
What is metabolism?
Every living organism is made up of chemicals. When we grow we must make ourselves bigger by putting those chemicals together to make larger molecules that we call macromolecules. Hair is made of a macromolecule called a protein. When we grow hair, we are building those hairs inside the cells of our body. Making hair requires energy and raw materials. We get those by breaking down the molecules in the food that we eat.
Therefore in every cell of our body, molecules are being broken down to provide energy and built up to make parts of ourselves every moment of every day. All of these reactions together are called our metabolism.
Metabolism = Catabolism + Anabolism
Metabolism is made of the reactions that tear molecules apart called catabolism, and reactions that build larger molecules called anabolism. Catabolic reactions tend to release energy, while anabolic reactions require energy to work. Living organisms use the power of catabolic reactions (such as breaking down food) to drive their anabolic reactions ( such as making hair). This happens even on the small scale where individual anabolic reactions are coupled together with catabolic reactions that will drive them.
Where do cells get energy?
The major food of cells is the sugar glucose. Cells break down sugar to make energy. Organisms that can make food are called autotrophes which means "self feeders". Organisms that eat other organisms are called heterotrophes.