Enzyme (noun, “EN-ZIME”)
This word describes a molecule that speeds up chemical reactions taking place in living things. An enzyme is a biological catalyst. A catalyst speeds up a reaction but isn’t used up or changed in the process.
Chemical reactions take place all the time inside the body. For example, digestion breaks apart big molecules in food into smaller molecules the body can use. Reactions also help store and release energy inside cells. Other reactions put molecules together to make the parts of cells. Enzymes manage these and many other reactions. That’s an important role. Without enzymes, many reactions in the body wouldn’t happen quickly enough.
Some chemical reactions need energy to get started. Enzymes reduce the amount of energy needed for these reactions to take place. They do this by helping to bring molecules together or making it easier to split them apart. And different enzymes work on different molecules. For example, lactose is a sugar in cow’s milk. Many people produce an enzyme called lactase inside their intestines. Lactase helps break the lactose down into smaller sugars. But some people lack that enzyme. Without lactase, their bodies can’t properly digest the sugar found in milk.
In a sentence
Enzymes in onions play a role in making people cry.