The body obtains vitamin A in two ways. One is by manufacturing it from carotene, a vitamin precursor found in such vegetables as carrots, broccoli, squash, spinach, kale, and sweet potatoes.The other is by absorbing ready-made vitamin A from plant-eating organisms.he body obtains vitamin A in two ways. One is by manufacturing it from carotene, a vitamin precursor found in such vegetables as carrots, broccoli, squash, spinach, kale, and sweet potatoes.
A catalyst is like adding a bit of magic to a chemical reaction. Reactions need a certain amount of energy in order to happen. If they don't have it, oh well, the reaction probably can't happen. A catalyst lowers the amount of energy needed so that a reaction can happen more easily. A catalyst is all about energy.
As the name implies, catalytic converters contain catalysts. A catalyst is something that participates in the reaction, lowering the activation energy and hence increasing the reaction rate. Catalysts are not consumed in the reaction. (See the tutorial, Drug Strategies to Target HIV: Enzyme Kinetics and Enzyme Inhibitors for a review of how enzymes function as catalysts.)