Because an antibody is "made" relative to the antigen, but kept at low levels when you are exposed the first time ("primary immune response"). The second time you're exposed to the same antigen, memory cells recognize it and the body produces a high level of antibodies, and the level of antibodies usually remains higher for a longer time ("secondary immune response"). This is your basic immune response (primary and secondary). 
This explains exactly why vaccines are effective to extremely effective.
        
             
        
        
        
Chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, commas and plus (+) and minus (−) signs. These are limited to a single typographic line of symbols, which may include subscripts and superscripts. A chemical formula is not a chemical name, and it contains no words. Although a chemical formula may imply certain simple chemical structures, it is not the same as a full chemical structural formula. Chemical formulas can fully specify the structure of only the simplest of molecules and chemical substances, and are generally more limited in power than are chemical names and structural formulas.
        
             
        
        
        
Scar tissue is made of a protein called collagen
        
             
        
        
        
<span>A scientist wants to create a florescent ornamental fish. He needs fluorescence similar to that of a firefly. Which of the send processes would help him create this fish?
The correct answer is </span><span>transformation of the DNA of a fish using a fluoroscent gene from a firefly. In order to do so, he would have to use the gene of the firefly as a reference in order to transform the DNA of a fish.</span>