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.
Given that a negatively charged rod is brought closer to two metal spheres which are in contact with each other as shown: So, free electrons from rod will be attracted towards the metal spheres.
Methyl groups most often added to guanine-cytosine base pairs because they are held by three hydrogen bonds, and this decreases the probability of gene expression.
