<span>Basically, the body needs to know what it is defending against. Your body can still (usually) fight off infection, even without an immunization, but it takes longer. Basically, your body creates cells with a receptor for a specific disease. When this cell finds the disease it is programmed for, it will send out signals to the "killer" cells to come and kill it. If your body doesn't have the "seeker" cells, it can't fight off the infection until it does. The opposite end are autoimmune diseases, where your immune system starts attacking itself.
brainlest answer</span>
<u><span>Ecologist study the varieties and interactions of organisms and their environment. </span></u>
No more than five trophic levels are present in an ecosystem, most have only 4.
The answer is pheromones. Hope that helps :)
