How and when do B-cells get activated?

When a mature B cell encounters antigen that binds to its B cell receptor it becomes activated. ... Plasma cells and memory B cells with a high-affinity for the original antigen stimuli are produced. These cells are long lived and plasma cells may secrete antibody for weeks after the initial infection.

B cell activation requires two distinct signals, and results in B cell differentiation into memory B cells or plasma cells. The first activation signal occurs upon antigen binding to B cell receptors (BCRs). When a mature B cell encounters antigen that binds to its B cell receptor it becomes activated. It then proliferates and becomes a blasting B cell. These B cells form germinal centres.

Explanation:

step 1

antigen recognition-B cell exposed to antigen and binds with matching complementary

step 2

antigen presentation-B cell displays epitope, Helper T cell binds secretes interleukin

step 3

clonal selection= interleukin stimulates B cell to divide

step 4

differentiation=become memory or plasma cells

step 5

attack- plasma cells secrete antibody

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the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.