Discuss how the human immune system responds to an initial pathogenic exposure and how this initial exposure can lead to a quicker response following a second exposure to the same pathogen.

Immediately, the pathogen has been recognized:

Macrophages acts as the first line of defence by engulfing pathogens identified by antigens which will now present the antibody shape to a helper T cell.

The Helper T cells produce a signal to plasma and Memory B cells to yield antibodies that attach to the antigens. The cytotoxic cells that leads to cell death are activated by the helper T cells.

Antibodies helps to immobilize pathogen for macrophage to feed on.

if the pathogen comes back a 2nd time the memory cells helps in quick and efficient recovery by producing the specific B and T cells for the antigen.

the answer is 100% density i've answered this question before and done the quiz myself.