A certain cell type has existed in the blood and tissue of its vertebrate host's immune system for over 20 years. One day, it recognizes a newly arrived antigen and binds to it, subsequently triggering a secondary immune response in the body. Which of the following cell types most accurately describes this cell?a. Plasma cell
b. Thyroid cell
c. Memory cell
d. Macrophage.

c. Memory cell

Explanation:

Memory cell is a type of cell or lymphocyte that is produced the first exposure to a particular antigen, and is capable of surviving long in the immune system to illicit an immune response when exposed again to the same antigen. In other words,  memory cell is able to trigger a secondary immune response or antibody-mediated immune response on reinfection of an antigen, long after first exposure to the antigen that led to its production.

Memory cells are swift to respond and attack an invading pathogen

The correct answer is c. Memory cell

Explanation:

Immune memory is a special feature that presents the specific response of the immune system. The basis of this memory must be found in lymphocytes, some of which, after the first contact with the antigen, transform into long-lasting memory (B or T) cells, surviving much of the animal's life. Immune memory is manifested in the secondary response, thus being the fastest and longest response. When a pathogen first comes into contact with the immune system, specific cells are activated, some of which are the active cells that will act on the antigens. The others are memory cells. Upon subsequent contact with the same antigen, memory cells act. They do not need to be activated, since they already are. Memory cells divide rapidly, creating a large population of activated cells, part of them will transform into attacking cells, and another part, again into other memory cells. The response produced by memory cells is faster and longer lasting. In this way, the antigen will be destroyed more quickly and disease will not occur.

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.