Problem 4 - Campbell Biology Concepts & Connections

Question

Which of the following best describes the difference in the way B cells and cytotoxic T cells deal with invaders? a. \(B\) cells confer active immunity; \(T\) cells confer passive immunity. b. B cells send out antibodies to attack; certain T cells can do the attacking themselves. c. T cells handle the primary immune response; B cells handle the secondary response. d. B cells are responsible for the cell-mediated immune response; T cells are responsible for the humoral immune response.

Step-by-Step Solution

Answer

B cells send out antibodies to attack; certain T cells can do the attacking themselves.

Step 1 - Understand the function of B cells

B cells are a type of white blood cell that recognize specific antigens. Once activated, they differentiate into plasma cells that produce antibodies, which are molecules designed to neutralize or destroy the invaders.

Step 2 - Understand the function of cytotoxic T cells

Cytotoxic T cells are another type of white blood cell. They directly attack and destroy cells that have been infected by viruses or transformed by cancer. They recognize infected cells through specific antigens on the cell surface.

Step 3 - Analyze option (a)

Option (a) states: 'B cells confer active immunity; T cells confer passive immunity.' This is incorrect because both B cells and T cells are involved in active immunity. Passive immunity involves the transfer of pre-formed antibodies from another source.

Step 4 - Analyze option (b)

Option (b) states: 'B cells send out antibodies to attack; certain T cells can do the attacking themselves.' This statement matches the functions described in Steps 1 and 2 and is a correct description of how B cells and T cells deal with invaders.

Step 5 - Analyze option (c)

Option (c) states: 'T cells handle the primary immune response; B cells handle the secondary response.' This is incorrect because both B cells and T cells are active in both primary and secondary immune responses.

Step 6 - Analyze option (d)

Option (d) states: 'B cells are responsible for the cell-mediated immune response; T cells are responsible for the humoral immune response.' This is incorrect because it is the opposite; B cells are responsible for the humoral immune response, while T cells are involved in the cell-mediated response.

Step 7 - Select the correct answer

Based on the analysis, the correct option that best describes the difference in the way B cells and cytotoxic T cells deal with invaders is (b).

Key Concepts

Immune Response

The immune response is the body's defense mechanism against harmful invaders like viruses, bacteria, and other pathogens. It can be broadly categorized into innate and adaptive immunity. Innate immunity is the first line of defense and acts quickly but is non-specific. Adaptive immunity, on the other hand, is slower to respond but highly specific. It recognizes specific pathogens and remembers them for faster response upon future encounters. The key players in the adaptive immune response are B cells (involved in humoral immunity) and T cells (involved in cell-mediated immunity).

Antibodies

Antibodies are specialized proteins produced by B cells. When B cells are activated by the presence of an antigen, such as a virus or bacterium, they differentiate into plasma cells. These plasma cells secrete large volumes of antibodies specific to the antigen. Antibodies help to neutralize or eliminate pathogens by binding specifically to them, preventing their spread, and marking them for destruction by other immune cells. Each antibody is highly specific, targeting a particular antigen only.

Cell-Mediated Immunity

Cell-mediated immunity is driven by T cells, specifically cytotoxic T cells. These T cells patrol the body for cells that display abnormal antigens on their surfaces, indicating infection or cancerous transformation. Once identified, cytotoxic T cells bind to these infected or cancerous cells and directly kill them by releasing cytotoxic molecules, such as perforin and granzymes, that induce apoptosis in the target cells. This form of immunity does not involve antibodies but depends on the direct action of T cells to control and eliminate intracellular pathogens.

Humoral Immunity

Humoral immunity involves B cells and the production of antibodies. It primarily targets extracellular pathogens. When B cells encounter their specific antigen, they undergo activation and proliferation, resulting in the formation of plasma cells that produce antibodies. These antibodies circulate in the bloodstream and lymphatic system, binding to antigens on the surface of pathogens. This binding neutralizes the pathogens and marks them for destruction by other immune cells, such as macrophages. Memory B cells are also produced, allowing for a quicker and more efficient response if the same antigen is encountered again.