AP Biology : Systems Physiology

Study concepts, example questions & explanations for AP Biology

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Example Questions

Example Question #1 : Understanding The Adaptive Immune Response

Once an individual becomes exposed to a pathogen, the body's immune system responds faster against a second exposure to the same pathogen. Why does this occur?

Possible Answers:

Specific lymphocytes quickly produce the proper antibodies

Pathogens are changed so they are no longer harmful

The proper antibodies are constantly circulating in the blood

Innate defenses are strengthened

Stimulated memory cells quickly engulf pathogens

Correct answer:

Specific lymphocytes quickly produce the proper antibodies

Explanation:

Innate defenses, such as skin and macrophages, are a primary defense against all diseases, but adaptive immunity is related to exposure to a specific disease. The ability for the body to produce specific antibodies quickly provides adaptive immunity. While some antibodies may remain in the blood after initial exposure, this small amount does not provide sufficient immunity. 

The specific lymphocytes that produce antibodies during a second exposure are called memory B-cells. When an antigen is presented to a memory B-cell that produces the appropriate antibody, the cell divides and differentiates into plasma cells. Plasma cells are then responsible for producing large amounts of antibodies against the specific antigen. Antibodies are cell-surface markers that attach to pathogens, signaling effector cells to rapidly destroy the pathogen. The rapid multiplication of B-cells to generate antibody to a specific threat is known as clonal selection.

Example Question #2 : Immune System

Which immune system response could best be characterized as adaptive?

Possible Answers:

In the inflammatory response, mast cells produce histamine to facilitate the travel of immune cells and plasma to the afflicted area

The epithelium of the skin blocks most pathogens from ever entering the body

A phagocyte engulfs and destroys bacteria, dead cells, and other potentially harmful particles that it encounters

After the first exposure to an antigen, memory B-lymphocytes are produced to recognize the same antigen upon a second exposure

Correct answer:

After the first exposure to an antigen, memory B-lymphocytes are produced to recognize the same antigen upon a second exposure

Explanation:

The two types of immune system responses are innate (nonspecific) and adaptive (specific). Innate responses are those that act on many pathogens in the same general way. For example, the skin and the mucus in the nasal cavity both physically block the entry of pathogens into the body, but they do not specifically target certain antigens. Other examples of the innate response are inflammation and the general activity of phagocytes. On the other hand, the adaptive immune system provides a second line of defense against certain, previously encountered pathogens. Here, the only answer choice that deals with the recognition of specific antigens is the production of memory B-lymphocytes. The adaptive immune response generally involves T-lymphocytes, B-lymphocytes, antigens, and antibodies.

Example Question #3 : Immune System

Which cell is responsible for stimulating differentiation of B-lymphocytes into specialized plasma cells?

Possible Answers:

Helper T-cells

Antibodies

Cytotoxic T-cells

Memory B-cells

Correct answer:

Helper T-cells

Explanation:

The differentiation of many acquired immune cells is largely dependent on helper T-cells. In the presence of a matching antigen, B-lymphocytes can be differentiated into plasma cells and memory B-cells with the assistance of helper T-cells. Memory B-cells are easily triggered if an antigen is presented during a second infection, while plasma cells are the final differentiated form of a B-cell responsible for mass-producing antibodies. Helper T-cells are also important in the activation of cytotoxic T-cells, which detect antibody-antigen complexes on cell membranes and help to destroy these tagged cells.

Example Question #1 : Understanding The Adaptive Immune Response

Which of the following is a characteristic of acquired immunity?

Possible Answers:

Recognition of shared traits by a wide array of pathogens

Acquired immunity is a rapid response

Response is driven by phagocytic cells

Use of basophils and mast cells to create inflammation

Recognition of traits specific to a particular pathogen

Correct answer:

Recognition of traits specific to a particular pathogen

Explanation:

Acquired, or adaptive, immunity is a second immune defense system and develops slowly after exposure to an initial infection. As a result, the immune system is "trained" and capable of recognizing many specific components or antigens from the pathogen. Acquired immunity stores the information from an initial infection in preparation for reintroduction of the pathogen; it does not immediately respond to the initial infection.

Upon reinfection or exposure to a pathogen, the acquired immunity is better able to detect and defend the body. This includes the generation of antibodies that can bind a pathogen and cytotoxic T-lymphocytes that can detect and eliminate infected cells.

Acquired immunity is balanced by innate immunity, which responds indiscriminately to all pathogens. Innate immunity is essential for fighting and preventing initial infections, before adaptive immunity has learned to recognize the specific pathogen present.

Example Question #10 : Immune System

Major histocompatibility molecules (MHC) are critical for the functioning of the immune system. These proteins are utilized allow for communication between the immune system and the cells. MHC I are utilized to show which cells are in fact part of the body and which are foreign. MHC II are utilized to show the immune system when there is an intruder.

MHC I molecules are derived from chromosome 6. On chromosome 6, there is a specific gene that encodes for the molecule. On the gene, there are 3 locus (A, B, C) which allows for variability in the binding site of the MHC I molecule. The MHC gene is co-dominance and therefore adds to its diversity. During development, the gene is transcribed into MHC I molecules. However, some of these are broken down and react with a particular MHC I molecule. The reaction allows for the MHC I molecule to surface onto the cellular membrane and to self-identify the protein for the cytotoxic T-cell.

After translation, MHC II molecules are transported to the endosome. When a pathogen binds to the proper MHC II binding site, these molecules are then presented to T-Helper cells. In comparison, MHC I molecules interact with endogenous antigens whereas MHC II molecules interact with exogenous antigens.

Patient A has a disorder which resulted in a nondisjunction of chromosome 6. Which might this disorder lower the chances of developing an autoimmune disease? 

Possible Answers:

Decrease  variability of MHC II binding site  

Increase variability of MHC II binding site  

Increase variability of MHC I binding site  

Decrease variability of MHC I binding site  

None of these

Correct answer:

Increase variability of MHC I binding site  

Explanation:

Since the genes in chromosome 6 is codominance, each gene will be expressed. With nondisjunction, there will be an extra chromosome. This will result in all three genes being expressed. The expression of all three genes will increase the diversity of the MHC I pool. Recall MHC I is responsible for notifying which cells are related to the body to prevent autoimmunity. 

Example Question #1 : Understanding Cell Types

Which leukocyte releases histamine in order to dilate blood vessels and increase blood flow to infected areas?

Possible Answers:

Plasma cells

Basophils

Eosinophils

Neutrophils

Correct answer:

Basophils

Explanation:

Basophils are the least common leukocyte found in the body, but play a key role in the inflammatory response. They contain histamine, which is a potent vasodilator. Upon release, histamine will increase blood flow to infected areas. Mast cells are another immune cell that is involved in histamine release, but are generally localized to various regions of the body rather than found in circulation.

Basophils, mast cells, eosinophils, and neutrophils are all considered granulocytes and are essential cells in the innate immune response. Plasma cells are differentiated B-lymphocytes that are responsible for mass-producing antibodies to a specific antigen.

Example Question #2 : Understanding Cell Types

Which of the following is not a characteristic of B-cell receptors?

Possible Answers:

They consist of two identical heavy chains and two identical light chains

They have transmembrane domains that anchor into the B-cell plasma membrane

They consist of two polypeptide chains

Upon further maturation, the B-cell receptor can become a secreted molecule

Correct answer:

They consist of two polypeptide chains

Explanation:

Each B-cell receptor is a Y-shape molecule that, upon maturation, can become a secretory form (an antibody). Each receptor is comprised of four polypeptide chains: two identical heavy chains and two identical light chains. The four chains are linked together by disulfide bridges. Both heavy and light chains consist of constant regions, as well as variable regions. The variable regions of each chain provide the specificity for antigen binding, which generates a signaling cascade within the B-cell.

Example Question #11 : Immune System

In what way do eosinophils differ from other innate immune system cells?

Possible Answers:

They produce anti-inflammatory cytokines

They have low phagocytic activity

They secrete antibodies

They detect and eliminate infected host cells

Correct answer:

They have low phagocytic activity

Explanation:

The granulocytes are responsible for numerous functions of innate immunity, from secreting histamine, to phagocytosis, to anti-inflammatory processes. These cells are the basophils, neutrophils, eosinophils, macrophages (monocytes), and mast cells.

Eosinophils have a more limited role in innate defense than the other granulocytes. They possess only low phagocytic activity, however, they are more specialized to respond to multi-cellular pathogens, such as parasitic worms. Rather than phagocytosing an invading organism, eosinophils function by releasing an arsenal of destructive enzymes and free radicals to ward off the organism. The other granulocytes are specialized for phagocytosis of bacteria, viruses, and cellular debris.

Example Question #12 : Immune System

Embryonic stem cells can go on to form any of the three germ layers (endoderm, mesoderm and ectoderm). How can they be defined? 

Possible Answers:

Totipotent

Multipotent

None of the other answers

Pluripotent

Progenitor cells

Correct answer:

Pluripotent

Explanation:

The ability to form any of the three germ layers is known as pluripotency. Totipotent cells, such as the zygote, are able to form an entire organism, multipotent cells are able to form any cell within the same germ layer lineage, and progenitor cells are cells closer to differentiation, often found in adult organisms. 

Example Question #13 : Immune System

What type of cell creates free antibodies that then circulate in the bloodstream?

Possible Answers:

Monocytes

Memory B-cells

Plasma cells

Cytotoxic T-cells

Helper T-cells

Correct answer:

Plasma cells

Explanation:

Humoral, or B-cell, immunity is associated with the formation of antibodies. Plasma cells are B-lymphocytes that have been differentiated with the help of a helper T-cell. They release antibodies, which are created to respond to a specific pathogen in the body.

Cytotoxic T-cells are also activates by help T-cells, but are involved in cell-mediated immunity rather than humoral immunity. They target infected cells based on antibody tagging. Monocytes are a part of the innate immune response and are not involved in antibody interactions. They primarily differentiate into macrophages, which engage in phagocytosis of pathogens.

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