Question
An antigen can induce an immune response in a host organism. Antigens are targeted by antibodies that are produced by the organism’s immune system in response to contact with the antigen. Antibodies are specific to antigens. Many different cell types are involved in immune responses.
Which of the following best explains the role of cell-to-cell communication during a response to an invasion of antigens?
A. Chemicals that are secreted from antigen-presenting cells then activate helper T cells.
B. A macrophage cell engulfs a pathogen in the blood.
C. Antigens attaching to receptors on memory B cells stimulate the memory B cells to become plasma cells.
D. Antigen-presenting cells engulf antigens at the first exposure.
▶️Answer/Explanation
Ans: A
Cell signaling pathways are activated by cell-to-cell communication.
Question
Adjacent plant cells have narrow channels called plasmodesmata that pass through the cell walls of the connected cells and allow a cytoplasmic connection between the cells.
Which of the following statements best explains a primary function of plasmodesmata?
A. They allow the movement of molecules from one cell to another, enabling communication between cells.
B. They prevent the cell membrane from pulling away from the cell wall during periods of drought.
C. They eliminate the need to produce signaling molecules and eliminate the need for cells to have receptors for signaling molecules.
D. They increase the surface area available for attachment of ribosomes and thus increase protein synthesis.
▶️Answer/Explanation
Ans: A
Plasmodesmata are channels through which cytosol exchange can occur, moving select molecules directly between cells. This enables cells enclosed by a cell wall to communicate.
Question
A hydrophilic peptide hormone is produced in the anterior pituitary gland located at the base of the brain. The hormone targets specific cells in many parts of the body.
Which of the following best explains a possible mechanism that would enable the hormone to efficiently reach all of the target cells in the body?
A. The hormone interacts with the nerves at the base of the brain and directs signals to the target cells through the nervous system.
B. The hormone diffuses into target cells adjacent to the anterior pituitary gland, where the hormone is degraded.
C. The hormone is released into the bloodstream where it can be transported to all cells with the correct receptors.
D. The hormone moves through cytoplasmic connections between cells until it has reached all cells with the correct intracellular binding sites.
▶️Answer/Explanation
Ans: C
The bloodstream is the most effective way to distribute a hormone that has to reach multiple target cells that are relatively long distances from the source of the hormone.
Question
Vertebrate immune responses involve communication over short and long distances. Which of the following statements best helps explain how cell surface proteins, such as
proteins and T cell receptors, mediate cell communication over short distances?
A. The proteins receive electrical signals from nerve cells.
B. The proteins leave the cell and travel in the bloodstream to other cells.
C. The proteins interact directly with proteins on the surfaces of other cells.
D. The proteins bind to molecules secreted by cells located in other parts of the body.
▶️Answer/Explanation
Ans: C
In vertebrate immune responses, cell surface proteins, including MHC proteins and T cell receptors, mediate cell communication over short distances by interacting directly with proteins on the surfaces of other cells. In many cases, the protein-protein interaction activates signal transduction pathways that control specific cellular responses. The interaction by cell surface proteins is an example of cell communication that is limited to short distances because the communicating cells must be near to each other.
Question
Notch is a receptor protein displayed on the surface of certain cells in developing fruit fly embryos. Notch’s ligand is a membrane-bound protein called Delta that is displayed on the surface of adjacent cells. When Notch is activated by its ligand, the intracellular tail of the Notch protein becomes separated from the rest of the protein. This allows the intracellular tail to move to the cell’s nucleus and alter the expression of specific genes.
Which of the following statements best explains Delta’s role in regulating cell communication through the Notch signaling pathway?
A. Delta transmits a chemical signal to all the cells of a developing embryo.
B. Delta allows the cells of a developing embryo to communicate without making direct contact.
C. Delta restricts cell communication to short distances within a developing embryo.
D. Delta determines which cells in a developing embryo express the gene that encodes the Notch protein.
▶️Answer/Explanation
Ans: C
Delta restricts cell communication to short distances by requiring direct cell-to-cell contact for activation of the Notch signaling pathway.