Question

scenario: a platelet plug forming over a cut releases chemical signals that attract more platelets, which, in turn, release more signals to attract even more platelets until the bleeding stops. which statement provides the most accurate analysis of this scenario using the concepts from the text? this is a positive feedback loop because it acts quickly, like the nervous system, and not slowly, like the endocrine system. this is a negative feedback loop because the final action (stopping the bleeding) ends the process. this is a negative feedback loop because it maintains the stability (homeostasis) of the internal environment. this is a positive feedback loop because the response (platelet aggregation) reinforces the initial stimulus (chemical signaling) to intensify the effect. a person is infected with a virus for the first time. if they are infected with the same virus again a year later, why will their secondary response be much faster and more effective? helper t cells will destroy the virus before b cells can be activated. the virus will be weaker the second time, making it easier for any b cell to destroy it the original plasma cells are still producing high levels of antibodies from the first infection. memory cells from the first infection will rapidly launch the response, quickly producing new plasma cells.

Explanation:

1. In the platelet - plug scenario, positive feedback loops amplify the initial stimulus. Here, platelet aggregation reinforces the chemical signaling to intensify the effect until bleeding stops. Negative feedback loops counteract changes to maintain stability, which is not the case here.
2. For the virus - infection scenario, memory cells are key to the secondary immune response. Memory B and T cells are formed during the first infection. When re - infected, they quickly recognize the virus and rapidly produce new plasma cells to secrete antibodies, making the secondary response faster and more effective.

Answer:

1. This is a positive feedback loop because the response (platelet aggregation) reinforces the initial stimulus (chemical signaling) to intensify the effect.
2. Memory cells from the first infection will rapidly launch the response, quickly producing new plasma cells.