Question
Refer to the following diagram of an experiment in which an animal was injected with antigen A on day 0. Samples of blood were taken every day and the concentrations of both anti-A and anti-B antibodies were measured. On day 28, equal amounts of antigens A and B were given to the organism (the amount of antigen A given on day 28 was the same as had been given on day 0).
(A) Explain why, for antigen A, the graph following first exposure differs from the graph following second exposure.
(B) Propose a purpose of the exposure to antigen B on day 28.
▶️Answer/Explanation
Ans:
The data show the relative concentrations of anti-A and anti-B
antibodies as a function of time. The purpose of the second exposure to
antigen A on day 28 was to ensure specificity of the (expected) increased
response at day 42. The profile of the first exposure to antigen B (from days
28–56) is almost the same as the first exposure to antigen A (days 1–28).
The second exposure to antigen A (on day 28) produced a much greater
response to antigen A, but not to antigen B (the concentration of antibody A
at day 42 is 1,000 times greater than the concentration of antibody B). This
means that the response was not a general overproduction of the particular
antibody (a type of hyper-vigilance of the immune system), but a specific
response to a familiar foreign invader.
Question
Organisms use both negative and positive feedback.
Compare and contrast their functions and mechanisms, using one example for each.
▶️Answer/Explanation
Ans:
Negative feedback maintains homeostasis, while positive feedback
amplifies a physiological variable to result in a specific culminating event
that, once accomplished, resets the variable back to pre-event levels.
Question
Choose one example of positive feedback in an organism (you may choose from the following list or use your own example) and
describe the mechanism by which positive feedback is able to amplify the physiological variable.
• Lactation in mammals
• Onset of labor in childbirth
• Ripening of fruit
• Ovulation in mammals
• Blood clotting
▶️Answer/Explanation
Ans:
The general mechanism of positive feedback is shown in the preceding
diagram: The product of a process amplifies the process, increasing the
product that further amplifies the process feedback, which amplifies a
physiological variable and results in a specific culminating event that, once
accomplished, resets the variable back to pre-event levels.