In the following diagram involving different factors (A, B, C, Z), arrows (→) cause an increase and red flathead arrows (⊣) causes a decrease.

Which statement is INCORRECT?

Question

In the following diagram involving different factors (A, B, C, Z), arrows (→) cause an increase and red flathead arrows (⊣) causes a decrease.

Which statement is INCORRECT?

BlackTom AI · Accepted Answer

Because C feeds back to inhibit A while Z activates A, the system is a negative feedback loop: Z → A → B → C and C ⊣ A. Key concepts: activation arrows cause increases, flathead arrows cause decreases, and in a feedback loop the downstream element (C) both depends on upstream activity and can modulate that same upstream activity.

1) Relevant knowledge points and concepts
- Direct activation: an increase in X causes an increase in its direct downstream target.
- Negative feedback: a downstream product that inhibits an upstream node can reduce or reverse upstream activation, producing steady-state or transient behavior depending on strengths and timing.
- C’s level depends on B (and B depends on A), so C’s inhibition of A is not an independent fixed input but is produced by the cascade.

2) Step‑by‑step reasoning
- If Z is present, Z increases A (Z → A).
- Increased A increases B (A → B).
- Increased B increases C (B → C).
- Increased C then inhibits A (C ⊣ A), reducing A’s level.

3) Intermediate logic steps
- Initially, when Z turns on, A rises immediately, so B and then C will rise sequentially (transient increase).
- The inhibition from C back onto A will build only after B and C rise; the net steady‑state level of A (and therefore B) depends on the balance of Z’s activating input and C’s inhibiting feedback.
- Therefore B can increase transiently even if eventual C-driven inhibition is strong; steady‑state increase requires net positive drive to A (Z’s activation greater than C’s inhibition in the long run).

4) Why the correct answer is correct
- The statement “B will only increase if Z is stronger than C.” is incorrect because it ignores transient dynamics and the fact that C itself depends on B/A. B can temporarily increase when Z is present even if, at steady state, strong feedback from C would suppress A and B. Thus “only increase if Z is stronger than C” is an oversimplification and not always true.

5) Why other options are correct (brief)
- “C will increase when Z is present.” True: Z → A → B → C causes C to rise (at least transiently).
- “B will always increase when A is present.” True in the direct sense: A activates B.
- “Without B, A will continue to increase if Z is present.” True: removing B prevents C production, so A lacks the inhibitory feedback and will continue to be driven up by Z.

6) Conclusion
The incorrect statement is “B will only increase if Z is stronger than C.” This matches the provided answer.

In the following diagram involving different factors (A, B, C, Z), arrows (→) cause an increase and red flathead arrows (⊣) causes a decrease. Which statement is INCORRECT?单项选择题

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