Question

researchers have discovered details about apoptosis (programmed cell death) by studying embryologic development of a nematode worm, caenorhabditis elegans. apoptosis is a normal developmental process in c. elegans. they found several genes involved in apoptosis, including ced - 9 and ced - 3. the ced - 3 gene was found to promote cell death, and ced - 9 to inhibit it. the ced - 9 gene serves as a regulator that prevents apoptosis in the absence of a signal promoting apoptosis.
which of the following statements best justifies the claim that changes in the expression of ced - 9 in c. elegans can affect regulation of apoptosis in the cell?
a an experiment showed that a mutation in the ced - 9 gene led to excessive cell death in c. elegans.
b an experiment showed that the ced - 9 gene normally produces a protein that promotes excessive cell death in c. elegans
c a mutation in ced - 3 will cause ced - 9 to be incorrectly transcribed
d apoptosis is dependent on a signal from the ced - 9 gene in c. elegans
question 19 of 24

Explanation:

The question asks for evidence that changes in ced-9 expression affect apoptosis regulation. The passage states ced-9 inhibits apoptosis (prevents cell death) unless an apoptosis signal is present.

• Option A: A ced-9 mutation causing excessive cell death makes sense—if the inhibitory gene is damaged, it can no longer block apoptosis, leading to more cell death. This directly links a change in ced-9 to altered apoptosis regulation.
• Option B is incorrect, as ced-9 inhibits, not promotes, cell death.
• Option C focuses on ced-3 affecting ced-9, which does not address how ced-9 itself regulates apoptosis.
• Option D is wrong, as apoptosis is triggered by a signal that overrides ced-9, not a signal from ced-9.

Answer:

A. An experiment showed that a mutation in the ced − 9 gene led to excessive cell death in C. elegans.