A scientist is comparing the outer structure of an onion cell, structure X, to the outer structure of a human skin cell, structure Y. Which generalization is true about the types of structures being examined? (A) Structure X is not living, and structure Y is living.
(B) Structure X can be found in some human cells, and structure Y can be found in some plant cells.
(C) Structure X is only found in plant cells, and structure Y is found in plant and animal cells.
(D) Structure X is semipermeable, and structure Y is selectively permeable.

Neelaredoxin is a 15-kda protein that is a gene product common in anaerobic prokaryotes. it has superoxide-scavenging activity, and it is constitutively expressed. in addition, its expression is not further induced during its exposure to o2 or h2o2 (silva, g., et al. 2001. j. bacteriol. 183: 4413–4420). which of the following statements best describes neelaredoxin synthesis? a-neelaredoxin is produced at all times; levels are constant even when exposed to o2 or h2o2.b-neelaredoxin is produced at all times; exposure to o2 or h2o2 increases expression.c-neelaredoxin is produced at all times; exposure to o2 or h2o2 decreases or prevents expression.d-neelaredoxin is only produced when there is exposure to o2 or h2o2.