A. Specific organ
B. Cell membrane
C. Cell wall
D. Nuclear membrane
Submitted by: Saba Irfan
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In unicellular organisms, as they do not have any organ or even tissues in their body. so, their whole body surface which is plasma membrane, acts as a respiratory surface from where the exchange of gases occur.
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The correct answer to the question: "The respiratory surface of unicellular organisms is__________?" is "Cell membrane".