Final answer:
Homeoviscous adaptation ensures membrane fluidity by modifying lipid composition in response to temperature, and occurs in both prokaryotic and eukaryotic organisms, not just prokaryotic cells.
Step-by-step explanation:
The subject of this question is homeoviscous adaptation in cell membranes, which is an essential biological process ensuring the regulation of membrane fluidity across different organisms in response to temperature changes. The correct statement regarding homeoviscous adaptation is that it maintains membrane fluidity, responds to temperature changes, and involves adjustments to lipid composition. However, the statement that homeoviscous adaptation occurs only in prokaryotic cells is incorrect and represents the exception in the list provided. This adaptation also occurs in poikilothermic organisms such as fish and reptiles and in homeothermic organisms like mammals and birds.