Membranes can be the location of some biochemical reactions. Which option is true?

• A. They are the location of some biochemical reactions
• B. They serve only as barriers with no reaction sites
• C. They are the sole site of transcription
• D. They do not participate in any reactions

Answer: (A)

Membranes provide surfaces and compartments where enzymes and protein complexes reside, allowing many biochemical reactions to occur right at the membrane or within its surrounding environment. For example, the inner mitochondrial membrane hosts the electron transport chain and ATP synthase, driving oxidative phosphorylation and ATP production. In chloroplasts, the thylakoid membranes contain photosystems that funnel light energy into electron flow. The plasma membrane also participates in signaling and metabolism through membrane-bound receptors and enzymes. So membranes are indeed active sites for reactions, not just barriers. The other statements misstate membrane roles: they are not only barriers with no reaction sites, transcription is not limited to membranes (it occurs in the nucleus and in organelles as appropriate), and membranes clearly participate in reactions rather than being inert.