The poison cyanide binds to the last complex of the electron transport chain and prevents it from accepting electrons. Assuming this is the only effect of cyanide what will be the primary effect of cyanide on aerobes (cells that require oxygen) ?

ATP synthesis by oxidative phosphorylation will stop.

Explanation:

Cyanide inhibits cytochrome oxidase that passes electrons to the molecule oxygen. Cytochrome oxidase also pumps two protons from the matrix to the intermembrane space during electron transfer. Inhibition of cytochrome oxidase would not allow the transfer of electrons to oxygen and the whole electron transport chain would be stopped. There would not be any generation of proton concentration gradient to drive the process of ATP synthesis. Hence, ATP synthesis by oxidative phosphorylation will be stopped after cyanide poisoning in aerobic cells.