Say that you are working with a bacterium that has two types of Methyl‐Accepting Chemotaxis Proteins, the full genetic circuitry for chemotaxis including CheA, CheB, CheR, CheW, CheY, CheZ, and a single polar flagellum. One of the Methyl‐Accepting Chemotaxis Proteins binds to sulfate ions, and the other binds to glucose. You mutate the sulfate‐binding Methyl‐Accepting Chemotaxis Protein so that it binds to nitrate ions instead of sulfate ions. What molecules will your mutant cell be able to use for chemotaxis?

Nitrate  

Explanation:

Bacteria can direct their movements according to the presence of particular molecules found in the environment. Chemotaxis enables the movement of bacteria in response to environmental factors, including chemical factors. Nitrate is an anion (i.e., negatively charged) that acts both as an electron acceptor during anaerobic respiration as well as a source of nitrogen during aerobic growth. Bacterial nitrate chemotaxis is a phenomenon that occurs under environmental conditions associated with nitrate starvation (i.e., nutrient stress), during the life cycle of diverse types of bacteria. Moreover, methyl-accepting chemotaxis proteins are receptors widely distributed in the cytoplasmic membrane of bacteria and archaea. These receptors form hexagonal arrays that act in signal transduction pathways by processing environmental inputs (in this case, nitrate conditions).

what are the choices?

a physical change is being made.