[Campbell Biology P.897] According to the acid growth hypothesis, what is the direct role of... | Practice Question

According to the acid growth hypothesis, what is the direct role of expansins in plant cell elongation?

  • A: They act as proton pumps, increasing H+ concentration in the cell wall.
  • B: They bind to nuclear receptors, stimulating cell growth directly.
  • C: They break cross-links between cellulose microfibrils and other cell wall constituents, loosening the wall.
  • D: They enhance ion uptake into the cell, increasing turgor pressure.

Explanation

The passage states that 'Acidification of the wall activates proteins called expansins that break the cross-links hydrogen bonds between cellulose microfibrils and other cell wall constituents, loosening the wall's fabric'. This loosening allows the cell to expand due to turgor pressure.