27. To move sucrose molecules from leaves to roots, the sucrose molecules must enter sieve elements. This involves: (A) moving the molecules through plasmodesmata. (B) the use of ATP to pump sucrose molecules with their concentration gradient across the plasma membrane. (C) the use of ATP to pump sucrose molecules against their concentration gradient across the plasma membrane. (D) the pumping of sucrose molecules across the plasma membrane with their concentration gradient without the use of ATP. (E) the pumping of sucrose molecules across the plasma membrane against their concentration gradient without the use of ATP.