Which of the following statements is false?

$\displaystyle \mathrm{Mg}^{2+}$ ions are important in the green parts of plants.

$\displaystyle \mathrm{Mg}^{2+}$ ions form a complex with ATP.

$\displaystyle \mathrm{Ca}^{2+}$ ions are important in blood clotting

$\displaystyle \mathrm{Ca}^{2+}$ ions are not important in maintaining the regular beating of the heart.