The correct answer for this question is option 3, which is "Apical meristem". The apical meristem is responsible for the primary growth of a plant, which includes the increase in length of stems and roots.

Option 1, "Lateral meristem", is incorrect. Lateral meristem is responsible for the secondary growth of a plant, which involves the increase in girth or thickness of stems and roots.

Option 2, "Intercalary meristem", is also incorrect. Intercalary meristem is found in some specialized plants like grasses and is responsible for the growth that occurs between the nodes or internodes.

Option 4, "Secondary growth", is incorrect because secondary growth is associated with the lateral meristem and not the apical meristem.

Therefore, the correct answer is option 3, "Apical meristem". This meristem is found at the tips of stems and roots and is responsible for the elongation of these plant parts.