Step 1: Different theories try to describe how cells are organised at growing tips of plants. At the shoot tip, tunica corpus theory applies, while at the root tip, a separate theory is needed because of the root cap.
Step 2: Schuepp's Korper Kappe theory addresses exactly this root tip organisation, splitting it into the Korper region forming the main body of the root and the Kappe region forming the protective root cap.
Step 3: This makes root apex the correct answer among the given options.