Define the following terms:
$(1)$ Kranz anatomy
$(2)$ Photo-oxidation

(N/A) $(1)$ In $C_4$ plants,the bundle sheath cells are arranged in a ring-like structure around the vascular bundles. This specific leaf anatomy is known as Kranz anatomy (where 'Kranz' means 'wreath').
$(2)$ Photo-oxidation refers to the process where,under conditions of insufficient $CO_2$ concentration,the light energy absorbed by chlorophyll cannot be fully utilized for photosynthesis. This excess energy leads to the oxidative destruction or decomposition of chlorophyll molecules.