Which side of a cactus develops a thicker tougher skin due to sun exposure?

• A. East Side
• B. South Side
• C. West Side
• D. North Side

Answer: (B)

Sun exposure drives protective thickening of the plant’s outer tissues on the side that gets the most light. In the northern hemisphere, the sun stays mostly in the southern sky, so the south-facing surface of a cactus receives the most intense sun and heat. To guard against UV damage and excessive water loss, that side develops a thicker, tougher skin—with a thicker cuticle and stronger epidermis. The other sides see less sun and don’t need as much protection, so the thickening is less pronounced there. If you were in the southern hemisphere, the mirror situation would apply, with the north side receiving the most sun.