Gaseous exchange between leaves and atmosphere would be disturbed due to blocked stomata.
Explanation:
Leaves have stomata on their surfaces. Through stomata, plants take the oxygen in for respiration. Carbon dioxide gas is also released into the atmosphere through stomata. Similarly, plants take the atmospheric CO2 through stomata to perform the process of photosynthesis. The molecular oxygen produced as a by-product during photosynthesis is also released through stomata.
Coating both sides of leaves with petroleum jelly or wax would block stomata. Leaves of the plant with coating would not be able to perform breathing and photosynthesis.
