Question

a leaf covered with with Vaseline is tested for starch

Answer 1

is the leaf is covered with Vaseline in the downside also . if yes , then the starch test would result negative . as the downward side contains stomata and Vaseline would cover the downside also and the supply of carbon would be insufficient as carbon dioxide(CO²) would be incomplete and carbon is required . also the guard cells would also die as they would be having so much water . my opinion is that the result would be negative

Answer 2

Covering the leaves with Vaseline will close the stomatal opening present on leaf epidermis. Stomata helps in gaseous exchange and water evaporation or loss from leaf surface . Hence two major process of plant survival will be affected, which are :
(i) Transpiration {loss of water from leaf surface}
(ii) Photosynthesis / Respiration