In a dicot pot herb, vaseline/vegetable oil was applied on the upper surface of one leaf (Experimental leaf 1) and on the lower surface of another leaf (Experimental leaf 2). Vaseline/Vegetable oil was not applied to the control leaf. The plant was deliberately not watered for several days. Which leaf will dry up last?

In dicot plants, stomata are primarily distributed on the lower (abaxial) surface of the leaf to prevent excessive water loss from direct sunlight exposure [4]. Transpiration is the process where water evaporates through these stomatal pores [2]. Applying vaseline or vegetable oil creates an airtight seal that blocks these pores, effectively stopping the exit of water vapor [3]. In this experiment, Experimental leaf 2 has its lower surface coated, which blocks the majority of its stomata. Consequently, its transpiration rate is significantly reduced compared to Experimental leaf 1 (coated on the upper surface where fewer stomata exist) and the control leaf (no coating). Because Experimental leaf 2 retains its internal water for the longest duration while the plant is not watered, it will be the last to dry up.

Sources

1. [1] Science-Class VII . NCERT(Revised ed 2025) > Chapter 10: Life Processes in Plants > 10.3.1 Transport of water and minerals > p. 147
2. [4] https://ncert.nic.in/pdf/publication/sciencelaboratorymanuals/classX/science/jelm103.pdf
3. [2] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Activity 5.8 > p. 95
4. [3] Science , class X (NCERT 2025 ed.) > Chapter 5: Life Processes > Activity 5.2 > p. 83