Which of the following factors is likely to increase the rate of transpiration in plants?

Step 1: Analyze the question We need the factor that increases the rate of transpiration, which is the loss of water vapour from the aerial parts of a plant, mainly through the stomata of the leaves.

Step 2: Concept Transpiration increases when:

• there are more stomata, or they are open wider
• the surface area for evaporation is larger
• temperature is higher
• wind speed is higher
• humidity is lower, which gives a steeper diffusion gradient
• light intensity is higher, because it makes the stomata open

Step 3: Check each option

• A. Fewer stomata per unit area. There are fewer pores for water vapour to escape, so transpiration decreases. ✘
• B. Increased humidity. The air is already moist, so the water vapour concentration gradient between leaf and air is smaller. Diffusion slows and transpiration decreases. ✘
• C. Increased leaf surface area to volume ratio. More surface is exposed for evaporation relative to the leaf's volume, so more water is lost and transpiration increases. ✔
• D. Removal of leaves. The leaves are the main site of transpiration, so removing them reduces it. ✘

Step 4: Answer The correct option is C.

Tip: Think of transpiration as "drying clothes." Clothes dry faster when they are spread out (large surface area), in heat, in wind, and in dry air. Anything that mimics those conditions raises transpiration. Anything that mimics damp, still, cool conditions, or removes the "clothes" (leaves), lowers it.