The rate of transpiration is NOT affected by

Analyze the question: We need the factor that does NOT affect the rate of transpiration (loss of water vapour from plant leaves, mainly through the stomata).

Concept: Transpiration is affected by:

• Environmental factors: temperature (higher temperature increases evaporation), humidity (high humidity reduces the diffusion gradient so transpiration slows), wind speed, and light intensity (light opens the stomata).
• Plant factors: the number, size and degree of opening of the stomata, the leaf surface area, and the presence of a cuticle.

Solving step by step:

• B. Humidity: It affects the water vapour concentration gradient between the leaf and the air, so it does affect transpiration.
• C. Temperature: It affects the rate of evaporation and diffusion, so it does affect transpiration.
• D. Size of the stomata pores: Wider pores allow more water vapour to escape, so this does affect transpiration.
• A. "Weight" of the stomata pores: Pores are openings, not objects, so they have no meaningful weight. Weight plays no role in the movement of water vapour, so it does not affect transpiration.

Note: The wording "weight of the stomata pores" is odd (the original question may have meant "number"), but as written, A is the only option that has no effect on transpiration.

Answer: A

Tip: For "NOT affected by" questions, eliminate options you know are real factors (temperature, humidity, wind, light, stomatal size or number). The odd one out is usually the answer.