Transpiration as Unavoidable Water Loss During Stomatal Gas Exchange

Steps:

• Stomata open to allow CO2 diffusion into leaves for photosynthesis.
• Open stomata expose moist leaf interiors to drier external air.
• Water vapor diffuses out via the concentration gradient, per Fick's law.
• This water loss, or transpiration, occurs inevitably with every gas exchange event.

Why D is correct:

• Only statement 3 accurately ties transpiration to the diffusion of water vapor through open stomata, as defined by the cohesive-adhesive properties of water and vapor pressure gradients in plant physiology.

Why the others are wrong:

• A includes statements 1 and 2, which misattribute transpiration to non-diffusion factors like root pressure or unrelated metabolic processes.
• B selects only 1 and 2, both incorrect as they ignore the core role of stomatal opening in gas exchange.
• C includes 2, which wrongly links transpiration solely to temperature without addressing gas exchange necessity.

Final answer: D