What is the difference between transpiration and evapotranspiration?

What you are being asked to compare

You are comparing a plant-only process (water leaving through plant tissues) with a broader land-surface water-loss term used in hydrology and meteorology.

Transpiration: water loss from the plant

• Water is pulled up from roots through the xylem.
• It exits mostly through stomata as water vapor.
• It is tightly linked to plant physiology, for example stomatal opening, photosynthesis, and plant stress.

Evapotranspiration: the combined loss to the atmosphere

Evapotranspiration (often written ET) adds together two fluxes:

• Evaporation: water vapor from soil, open water, intercepted rainfall on leaves, and other wet surfaces.
• Transpiration: water vapor released by plants.

A simple way to write it is: $$ET = E + T$$ where $E$ is evaporation and $T$ is transpiration.

Why the distinction matters

• In plant biology, you often care specifically about transpiration because it affects plant water use.
• In water balance, irrigation planning, and climate studies, you usually use evapotranspiration because it represents the total atmospheric water loss from a field, watershed, or region.

Quick example

If a crop field loses water because the soil dries after irrigation and the plants are also releasing water through leaves, the soil component is evaporation and the plant component is transpiration; together they make evapotranspiration.