Question

What is common between respiration and transpiration process in plants?

Answer 1

Transpiration is the evaporation of excess water from leaves. This happens when the guard cells are open to facilitate gaseous exchange(get in Carbon dioxide and throw out Oxygen). Transpiration just happens as an unwanted spontaneous process. Read Potassium-ion influx theory for more details regarding the opening of guard cells.

Respiration is a process that happens all the time. In the day as well as in the night as it is vital for the life of a plant.

Answer 2

Both of them involve exchange of gases through stomata and both of them release water (though from different places).