If a potted plant is covered with a glass jar, water vapors appear on the wall of the jar. Explain why and which structure is responsible for this.

Epidermis of a leaf is not continuous at all the places due to the presence of small pores, called stomata. Each stoma is bounded by a pair of specialized epidermal cells or two kidney-shaped cells called guard cells. The concave sides of these guard cells face each other and have a space forming the stomata opening. The stoma allows gaseous exchange to occur during photosynthesis and respiration. Maximum loss of water from plants tissues takes place through the stomatal openings.

Plants keep themselves cool by releasing water vapour through a process called Transpiration. Transpiration is the process by which the evaporation of water takes place from the leaves of the plant and is released into the atmosphere.

During transpiration water vapor escapes through stomata opening, this results in appearance of water vapor.

When we cover a potted plant with glass jar, we observe water droplets on walls of glass because the vapor can't escape the jar it condenses on wall of jar and as a result, we can see water droplets on glass jar.