A greenhouse is a building where plants are cultivated. A greenhouse is built of glass or plastic; it heats up because the sun's incoming electromagnetic radiation (particularly infrared light) warms plants, soil, and other things inside the building. Air warmed by the heat from hot interior surfaces is retained in the building by the roof and wall.
The glass used for a greenhouse acts as a selective transmission medium for different spectral frequencies, and its effect is to trap energy within the greenhouse, which heats both the plants and the ground inside it. This warms the air near the ground, and this air is prevented from rising and flowing away. This can be demonstrated by opening a small window near the roof of a greenhouse: the temperature drops considerably. Greenhouses thus work by trapping electromagnetic radiation and preventing convection.
Greenhouses are often used for growing flowers, vegetables, and fruits. Bumblebees are the pollinators of choice for most greenhouse pollination, although other types of bees have been used, as well as artificial pollination.
Compare: greenhouse effect