CBSE Class 7 Answered

In a greenhouse, the regulation of light, water and carbon dioxide takes place in the following ways:

• Light: Greenhouses are constructed with long-sides facing south-east to south-west to maximize sunlight. The objects in a greenhouse are painted so they reflect as much light as possible. The covers used in a greenhouse are either made of glass or plastic which are transparent, which enables light to easily enter inside.
• Water: Many greenhouses use capillary mats for watering the plants. These mats are placed under plant pots. They ooze water slowly, which the drip holes of the containers take up to the plant roots. This reduces evaporation and prevents overwatering. The excess water is collected by plastic liners or a flood floor that directs the water back into the system to reuse for watering greenhouse plants in other drip lines. Another method of watering plants is the simple drip system, which can be used to direct larger or smaller flows of water directly to the pots. This type of water for greenhouses can be regulated with a timer and a flow gauge.
• Carbon dioxide: Controlling indoor air movement provides the greenhouse plants with a constant supply of carbon dioxide. Strategically placed horizontal fans throughout a greenhouse allow air to press closer to the foliage for peak photosynthesis action. The concentrated carbon dioxide results in larger leaves, stronger plant stems and possible early flowering and fruiting. However, air movement must be coupled with proper ventilation. Closing off the greenhouse to outside air circulation lowers indoor carbon dioxide levels because the plants use the gas quickly while transferring oxygen to the air in exchange.