5.1 Glasshouses

5.1 describe how glasshouses and polythene tunnels can be used to increase the yield of certain crops

Both Glasshouses (a.k.a. greenhouses) and Polythene tunnels aim to have the same effect on plants: provide warmth for plants to grow in a humid environment.

How they work

1. Heat enters the greenhouse from the sun (in short IR waves)
2. The surfaces in the greenhouse absorb the short waves and reemit this energy as heat
3. The heat warms the air inside the greenhouse
4. Most of the heat is reflected back into the greenhouse and doesn't escape

This increases crop yield because…

• … Warmer temperatures allow enzyme reactions to occur more efficiently
• … Less water is lost to the environment
• … Constant temperature around the year

Polythene tunnels are also used to the same effect but are cheaper, easier to move and easier to use for farmers because they can be placed over rows of plants to protect from the frost as in a greenhouse plants must be potted.