5.1 Glasshouses and Polythene Tunnels

Glasshouse (or greenhouse) constructed as a simple house structure but all surfaces are made of glass in which it allows light to penetrate through to the interior.


How the glasshouse works

•  Solar radiation - the initial source of energy (in the form of light)
•  Light can be able to penetrates through the glass into the internal surfaces and is absorbed by surfaces inside the glasshouse - this could be the soil, wooden surface and plants themselves
• These surfaces then reemit this energy as heat where it warms the air ,  raising its average kinetic energy which in other words temperature increases

How warm air in the glass house increase the crops yield? 

• The higher temperature leads to closer, or optimum temperature for enzyme reaction such as photosynthesis. This is when enzymes work most efficiently allowing the fastest rate of reaction so more product is being produced.
• This  provide constant temperature throughout the year -> making constant production 
• Prevention of loss of water vapor  - they have a constant supply of water making the crops don't dried out
•  Avoid frost damage to seedlings in the spring time 
•  Glasshouses are often warmed by the burning of fossil fuels  -> making an increase of carbon dioxide level ->increase concentration of substrate for photosynthesis- --> increase product of photosynthesis
• Ethene may form through  incomplete combustion and as the product which can help stimulate fruit ripening, particularly with the tomato.

The polythene tunnels, 

usually a framework with polythene over the surface which also allows light to penetrate through to the interior.The advantage of polythene tunnels is because of the cheaper costs but also more adjustable and movable .The disadvantages of polythene tunnels provide less shelter for the plants and may be less effective which may have an effect of the output.