5.1 Glasshouses

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



Glasshouses are sometimes know as greenhouses.
Constructed on a framework (like a house) where all surfaces are made of glass, which allows light to penetrate though to the interior.

Polythene tunnels are a framework with polythene over the surface that allows light to penetrate through. Associated with market gardening, also used in less developed countries since its cheaper with glass and easier adjustable.

How does the glasshouse work:
- Solar radiation – initial source of energy in the form of light.
- Light is able to penetrate though the glass into the interior surfaces.
- The light is absorbed by surfaces inside the glasshouse (soil, wooden surfaces, plants)
- The surfaces will readmit the energy as heat.
- The heat warms the air – raising its average kinetic energy = temp increase
- The warm air is trapped, sending it back down to bottom of glasshouse
- protects from stop winds and heavy rain

Warm air in glasshouse ---→ increase in crop yield

- High temps in the class house lead to closer/optimum temp for enzyme reactions (photosynthesis)
- Provides constant tem throughout year. Which = constant production.
- Prevention of loss of water vapour – crops don’t dry out because they have a constant supply of water vapour
- Avoid frost damage – particularly to seedlings in springtime.
- Glasshouses are often warmed by the burning of fossil fuels, which leads to an increase in the CO2 levels in the glasshouse. This increases the concentration of the substrate for photosynthesis causing more product and growth. Inefficient burning of fossil fuel ethane, this gas stimulates fruit ripening(tomato)