Glasshouses / Greenhouses
- it is constructed on a framework and all of the surfaces are glass --> allows light to penetrate through to the interior.
Polythene tunnels
- usually a frame work with polythene on the surface
- Polythene allows light to penetrate through to the interior as well
- Associated with market gardening and used in less-developed countries because cheaper than the glass
- it is adjustable and can be taken down and replaced much more regularly than the glasshouse
How it works:
1. start: solar radiation - initial source of energy in the form of light
2. light penetrates through the glass into the internal surfaces
3. the light is absorbed by surfaces inside the glasshouse e.g. soil, wooden bench surfaces, plants, etc.
4. the surfaces then re-emit the energy as heat
5. the heat warms the air - raising the average kinetic energy = temperature increases
6. the warm air is trapped. It would cool at the upper surface and then sink to the floor to be re-warmed by the surfaces within the glasshouse
- Warm air ---> increase in crop yield
1. the higher temps in the glasshouse lead to optimum temperatures for enzyme reactions (including photosynthesis)
2. provides constant temperatures throughout the growing year ---> constant production
3. prevention of loss of water vapour. The crops dont dry out - have a constant supply of water.
4. avoid frost damage (particularly to seedlings in the spring time)
5. it is warmed by the burning of fossil fuels
---> 1. increase in CO2 levels inside the glasshouse --> increase the concentration of the substrate for photosynthesis = more product and more growth
---> 2. inefficient burning of fossil fuels --> ethene ---> it stimulates fruit ripening
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