5.1 Glasshouses

describe how glasshouses and polythene tunnels can be used to increase the yields of certain crops.

-in some countries known as greenhouses.
-simple house structure but all surfaces are glass allowing light to enter.
-the polythene tunnels usually a frame work with polythene. allows light to enter- cheaper that glass house somewhat ajustable can be taken down and replaced. (used in less developed countries)

-solar radiation -> source of energy -> in the form of light.
-light is able to penetrate through the glass to the internal surfaces.
-the light is absorbed by surfaces inside the glass house. (soil, plants, whatever is in the glass house)
-the surfaces will reemit the energy as heat.
-heat warms the air and raising the average kinetic energy -> the temperature increases.
-the warm air which is raising the temperature is trapped (it would cool at the upper surfaces and sink to the floor again to be rewarmed by the surfaces within the glasshouse)

how does this cause an increase the crop yield?
-warm air in glass house -> increase in crop yield.
1: - higher temperature in glass house causes a closer optimum temperature for enzyme reactions (includes photosynthesis)
2: - it provides constant temperature through out the growing year- constant production.
3: - the prevention of loss of water vapour. crops don't dry out. constant supply of water. water vapour doesn't escape to atmosphere.
4: - avoid frost damage- seedlings in the spring time.
5: - glass house is often warmed by burning of fossil fuels
a) increase in CO2 - increased concentration of substrate for photosynthesis. more product and more growth.
b) inefficient burning of fossil fuels leads to the production of ethene. -> this stimulates fruit ripening (particularly in the tomato)