5.1

Describe how glasshouses and polthene tunnels can be used to increase the yield of certain crops:

Glasshouses are also known as Greenhouses - built on a framework and is very similar to a house, but it is all glass - allowing light to get the to interior

Polythene tunnels are also a framework with polythene layed over it that allows light to penetrate through. They are associated with market gardening in less developed countries because they are cheaper and glass is easy to adjust.

How the Glasshouse works:
1. Solar radiation is initial source of energy in form of light
2. Light can penetrate through glass to internal surfaces.
3. Light is absorbed by internal surfaces.
4. Surfaces re-emit energy as heat
5. Heat warms the air, therefore raising average Kinetic Energy = Temperature increase.
6. Warm air is trapped, (cool at top, sink, re warms, back to top again

Warm air àincrease crop yield

1. Rate vs. Temp graph, = closer/ optimum temperature for enzyme reactions (photosynthesis)

2. Constant temperature throughout the year.

3. Prevention of loss of water vapour

4. Avoid frost damaged (to seedlings) in winter/spring

5. Glasshouses = burning of fossil fuels

a) increase CO2 levels inside --> increase concentration of substrate for photosynthesis

b) Ethene produced is insufficient - this stimulates the fruit ripening.