Sunday, February 12, 2012

OBJ 5.1 Glasshouses

Describe how glasshouses and polythene tunnels can be used to increase the yield of certain crops.

1. Source: Solar radiation (initial source of energy).

2. The transparent material allows light to penetrate through the glass 
to the internal surfaces, where it is absorbed  (this natural light allows photosynthesis to take place).

3. The short wave radiation entering the greenhouse becomes longer wave radiation as it reflects off surfaces.

4. (surfaces RE EMIT the energy as heat) the  This longer wave radiation cannot leave as easily so the greenhouse heats up.

5. This raises the average KE of air particles therefore temperature is increased.  

6. Warm air, is trapped (cools as it raises to the roof, then sinks back down to the surface and is warmed again. (convection current).


The glasshouse provides the right conditions for plants to grow: 

1. Higher temperatures lead to optimum temp for enzyme reactions + photosynthesis.

2. Provides constant temp throughout the growing year = constant production.

- Enough natural light penetrates in the glasshouse for photosynthesis during the summer months, while extra lighting gives a longer day during the winter.

3. Prevention of loss of water vapor

 - Crops dont dry out, as the vapor cannot escape to the atmosphere.
- The water vapor maintains a moist atmosphere and reduces water loss by transpiration (water evaporated from leafs)

4. Can avoid frost damage - (seedlings).

5. Burning of fossil fuels 

a) burning fuels to raise the temp when the external temp is too low also produces CO2 --> increases concentration of the substrate for photosynthesis = more product +growth.

b) Side effect: Inefficient burning = ethene  gas --> stimulates fruit ripening eg:tomato. 

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