5.1 Glasshouses

1. Glass houses (greenhouses)- are constructed on a framework, like a house, all their surfaces are glass, allowing light to penetrate through to the interior. 

1. Ploythene tunnels- also framework with polythene over the surface. Polythene allows light to penetrate through. Associated with things like market gardening. Can be taken down and replaced. Used in cheaper countries. 

Glasshouse:

1. Firstly, we have solar radiation which is our initial source of energy in the form of light. 
2. The light is able to penetrate through the glass to the internal surfaces. 
3. The light is absorbed by surfaces inside the glasshouse. eg the soil the wooden bench surfaces or the plants
4. these surfaces re-emit this energy as heat. 
5. The heat warms the air, raising its average kinetic energy (the temperature increases)
6. The warm air is trapped. Generally it would cool at the upper surfaces and then sink to the floor again to be rewarmed by the surfaces. 

How does this cause an increase in crop yield?

1. Warm air in the glasshouse increases crop yield 
2. The higher temperature in the glasshouse, lead to closer or optimum temperature for enzyme reactions including photosynthesis. 
3. It provides constant temperatures throughout the growing year therefore we have constant production. 
4. The prevention of loss of water vapour. Crops don't dry out. 
5. Able to avoid frost damage to seedlings in the spring time. 
6. Glasshouses are often warmed by the burning of fossil fuels. This leave to two effects. 
1. Increase in Carbon dioxide, which means we have increased the concentration of the substrate for photosynthesis.  
2. burning of the fossil fuels also results in the production of ethene. This gas stimulates fruit ripening.