5.1 glass houses

• glasshouses/greenhouses have frameworks made of glass which lets light penetrate through
• the frame is made out of polythene which also lets light penetrate

how greenhouses work:
• solar radiation from the sun
• light goes through glass
• light is absorbed by surfaces inside greenhouse e.g. soil, plants
•  these surfaces will re-emit this energy as heat
• the heat warms the air raising its average KE, raising the overall temperature
• the warm air is trapped

warm air glasshouse = higher crop yield

this is because:
- high temp = optimum temperature for enzyme reactions (photosynthesis)
- temperature is constant throughout the year
- prevention of loss of water vapour - crops do not dry out, because they have a constant supply of water (vapour)
- avoid frost damage (especially seedlings)
- glasshouses are warmed by the burning of fossil fuels which leads to an increase in the CO2 levels inside the glasshouse (increased substrate for photosynthesis, increasing growth). inefficient burning of fossil fuels results in ethane being produced which is a gas that stimulates fruit ripening