5.1- Glasshouses

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

Glasshouses- Simple house structure, all surfaces are glass which allow light to pass through

1. The initial source of energy is solar radiation
2. Light goes through the glass
3. Light is absorbed by surfaces inside the glasshouse
4. Energy is re-emitted as heat
5. Heat warms the air- raising the temperature
6. Warm air is trapped inside which causes convection currents (warm air rises and moves back down after being cooled at the top of the glasshouse)

Polythene tunnels- Framework with polythene over it, allows light to pass through, cheaper and more adjustable than the glasshouse

Increasing crop yield: 

• High temperatures --> optimum temp. for enzyme reactions (photosynthesis)
• Constant temp. throughout the growing year--> constant production
• Prevention of loss of water vapour --> crops do not dry out
• Avoid frost damage (particularly seedlings)
• Glasshouses are often warmed by burning fossil fuels:
• Increase in carbon dioxide levels inside the glasshouse
• Increased concentration of substrate for photosynthesis
• Production of ethene --> Stimulate fruit ripening