5.1 Glasshouses

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

Both polythene tunnel and greenhouse provide warmth for the growth of plant. 

The glasshouse (or greenhouse) is constructed on a framework of a simple house structure.

All surfaces are glass, allowing the light to penetrate through to the interior.

How it works

1. Solar radiation, which is initial source of energy, in the form of light

2. Light penetrates through the glass into the internal surfaces

3. Light is absorbed by surfaces inside the glasshouse, which can be soil, wooden surfaces, and plants themselves

4. These surfaces then reemit this energy as heat

5. The heat warms the air, raising its average kinetic energy = temperature increases

6. The warm air which is raising the temperature is trapped and create convection current within the glasshouse

This cause the increase of crop yield because…

How it works: Warm air in glasshouse ---> Increase in crop yield 

1. The higher temperature leads to closer, or optimum temperature, for enzyme reaction such as photosynthesis. (enzymes work most efficiently, allowing the fastest rate of reaction)

2. Allows constant temperature throughout the year = constant production (especially high altitude area) 

3. Prevention of loss of water vapor (they have a constant supply of water) 

4. Avoid frost damage to seedlings (in the spring time) Polythene tunnels are usually used to protect growth of seedlings in spring time, and removed to allow full growth in summer 

5. Glasshouses are often warmed by the burning of fossil fuels

= increase carbon dioxide level (increase concentration of substrate for photosynthesis) --> more product and growth

= inefficient burning of fossil fuels lead to the production of ethene gas, which turns out to stimulate fruit ripening (especially tomato) 

The polythene tunnels has polythene as surface on its framework and again allows light to penetrate to the interior.

This is used in less developed country as it is cheaper.

Advantage: more adjustable and movable

Disadvantage: less shelter for plant; less effective (which may decrease total output)