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

5.1 •glasshouses and polythene tunnels can be used to increase crop yields 

                •they warming up the growing area to speed up photosynthesis 

                •carbon dioxide can be controlled to speed up the rate of photosynthesis, by using a paraffin heater, where CO2 is a by-product  

                •commercial farms provide artificial light after the Sun goes down 

                •plants are enclosed to protect them from pests and diseases 

                •in winter a heater is used to keep the temperature ideal

                •water loss through transpiration is stopped, preventing dehydration