Greenhouse Assignment Essay

Many factors affect crop growth, for example, light intensity, temperature, carbon dioxide concentration and the supply of water and minerals. These abiotic factors can slow down the rate of metabolic reactions and limit plant growth, they are therefore also known as limiting factors. All these factors can affect plant growth, however there can only be one limiting factor at any particular time. This would be the factor that is furthest away from its optimum, for example the concentration of CO2 would be the limiting factor if there is high light intensity, a high temperature and a good supply of water and minerals. Commercial growers have found a way to control these factors and maximise crop production; by using glasshouses.
For example, glasshouses can be used to hang artificial lighting; this extends daylight hours so that the light dependant reaction can repeat more times in a day which decreases growing time. The use of artificial lighting also increases the light intensity above the optimum of 10 Kilolux which maximises crop growth because light is the source of energy for the production of ATP and reduced NADP in the light dependant reaction. Because of the increase in light intensity, there is an increase in these products which means the light independent reaction can go around more times, more GP can be reduced into TP and more glucose can be produced. It can now be used as energy for the plant cells and aid growth. In summary the artificial light increases light intensity which increases the rate of photosynthesis and plant growth. Some people do not use light bulbs but instead use paraffin lamps, this is because not only do the lamps increase light intensity but they also emit heat and give out CO2 which increases its concentration in the glasshouse. This method of using artificial lighting has enabled farmers in the Netherlands to decrease growing time by 4 weeks.

Commercial growers can also use green houses to put in heating and cooling systems to increase and regulate the temperature. This maximises crop growth because an increase in temperature also increases the rate of all enzyme catalysed reactions, this includes the use of the enzyme Rubisco in the light independent reaction. This means that the reaction between CO2 and RuBP to form two GP molecules can take place much more rapidly which would increase the rate of the whole Calvin cycle, meaning glucose and other useful organic substances that can be used for growth are produced at a much faster rate. The cooling system is there to regulate the temperature because if it goes above 35 degrees Celsius then enzyme catalysed reactions begin to slow down, which means photosynthesis and plant growth will too. This is because the heat begins to break the bonds in the enzymes tertiary structure which alters the enzymes shape and denatures it. This means the substrates (for example CO2 and RuBP) can no longer bind to its active site and react with each other.
The third main factor which commercial growers can control with the use of glasshouses is the concentration of CO2. The normal concentration of this gas in the air is around 400ppm, however glasshouses can increase this closer to the plants optimum levels of nearer 1000ppm by siphoning waste CO2 from nearby factories and supplying it to the crops via tubes covered in tiny holes. This means that there is more substrate to react with RuBP with the aid of Rubisco

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