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Alleopathy

Extracts from this document...

Introduction

Will the allelochemicals produced by grass seeds inhibit the growth of wheat seeds? Abstract: This investigation was designed to see what effect the allelopathic chemicals of grass seeds had on wheat seeds. This was done by placing 20 grass seeds on a petri dish, with two sheets of filter paper inside, which was watered with 5ml of distilled water every three days for a week. After one week of growth the seeds were removed, then another 20 wheat seeds were placed on the second piece of filter paper as the first was discarded, and the same process was repeated. This was repeated in five more petri dishes. At the same time 60 wheat seeds were grown as a control, so the results could be compared. A clear inhibition of root and shoot growth could be seen in the experimental group compared to the control group. Many wheat seeds in the test group did not even germinate. In conclusion the allelochemicals produced by grass seeds have an inhibitory effect on the wheat seeds. Aim: The aim of this investigation is to see whether the allelochemicals produced by grass at germination inhibit the growth of wheat seeds. Background: What is allelopathy? Allelopathy is any direct or indirect harmful effect by one plant (including micro-organisms) on another through the production of chemical compounds, known as allelochemicals, that escape into the environment.1 Chemicals that impose allelopathic influences are called allelochemicals. Conceptually, biomolecules (specifically termed allelochemicals) produced by a plant are released into the environment and subsequently influence growth and development of neighbouring plants.2 How does it work? Allelochemicals are present in virtually all plant tissues, including leaves, flowers, fruits, stems, roots, rhizomes, seeds and pollen. They may be released from plants into the environment by means of four ecological processes: volatilisation, leaching, root exudation, and decomposition of plant residues.3 * Volatilisation is a process where allelopathic plants release a chemical in the form of a gas through small openings in their leaves. ...read more.

Middle

The seeds will be watered and measured at the same time as the water may be used more at a certain time of day when the rate of photosynthesis is high. Biocide will be used as any bacteria present in the petri dishes could have affected growth of the seeds, also the bacteria could have affected the way in which the allelochemicals worked. All this could have an impact on the reliability of the investigation. The ethanol used in the investigation was also to prevent contaminating the petri dishes. The same type of seeds will be used, from the same packet, however individual differences are uncontrollable. Two layers of filter paper will be used in each petri dish. This will be done because if there was debris left from the roots of the grass, the decomposing plant tissue may release chemicals, which could affect the growth of the wheat seeds. Safety precautions: Caution will need to be taken when using the Bunsen burner, it must be used responsibly, never left unattended and when not in use the safety flame should be used. Ethanol is flammable therefore it should be kept away from the bunsen burner. Work areas should be kept clean and tidy at all times. Also long hair should be tied back. Care must be taken when using biocide as it may irritate the skin, wash the effected area immediately with water and do not ingest. Goggles should be worn, in order to prevent potential harm to the eyes. Result: The following table shows the average length of the wheat roots and shoots of the two groups. Each petri dish contained 20 seeds. Table 1- Control Group: wheat seeds grown in petri dish. Petri Dish Average length of root (mm) Average length of shoot (mm) 1 84 50 2 104 61 3 92 58 4 111 75 5 90 64 6 117 80 Total Average 100 65 Table 2- experimental group: Wheat seeds grown in petri dish previously occupied by grass seeds. ...read more.

Conclusion

There are several reasons why there was an inhibition of growth. Firstly, the grasses grown secrete allelochemicals (phytotoxins) from their roots into the surrounding area. The roots of the wheat grown absorb these chemicals. The toxins may inhibit the germination of seeds, growth or photosynthesis. Or they may block the absorption of critical nutrients. The allelochemicals secreted from the grass could have inhibited the enzymatic activity of the amylase in the wheat seed. Amylase is needed to convert starch into sugars, which in turn are used in respiration. If the allelochemicals hinder this activity then the growth of the seed will be inhibited. This could also explain why so many of the experimental group's seeds did not germinate. The investigation does have some limitations. Various improvements could be made including, the use of more sensitive equipment, such as a microscope to measure the root and shoot lengths and a micrometer for accuracy. However as a ruler was used an appropriate degree of accuracy was obtained as when measuring in mm whole numbers can only be used. An incubator could have been used, as it is possible that the temperature could have fluctuated in the room and had an effect on the growth of the seeds. The incubator could have been used to keep a constant temperature. The anomalous results obtained from petri dish 6 could have been avoided if a UV light was used, as it would have controlled the light exposure to the seeds. Different plants could be used to investigate the prevalence of allelopathy. Other factors could have been measured such as, the colour of leaves or the amount of metabolism. My aim was to investigate whether the allelochemicals produced by grass seeds at germination inhibited the growth of wheat seeds. My investigation has shown that it does. Further investigation: An experiment could have been conducted to investigate the effect of wheat on allelopathy. In order to determine whether allelopathy can be used as a natural herbicide. ...read more.

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