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An investigation into the inhibiting effect of tomato juice on the germination of cress seeds.

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An investigation into the inhibiting effect of tomato juice on the germination of cress seeds Introduction I intend to analyse the inhibiting effect of tomato juice on the germination of tomato juice. In this introduction I will answer important questions such as; what are inhibitors? How might inhibitors affect germination? , etc. When answering the questions, I will be considering different areas of the syllabus (e.g. genetics, inter-specific competition, enzymes and inhibitors, practical skills, etc.) This will help me appreciate the theory behind the investigation and hence help me formulate an effective plan and method. Inhibitors are chemicals, which inhibit the action of an enzyme. There are two main types of inhibitors: reversible and non-reversible. Non-reversible inhibitors permanently damage enzymes. They attach themselves to the enzyme molecule and cause important bonds to break, causing irreparable damage. This denatures the enzyme and does not allow it to function. Diagram showing non-reversible inhibition: Normal arrangement Change caused by non-reversible inhibitor Reversible inhibitors inhibit the action of enzymes but do not do permanent damage. Once the reversible inhibitor is removed; the enzyme will return to normal. Reversible inhibitors can be divided into two types: competitive and non-competitive. Competitive inhibitors compete with the substrate molecules for a place on the enzyme's active site. Although enzymes are specific the inhibitors have a structure similar to the substrate molecule and so can fit into the active site. This will stop the substrate locking with the active site and therefore decrease the rate of reaction. The greater the concentration of inhibitors the less chance the substrate molecules have of binding with the active site (hence reactions slow and no germination). Diagram to show competitive inhibition: Normal substrate molecule substrate molecule can no longer Fitting into active site due to presence of inhibitor molecule Non-competitive inhibitors do not compete for a place on the active site, they attach themselves to the enzyme, and the shape of the active site is altered so that the substrate molecule can no longer fit. ...read more.


the inhibitors have already taken up most of the active sites so if you add more they will have less of a impact). My results do show that tomato juice has a significant effect on the germination of cress seeds. I can state this confidently because in the control experiment of 0% concentration of tomato juice there was an average of 98% germination; this percentage rapidly fell as I increased the tomato juice concentration (at 25% concentrated tomato juice only 8% of the seeds germinated). So the only factor that could have instigated this rapid decline in germination is the tomato juice (because everything else was kept constant). What can be debated, however, is how the tomato juice actually brings about this decline in germination. Is it because tomato juice contains inhibitors? This is probably the most credible explanation but this experiment does not beyond doubt prove that tomato juice does contain inhibitors. It could be that tomato juice does not contain inhibitors, and in fact other properties of the tomato juice affected the percentage of germination. For instance, it might have been that the tomato juice altered the pH so that the enzymes could not have functioned properly. Enzymes are complex molecules held together partly by hydrogen bonding. Hydrogen bonding occurs between negative and positive charges on the enzyme molecule. If the tomato juice decreased the pH to acidic conditions this will mean there is an excess of H+ ions. These can cause bonds to break, and change the nature of the enzyme (make them denatured). If the tomato juice increased the pH to alkaline conditions there would be an excess of OH- ions, which will have a similar effect. Another factor that might have affected germination is that the tomato juice might have had an osmotic effect (by making the water potential of the soil more negative) not allowing the water to enter the seeds. ...read more.


I tried to ensure that the other variables, for each experiment, were controlled and consistent. For instance to keep the light intensity, temperature, etc., the same I carried out the experiments in the same temperature-controlled room with the curtains closed. I made sure that the seeds were spread evenly in each experiment to ensure that they could all get equal access to water light, etc. I also made sure to check the filter paper from time to time o make sure that it was still damp. I was worried that some of the seeds might go mouldy during the experiment and hence affect germination, but this did not happen. There are numerous ways in which I can improve the experiment. I could: * Use a wider range of dilutions of tomato juice * Use more seeds in each batch (reduce percentage error) * Have a more reliable method of counting the seeds * Do more batches (increase reliability by showing more consistency) * Get everyone in the group to do it exactly the same way so I can pool the results and therefore increase reliability * Try the effect of tomato juice inhibitors on a variety of different seeds. * Repeat the experiment with the juice of other fruit to see if they have the same effect * Disinfect the seeds before use to destroy any bacteria and mould that could affect the results * Carry out the experiment in a temperature controlled lab. * Carry out the experiment in a lab where the light intensity is monitored and kept constant * Use more reliable apparatus * Ensure the pH does not change (buffer solution) * Use more accurate measuring equipment (e.g. pipette) to reduce percentage error) * Read measurement at eye level to reduce parallax error * Give the seeds longer to germinate and hence make it easier to distinguish between seeds that have germinated and those that have not. A Level Biology coursework: AN INVESTIGATION INTO THE INHIBITING EFFECT OF TOMATO JUICE ON THE GERMINATION OF CRESS SEEDS Written by Adil Lone ...read more.

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3 star(s)

An impressive piece of work which details an investigation into the effect of varying concentrations of tomato juice on the germination rates of cress seeds. The writer has produced a well-organised report with most of the key sections covered in detail. Improvements could be made in the following areas: [1] A clear aim needs to be stated from the start together with the hypothesis to be tested. [2] The introduction needs to be focused on the area under investigation with a good level of research into previous work carried out on tomato inhibition. [3] The method needs to be more concise with as little repetition as possible. [4] The conclusion needs to encompass knowledge from previous work carried out on tomato inhibitors to explain the results obtained in this experiment. Overall, however, this is a substantial effort and with the improvements outlined above, would merit a good grade at A'Level.

Marked by teacher Ross Robertson 10/04/2013

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