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An investigation into the effect of a germination inhibitor on the germination of seeds.

Extracts from this document...

Introduction

GERMINATION INHIBITORS An investigation into the effect of a germination inhibitor on the germination of seeds. INTRODUCTION The necessary conditions For a seed to germinate there are specific conditions different seeds need. In this experiment, cress seeds are to be used. Going through the basics first though, for a seed to successfully germinate there needs to be: o An adequate supply of water o A suitable temperature o An appropriate partial pressure of oxygen o A suitable supply of light Water uptake is a crucial part of the necessary conditions because germination can only commence after the uptake of water by the seed. Water absorption is imbibition. The optimum temperature for germination is the optimum for the enzymes involved in mobilisation of food reserves, provided that other factors are not limiting. This temperature varies from species to species (i.e. 1 - 45�C). Respiration makes available the energy for metabolism and growth. Germinating seeds respire very rapidly, and require oxygen for aerobic respiration. Seeds will not germinate in the total absence of oxygen. Diffusion of oxygen through the testa may be slow, however, and in the early stages of germination seeds may rely on some anaerobic respiration, at least until the testa has ruptured. So this explains why water, oxygen and a suitable temperature are needed for germination, therefore needed for this experiment. Light is obviously the last condition that comes into place (though not in all seeds) with the cress seeds being used in this experiment. Inhibitors A germination inhibitor is to be used in this experiment. The hypothesis is that it will affect the germination of the seed. Inhibitors are not just used in plants; they are also used in enzymes (Enzyme inhibitors). They alter the rate of enzyme catalysed reactions. The reactions of enzymes may be enhanced or inhibited by various substances, some formed in the cell and others absorbed from the external environment. ...read more.

Middle

6 separate results are being used because 6 was thought to be enough for it to be reliable and it shows the variety of number of seeds that germinated. If just the Individual Data was used then this would not be reliable because something could have gone wrong with the experiment and the results would not answer the question of the investigation, therefore more data is used (to reduce the risk of 'flukes'). For each different inhibitor concentration the 6 different results shown used 50 seeds each, and since there are 6 people then this is based on 300 seeds for each concentration in each day. There will be two sets of data used for chi-squared: my individual results and an average of the class extract results. And because there is 4 days that the results were collected then 2 days will be chosen to represent all the days (i.e. day 2 and day 6). This means there will be 4 chi-squared tests. Chi-squared is a statistical test to compare experimental data with predicted results (i.e. hypothesis with null hypothesis). The test relies on comparing observed results with expected results. The Chi-Squared Test Observed results - In a sample of 6 Petri dishes of varying tomato inhibitor concentration (the concentrations are indicated on the class investigation table), 50 seeds are put in each Petri dish and so therefore there are 300 seeds being used. Not all of the seeds germinated and the ones that did are the "Observed results" (see the first test below). Expected results - According to the null hypothesis there is no relationship between concentration inhibitor and seed germination, therefore all the results should be the same (the same amount of seeds should germinate in each Petri dish). The first test is my individual results on day 2. Individual results (Day 1) Tomato Inhibitor Concentration (%) 0 10 25 50 75 100 Germinated 20 8 1 0 0 Not Germinated 30 42 49 50 50 50 This is an example of how the chi-squared test is carried out; this is for individual day 1 results. ...read more.

Conclusion

o Anomalies These were mentioned earlier as evidence that things have gone wrong with the experiment. Usually it's a lone result not in sync with the others. So the hypothesis, that the results support, states that "in high concentration conditions of inhibitor then the seeds will germinate very slowly or none at all - showing a relationship between inhibitor concentration and germination" and so anomalies would be results that do not follow this statement. The table of results does not show any obvious anomalies but the graph does show one result that is not in sync with the others (it is indicated on the graph). It is for individual data day 6. This is to be expected because the individual data is just my experiment and so if something goes wrong it is much more significant than if it happened to one of the group data experiments because the averages are taken. So it is one Petri dish of 10% concentration therefore it can be presumed that something happened to the Petri dish during the 6 days which altered the seeds germination process. This could be due to one of the 'error' possibilities stated earlier (e.g. due to light intensity changing), or somebody may have moved the Petri dish by accident, when getting to theirs and the seeds got moved about in the dish and cramped into one spot therefore competition (for water) would be fiercer than if they were spread out. Also some of the seeds may have just got a smaller dose of the inhibitor than the other seeds, and therefore the variety of germination would be greater than in other Petri dishes (see "intraspecific competition" in analysis of results). There are not any other anomalies on the results table or on the graph, they all follow the hypothesis. The validity of this experiment is quite high because of the high reliability and wide range of concentrations etc. but it is not 100% authentic because like all experiments there are uncertainties; things changing in or around the experiment that could affect the outcome. Alana Russell Page 1 07/05/2007 ...read more.

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Here's what a teacher thought of this essay

3 star(s)

This is a very lengthy account of a relatively straightforward investigation into the effect of tomato pulp concentration on the germination success of cress seeds. While the basic science behind the investigation is good (one variable changed, all others kept constant), the written account is very wordy and often confusing. The following issues need to be improved if this essay is to gain the higher grades at A' Level.

[1] A clear hypothesis is needed which links IV and DV.

[2] The identity of the inhibitor needs to be discussed from the start, or at least the source (tomatoes) stated.

[3] The DV needs to be very clear from the start, i.e. % germination.

[4] The Chi Squared tests are entirely unnecessary since the data speaks for itself.

[5] Group results and mean values need to be clearly presented in a table.

[6] Every section needs to be shortened by around 50-75%. The whole report should be no longer than 4 pages.

While the writer is to be commended for the obvious effort which has gone into this work, it could have been written in 4-5 pages. Long does not necessarily equal high grades. Examiners penalise lack of conciseness.

3 stars

Marked by teacher Ross Robertson 24/06/2013

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