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

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.

If the inhibitors of the tomato juice are to inhibit germination there are various factors they can affect. For instance, the inhibitors can affect the enzyme amylase. Amylase is used to convert starch into glucose. The glucose is then used as a respiratory substrate to produce ATP. Without respiration the seed cannot germinate (because energy/ATP is needed for metabolisms for growth). So by inhibiting the enzyme amylase the inhibitors will prevent germination.

The presence of inhibitors in tomatoes can provide benefits for the tomatoes. By inhibiting the growth of other seeds they are in effect reducing inter-specific competition for essential nutrients and therefore are more likely to flourish. They will be able to gain the light, carbon dioxide, heat, etc, first and hence grow taller and maybe even block off light to the plants below them. They will be able to photosynthesise more, grow more and hence have greater productivity.

There are a number of ways in which the tomato plants could have gained the ability to produce these inhibitor chemicals. It could be as a result of mutations. Changes in the sequence of bases on the DNA are known as mutations. They occur naturally in about 1 in a million bases copied. Some environmental factors such as radiation increase the rates of mutations. Part of the genetic code could have been deleted or substituted, making a mutated genetic code that provided the information to produce the inhibitors. This can result in natural selection or survival of the fittest because this variation will help the tomato plants with this ability to have a greater share of the limited resources (because they are able to inhibit the growth of other seeds and therefore reduce competition). So the tomato plants with the inhibitors will grow more and produce more offspring. Over a long period of time only those tomato plants with the inhibitors will survive to pass on their genes (the tomato plants with the variations are able to gain light, heat, etc, more easily; they are biologically fit. The less fit tomato plants will not be able to compete in the environment and will die and not pass on their genes.) However, there still may be variation in the amount of inhibitor they produce (this is why it will be important to use the same tomato juice in all of my experiments and stir the juice to ensure constant amounts of inhibitors). So some might produce more inhibitors and therefore grow faster.

Justifying the procedure

I will now present a justification of my procedure. I plan to use large numbers of seeds in each experiment; this will lower the percentage error. The reason for this is that it is unlikely to get 100% germination, even in ideal conditions. For instance, if 15 seeds are sown and 1 doesn't germinate or I miscount by 1 then there will be an error of 6.7%. If I plant a 100 seeds and miscount by 1, then that is a 1% error. So just by increasing the number of seeds I will drastically reduce the percentage error.

I will make sure to repeat each experiment many times. This will also act to reduce the error because there will be more results and hence the experiment is more reliable. If I only do the experiment once the result could just be coincidence, by repeating the experiment 20 times, and getting similar results, it will show consistency and reliability. Furthermore I will need lots of results to carry out a significant statistical test.

I plan to use tomato juice from a carton. I will make sure that I use tomato juice from the same carton because different cartons will have different amounts of inhibitors and hence lead to inconsistencies in the results. Also, because its prepared tomato juice from a carton, I will shake it thoroughly before adding the juice so as to ensure any inhibitors are evenly spread.

Ripe tomatoes are likely to splodge onto the ground and spend the winter in the ground before germinating the following spring. The juice is likely to be diluted by the winter rain. I therefore plan to use various dilutions of juice to try and stimulate this. The concentrated tomato juice, however, might have an osmotic effect and prevent the water needed for the mobilisation of enzymes entering the seed.

I plan to use the same type of seeds in all the experiments since some seeds may have developed a resistance to the inhibitor or be more sensitive to it than others. Therefore some seeds will grow faster or slower than others, leading to inconsistencies. Also, I will use fresh seeds because they are more like to germinate (I do not want age to be a factor hindering rate of germination).

It will be important to keep the temperature the same for all experiments. I can do this in a number of ways for instance doing the experiment in a temperature-controlled room or doing all of the experiments at the same time. This is important because temperature affects the rate of enzyme activity and will affect the enzyme's controlling factors associated with germination. If the temperature is not kept constant anomalies will result. For instance, if the temperature is warm for one experiment, really hot for another and cold for a third the results will be inconsistent. In the warm experiment germination will be the quickest because the enzymes will have lots of kinetic energy, do their job quicker hence faster germination. In the really hot experiment the enzymes will be denatured and there will be no germination. Germination in the cold experiment, due to a lack of kinetic energy, will be very slow. So therefore it is very important to keep the temperature constant.

I plan to give all the seeds the same amount of water/solution since the availability of water will affect germination.

The pH has an effect on the enzymes controlling germination; I will therefore keep this constant (maybe by using a buffer solution).

I plan to put the seeds in a dark room since those are the conditions the seeds are familiar with when they germinate in the soil.

Plan

Equipment List

* 150 cupcakes

* Packet of cress seeds (with at least 6000)

* Paper towels (for absorbing ...

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Teacher Reviews

Here's what a teacher thought of this essay

Ross Robertson

10th of Apr 2013

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.

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