I am going to attempt to calculate the effects of adjacent pH on the germination of a mustard seed by first placing a piece of filter paper in a petri dish. I will then use a syringe to measure 8cc’s of buffer solution to place into the petri dish, thereby saturating the filter paper. I will then place 20 seeds onto the paper at regular intervals, uniformly spaced. After replacing the lid of the petri dish, I will move it to a windowsill exposed to light.
I will then leave the seeds to experience natural light patterns and temperature changes.I will repeat the experiment, increasing the pH of the buffer solution from 3 to 8 with intervals of for each new set of petri dishes. I will also use pH 9.2 buffer, as it is available and would allow more results to draw my conclusion from. As well as testing the effect of buffers, I am going to do an experiment using water as well. Seeds need water, correct illumination, suitable temperatures and the presence of oxygen to grow. All of these factors have been taken into account, and have been made provision for in my plan:pH is the changing variable in my experiment, and the seeds will receive natural lighting and room temperatures throughout the experiment.
Oxygen will be constantly available as the petri dish lids are unsealed and will be removed daily to allow oxygen refreshment. To measure the effect of pH on germination, I will take percentages of seeds that have germinated (produced external shoots), and I will also take the average length of these growths. It will be a fair test, as I will repeat each experiment three times, and will use the same amount of buffer for each. I will also use the same amount of seeds, and place them equally each time. I will also set them up at the same time, so the light patterns they receive will be the same. This is so any anomalous results that could happen can be compared with the others to check accuracy.I am choosing to use the syringe to measure liquid volumes in the experiment as beakers are too inaccurate, and none are available that are small enough for this test.
Also the intervals marked are too large which increases the margin for error when measuring precision amounts. Prediction Germination starts with the rapid uptake of water by the seed, usually through the microphyle, resulting in a large increase in mass. The initial uptake of water is caused by colloidal particles in the seed coat.
Later on, the endosperm and embryo itself absorbs moisture.The subsequent increase in the number of solute molecules in the embryonic tissues, water is taken up by osmosis. This is the movement of a liquid (in this case water) from one side of a semi-permeable membrane (one which will let only small molecules through) to the other. In this experiment, osmosis happens when on one side of the membrane (in this case outside the seed) there is a solution of both large and small molecules, but on the other side (inside the seed) there are fewer or no large molecules. The buffer molecules diffuse into the seed, as the concentration of buffer outside the seed is greater than inside the seed. The quickest diffusion is experienced at the start of germination, as that is when the concentration gradient (difference) is highest.As the seed continues germination, the swelling of the embryonic tissues ruptures the seed coat, thereby allowing the growing plumule and radical to emerge.
The absorbed water activates the enzymes contained within the seed, and allows the hydrolysis (combining with water) of stored food materials (e.g. starch) into soluble products capable of being translocated from the storage tissues to the growing points of the embryo. I think the seeds will grow best in a pH 7 buffer solution, as the seed requires water to grow.
Water has a pH of 7 so I predict that the closer to this the buffer pH is – the more it will grow. I think that as the further the pH is from 7, the worse the seeds will grow and germinate.ResultsBy looking at my graph I can see that my prediction is incorrect. I predicted that the further the pH of the buffer solution was from pH 7, the lower the percentage of seeds would germinate. My results show that the optimum pH for growth and germination was pH 4 and not pH 7 as I had predicted. From my results, I can also see that any solutions above pH 4 did not support any germination and those below pH 4 supported very little. There are no results that are particularly anomalous results but I was interested to see that the solution at pH 7 did not support any germination.ConclusionI think the reason why the pH 7 solution did not support germination is because the buffer is a mixture of two chemicals, designed to keep at the same pH constantly.
The chemicals may have been a different density, so that the ones that were mostly the denser of the two chemicals were absorbed, and the other was not. They may also have been different at the atomic level. If one chemical had molecules made up of large atoms, they may have been too big to be absorbed by diffusion.Thus, if the pH with the largest proportion of this chemical was put on a set of seeds; they would not have grown. I do not know why, as is possible to see from my graph, that far more germination took place in water than in any of the other solutions. The molecule size difference would not have applied unless the sites where osmosis occurs may be different sizes, or water molecules are so small, 2 or more fit through the cell membrane at one point at once.
EvaluationOne factor that may have affected the accuracy of the results is the spacing of the seeds. It was very difficult to make certain that all the seeds were exactly equally spaced and some seeds may have been closer to each other than others. This may have affected the levels of moisture available to each seed and therefore depressed (or increased) its rate of growth. The accuracy of the density of the seeds could have been improved by increasing the amount of time spent on positioning them.
It would not possible to remove this problem completely and would also be difficult to achieve as the seeds were distribute, before being put out of reach by the window – thus allowing a possible handlers error in handling, and damaging the results.Another factor that may have affected my results is the accuracy of the measurements of the solutions. I kept a consistent accuracy, but (down to small measures) it is possible that the measurements could have varied a little. Again this problem could have been reduced by spending more time on this task, but would have had negligible effects. When looking at measuring accuracy, another obvious flaw is the accuracy of the pH solutions themselves. As I shared the pH solutions with several other groups it is impossible to guarantee that there was absolutely no mixing of the different solutions due to inadequate procedure knowledge by other people. Some pipettes were used to gather the solutions and this will have altered the effects of the mixing even more.
I could have avoided this problem by having an exclusive set of solutions for my group, but if done, the effects would be also negligible.The main factor that I think caused the atypical set of results for pH buffer compared to water, are the buffers themselves. As I have stated before, buffers are made using different chemicals. I believe these chemicals have a detrimental effect on germination and are therefore providing different information if pH set water was used instead.
To extend this investigation I would try to research the effects of pH on germination. If possible, I would try to find alternative ways of changing the pH of a solution without germination suppressing chemicals. I could also find out about the effects of temperature and density on germination.