Investigating a pollutants effect on cress seeds Essay Example

Investigating a pollutants effect on cress seeds Paper To investigate the effect of phosphates from detergent liquid, at different concentrations, on the germination of cress seeds. Hypothesis: I predict that, at lower concentrations, the detergent liquid containing phosphates will have a small positive effect on growth. However, I believe at stronger concentrations, the detergent liquid will have a negative effect on growth, causing stunted and malformed cress plants. Introduction: Many commercial detergent liquids contain phosphate. Phosphate, (PO43-) is an important inorganic macronutrient which is needed to help plant growth, and as such is a part of the essential small molecule ATP. Although it can be hard to test whether minerals are important in animals, it is far easier to test the effects of phosphate (which in this case will form part of a pollutant). The main reason for my hypothesis is that phosphates can cause eutrophication when found in a water supply, and as such I believe that small percentages (10-20%) detergent liquid will case minor positive changes in growth. However, there are other chemicals present (such as Benzotriazole, colorants and purfumes) in detergent liquid that may cause the cell wall and cell membrane of the cell to break down allowing the cell contents to spill out and the leaves will appear discolored. This may also cause the cress to grow slowly or die prematurely. There may also be an appearance of leaf tip necrosis, iron deficiencies, and some seeds may fail to germinate due to imbalances in the pH of the soil. You dont say why there may be a pH imbalance. We will write a custom essay sample on Investigating a pollutants effect on cress seeds specifically for you for only $16.38 $13.9/page Order now We will write a custom essay sample on Investigating a pollutants effect on cress seeds specifically for you FOR ONLY $16.38 $13.9/page Hire Writer We will write a custom essay sample on Investigating a pollutants effect on cress seeds specifically for you FOR ONLY $16.38 $13.9/page Hire Writer Cress is a seed which is exceptionally easy to cultivate, and as such will be the plant used for my experiment. Germination in plants occurs when there are suitable conditions. Germination requires water, oxygen and an appropriate temperature. Water is necessary because the final stage in the creation of a seed is a drying out of embryonic tissues. This means that a huge inward water gradient is created, allowing easy osmosis into the seed. Seeds typically absorb so much water that they swell into 1.5 times the size of the seed (statistic taken from broad beans). This is obviously important in measuring the different growth patterns when using different concentrations of a pollutant, as my pollutant (as many pollutants are) will be found solely in the water source of the plant, and will thus have a great effect on a germinating plant. Plan: Some preliminary tests were carried out prior to the experiment to find the best medium for cress growth and the preferable environment for their germination. These are presented and discussed in my appendix, which is found below. This is the reason for using 2 layers of kitchen paper to grow my seeds in, as well as placing them by a large, light window. The aim of this experiment is to add variable concentrations of a phosphate containing detergent to cress seeds water supply and measure the effect upon their germination and growth. The independent variable used will be the detergent concentration and the dependent variables are percentage germinated and the growth rate. I will use a Spearman rank correlation test to determine whether these two variables are linked. Justifications I will be using pipettes and a pipette filler because these are more accurate than traditional pipettes. I require several different pipettes to ensure that each one is not contaminated with a previous concentration of liquid. I will be using tweezers to place my seeds in the grid as these allow me to grip and place my seeds accurately. I plan to repeat each experiment (to obtain two results for each value). This is to restrict the chances of a faulty result skewing results. Ideally, I would repeat these tests many times, but as the experiment is quite slow, and placing too many petri dishes by my window might obscure the light available, Ive decided upon two results. The seeds will be grown for 7 days as my preliminary tests show that 7 days is perfectly adequate time for the cress seeds to germinate and grow to a measurable length. I plan to use cress seeds from the same packet throughout my experiment, as cress seeds found in different places may have different resistance to phosphates. This is because the detergent I am using may have been present in an irrigation system used to when the seeds were produced, and thus using a mixture of seeds would give a mixture of tolerances against phosphates. I plan to use the same amount of liquid throughout my experiment (20ml initially) as using varying amounts may affect my results. This is because plants need water to grow, and thus those with access to more water will probably grow both faster and further than those with less water. It is thus important to keep them as constant as possible. I have chosen to use 50 seeds at each concentration. This will reduce the chance of a percentage error. If using 10 seeds and one fails to germinate, this will be a 10% percentage error, whereas if one fails to germinate with 50 seeds, this gives only a 2% percentage error. This is a simple and effective way of reducing the percentage error. Sufficient replicates to assess reliability of data. Issues highlighted by my preliminary experiments Considering the results of my preliminary tests, I will be growing my cress inside by a window so that it has plenty of access to light and warmth. I will be growing my cress in petri dishes on two circular pieces of kitchen paper. I will be covering each dish with a piece of transparent film slightly larger than the dish itself. This is because the kitchen paper tends to dry out quickly, which would obviously prevent germination and negatively effect plant growth. The reason for using a piece of transparent film is because this will let light through. I will not be sealing these, as this will prevent air getting to the cress, which it requires for growth. This method prevents the seeds from drying out too quickly, although I will still be watering them at intervals specified before. In my preliminary tests, I measured the seed growth by their length above the seed and root length. However, this may not be accurate as some cress seedlings may have longer roots, and longer roots also indicate growth. For this reason I have decided to measure the shoot and root length combined of my seedlings. Ensuring consistancy I need to ensure that the amount of liquid present stays constant, and thus need to ensure that the dilutions of detergent liquid have appropriate amounts of distilled water. I will be using 20ml of water for the control, and various concentrations made up to 20ml for the other experiments. I need to ensure that the environment of the plants stays as consistent as possible throughout the experiment, and thus need to choose a window with enough space beneath it to give equal light to all the plants. I need to ensure that the cress is spread in the same way in each experiment. To give maximum space to each seed, I have chosen the following layout: This gives me enough room for 25 cress seeds in each experiment. I will need to ensure that the temperature around the petri dishes is kept constant between all petri dishes, as an inconsistency will have a small effect on growth. To do this, I shall measure the temperatures near each dish twice daily and record and adjust any anomalies. The petri dishes will need to be clearly labeled with concentration and experiment number (either 1 or 2) so as to avoid confusion when collecting results.