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How is the height of growing Garden cress (Lepidium sativum L.) affected by the level of pH in the water given to the plant? -Biology-

Candidate number: XXX IB14 Katedralskolan Skara

Introduction: A common plant called Garden cress (Lepidium sativum L.), will be the plant used in this lab. This type of cress is a leafy vegetable, which leaves are edible. Garden cress belongs to the family of Brassicaceae.1 It is popular to grow in homes as it is so easy to germinate. Approximately 10 days is needed for fully growing the plants. Although Garden cress is easy to grow, they still prefer a certain environment. Therefore, pH-environment is essential to its growth. PH determines how acidic or basic a solution or substances is. The pH-scale goes from 0 to 14. From 0 to 7, the acidic values are found and from 7-14 on the scale, the basic values are situated. 7 is a neutral value.2 This lab is going to investigate how different pHenvironments affect garden cress. 250 seeds will be planted and distributed between 5 different pH-values; 3, 5, 7, 9 and 11. This lab is important because seeing the effect of different pH on a common plant such as cress, can give us better understanding about how pH effects nature as a whole. Pollution affects pH values in nature, which may lead to the extortion of certain wildlife species. Therefore, studying the effect of pH on common plants is important also because if we have better understanding of the effect of pH and in extension, pollution, we have a better chance of impeding the destruction of wildlife. As this experiment examines how different pH-environments in the water given to Garden cress affects which height it grows to, the question of how pollution affect and change the water resources of the world, is of great interest and importance. There are a number of things which occurs in nature that have an impact on the pH of the waters. One of them is calcium carbonate. It is a substance which is often found in limestone as minerals.3 Calcium carbonate is able to combine with hydrogen or hydroxyl ions, which can alter the pH in the water. When these minerals are present, the pH will not change too much due to the alkalinity of calcium carbonate. We say that this kind of water is buffered.4 If water is alkaline, it is able to resist alterations in pH, something which is positive for the environment as it hinders sudden fluctuations in pH-environment.5 But, there are however other things in nature which performs the exact opposite of keeping the pH under control. An example of this is decomposing. During the different seasons, leaves, pine needles and such will fall to the ground and be decomposed. They are slightly acidic and should they fall into the water, or be led to the water through the soil and streams, the can lower the pH of the water. The same is accurate for unpolluted precipitation, which is also slightly acidic.6 These factors are matters which occur naturally, and little can be done about them. There are however, things which affects pH-levels in water that humans have control over, and thereby also possess the ability to change. There are some main things caused by humans which alter the pH in nature. Three of these are acid rain, point source pollution and mining. Sulphuric acid and nitric acid are produced by the coal mining burning industries and automobile engines, respectively. These 1 Naturhistoriska Riksmuseet, last modified August 7, 2000, http://linnaeus.nrm.se/flora/di/brassica/lepid/lepisat.html 2 Fundamentals of environmental measurements, no date, accurate at May 4, 2016, http://www.fondriest.com/environmental-measurements/ 3 “Geology.com”, no date, accurate at May 17, 2016, http://geology.com/usgs/limestone/ 4 “Utah State University Extension”, no date, accurate at May 17, 2016, http://extension.usu.edu/waterquality/whats-in-your-water/ph 5 “Water research centre”, no date, accurate at May 1, 2016, http://www.water-research.net/index.php/therole-of-alkalinity-citizen-monitoring 6 “Utah State University Extension”, no date, accurate at May 17, 2016, http://extension.usu.edu/waterquality/whats-in-your-water/ph

two are the main contributors to the acid rain which lowers the pH in water and soil.7 Point source pollution is caused by humans getting rid of industrial pollutants by releasing them into water. This affects the pH values in the water and in extension, it can cause alterations of the chemicals in the water. It may also dissolve heavy metals in the water, which can become toxic. The alterations of pH can lead to that the species living there are at danger, as their optimum environment has suddenly changed and given them little time to adjust.8 Lastly, drainage from mining can add acid to waterways and change its pH.9 Having listed these different pH-altering factors that are man-made, it is easy to realize that the nature has a built in defense mechanism, and things that are harmful, but occur naturally, are things it can fend itself from, whereas the pollution that humans create, is something nature cannot withstand in the long run. Most species have an optimum pH-environment, as does Garden cress, the plant to be examined in this lab. PH also have a big impact on enzymes. Enzymes are used as catalysers, which are found within a plant cell and all enzymes all have a particular shape, depending on their type. The enzymes are crucial to the plants metabolism, as they help speed up and make reactions occur. Had there been no enzymes, an organism would have to rely on mostly chance in order for molecules to collide and create a powerful enough reaction to produce energy.10 So, as the enzymes are vital to a plant cell, it is essential that nothing disturbs their work. But, pH can actually do just that. When the pH of a cell changes from its optimum pH, the enzymes in that cell can become denaturated. That means that they will lose their shape, and thereby also their properties as an enzyme.11 In the worst case scenario, that may lead to the death of the cell and in extension, the organism. As we know the impact that pH can have on plants, it is important to start looking for solutions to the problem. A start can be to gain more knowledge about the problem by performing labs such as this one and document how it affects different species, such as Garden cress. That is what this experiment aims to achieve.

Research question: How is the height of Garden cress (Lepidium sativum L.) affected by the level of pH in water?

Variables: a. Independent Variable: The level of pH in the water given to the plants (pH 3, 5, 7, 9, 11). The level of pH will be controlled using two separate pH meters to ensure that the desired level is as accurate as possible. The solutions will then be kept in separate bottles. It is essential that the pH levels are measured precisely and are correct. The entire experiment aims 7 “Utah State University Extension”, no date, accurate at May 17, 2016, http://extension.usu.edu/waterquality/whats-in-your-water/ph 8 Ibid 9 Ibid 10 “Encyclopaedia Britannica”, last modified April 7, 2016, http://global.britannica.com/science/protein/Enzymes 11 “Worthington Biochemical Corporation”, no date, accurate at May 17, 2016, http://www.worthingtonbiochem.com/introbiochem/effectsph.html

to investigate how different pH levels affect the growth of cress, and if the pH-values are not exact measurements, then the results will not be 100% accurate. b. Dependent Variable: The height of the Cress (measured in cm). The height of the cress will be measured 10 days after they were first planted. A ruler (300 millimetres) will be used for the measuring. Correct measurements are important as they make up the results of the lab and should they be inaccurate the results will be as well. c. Controlled Variable (constant): The amount of water given to the plants (15 drops per day), amount of sunlight, the temperature and the same amount of space to grow in. The amount of water given to the plants will be measured with the help of pipette. This device will ensure that the drops being released onto the plants will be of equal size and that they will also be easy to count. The five flasks containing the different pH-levels (3, 5, 7, 9, and 11) will from the beginning all have 100 millilitres of water in them, excluding the Sodium hydroxide and Hydrochloric acid added later. It will be made sure that the same amount of water is left each bottle after all plants being watered. This will help control that all plants are given the same amount of water. This is important as firstly, the amount of water given to the plant will affect the rate of photosynthesis. Therefore the plants must all be given the same amount in order to ensure that they are equal. It is also important because if one plant is given more water, it will also be given a higher concentration of the pH they are watered with. The temperature must be controlled as well, to avoid fluctuations in temperature affecting the plants ability to photosynthesize and grow. This will be controlled using a room thermometer being regularly observed. The temperature will never go below 20 degrees Celsius and it will never go above 24 degrees Celsius and thereby the temperature will be kept constant. The heat will also be evenly distributed between the plants as they will be kept on the same table in the same room. The sunlight has to be evenly distributed between the plants as also this has a big impact on the rate of photosynthesis. It will be regulated by the plants being kept at the same table in the same room as stated above. In order for every plant to receive the same amount of light, the cloth upon which they are placed will be turned clockwise once every evening so that all conditions will have had the opportunity to be closer to the window and further away.

Risk assessment: As basic and acidic substances are utilized in the lab, use a lab coat and safety goggles. Avoid any spill on exposed skin. Should exposed skin come in contact with any of the two substances, rinse thoroughly with water. Be careful to dissolve it in a few hundred millilitres of water before pouring it down the drain. This is a precaution made to ensure that there will not be any high concentrations of sodium hydroxide and hydrochloric acid released into the drainage leading to our natural water preserves as it is damaging to the wildlife and ourselves as it affects our drinking water.

Apparatus:               

25 ml of sodium hydroxide (NaOH) 25 ml of hydrochloric acid (HCI) 1 ruler (1 to 30 cm) 1 roll of masking tape 5 bottles (at least 100 ml) 25 Petri dishes 15 Paper towels 250 seeds of Garden cress 5 pipettes 500 ml of water 1 beaker (at least 200 ml) 2 beakers (at least 50 ml) 1 yellow marker 1 red marker 1 pair of scissors

Method: Preparing the solutions: 1. Pour 100 ml of water into a 200 ml beaker. 2. Put 2 pH-meters into the water. 3. Carefully add drops of the hydrochloric acid until you reach pH 3. 4. Repeat the process for pH-values; 5, 7, 9, 11 (for 7, 9, 11 add sodium hydroxide instead).

Experiment: 1. Cut out pieces of paper towels and place them into the Petri dishes.

2. Add 10 cress seeds to each Petri dish. 3. Supply all Petri dishes in the pH 3 condition with 5 drops of the pH 3 solution in the morning and 10 drops in the evening. 4. Supply all Petri dishes in the pH 5 condition with 5 drops of the pH 5 solution in the morning and 10 drops in the evening. 5. Supply all Petri dishes in the pH 7 condition with 5 drops of the pH 7 solution in the morning and 10 drops in the evening. 6. Supply all Petri dishes in the pH 9 condition with 5 drops of the pH 9 solution in the morning and 10 drops in the evening. 7. Supply all Petri dishes in the pH 11 condition with 5 drops of the pH 11 solution in the morning and 10 drops in the evening. 8. Repeat the watering-process each day for the next 10 days.

Raw data tables: The results of pH 3- environment on Cress:

The results of pH 5- environment on Cress:

The results of pH 7- environment on Cress:

The results of pH 9- environment on Cress:

The results of pH 11- environment on Cress:

Processed data:

Table showing the mean values of the results of each pH-environment:

Diagram showing the mean values for the results of each pH-environment:

Conclusion: By examining the results above, in particular the mean values shown in a table and a diagram, certain conclusions can be drawn. There is quite an obvious result portrayed among the mean values. The mean of all 50 seeds planted in pH-environment 3, turned out to be to 2.0 cm. That is the highest value among all five of the different conditions. The lowest mean height of the sprouts produced is situated in the pH 5 environment. That shows that the seeds thrived the most in pH 9 environment and the least in pH 5 environment. From that result the conclusion that Garden cress grows the best in a slightly basic environment, can be drawn. However, as pH 7 environment produced the second best result, one can also state that Garden cress can survive and germinate reasonably well in a neutral environment also. Another conclusion which may be drawn from the results of this lab is that pH does in fact have a very big impact on a plants ability to germinate.

Evaluation: When evaluating this experiment and the method through which it was carried out, one might say that it as a whole was to a large extent successful. To get a wider variety of results, one could have used more than 5 conditions, but still, 5 conditions was quite enough for extracting a good result. There were also no errors so big that the experiment failed to acquire a clear result. However, there were still some weaknesses observed. One weakness of this experiment is that a large part of the seeds did not even begin to germinate, possibly because of the age of the seeds or the environment in which they were stored prior to the experiment. Another weakness is that it is likely that there may have been fluctuations in temperature in the room which they were during the germination process, which could have influenced the growing cress in a negative way.

Improvements: In every lab, there are possible improvements. As the results of this lab gave some seeds which did not sprout at all, in each condition, there must be something which may be

improved. One reason for the some of the seeds in each condition not germinating properly could be the age of the seeds or the way they were stored. As many types of seeds need to be stored in a certain type of environment, while waiting to be planted, there is a possibility that the Cress seeds had not been stored as they ought to have been, and therefor did not grow not grow as well as they ought to have done. Things to think about when storing seeds is to never keep them somewhere which is either too hot or moist. Most types of seeds can withstand a few degrees below zero and still be usable.12 This could be seen as an improvement when repeating this experiment. Also, the seeds were kept by a sunny window, lined up 5 in a row, all 25 Petri dishes creating a quadratic shape. Each day the square of Petri dishes were turned clockwise once, to ensure that each Petri dish with seeds would get the same amount of sunlight. There is however no possible way for all the seeds to have gotten the exact amount of sunlight the way that they were placed. As the plants are autotrophs, they make their own energy. To do this, they are entirely dependent on sunlight, in order to carry out photosynthesis. The energy gained from the sun is absorbed by the pigment Chlorophyll which resides in all green plants and is converted into chemical energy. The energy created is vital for the plants metabolism.13 Therefore, we can conclude that if the plants have received different, all though small differences in sunlight, will have an impact on how much energy each plant produced and thereby how they grow. So, this can be seen as something which may be improved. A way to make sure that sunlight is distributed equally between each plant is to use artificial lights. Also, as they plants germinated in a regular home, they temperature is unlikely to have been kept entirely constant. Heat stress can have a great impact on a growing plant, as it can cause both physiological impacts and disturbances in the metabolism.14 Therefore, this is also a possible improvement. So, then one can conclude that the three main things which may be improved in this lab is distribution of sunlight, a more constant temperature and the storage of the seeds prior to the experiment being executed.

Bibliography:

Act for libraries.org, “How sunlight affects a plants growth”, http://www.actforlibraries.org/how-sunlight-affects-a-plants-growth/. (accessed at May 17, 2016). 12 Runåbergs Fröer, no date, accurate at May 16, 2016, http://en.runabergsfroer.se/?m=25 13 Actforlibraries.org, no date, accurate at May 17, 2016, http://www.actforlibraries.org/how-sunlight-affects-aplants-growth/ 14 Craita E. Bita and Tom Gerats, Plant tolerance to high temperature in a changing environment: scientific fundamentals and production of heat stress-tolerant crops, 4 (2013): 273, accessed May 17, 2016, doi: 10.3389/fpls.2013.00273

Arne Anderberg. “Den virtuella floran”, Naturhistoriska Riksmuseet, http://linnaeus.nrm.se/flora/welcome.html. (accessed May 4, 2016).

Brian Oram. ”What is alkalinity?”, Water research centre, http://www.waterresearch.net/index.php/the-role-of-alkalinity-citizen-monitoring. (accessed May 17 2016).

Daniel E. Koshland, “Enzymes”, Encyclopaedia Britannica, http://global.britannica.com/science/protein/Enzymes. (accessed May 17, 2016).

Fundamentals of environmental measurements, ”pH of water”, http://www.fondriest.com/environmentalmeasurements/parameters/water-quality/ph/. (accessed May 4, 2016).

Greta J. Orris, James D. Bliss, Timothy S. Hayes, “Limestone: A Crucial and Versatile Industrial Mineral Commodity”, Geology.com, http://geology.com/usgs/limestone/. (accessed, at May 17, 2016).

Utah State University Extension, “Water quality”, http://extension.usu.edu/waterquality/whats-in-your-water/ph. (accessed, at May 17, 2016)

Worthington Biochemical Corporation, “Introduction to Enzymes”, http://www.worthington-biochem.com/introbiochem/effectsph.html. (accessed at May 17, 2016)

Runåbergs Fröer, “Storage and Germination”, http://en.runabergsfroer.se/?m=25. (accessed May 17, 2016)

Craita E. Bita, Tom Gerats, “Plant tolerance to high temperature in a changing environment: scientific fundamentals and production of heat stress-tolerant”, National Centre for Biotechnology Information, http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3728475/. (accessed May 17, 2016)....