Effects of coffee and caffeine on the growth of plants

Use of tea grounds for the growth of plants is a common practice in horticulture. Tea contains tannic acid and many other nutrients. When added to soil, they decompose to liberate many useful organic compounds which are essential for the growth of plants. Coffee is used as a fertilizer in kitchen gardens and I wanted to check the extent to which growth of plants is affected by the presence of coffee in the soil. I will be comparing the growth in the presence of coffee and the growth in presence of pure caffeine to check whether only caffeine stimulates the plant growth or other factors of the coffee also help stimulate growth within plants. Caffeine has been reported to be a potential stimulant for both central nervous system and cardiac system. It has an ability to prevent cancer caused by the carcinogens present in environment and foods. Mutagenic potential of caffeine has also been proved against bacterium E. coli. It has also been found to show a major synergistic effect in mutation of chromosomes. Effect of caffeine on the quantitative and qualitative parameters of plant has been a significant area of research. The current investigation deals with the study of effect of caffeine on the growth of plants. Thus, I have decided to narrow down my Internal Assessment in Biology based on the research question stated below-

How do different concentrations of 1,3,7-Trimethylpurine-2,6-dione (caffeine) and Coffea (coffee) (0.3%,0.6%,0.9%,1.2%,1.5% and 1.8%) effect the root growth in the plant Vigna radiata?

Vigna radiata is a widely grown plant. This plant is germinated overnight and then eaten. People generally refer Vigna radiata to green gram and sprouts. Green gram is very good for human health if consumed directly after germination when it has sprouted a radicle. Green gram is very rich in protein and other nutrients and also is a powerful antioxidant and is also rich in nutrients and protein. This particular plant belongs to the category of legume because of which they contain bacteria in their roots. This bacteria fixes the free nitrogen from the atmosphere into nitrogenous compounds in the plant body through the process of nitrogen fixation. Apart from a rich source of protein for vegetarian diets, it is also the source of trace amounts of Riboflavin, Vitamin-C and thyamine. It can also be used as a manure crop and a cattle feed.

Coffee is a widely used stimulant for human beings. It is used especially by people who have stress and long working hours. The component in coffee that helps people keep awake and calm their nerves is caffeine. Caffeine is naturally found in coffee in small amounts. Coffee is acidic in nature and contains nutrients like phosphorous, nitrogen and potassium. Coffee has its benefits to humans and has shown to have positive impacts on the growth of plants too. Coffee stimulates shoot and root growth in plants. Coffee grounds are a very rich source of Potassium, Phosphorous and Nitrogen for the plant. Phosphorous is very useful in the maturation process of the plant. Due to the presence of excess phosphorous the cells in the root of the plant there is a higher rate of cell division and the size of cells is larger. These effects of coffee are the reason for longer shoot and root growth. The coffee tree belongs to tropical evergreen shrub in the genus Coffea. It is mainly found in the regions of Tropics of Cancer and Capricorn. The main varieties are - Coffea arabica (Arabicas) and Coffea canephora (Robustas). One cup of coffee is reported to contain around 180 mg of caffeine. For an adult, it is safe to consume around 200-300 mg of caffeine per day. Decaf coffee is another variety of coffee which contains much less amount of caffeine in comparison to normal coffee. A cup of decaf coffee contains 7mg of caffeine in comparison to 70-80 mg of caffeine in a normal cup of coffee.

1,3,7-Trimethylpurine-2,6-dione also known as caffeine in its pure form is a white powder. Pure caffeine has antibacterial properties. When coffee leaves fall to the ground they release caffeine as they decompose and the caffeine which is released acts like a natural pesticide to some of the insects. Caffeine is also very slightly basic in nature. Pure caffeine can also be used by humans as a stimulant by mixing with water to boost body processes to make people feel more alert and awake.

The independent variable of the investigation is the concentration of coffee and caffeine used during the growth of the plants. The concentration chosen were - 0.3%,0.6%,0.9%,1.2%,1.5% and 1.8%. The solutions were prepared by adding the requisite amount of solid in distilled water within a glass beaker. A 30% stock solution was prepared by adding 30 g of solid coffee powder and caffeine in 100 cc of distilled water. The other solutions were made by dilution of this stock solution. A research article- Caffeine: The Allelochemical Responsible for the Plant Growth Inhibitory Activity of Vietnamese Tea (Camellia sinensis L. Kuntze) reported that growth of plant (red clover) was inhibited by 1.00% by caffeine solution while 0.50% solution has been proved to be effective. Thus, the concentration range of this investigation has been kept within the range of 0.30% to 1.80% so that it also gives us an idea about the effect of the concentration both below and above the permissible range. A very high concentration could lead to possible stunting of the growth of the plant.

The dependent variable is the shoot growth because the coffee provides the nutrients like phosphorous which help with the maturation of the plant and increased growth in root. The caffeine prevents the plants from getting infected and boosts the growth due to its ability to stimulate the body processes. We take shoot (radicle) length because in seeds that is the first part to come out. The shoot is most affected by different factors and root helps absorption of nutrients and grows extremely fast in the initial stages and so it is easy to measure using a ruler.

30.00 ± 0.01 g of caffeine powder was weighed on a watch glass placed over a digital mass balance using a spatula to transfer the solid to the watch glass. The exact mass of the solid was transferred to a 250 cc glass beaker and dissolved in 100 cc tap water. A graduated measuring cylinder was used to transfer tap water to the beaker. 1.00 ± 0.05 cc of this stock solution was transferred to a 100 cc reagent bottle using a graduated pipette and diluted to 0.30% by adding tap water. The other solutions of caffeine were prepared in the same method. 2.00 ± 0.05 cc, 3.00 ± 0.05 cc, 4.00 ± 0.05 cc, 5.00 ± 0.05 cc and 6.00 ± 0.05 cc of the stock solutions were diluted to 100 cc in a reagent bottle to prepare 0.60%, 0.90%, 1.20 %, 1.50% and 1.80% solutions respectively.

The same process was followed to prepare coffee solutions of the same concentration.

• Seeds of Vigna radiata were soaked overnight in water to start the germination process.

• After preparing different concentrations of coffee and caffeine 2 petri plates per concentration were taken for each concentration including three for water (0.0%) which represents our control solution.
• In each petri plate 15 cc of their respective solutions were added to each petri dish using a measuring cylinder. The solution was soaked in cotton plugs and kept within the petri dish.
• Five germinated seeds were then added to each petri dish. A total of 140 seeds and 28 petri plates were used in total.

• The plants were let to grow for 5 days and measurements of the length of the roots were measured at the end of five days using a ruler.
• The results were taken down and average for every concentration of coffee and caffeine were taken.

• The use of safety gloves to avoid direct contact with caffeine as it is a possibly addicting substance and can impact body if ingested.
• Use of mittens to move the hot beakers containing boiled coffee grounds. Mittens help avoid burning of skin as beaker can be hot after preparing coffee.
• Use of mittens to move the hot beakers containing boiled coffee grounds. Mittens help avoid burning of skin as beaker can be hot after preparing coffee.
• The use of lab coats as the stain of coffee is very tough to get rid of and can be permanent.
• Use of a well ventilated area or an area with an exhaust to remove fumes produced during boiling coffee and caffeine.

For control (0.0%)

Average length of root = \(\frac{4.10\ +\ 3.30\ +\ 4.30\ +\ 3.00\ +\ 3.30\ +\ 3.70\ +\ 3.60\ +\ 3.00}{8}\) = 2.83 ± 0.05cm

Standard deviation (SD) = \(\frac{(4.10-4.63)^2+(3.30-4.63)^2+(4.30-4.63)^2+(3.00-4.63)^2+(3.30-4.63)^2+(3.70-4.63)^2+(3.60-4.63)^2(3.00-4.63)^2}{8}\) = 1.47

The readings highlighted in red are anomalous and thus discarded.

The scattered plot above depicts the variation of mean length of root of the plant against the concentration of caffeine solution used. The mean length of the root has been plotted along the y axes as it is the dependent variable while the % concentration of caffeine solution along the x axes as it is the dependent variable. As it is visible from the graph, there is a gradual increase in the root height from 3.56 ± 0.05 cm to 5.73 ± 0.05 cm as the concentration of caffeine increases from 0.3% to 1.5%. At the concentration of 1.8%, the mean height is found to decrease to 4.55 ± 0.05 cm. The data displayed here are in support of the literature references mentioned. 0.5% to 1.5% is found to be the optimum range for the growth while the growth is found to be inhibited beyond that.

There is an initial increase in the growth of the plants with both coffee and caffeine till the concentration of 1.5% after which there is a decline to the 1.8%. This shows that both coffee and caffeine do boost growth of plants to some extent after which the act as inhibitors. The graphs show that there is more growth in the plants with coffee solutions than in caffeine solutions. The roots grew longer in coffee and caffeine solutions than in control. 0% coffee and caffeine solutions grew lesser than 1.5% coffee and caffeine solutions. The error bars for coffee are very big showing that variation in the plant lengths for coffee in the plants was a lot whereas the error bars for caffeine are smaller showing that lengths of plants are more or less similar and closer to each other. The overlapping error bars show that there is a possibility that lengths of some coffee plants of the plants could range down to the lengths of the caffeine plants and vice versa.There is an initial increase in the growth of the plants with both coffee and caffeine till the concentration of 1.5% after which there is a decline to the 1.8%. This shows that both coffee and caffeine do boost growth of plants to some extent after which the act as inhibitors. The graphs show that there is more growth in the plants with coffee solutions than in caffeine solutions. The roots grew longer in coffee and caffeine solutions than in control. 0% coffee and caffeine solutions grew lesser than 1.5% coffee and caffeine solutions. The error bars for coffee are very big showing that variation in the plant lengths for coffee in the plants was a lot whereas the error bars for caffeine are smaller showing that lengths of plants are more or less similar and closer to each other. The overlapping error bars show that there is a possibility that lengths of some coffee plants of the plants could range down to the lengths of the caffeine plants and vice versa.

A T-test is a statistical analysis performed on results to be able prove the significance of our results and checking the validity of our hypothesis. In this case the analysis is going to be performed on caffeine and coffee and compare their results to the control. I will be using the t-test to show that the data I have from my experiment is valid. I will also use this test to prove that the data is valid despite the large and overlapping error bars.

Null hypothesis (H0):

There is no significant difference between the growth of plants in between coffee and caffeine Alternate hypothesis:

H1: There is a positive correlation between the growth of plants and the % concentration of coffee and caffeine solutions used.

H2: There is a negative correlation between the growth of plants and the % concentration of coffee or caffeine solutions used.

As seen in Figure - 13 and Figure - 14 , the calculated value of t value exceeds the critical value (p value) which means that for both independent t tests of coffee versus control and independent t tests for caffeine versus control, it is evident that there is a significant statistical difference between the growth of plants in presence of coffee or caffeine and in absence of it. Thus, we can claim that presence of coffee or caffeine has a significant impact on the growth of plants. Thus, the null hypothesis is rejected and the alternate hypothesis is accepted. If we consider Figure - 10 and Figure - 12 along with the results of the statistical test, we can claim that till 1.5% the concentration of coffee or caffeine solution used has a positive impact on the growth of plants while beyond it, the growth gets inhibited. Thus, both the alternate hypothesis (H₁ and H₂) are accepted.

The null hypothesis stated that Coffee and Caffeine will have no effect on the growth of the plants. The alternate hypothesis stated that Coffee and caffeine will initially increase the growth of the plant to some extent. The results support the alternate hypothesis. According to the graph, the growth in plants increased till concentration 1.5% and then reduced. The processed data table shows the trend in the length of the roots of Vigna radiata. With increasing concentrations the length of the roots also increases. The relationship between my independent and dependent variables is weak positive till 1.5% and then weak negative. The optimal growth is at 1.5% of both coffee and caffeine. The presence of nutrients, antibacterial properties and stimulating effect of coffee and caffeine on Vigna radiata should increase the growth as coffee and caffeine stimulate cell division, the antibacterial properties of coffee grounds prevent disease helping plants grow and the nutrients in coffee and caffeine help the plant to be nutrient rich and increase the growth rate of the plant in the root and the shoot.

The results obtained during the experiment are comparable to the control. The use of dilute concentrations of my solutions helped boost the growth of the plants. The growth in the plants was boosted using coffee and caffeine solutions. The plants grew till the 1.5% concentration and then stopped growing for both coffee and caffeine. The growth in caffeine was more than the growth in coffee solutions, although the growth in both solutions was comparably larger than the control setup. The root lengths were measured because radicles are the first part from a seed which is visible. The coffee solution helps the plant grow because it contains nutrients like phosphorous, nitrogen and potassium. Phosphorous is important in plants because it promotes cell division by helping in complex energy transformations during cell division. The nitrogen is also important because it helps in amino acid production and formation of proteins to help the plant grow faster. Nitrogen is also an important part of chlorophyll in the leaves and helps leaves trap sunlight and grow. The potassium helps keep the internal conditions of plants constant. The potassium helps keep the plant cells in an isotonic condition helping control entry of water and nutrients in and out of cell. Caffeine can help boost root growth because it has antibacterial properties which helps the plants grow better and prevents bacteria from stunting plant growth. Caffeine also acts like a pesticide for some insects keeping the plants safe from insects. Stimulating properties of caffeine such as boosting metabolic processes helps with boosting the growth of the roots.

• The quality of the experiment have been improved by taking more precautions making the experiment more accurate and improving the reliability of the results.
• Anomalous data in the experiment was chosen by looking at values that seem to have an extreme range and did not seem to fit into the shoot lengths. The anomalous data has been highlighted in the raw data table.

• The length of the roots has been measured with a ruler. There is a chance of reading the ruler at an angle leading to parallax error which will reduce the accuracy of the investigation. To avoid this, the ruler must always be kept at the eye level.
• The type and amount of soil will have an impact on the growth of the plant. Thus, variations in the type and mass of soil used will interfere with the growth of soil. To combat this source of systematic error, the seeds were grown in petri dish with the cotton soaked in solutions. Thus, use of soil was avoided to discard the other factors that could arise due to the presence of variation of nutrients.
• Intensity of light and temperature are important factors for the growth of plants. Both of these are limiting factors for the growth of plants. Thus, these two factors were not controlled. Again, it must be noted that how can we ensure that all plants have received the same intensity of light. Moreover, the study was conducted over a time period of 5 days and hence there is unavoidable variation of temperature for these days. This can be fixed by carrying out the investigation in potted plants and storing the pots in an incubation chamber where temperature can be controlled. To sort out the variations of light intensity, the position of the plants were changed at regular intervals so that all of them receive the same intensity of light.

For further investigation I would like to find how different daily use house hold effects affect the growth of plants in the garden. Plotting the graph to compare the growth of plants in household substances will help us see which of the substances are most harmful to the environment and should not be directly discarded into the garden. Substances which are extremes of pH will be more harmful to the plants than neutral substances. The neutral substances which are rich in nutrients and minerals is more likely to promote growth.

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