Biology has always been one of my favorite subject as it provides me an opportunity to explore the real life observations and aspires me in the medical field. Having a curiosity to interlink subjects and establish a coherence between them to predict, analyze and explain the facts we observe around us, I have always been more fascinated in studying the science from nature than doing it from empirical equations or theoretical discussions in a text book. In my chemistry classes, I learnt about the importance of controlling the pH of the soil for the adequate growth of certain plants. The discussion made in the class while studying this topic evoked me to explore more in this topic and study in details how the growth of plants are affected by the nature of the medium.
Is there any correlation between the nature of medium (acidic, alkaline and neutral) for the growth of pea plant (Pisum sativum) and its growth (vertical height, dry mass), determined using graphical analysis and one variable statistics?
The growth of a plant can be measured in various ways –
The current investigation deals with monitoring the growth of plants in terms of measuring vertical height and dry mass of the plant.
Plants require six critical conditions to optimize the growth –
Although the nature of the soil medium used (acidic or alkaline) or the pH of the medium to be precise does not control the growth of plants directly, it interferes with the availability of nutrients in the soil and the process through which it is absorbed by the root hairs.
The acidity or alkalinity of the soil do plays a major role in the growth of the plants. Although a pH range of 6-7 is an optimum range for the plants to grow yet there are certain plants which might grow well in a more acidic (pH lower than 6) or more basic (pH more than 7) soils. The value of pH of the soils do interfere with the availability of the nutrients in the soil which are essential for the growth of the plant. If a soil is found to be too acidic, liming reagents like CaCO3, MgCO3 are used to increase the acidity of the soil. Plant grown in too acidic region or too basic region suffers from iron chlorosis with a symptoms of yellowing in the leaves and wilting.
Most plants grows better in an optimum pH range of 6-7. Pea plant favors the growth in acidic medium as reported in literature. Any medium which is too basic or too acidic is not at all favorable for the growth of the plants. Hence pH =6 (6 moldm-3 HCl) , pH =8 (6 moldm-3 KOH) and pH=7(tap water as control medium) are used in this investigation.
There is no correlation between the nature of the medium and the growth of the plants.
There is a correlation between the growth of plants and the nature of the medium used.
Variable | Why was it controlled? | How was it controlled? |
---|---|---|
Type of soil | The growth of a plant depends on the nutrient amount and thus the type and the mass of the soil. | Same type of soil procured from a local nursery was used in all pots. |
Mass of soil | The same mass of soil was used as the pots where the plants were grown were of same size. | |
Intensity of sunlight | Sunlight can be one of the limiting factor for the growth of the plant. | All the plants were kept in the same place (near the window ) so that they receive enough and same amount of sunlight. |
Volume of water added | The volume of water controls the lateral as well as the mass gained by the plant. | Graduated measuring cylinder was used to control the volume of water added. |
Method of data collection | Changes in procedures to collect data incorporate random error and lack of precision. | The vertical height of all samples were measured using string and ruler and the dry mass was recorded using a digital mass balance. |
Investigations does not give rise to any ethical issues in context to designing and conduction.
Environment was not harmed in any way. Growth of plants is a carbon negative process and has thus contributes towards reduction of CO2 level in the atmosphere.
Preparation of 6moldm-3 HCl
Concentration of stock solution (C1) = 11 moldm-3
Concentration of final solution (C2) = 6 moldm-3
Volume of final solution to be prepared (V2) = 500 cm3
C1V1 =C2V2
(11 × V1) = (100 × 6)
\(V_1 = \frac{(100 × 6)}{11} = 54.5 \)
A clean and dry 100 cm3 of volumetric flask was taken and 30 cm3 of distilled water was transferred to it using a graduated measuring cylinder, 54.5 cm3 of concentrated HCl (11 moldm-3 ) was transferred to the same flask using a 10 cm3 graduated pipette. Distilled water was added till the mark, the lid of the flask was closed and shaken to make it a homogenous solution. The pH of the solution was checked using a pH meter and found to be 6.
Preparation of 6 moldm-3 KOH
Molar concentration = 6 moldm-3
Volume = 100 cm3 = ( 100/1000) dm3 = 0.1 dm3
Mass of KOH = number of moles X Molar mass = (Concentration X volume ) X Molar mass = (6 X 0.1 ) X 56.10 = 33.660 g
33.660 g of solid KOH pellets was weighed on a watch glass using a spatula on a digital mass balance. The weighed solid was transferred to a clean and dry 100 cm3 volumetric flask using a funnel and distilled water was added till the mark. The lid of the flask was closed and shaken upside down to dissolve the solid.
9 seeds of pea plants were taken and soaked in 100 cm3 of normal and clean water taken in a 250 cm3 beaker. The seeds were left overnight for germination. 9 plastic cups of equal size were taken and filled up with the soil procured from the local nursery. The germinated seeds were planted within the soil in the pots. The pots were kept near the window so that they are exposed to enough amount of sunlight. The soil was watered using normal and clean water everyday twice for seven consecutive days. The investigation was started from the eigth day.
After the plant has been allowed to grow for seven days, the data recording has been started.
A string was taken and aligned from the border of the container to the tip of the stem to measure the vertical height of the plant. The string was placed against a ruler to record the vertical height of the plant. The recording was noted down in a tabular form. This action was continued on every alternate days. The 9 pots were divided into three sets – each set having three pots. The pots were labeled as A-1,A-2 and A-3 (in acidic set), B-1,B-2 and B-3 in basic set and N-1,N-2 and N-3 in neutral set. The plants in set 1 was (acidic set) was watered with 6 moldm-3 HCl, the plants in basic set was watered with 6 moldm-3 KOH and the plants in neutral set was watered with normal tap water. The same apparatus ( a 100 cm3 glass beaker ) was used to water the plants. The volume of water added was kept same. 20 cm3 of water was added to each of the pots everyday. The volume of water added was controlled using a graduated measuring cylinder. The whole process was continued for 21 days.
At the last day of the investigation, the soil was removed off carefully around the roots without tampering the roots in any way. The plant was uplifted from the pot. The clump of soil adhered to the roots was washed off carefully in gentle stream of tap water and the dirt from the leaves and branches were also washed off in the same way. The plant was kept overnight in the hot air oven (at 600C) to loss the moisture content of it and allow it to dry. The dried plant was weighed on a digital mass balance and the mass was noted down.
Sampleno. | Acidic medium | Basic medium | Neutral medium |
---|---|---|---|
1 | 3.201 | 2.201 | 2.876 |
2 | 3.302 | 2.202 | 2.879 |
3 | 3.209 | 2.210 | 2.768 |
Average | 3.237 | 2.204 | 2.841 |
For sample- 1 -
Initial height = Height of the plant on Day-1 = 2.3 cm ± 0.05
Final height = Height of the plant on Day-21 = 3.5 cm ± 0.05
Difference in height = Final height – Initial height = ( 3.5 – 2.3 ) cm ± (0.05 + 0.05) = 1.2 cm ± 0.1
Mean difference of three samples -
\(Mean = \frac{(1.2+1.3+1.3)}{3} = 1.3 \, \,cm\)
The maximum achieved by the plant has been considered as the final height as the plants did not survive till 21 days.
Type of medium | Mean difference in height in cm / ±0.1 |
---|---|
Acidic | 1.3 |
Basic | 0.1 |
Neutral (Control) | 0.9 |
The bar graph plotted above clearly depicts the variation in the growth of the plant in terms of vertical height in various medium. A clear difference has been observed between the growth of plants in treated and untreated soil. It is observed that the growth of plants is more in acidic medium than in neutral medium and less in basic medium it is less.
In acidic medium, the change in vertical height of the plant is 1.3 cm for 21 days while in basic medium it is 0.1 cm for 21 days. The growth in acidic medium is around 13 times more than that in basic medium. The growth in basic medium is around 9 fold less in basic medium than in neutral medium. This set of data collected shows that the growth of plants is most favored in acidic medium and least favored in basic medium while it is moderate in the neutral medium.
To express the relationship or correlation between the type of medium and the vertical height of the plants, the pH of the medium is reffered to. The pH of the acidic medium is considered to 6 as 6 moldm-3 of HCl has been used while the pH of the basic medium is considered to be 8, as 6 moldm-3 of KOH is used. Kindly refer to the appendix for the pH calculations. The pH of the neutral medium (tap water) is considered to be 7. Thus to express qualitatively, we may say that the growth is most favored at pH=6 and least favored in pH =8. Thus as the pH of the medium decreases from 7 (tap water, control ) to pH=6 (acidic medium), the change in vertical height increases from 0.9 cm to 1.3 cm. So, a decrease in pH by one fold increases the growth by four fold. Again as the pH changes from 7 (tap water, control) to pH =8 (basic medium) the change in vertical height decreases from 0.9 cm to 0.1 cm; it means that increase in basicity of the medium by one fold decreases the height of the plant by 9 folds.
Thus it is also conclusively shown that the growth of the plant is more affected and significantly correlated to the alkalinity or the basicity of the medium and less significantly affected by the acidity of the medium as the increase in growth of plant due to change of the medium from neutral to acidic is higher than the decrease in growth of plants due to change in medium from neutral to basic.
The above graph clearly shows the effect of nature of the medium on the dry mass of the plant. The trends or pattern noted has similarity the one in observed while comparing the vertical height of the plant. The increase of dry mass is most in acidic medium and least in the basic medium. The dry mass is acidic medium is 3.237 g while that in neutral medium (control) is 2.841 g. So the dry mass of the plant increases by (3.237-2.841) = 0.396 g while the medium is changed from neutral to acidic. The dry mass of the plant in basic medium is 2.204 g while that in neutral medium is 2.841 g. Thus the dry mass of the plant is decreased by (2.841 – 2.204) = 0.637 g when the medium is changed from neutral to basic.
In similarity to the analysis of the effect of acidity or basicity on the vertical growth of the plants, it is observed that alkalinity of the medium has a major impact on the dry mass in comparison to acidity.
Null hypotheses -
There is no correlation between nature of the medium and the increase in vertical height of the medium.
Alternate hypotheses -
There is a correlation between nature of the medium (expressed in terms of pH) and the change in vertical height of the plant.
As the samples were chosen following a simple random sampling and the data were presented in a categorical table, the chi square test of independence is an appropriate one variable statistical approach to this case. The chi square test was conducted at a significance level of 95%, α = 0.05
Medium(pH) | Sample-1 | Sample-2 | Sample-3 | Row total |
---|---|---|---|---|
Acidic (pH=6) | 1.2 | 1.3 | 1.3 | 3.8 |
Basic (pH=8) | 0.2 | 0.1 | 0.1 | 0.4 |
Column total | 1.4 | 1.4 | 1.4 | 4.2 |
Degrees of freedom (DF) = (r-1 ) * (c-1 ) = (2-1)*(3-1) = 1*2 = 2
n = (3.8 + 0.4) = 4.2
\(Ei , j = \frac{n_in_j}{n}=\frac{3.8×1.4}{4.2}= 1.27\)
With two degrees of freedom, at α = 0.05 , the critical value of chi square statistic = 0.103 As the calculated value of chi square statistic (0.055263) is less than the critical value of chi square statistic (0.103), the null hypotheses cannot be rejected and it thus concludes that we cannot confirm the correlation between the nature of medium and the vertical height of the plant.
The basic aim of the investigation was to address the following research question-
Is there any correlation between the nature of medium (acidic, alkaline and neutral) for the growth of pea plant (Pisum sativum) and its growth (vertical height, dry mass), determined using graphical analysis and one variable statistics?
The investigation conducted can be extended further to study how the correlation varies with other species of plants. We can also vary other conditions like temperature, nature of fertilizers used apart from nature of medium to have a detail idea about the optimized conditions for the growth of the plant.