Effect of acidity, alkalinity & neutrality of the medium on the growth of plants

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 –

• Recording the time in terms of number of days from planting the seed to the emergence of the first cotyledon.
• Calculating the percentage of seeds which germinates under the specified conditions.
• Measuring the number of leaves appearing in the plant.
• Measuring the surface area of the leaves.
• Measuring the vertical height of the plant
• Measuring the dry mass of the plant.
• Measuring the ratio of the height of root and shoot.

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 –

• Temperature
• Moisture
• Carbon dioxide
• Water
• Sunlight
• Nutrients

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.

• The major reasons to justify the choice of pea plant for the investigation are-
• These are easily available and reproducible.
• They have a short life cycle.
• They can propagate easily and have several observable traits like seed color, height, flower position, stem height and many more.
• As the flowers in pea plants are not of a regular shape and the top part of the corolla is much larger than the lower part, they can undergo self pollination.

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.

• Protective clothing was used.
• No chemicals were ingested or exposed to skin.
• The workstation was always kept organized and clean.
• Apparatus were handled carefully.

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.

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.

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.

• The seed coats were cracked and growth of radicles were noted during germination of the seeds.
• With the progress of time, growth of branches and leaves were noted indicating the lateral growth of the plant.
• The plants potted in basic medium turned yellow and stopped growing after 2 weeks.