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Research Question

Research question

To what extent does the amount of sodium chloride added into soil affect the growth of corn during winter?

Aim

To investigate the effect of different concentrations of sodium chloride treatments on the growth of corn. Hypothesis

If the concentration of sodium chloride is increased then the growth rate of the corn plants will slow down or cause it to die because sodium chloride in plants disrupts transpiration and photosynthesis patterns by interfering with the plant’s nutrient uptake which is necessary for the development of the plant.

Justification of hypothesis

This is because sodium chloride prevents the process of osmosis happening which results in a less water and nutrient intake thus disrupting all other plant processes such as transpiration and photosynthesis which would stunt the growth of the plant and may result in the plant’s death.

Experimental overview

Corn which generally thrives during summer, was able to be grown over a period of over 2 weeks despite the season being winter. However, despite this off seasonal drawback in corn growth, Queensland is able to support corn growth due to its unusually warm climate during winter. The growth rate of corn was measured after different concentrations of sodium chloride was added.

1.0 Background research

1.1 Plant Morphology

Corn, scientifically known as Zea Mays is a photosynthetic eukaryotic plant classified under the Kingdom Plantae which comprises of a single stem called stalk which typically holds between 16-22 photosynthetic leaves which helps the plant with its respiration process and food production. A sophisticated root system (see Figure 1.) is responsible for taking up water and nutrients and anchors the plant to the ground. Zea Mays also consists of nodal roots and seminal roots which are important for the survival of the seedling as damage can stunt the plant’s development as the plant itself depends on the roots for its nutrients and water (thoughtco.com)

1.2 Photosynthesis

Figure 2.0- Labelled diagram of photosynthesis. (Socratic.org 2017)

The production of food is an integral part in determining the survival of a plant. Photosynthesis which is the process in which plants utilise the energy from sunlight, Carbon dioxide and water to produce oxygen and glucose. Figure 2.0 depicts a clear representation of photosynthesis. The leaves possess chloroplasts which have a green pigment called chlorophyll that absorbs light energy. Water and carbon dioxide too are absorbed which combine to make glucose with oxygen and water vapour being released. Figure2.1 depicts, specialised cells called phloem, transports the glucose into other parts of the plant such as the roots, stem thus repleting their energy levels necessary for plant growth and development (ucdavis.edu). Since water vapour is a product of photosynthesis, it can also be directly inferred that photosynthesis aids in the process of transpiration where water leaves the plant via the stomata. The glucose which is made by the process of photosynthesis can be converted into pyruvate which in turn releases adenosine triphosphate (ATP) by cellular respiration. Additionally to that, glucose can also be converted into chemicals such as cellulose required for plant growth (rsc.org)

The below equations depict the process of photosynthesis:

6CO2 + 6H2O C6H12O6 + 6O2

1.3 Cellular Respiration

Cellular respiration is the metabolic process in which sugars are broken down into nutrients such as adenosine triphosphate (ATP) which transport the energy, plants derive from light during photosynthesis for all cellular metabolic activities (worldofmolecules.com).

The process of cellular respiration can be derived from the following equation:

C6H12O6 + 6O2 ——————-> 6CO2 + 6H2O + ~38 ATP

(iupui.edu)

Figure 3.0- The energy cycle illustrating the relationship between photosynthesis and cellular respiration. (actforlibraries.org. 2017)

It is evident from this equation that cellular respiration can be directly linked to photosynthesis as this equation is the reverse reaction of photosynthesis. Furthermore as figure 3 shows, both processes are dependant on each other to carry out their functions. Cells that break down sugar are dependant on photosynthetic cells since these cells solely make sugar which is necessary for the plant to carry out its metabolic activities once these sugars are converted into ATP. In addition to that, in order for photosynthetic cells to carry out their function, they need the carbon dioxide and water produced from cellular respiration.

1.4 Transpiration and osmosis

Figure 4.0- pathway of water from the root hair cells to the xylem. (bbc.co.uk, n.d)

Transpiration is the process in which moisture is transferred up the plant from roots through tubes made of xylem cells to the small pores found on the underside of leaves. This water eventually changes into vapour and released into the atmosphere (usgs.gov). Figure 4.1 is a clear representation of transpiration. Through the process of osmosis, water enters the root cortex along a concentration gradient via the specialised root hair cells that are hypertonic to the surrounding soil water (as seen in figure 4.0) meaning that it has a lower concentration of water molecules. With the help of specialised cells called the xylem, the water is transported to the leaves where they will later be released into the atmosphere. As figure 4.2 shows, transpiration aids in the process of photosynthesis as photosynthesis requires water which traverses up the plant via the xylem. Once the water passes into the guard cells, their internal fluid pressure or turgor, will increase thus allowing the guard cells to expand which in turn opens the stoma, allowing carbon dioxide to diffuse in resulting in

photosynthesis (REFERENCE TEXT BOOK) This consequently allows the production of glucose which would be broken down in the form of ATP to provide energy to the roots, stem and other important components of the plant resulting in the growth of the plant.

Figure 4.1- Labelled diagram of the process of Transpiration. (Soffar, H. 2015)

Figure 4.2- labelled diagram of the relationship between transpiration and photosynthesis in plants.

(shutterstock.com, n.d)

1.5 How does salinity affect plant processes?

Salinity is the concentration of salt that is evident in a sample of soil (mdba.gov.au).

Figure 5.1- Effects of salinity stress on plants. (Kumar, V. 2018)

Sodium chloride present in soil may hinder the growth of the plant in many ways which has been clearly illustrated by Figure 5.1. A major effect of excess salt accumulation is dehydration. Dehydration is caused when the highly permeable specialised root hair cells work against the plant when there’s a high salt content present in the soil. The high content of the soil creates a hypotonic environment due to there being less water and more sodium chloride inside of the cell as compared to the outside. This inhibits the process of osmosis in the root hair cells which consequently results in the inability of transpiration which in turn results in a decline in photosynthesis causing the plant to dehydrate and eventually die (education.com). Another effect of excess salt present in soil is the ion separation of sodium and chlorine that is dissolved in water. These dissolved ions, in high concentrations has the potential to displace important nutrients such as potassium and phosphorus essential for the growth of the plant thus leading to deficiencies and causing damage to the plant such as die back as seen in figure 5.2 (umass.edu).

Figure 5.2- Chalara ash die back as a result of soil salinity. (Morgan, T. 2016)