Different plant cells have different response to water permeability. Water is essential in al plant lives and plants are adapted to different climatic conditions ranging from swamps and seabed to desert plants. Through transpiration, plants are able to control water loss as a way of adapting to their climatic conditions. This research project is aimed at finding out how and why different tree species all growing under the same climatic conditions respond differently to changes in percent water permeability. The role of transpiration in plant water permeability have been studied for a long time and different scholars have carried out different experiments with the aim of finding that relationship. Experiments have been carried out by another group of scholars to find out the relationship between permeability and plant stem fluctuations. 

Null hypothesis. We have noticed that daily stem fluctuations are dependent the rate of flow of water into the plant. When there is an increased water flow in plants, the stem diameter increases and when the water flow decreases, the stem diameter decreases as well. This has been noticed on crops under irrigation.

Alternative hypothesis. If there is an increase the percent water permeability of a plant, the stem diameter of the plant is likely to change or not. 

What are the Effects of Percent of Water Permeability and the Diameter of the California Sycamore and the Southern Magnolia Plants?


Hypothesis. If we increase the percent water permeability, then we will increase the plant stem diameter

An online biology dictionary defines permeability as the property of being permeable or as the property of a porous material to allow a liquid or gas to pass through it. The unit of measurement of permeability is the Darcy that was named after the French scientist who discovered the phenomenon. Permeability can be measured using chemical changes, volume changes and methods that depend on hemolysis and fragility changes (Brachet & Mirsky, 2014).

Selective permeability is achieved by regulating the passage of some substances while at the same time preventing others from entering the cell. This selectivity is due to the nature of the plasma membrane, which is composed of hydrophobic phospholipids and proteins that normally act as transporters of certain molecules (Hohenberger et al., 2011).

Permeability have been studied in both plant and animal cells. The role of permeability is very wide all living things. Osmotic water permeability is normally focused in these studies and normally carried out on cuticular membranes.

In plants, permeability is a crucial activity and the plants’ lives depend on it. However, it is not possible to focus on water permeability and forget about transpiration rates and how the two influence growth in plants. Plants growing in areas that are highly humid are likely to have high rates of transpiration and high rates of water permeability. The uptake of water through the xylem helps in transportation of crucial minerals to the leaves for photosynthesis. The transport of the manufactured food to all the other plant organs is dependent on the flow of water through the phloem. Al these are dependent on water permeability of the plant cells.

Plants growing in dry areas have low rates of transpiration as they have to conserve the little water available. Plants under irrigation or those that grow in highly humid areas have high rates of transpiration as the water is constantly available. With the increase in the amount of water, the percent water permeability also increases. This increase is due to the need to replace the water lost through transpiration. Plants growing in salty waters have low rates of transpiration as fresh water is in limited supply. They also have low percent water permeability.

Role of Water in Plant Growth

Plants often lack mobility in their challenging environment, and for this reason, they depend on water supply for growth and development. The mechanisms of plant cell membrane water permeability remained vague for a long time until the discovery of aquaporins. These proteins act as facilitators of passive water exchange through the cell membranes (De Swaef & Steppe, 2010).

Water plays an important role in the life of a plant. The role includes acting as the primary component of photosynthesis and transpiration, while the lack of it leads to reduced growth. It also provides turgor pressure that holds the plant erect and inflates the cells; it is the solvent through which minerals from the soil move up to the plant. It is also the medium through which the products of photosynthesis move throughout the plant; moreover, it is the source of pressure that is required to push roots through the soil. Water also acts as the medium for biochemical reactions (De Swaef & Steppe, 2010).

Factors Affecting Permeability of Cell Membrane

Nature of molecules. Cell membranes are naturally permeable to water, water soluble neutral substances, fat soluble neutral substances, and electrolytes. Another factor that affects permeability is the size of the molecules passing through. It is impossible for large molecules to pass through natural membranes, but they can pass through endocytosis. Some chemicals like organic solvents will dissolve the membrane, thus destroying its selective permeability. High temperature denatures the proteins that make up the membrane and thus destroy its selective permeability.

Osmotic and hydrostatic pressure gradients are the primary determinants of transmembrane water movements. Hydrostatic pressure increase, also known as turgor, is the result of the cell wall mechanical resistance (ε) (De Swaef & Steppe, 2010).

Materials and methods

Choosing the method of data collection and the material to use, some assumptions were made. The two plant species were chosen considering their ideal environmental conditions.

California Sycamore

Platanus racemosa, California sycamore or western sycamore, is native and common in California although it is also available in other areas such as the western North America region. It usually grows in wetlands and in both acidic and alkaline soils that are also moist, rich, and well-drained. It has moderate drought perseverance if well-established. It should get direct sunlight for a minimum of six hours each day.

Southern Magnolia

Magnolia grandiflora is a tree adapted to edges of water bodies and swamps. It can also grow in moderately dry areas with moist soil and requires minimum sunshine of about four hours a day.

The method used for data collection is known as Focal Tree Data Collection (Cal State LA). The first step involved is finding a focal tree in the location. The trees picked were of different species and the Focal Tree UD Key was used in identifying the species. Using the cell phones, the GPS location of the trees was recorded to at least four decimal places for greater accuracy. The GPS device was held by the trunk so as to get the most accurate data. The estimated time for this process was about four minutes.

The point on the trunk was located 4 feet 6 inches off the ground. A measuring tape was wrapped at this point to measure the circumference of the tree. The diameter was then calculated. Each tree condition was then verified either as excellent, no major structural problems, or good, with minor structural problems or a mechanical damage among others.

The canopy size was then measured in all four cardinal points using the shade cover. Finally, the percent of ground permeable to water was estimated for each tree. A 33-feet string was used, and the percent of permeability to water around the trees was determined. The percent space around each tree that is permeable to water was estimated.


Figure 1 demonstrated the percent of water permeability versus the diameter of the Southern Magnolia plant in the park and street. According to Figure 1, there is no correlation between the percent of water permeability and the diameter since there is no change in the diameter as the percent of permeability increases. The average of the permeability of water was calculated to find the mean and standard deviation for all percent of water permeability and its diameter. For example, in the Southern Magnolia plant the 0-5% permeability mean is 33.25. Whereas the standard deviation is 19.887657. Also, at 6-35%, the mean is 44.5633333, while the standard deviation is 5.21358162. The mean of 36-65% permeability of water is 20.476 although the standard deviation is 5.4875796, and so on. According to the graph and the data listed above, there is no correlation between the permeability of water and the diameter. 

Figure 1 It demonstrates the percent of water permeability in (%) versus the diameter in inches for the Southern Magnolia plants in both streets and park.

California Sycamore plant is very common plant that affects our environment. In fact, the California Sycamore plant was tested to see if there is any correlation between the percent of water permeability and the diameter of the tree trunk. In fact, as the percent of water permeability increases, the diameter should increase too.

According to Figure 2, California Sycamore plant has no correspondence between the percent of water permeability and the diameter. As the percent of water permeability increases, the diameter changes: it either increases or decreases. In relation to the calculations, the mean is 17.04833, but the standard deviation is 15.52456 at 0-5% permeability. At 6-35%, the mean is 22.53833, while the standard deviation is 14.21247, which establishes that there is no correlation between the permeability and the diameter. At 36-65%, the mean is 16.81714, whereas its standard deviation is 15.40601. At 66-95%, the mean is calculated to be 20.9475, but the standard deviation is 21.49046. Finally, at 96-100%, the mean is 15.73714, and the standard deviation is 7.41782. According to the calculations and Figure 2, there is no relationship between permeability and diameter of the tree trunk “A.” 

Figure 2 Graph showed the percent of water permeability versus the diameter for the California Sycamore plant

Southern Magnolia    Mean       STD. Dev

0-5%               33.25                19.887657

6-35%             44.563333       5.21358162

36-65%           20.476    5.48757961

96-100%         21.06683        13.360174

California Sycamore    Mean     STD. Dev

0-5%                           17.04833         15.52456

6-35%                         22.53833         14.21247

36-65%                       16.81714         15.40601

66-95%                       20.9475           21.49046

96-100%                     15.73714         7.41782


The water content of the stem plays a great role in changes in the tree stem diameter. This diameter constantly changes on a daily basis. These adjustments in the diameter of the stem have been studied since the 19th century. Stem diameter continually changes during the growing season as a result of the cambial growth in the tree as well as diurnal changes that are associated with the movement of water within the tree trunk. Due to the amount of stored water, the xylem and phloem keep expanding and then contracting. However, daily adjustments in the diameter of the stem are caused by the continuous thickness changes in the phloem and cambial tissues, other than variations experienced in the radial growth or xylem diameter. These changes result in cell membrane changes in its vigor and thus changes in stem thickness variations (Kumar & Mishra, 2014).

Water exchange between the two layers (phloem and xylem) is due to the transportation of water in the stem and is also greatly influenced by soil water uptake rate through the roots. The water content in the phloem is just a small proportion of the amount of water transpired by the tree in a day (Devine & Harrington, 2011).

Earlier studies show that the diameter of the stem is the largest during the night time and continues decreasing as dawn breaks. As darkness approaches, the diameter starts increasing again (Kumar & Mishra, 2014).

The results obtained for the two sets of plants were different from each other. This could be due to several factors. One such factor is due to their different environmental habitats. It is known that temperature denatures the cell membrane of plant cells or all cells including those of animals, thus increasing their permeability to water.

This might explain why there was some change in diameter with the increase in the percentage of water permeability for the California sycamore plant that is adapted to drier conditions compared to the southern magnolia plant. When the plant is placed under conditions where water permeability percentage is high, it takes in more water due to the increased permeability. Therefore, the xylem has more water intake, and the cells become rigid; thus appears the increase in diameter with the upsurge in water permeability percentage. Another factor that could lead to the increase in stem diameter is the rate of transpiration. Due to the limited water availability in its habitat, the California sycamore plant is adapted to controlled transpiration rates. When the increase in percent of water permeability is recorded, the plant is still under the controlled transpiration, thus the increase in the diameter of the stem as there is too much water in the xylem.

When there is continuous water supply, the rate of transpiration changes and more stomata opens to allow more water to escape. The aim is to prevent damage to the cells, and thus the decrease in diameter between 95%-100%.

However, the decrease in stem diameter is noted when the percent of water permeability reaches 36%-65%. This can as well be explained using transpiration. After the cells become rigid and impermeable due to the high concentration of water, transpiration process is triggered and the gradient of the xylem increases, allowing water to flow back to the xylem and up to the leaves for the transpiration process to take place. Consequently, the cells have low water concentration, thus regaining their permeability. Furthermore, water flows from the xylem due to the changes in gradient, and the cells become rigid again, leading to the increase in diameter of the stem. This can be noted when the percent of water permeability reaches 66%-95%, and the process repeats itself.

The southern magnolia plant, under ideal conditions, is adapted to areas with high moist soils. Its cells are adapted to dealing with the excess water, and its leaves are wide enough to allow high rates of transpiration. At first, there is increase in diameter when the percent of water permeability reaches 6%-35%. Consequently, the difference in gradient between the xylem and the cell membrane causes the flow of water into the cells, causing rigidity and thus the increase in the plant diameter. However, due to its cell adaptation to dealing with excess water, the situation changes as more transpiration takes place. This accounts for the decrease in stem diameter as recorded between 36%-100%.

With the study and observations made, it is easier to conclude why there occur variations in stem diameters of plants. These changes in xylem diameter can be attributed to the dynamics of sap ascent and the rates of transpiration, whereas sugar transportation can be said to be the main contributor to the stem diameter variations pattern. Stem diameter variations have a role to play in the physiological and ecological measurements of trees. Transpiration plays a great role in the diurnal stem diameter variations as showcased in the experiment between the two sets of plants and in the way they respond individually to the increase in the percent of water permeability.


Our gratitude and high regard go to all who made this project a success. The university played an important role in the provision of research equipment. We would also like to thank our lecturer who worked tirelessly to make sure the project was a success and was always available for any enquiries. We cannot fail to thank the library fraternity for providing us with the required set of study materials for our research and compilation. We cannot also forget to thank our fellow students and the whole community at large.

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