Effects of Plant Dehydration Study

• Brodie Smart

Background:

Plants need water to sustain life and vitality and to maintain turgor pressure, therefore vast amounts of water pass through plants. However, 99% of it evaporates from the leaves and is lost into the atmosphere. The remaining 1% of water is actually used for growth (http://academic.evergreen.edu, 2015). The movement of water through a plant can be spilt into three sections: The Roots, The Stem and The Leaves (BBC.co.uk, 2015).

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Initially water moves from the soil through the roots and into the plant. There are two pathways that can be taken at this point (http://www.uic.edu, 2015). The first is The Symplast Pathway. The Symplast Pathway consists of the living cytoplasm of the cells in the root. The root hair cells absorb water by osmosis and then the water diffuses from the epidermis through the roots down a water potential gradient to the xylem.

The second pathway is called The Apoplast Pathway; which consists of the cell walls between cells. These walls are thick and open, so water can easily diffuse without having to cross any cell membranes by osmosis. However, this pathway stops at the endodermis because of the waterproof casparian strip which seals off the cell walls. Therefore the water then has to cross the cell membrane by osmosis to enter the Symplast. This means that the plant has some control over the uptake of water into the xylem. (http://passel.unl.edu, 2015)

Once the water has passed through the roots it then moves onto the Stem, passing through the Xylem Vessels. These vessels form continuous pipes from the roots to the leaves. As the Xylem vessels are dead tubes, osmosis cannot occur. Therefore the force that drives the water movement in the Stem is, Transpiration in the leaves (https://sahiljhamb.wordpress.com, 2012).

Transpiration causes low pressure of water in the leaves so that more water can be drawn up to replace the lost water (Clegg, 2008, p.158). The xylem vessels then branch out into the leaves to form a system of fine vessels, called leaf veins. The water diffuses from the xylem vessels into these fine veins, through the cells and then down its potential water gradient. The water will then evaporate from the spongy cells in the sub-stomatal air pass to be diffused out through the stomata (Oxford Learning College, Edexcel, 2008 p.15).

Objective:

The objectives behind this study is to observe and record the effects of restricting a plants water intake, by observing how plants cope with varying and restricting amounts of water, over a fourteen day period. This study will give a basis on how well plants can survive in order to aid methods of plant growth in environments that have less or little water than ideal.

Hypothesis: Restricting a plants water intake will effect its growth, colour and vitality negatively.

Equipment:

• Plant x4
• Plant Pots and dishes x 4
• Ruler
• Measuring Cylinder
• Compost

Choice of plant:

When choosing a type of plant for this experiment; several factors were considered; such as time periods; therefore a plant that grew at a steady rate was required, as well as a plant that normally needs an average amount of water to sustain it healthily.

Four plants were selected that were similar in size, shape and height. They were then placed in identical containers with nine cm depth of soil; also ensuring that the plants were placed in the same amount of light- to restrict variables.

For this experiment pea plants were used- as shown in figure one. As they cover all the factors required; they grow extremely fast, with visible growth spurts that can easily be measured. This plant also sprouts large leaves, with many petioles; both of which can easily be examined, counted and observed during experiments.

Figure 1- Taken on day 14 of the experiment.

Method:

On Day One four plants of the same species, were potted in 9 cm of soil, to fill the pots. Upon labelling pots 1 -4 a leaf count was carried out and the height of each plant recorded along with the colour and vitality of the plant. 150ml of water was then added to each pot.

Over a fourteen day period the plants were observed, each plant receiving different amounts of water, every other day, to observe the effects this has on colour, growth and vitality.

The plants received-

-Plant One: 10ml.

-Plant Two: 30ml.

-Plant Three: 50ml.

-Plant Four: 70ml.

Each plant received the appropriate amount of water every other day; starting on Day 1. After watering each plant, the stem length was measured and recorded- to show growth. The number of leaves was counted and the colour and vitality of each plant was noted.

The amount of water given to each plant was the independent variable in this experiment; whereas, the dependent variables were the growth, colour and vitality.

For this experiment two types of research were used to observe the effects of the restriction of water on plants. This ensured the results covered as many effects as possible, to draw a full conclusion. The first type of research that was used is Quantitative Research, this was the stem length measurements in cm and the number of leaves the plant has; as both of these methods were based on statistical data and gave firm evidence to show the effects of the restriction of water on plants.

The second method of research that was used was Qualitative Research; this was colour observations and vitality. These results were based on the interruptions of the experimenter and subject to opinion, but still showed the effects of restriction of water on plants.

All of these research methods were noted down on a table; every other day, when the plant received water. These results were then used collectively at the end of the 14 day period to draw the conclusive results together.

Figure 2- Tabled used to record results over the 14 day experiment.

Results:

• Growth: Each plant’s stem growth was measured, every other day, over a fourteen day period. The graph below shows the conclusive results (fig.3).

-Plant One progressed from 3.9cm to 11.5cm by day fourteen.

-Plant Two progressed from 4.8cm to 16.0 cm by day fourteen.

-Plant Three progressed also from 4.8cm to 15.3 cm by day fourteen.

-Plant Four progressed from the shortest at 3.7cm to the tallest at 16.2 cm on day fourteen.

A Leaf Count was also recorded to measure each plants growth. These results are shown below (fig 4).

Figure 4- Leaf Count Line graph.

-Plant One began the experiment with six leaves and by day fourteen it had fourteen leaves.

-Plant Two started with six leaves as well, but by day fourteen it had sixteen leaves.

-Plant Three started with the least number of leaves, at four, but by day fourteen it also had sixteen leaves.

-Plant Four started with five leaves and by day fourteen it had eighteen leaves, the highest number of leaves recorded.

• Colour Observations:

During the fourteen day period, the experimenter observed and recorded notes on the colour of each plant. The notes shown recorded, in the table below. (Fig 5).

• Plant One began on day zero looking healthy but quickly became discoloured resulting in being green but with large patches of yellowing appearing on the leaves, by day fourteen.
• Plant Two was green and healthy on day zero but by day fourteen there were increased yellow patches observed on the leaves.
• Plant Three successfully maintained a green and healthy appearance of its leaves from day zero throughout the experiment to day fourteen.
• Plant Four also successfully maintained a green and very healthy appearance of its leaves throughout the experiment.

Vitality:

Throughout the experiment the experimenter also observed the vitality of each plant, the observations made are shown in the table below (Fig. 6).

• Plant One appeared lively and healthy on day zero, however its vitality decreased progressively over the fourteen day experiment and by day fourteen the plant appeared dehydrated and the soil extremely dry.
• Plant Two appeared lively and healthy and continued to appear so throughout the experiment and by day fourteen looked healthy and the soil was moist.
• Plant Three looked lively and healthy and progressed well over the course of the experiment and by day fourteen the plant appeared very fresh and lively, with the soil appearing healthy and damn.
• Plant Four looked lively and healthy and progressed well, however over the course of the experiment the plant’s soil and dish appeared to become water logged and by day fourteen, excessive water was observed.

Discussion:

• Growth:

From this it can be seen that restricting a plants water intake can have an effect on a plants growth; as the stem length in Plant One is significantly less developed to that of plants three and four, which received more water.

Although each plant’s stem length was slightly different at the beginning of the experiment; a variable that was difficult to control as no two plants are ever exactly the same; this does not seem to have affected the results. However, if this experiment were to be carried out again plants with the exact same height would be used to limit variables.

Plant four started off on Day Zero at 3.7cm never the less as this plant received more water than the other three plants; it steadily progressed over the fourteen days, to become the tallest of the four plants at 16.2. Whereas, Plant One started at 3.9 cm and due receiving less water it only grew to 11.5 cm; showing that restricting a plants water intake will affect its growth.

The only anomaly was plant two which started on day zero at 4.8 cm and finished on day fourteen at 16.0 cm, the second tallest, even though it received only 30ml of water every other day. The reason for this is that the plant did start out as one of the tallest in the experiment, so this could have given it a slight advantage, an unfortunate variable that was impossible to control completely.

If this experiment were to be performed again a plant receiving an average amount of water every day would be used as a control group, to give average and expected readings of a plant receiving an average amount of water. This would then be used alongside the other results to compare the effects of restriction of water on plants.

Another method that was used to observe the plants growth was to count the number of leaves on each plant. This is a discrete variable as it deals with whole figures. The results show that the plants that received the most water had a high number of leaves as the fourteen day period progressed. As Plant One started with six leaves and ended with fourteen; whereas Plant four received the most water and by the end of the experiment had eighteen leaves in total.

These results show that restricting a plants water does affect its growth as this can be seen from the measurements of plant ones stem length and number of leaves over the fourteen day period.

• Colour Observations:

The colour of each plant was noted down when the plant received its water; it was then recorded by the experimenter. Once the results were drawn together it was clear to see that the plants that received less water began to lose colour and the leaves begin to have some yellow pigmentation. This shows that restricting a plants water can and will have a negative effect on its colour.

Although this research method was Qualitative and was subject to opinion and change, as long as consistency is kept as to who does these observations and what time of day they are done, these results can still be a very effective measure of how the restriction of water affects plants.

If this experiment were to be performed again photographs of each plant would be taken when they receive water, as photographical evidence to be used to show the effects of restriction of water on plants. These images would also support the experimenter’s observation notes.

• Vitality:

The experimenter also observed the vitality of the plant as a second Qualitative Research method to record the effects on vitality when plants have had a restricted water intake. From the results it can be seen that all four plants started out lively and healthy but as the experiment progressed plant one, receiving less water throughout, began to show signs of it leaves wrinkling and the soil becoming dry and by day fourteen was observed to be dehydrated. Although plant two, which received 30ml of water continued to appear lively and healthy throughout the experiment, the soil was observed to be moist showing that it although it managed to sustain its vitality it could have used more water to help maintain it.

plant three appeared healthy and maintained its water levels successfully with damp to wet soil to maintain the plant. Whereas plant four although it kept healthy by day nine there was excessive water in the soil and in the dish underneath the pot showing that too much water can also be of a negative effect to a plant.

As stated above, if this experiment were to be run again, photographs would be taken of each plant to ensure that there is photographic evidence to go in conjunction with the experimenter’s observations.

Conclusion:

Over the fourteen day experiment three factors were observed to monitor the effects of restriction of water on plants, these were; the growth- shown through stem length and leaf count- colour observations and plant Vitality.

From these observations and recordings, it is clear that if a plants water intake is restricted there is then a negative impact on the growth, colour and vitality of a plant. As plant one progressed less and slower than that of plant four which received the most water and ended the tallest and healthiest.

This experiment can help to a give a basis on how much water is suitable to give to a plant in order for it to grow effectively. As it covers, too little, seen in plant one and slightly too much in plant four which by the end of the experiment had excessive amounts of water left over in the pot and dish.

Overall, these results show that restricting a plants water intake will affect its growth, colour and vitality negatively; and from the trend set by these fourteen days results, it can be assumed that over a prolonged period of time these negative effects would increase.

Brodie Smart

Word Count: 2818

Bibliography of Book Reference:

• Clegg CJ (2008) Edexcel Biology for AS. London, United Kingdom. Hodder Education, An Hachette UK Company.
• Edexcel, Oxford Learning College (2008) A2 Level Biology. United Kingdom. Oxford Learning College.

Bibliography of Internet Resources:

• http://water.usgs.gov/edu/watercycleevapotranspiration.htm l (Accessed 17^th March 2015).
• http://academic.evergreen.edu/c/clejen03/transpiration.html – (Accessed 17^th March 2015).
• http://www.uic.edu/classes/bios/bios100/lecturesf04am/lect19.htm – (Accessed 17^th of March 2015).
• http://www.bbc.co.uk/bitesize/higher/biology/genetics_adaptation/maintaining_water_balance/revision/3/ – (Accessed 19^th of March 2015).
• http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1057703469&topicorder=3&maxto=4&minto=0 – (Accessed 19^th of March 2015)
• https://sahiljhamb.wordpress.com/2012/11/13/water-uptake-and-movement-up-the-stem/- (Accessed 19^th of March 2015)