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Effect of Salinity on Germination Essay Sample

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Introduction of TOPIC

Colour used to indicate the raw data used to calculate example mean

Colour used to indicate the raw data used to calculate example standard deviation

Raw Data table 2 showing the effect changing the salinity of water added to ten ungerminated Vigna radiate (mung bean) seeds has on the seeds ability to successfully germinate as determined by the visible presence of a radicle seven days after the solution was added to the seeds?

Salinity of Water (mol L-1)

Number of mung bean seeds successfully germinated as determined by the visible presence of a radicle seven days after being exposed to the solution ±1 seed

Observations

* There were differences in colour, size and texture of the dry seeds, with some displaying wrinkles, colour varying from brown to green, the sizes also varied.

* When placing the seeds in the petri dish their distribution was unequal.

* The filter paper did not fit the petri dish perfectly causing some bubbles to form.

* The thickness of the cotton wool was uneven

* 4 days after exposure to the solution the seeds gave of an unpleasant odour.

* The testa of the seed had began to crack when we checked our seeds on day 4.

* On the 10th day there was mould present in the 0.0 petri dishes

Processed Data Table 1 showing the effect changing the salinity of water added to ten ungerminated Vigna radiate (mung bean) seeds has on the seeds ability to begin germination as shown by the mean number of seeds with a cracked testa four days after solution was added to the seeds?

Salinity of Water (mol L-1)

Mean number of mung bean seeds with a cracked testa four days after being exposed to the solution

Key

Colour used to indicate the calculated example mean

Colour used to indicate the data used to calculate example standard deviation

Note: All results have been rounded to one whole number, as living organisms including seeds can only be counted whole numbers.

Processed Data Table 2 showing the effect changing the salinity of water added to ten ungerminated Vigna radiate (mung bean) seeds has on the seeds ability to successfully germinate as determined by the mean number of seeds with the visible presence of a radicle seven days after the solution was added to the seeds

Salinity of Water (mol L-1)

Number of mung bean seeds successfully germinated as determined by the visible presence of a radicle seven days after being exposed to the solution

Example:

Standard Deviation

From – http://easycalculation.com/statistics/standard-deviation.php

Graph 1 showing the showing the effect changing the salinity of water added to ten ungerminated Vigna radiate (mung bean) seeds has on the seeds ability to begin germination as shown by the mean number of seeds with a cracked testa four days after solution was added to the seeds

Comment on the graph:

The calculated standard deviation and error bars for two of my results (0.3 and 0.5) were small, indicating that these the values were close to the mean and therefore valid. However, at 0, the error bar is very large (1SD is 3) this indicates that the values recorded for this percentage was less valid and some other factor may have been affecting the results. This error bar also overlaps 1 other data point at 0.2, indicates that this first decrease may not be a clear trend due to this overlap. The error bar for 0.2 and 0.4 is also large (1SD is 2), indicating that it was not very valid. The line of best fit is reasonably accurate and it passes through all of the error bars. This indicates that the trend indicated by the line is accurate.

Graph 2 showing the effect changing the salinity of water added to ten ungerminated Vigna radiate (mung bean) seeds has on the seeds ability to successfully germinate as determined by the mean number of seeds with the visible presence of a radicle seven days after the solution was added to the seeds

Comment on the graph

As we had no radicles present at 0.3 0.4 and 0.5 the standard deviation is zero and therfore it is reliable, however it is not the expected trend, indicating that there were other factors which effect the germination at the aforementioned salinities. The calculated standard deviation and error bars for the other two of my results (0.0 and 0.2) varied in size. As at 0, the error bar is very large (1SD is 2) this indicates that the values recorded for this percentage was less valid and some other factor may have been affecting the results. This error bar also overlaps the 1 other data point at 0.2, indicates that this first decrease may not be a clear trend due to this overlap. The line of best fit is not accurate and it does not passes through all of the error bars and point. This indicates that the trend indicated by the line is inaccurate and more likely to be less extreme.

Conclusion:

In my experiment I investigated whether changing the salinity of water effected the germination capabilities of mung beans, originially this was going to be indicated by the visible presence of a radicle, 10 days after being exposed to the solution, however these results were inconclusive so we also indluded our data from the fourth day which measured how many seeds testas had begun to crack. Both of these results indicate that the salinity of water significantly affects the ability for mung been seeds to germinate. As our research question investigates the effect of salinity on germination my conclusion shall be primarily concerned with my results for the visible presence of a radicle as that was what our research question was in relation to.

As we increased the salinity of the water the indicators of successful germination decreased. This is shown by the overall negative trend of our data as at 0, 6 seeds had successfully germinated while at 0.5 no seeds had germinated. As we had no radicles present at 0.3 0.4 and 0.5 the standard deviation is zero and therfore it is reliable, however it is not the expected trend, indicating that there were other factors which effect the germination at the aforementioned salinities. The calculated standard deviation and error bars for the other two of my results (0.0 and 0.2) varied in size. As at 0, the error bar is very large (1SD is 2) this indicates that the values recorded for this percentage was less valid and some other factor may have been affecting the results. This error bar also overlaps the 1 other data point at 0.2, indicates that this first decrease may n

ot be a clear trend due to this overlap. The line of best fit is not accurate and it does not passes

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through all of the error bars and point. This indicates that the trend indicated by the line is inaccurate and more likely to be less extreme. In otherwords it is more likely that salinity has a more gradual effect on the inhibition of germination than the trend seen in our results.

We were able to do a total of 5 repeats for each concentration which meant we were able to ensure greater reliability of our results. However there were still some anomilies which would have caused our error bars to increase. Though there are no single outliers the results for our 0 salinity trial had a large range of results from 4 to 9. Although some level of variation is expected due to seeds being biological in nature, this level of range is unprecidented and indicates that this trial in particular was effected by other factors.

The data we collected was insufficient as we only had 8 out of 25 petri dishes have seeds with visible radicles. This led to the inclusion of the data from day four, as the testa cracking is an indicator of the start of germination. This data presented a clearer trend, though still negative it is less extreme, however it also has anomilies, such as recording zero seeds with cracked testas in one trial of the 0 salinity solution, this would have greatly decreased the mean and would have also increased the error bar seen in this graph, as discussed above, this adds to the theory that the 0 salinity results were greatly effected. Another anomily exists in the 0.4 salinity where we recorded 6 seeds with cracked testas, this would have increased the mean therefore it is this result which caused the slight mean increase at 0.4, which does not follow our otherwise negative trend. However the exclusion of this data point would not have effected our graph as the mean would still be 3 seeds.

Our results are explained by the science behind plant germination, and the factors which effect this process. For germination to occur the seed must have the correct abiotic conditions to begin. These conditions include:

1. Water – to metabolically activate the cells within the seed

2. Oxygen – to enable aerobic respiration

3. Warmth – for optimal enzyme function

If these three factors are present then germination can begin. The first step of germination is the absorption of water, this causes gibberellic acid to be produced and as the seed absorbs water and swells the testa will begin to crack. Gibberellic acid in tern causes the synthesis of amylase, which breaks down the starch contained within the cotyledon into maltose. The maltose can then be hydrolysed to glucose for respiration of polymerised to form cellulose, necessary for plant walls. The starch contained within the cotyledon sustains the seed until the plumule reaches light and the radicle can absorb water, and photosynthesis can begin. Though important this is a very vulnerable stage in the plants life and can be negatively affected by abiotic factors.

The solutions we were adding to our seeds with the exception of 0.0 contained water and dissolved NaCl. When dissolved in water the ions in the salt dissociate resulting in the ions Na+ and Cl- to be present in the water. Although plants require Na+, in excess this mineral can begin to have toxic effects on the plant that affects it capacity to germinate. Excess salt can cause “reduced cell turgor and depressed rates of [radicle] … elongation… Furthermore, high intracellular concentrations of both Na+ and Cl- can inhibit the metabolism of dividing and expanding cells, retarding germination and even leading to seed death.”[1] The reduced cell turgor is explained though osmosis, “as osmosis is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration”[2]. Therefore when we placed our seeds in high salt solutions there was a high concentration of salt in the area surrounding the seed, which would cause movement of water out of the seed, and thus water, which is necessary for germination would not be absorbed in the needed quantities, inhibiting germination. At zero salt concentrations this would not have affected the seed, and it would have been able to absorb water, and thus would be able to begin germination.

Our results are supported by multiple experiments, including this one conducted primarily by the Department of Agronomy in Zabol University, Iran. This particular study took many measurements investigating the effect of salinity on germination, including investigating the effect salinity had on radicle length. As you can see, though it would appear our results are more extreme, their results to reflect our negative trend.

Their justification of their results also reflects my own justification, namely that “salinity … leads reduction in water absorbance so cell division and differentiation reduce and [causing the] reduction of … radicle length”.

It is important to understand the factor which effect seed germination as germination is the first stage in a plants life cycle, and without plants to convert carbon dioxide into oxygen life would not be sustainable on earth, plants also play a hugely important role in the agriculture and food industry.

Evaluation:

Limitation of the method

How significantly could this have impacted on your results and why

Improvement

The seeds were different colours and they also had different textures from wrinkled to smooth

The different colour of the seeds indicate different ages, with the darker the seed indicating the older more dried out seeds. “Seed age affected days to initial germination, six month old seeds germinated significantly earlier than freshly shed seeds but the soil types had no significant effect on days”[3] Therefore the different ages of the seeds could have significantly impacted on the speed of germination…

I would select seeds that were similar in colour, shape and size. I would ensure that all of my seeds smooth seeds that matched the dark olive green of the seeds below. I would also ensure that the length of the seeds was consistent at 5-6mm.

Varying cotton wool thickness

The cotton wool varied in thickness across the different petri dishes. This means that some seeds would have been better insulated than others. And since temperature does impact on the rate of germination due to the enzymes involved in this process this may have had a significant effect on the validity of our data. Petri dishes with less cotton wool would be less insulated and thus would be cooler, causing the seed to germinate slower, the opposite would also be true at higher temperatures. However cotton wool also played a significant role in ensuring, that though the seed was exposed to water on all sides it was not saturated, which would have negative effects. Saturation results in the seed not being able to have access to oxygen, necessary for respiration. Thus in those petri dishes with less cotton wool the seed would be less likely to successfully germinate as the seed would be more saturated and thus would not germinate. In petri dishes with excessive cotton wool to much solution may have been absorbed and thus the seed would not have sufficient access to water to germinate. Therefore though it is difficult to conclude exactly what effect varying thickness in cotton wool would have had on our results, it is most likely that it would have decreased the number of seeds germinated, causing our mean to decrease, effecting our validity.

If I were to repeat this experiment I would use large circular cotton wool pads[4], which would evenly cover the petri dish, causing there to be even insulation and absorbance of solution.

Uneven distribution of solution on to the filter paper and the cotton wool

As we utilised a measuring cylinder to pour the solution on to our seeds it was not able to give even cover, particularly on the cotton wool. This would have resulted in some seeds being more saturated than others, which may have negatively impacted the seeds ability to absorb oxygen, and thus germination would have been negatively impacted. However seeds with less water may have also been negatively effected as water is also necessary for germination and insufficient water absorbance will result in delayed or lack of germination. Therefore though this would have impacted on the validity of our results as it would have decreased the number of seeds which successfully germinated, decreasing our mean, our results indicate that some dishes (0.3,0.4, 0.5) were more heavily effected by things like this than others.

To ensure an even cover of solution on the cotton wool I would utilise a spray bottle[5] containing 5ml of solution, which I would hold 10cm above the centre of the petri dish, and spray my solution to ensure an even cover.

The petri dish’s were exposed to differing degrees of light during storage

Though light is not a needed factor for germination, light energy does provide heat and therefore imbalances in light exposure may have caused there to be temperature imbalances. As discussed, temperature is important as germination is an enzyme catalysed process and thus the enzymes work fastest at their optimum temperature, with lower temperatures causing the enzymes to work slower.

To ensure that the light level was even I would place the seeds in a lidded container so no light will reach the seeds. I would leave the lid slightly agar and place the container in storage.

Two of our 0.0 salinity petri dishes grew a substantial amount of mould. All of our seeds also gave off an unpleasant odour after 4 days which continued to the tenth day.

The unpleasant smell indicates that our seeds began to rot this is most likely due to excessive water exposure. Therefore our seeds would have had lower germination rates than if we had used less solution. However as we utilised the same amount of solution in all trials, all trials would have been equally effected. However, this may have caused the complete lack of germination in the 0.3, 0.4 and 0.5 trials.

To ensure this wouldn’t happen again I would reduce the amount of liquid added to the cotton wool from 10mL to 5mL

Bibliography

1. http://www.amjbot.org/content/88/1/62.abstract

2. http://www.academia.edu/2359325/Impact_of_Salinity_on_Seed_Germination_and_Early_Seedling_Growth_of_Three_Sorghum_Sorghum_biolor_L._Moench_Cultivars

[1] http://scholarsresearchlibrary.com/ABR-vol2-iss4/ABR-2011-2-4-490-497.pdf

[2] IB biology syllabus

[3]http://www.researchgate.net/publication/47511708_Effect_of_seed_age_and_soil_texture_on_germination_of_some_Ludwigia_species_(Onagraceae)_in_Nigeria/file/9fcfd506303f303bc6.pd

[4] http://www.econosupplies.com/cotton-wool/cleansing-pads/cleansing-pads-large-round-smooth-50

[5] http://www.thomassci.com/Supplies/Spray-Bottles/_/ATOMIZER-SPRAY-BOTTLES?q=*

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