Trend A:
At 0% x 10-3 of nitrate concentration, the number of fronds increased from the initial 8 frond to an average of 20.67 fronds, this increase took place without the presence of any nitrates in the solution. This is because there were already some nitrates present inside the cell, in the required form such as proteins, coenzymes and other nitrogen containing components, essential for the plant to survive and grow. Since nitrogen is already available inside the plant cells the duckweeds in this concentration are able to carry on growing until nitrogen becomes a limiting factor. The presence of nitrogen in the components of the cells meant that the metabolism for respiration, photosynthesis and plant growth could still take place. Without nitrates in the solution, it had a higher water potential so osmosis occurred where the water in the solution moved from the solution into the plant cells of the root, where the water potential of the plant cell was lower, as water moved into the cells, the macro and micro nutrients within the solution were also able to diffuse through. Plant growth still occurred as the plant still used energy obtained from the light bank, water from the solution and carbon dioxide to produce oxygen and simple sugars (photosynthesize). The plant cells were then able to use these sugars to make more complex sugars and starches for storages as energy reserves, to make any stored nitrogen into amino acids then to proteins. This required energy for growth comes from reserve carbohydrates and from actively photosynthesizing fronds.
The present nitrogen performed nitrogen metabolism, which is vital for plant growth.
After the addition of 0.4% x 10-3 nitrates to the duckweeds, the graph shows an increase in growth to an optimum. This increase aids rapid growth as there is the right amount of nitrogen present inside and outside the cells of the roots. This optimum growth suggests that 0.4% concentration is the most favoured environment, for the growth of the duckweeds. The no. of fronds increases from the initial 8 fronds to an optimum average of 32 fronds, so this concentration aided the maximum growth through out investigation.
As there is the correct amount of nitrates and solutes outside the root cells, this gives a favourable water potential value outside the cell. The net uptake of water occurs by osmosis. Osmosis is the passive transport of water across a semi permeable membrane. Because a plant cell has a wall, this affects Osmosis which occurs between the cell and its extra cellular fluid. The combined effects of solute concentration and physical pressure are incorporated into a measurement that is called Water Potential. Water potential determines the direction of movement of water, so water moves from a region of higher water potential to regions of lower potential. So the solutions containing 0%- 0.4% x 10-3 nitrate concentration had a higher water potential than the fluid inside the cells cytoplasm. Therefore this caused water from the solution to move inside the root cells of the duckweeds, and prevent dehydration. So these two solutions had the most favourable uptake of water.
Water is a very important component for plant, especially in photosynthesis and in nutrients uptake. The more water taken inside by the cells means that the photolysis part of water during photosynthesis takes place more, and therefore H+ from water is used for reducing the co- enzyme NADP. Reduced NADP is then used to transport the H+ and reduce organic molecules for the synthesis of carbohydrates and sugar. The high water potential outside the root cells of the duckweeds led to more water entering the cells, so more hydrogen ions were produced from the splitting of water by the light energy absorbed from the light banks. The increased amount of H+ ions helped the plant to grow and photosynthesize. This is because the most important active transport protein in the plasma membrane of the plants cell is the proton pump. This uses energy from ATP to pump H+ out of the cells, more H+ pumped out results in a proton gradient, with a higher H+ concentration outside the cell than inside. The gradient is a form of stored energy, because the H+ ions tend to diffuse ‘downhill’ back into the cell. Plant cells use energy stored in the proton gradient to drive the transport of many different solutes. This proton pump contributes the uptake of k+ ions by the root cells as it is a cation so it is driven into the cell by the membrane potential, through transport protein.
Nitrogen in the solution were taken up in the form NO3 - , so the root cells accumulates these anions by coupling their transport to the inwards diffusion of H+ ions through a Cotransporter. Since the investigation was on the effect of the nitrate concentration on growth, all the other nutrients needed for the plant were obtained from the tap water and solution, to prevent the growth to be affected by any other limiting factor.
The macro nutrients required for growth apart from Nitrogen are potassium, phosphorus, Magnesium and Sulphur. Micro nutrients needed are Chlorine, iron and Manganese. These nutrients were provided from both the solution and tap water.
In both of the 0% and 0.4% x 10-3 concentration of nitrates, the high water potential meant that enough water entered the root cells and generated the uptake of both the macro and micro nutrients needed for growth. This is why all the fronds in both the concentrations were dark healthy green coloured, as they were rich in water and all nutrients. The solution in these two concentration of nitrates were hypotonic, so the cell wall in these duckweeds helped maintain the water balance, the plant cells swell as water enters by osmosis, but however the elastic wall expands only to so much before it exerts a back pressure on the cell that opposes further uptake. At this point the cell is turgid (very firm), which is the healthiest state for the plants generally; this is why the fronds in this condition looked very healthy and green.
This is also the reason why maximum amount of growth did not occur in the 0% concentration and it proves that growth is favoured by nitrogen, as the duckweeds in 0% x 10-3 concentration of nitrates although had a higher water potential solution, did not have any nitrogen present so were not able to grow to their maximum. In 0.4% concentration, the presence of nitrates allowed the duckweeds to grow to their maximum.
Trend B:
At 0.8% x 10-3 concentration of nitrates, there is a rapid decrease in the number of fronds, to an average of 15.33, the observations that were made were that the fronds were of pale green/ yellow in colour.
At 1.2 % x 10 -3 the number of fronds continued to decrease more to an average of 4.67, at 1.6% x10-3 there was an average of 2.33, so there was significantly less fronds compared to in trend B. The colour observations made here was that fronds were in pale green/ brown in colour. Finally the highest concentration of nitrates in the experiment 2% x 10-3 had 0 fronds, as the initial Duckweeds died.
There was a decrease in the number of fronds in all the concentrations in trend B. This is due to Osmosis. The solution outside each of these root cells had a lower potential water potential, and so in the 0.8% x 10-3 concentration there was a vast amount of decrease in water uptake, resulting in less nitrates uptake, which therefore decreased the growth of fronds.
However the water potential in the solutions 1.2%- 2% x 10-3 of nitrates concentration was so low that the water potential in the plant cells cytoplasm was higher, and therefore resulted in water moving out of the cells cytoplasm and into the solutions. And so as a result there was no nutrient uptake, the exposed solutions were hypertonic, which meant that the cells lost water to their surroundings and shrunk. This caused the plant to wilt and die, and so no growth takes place. The dead fronds turned brown in colour.
At 2% x 10-3 concentration all the fronds in the duckweeds died, because due to the lower water potential in the solution, the water carried on moving out of the cell, and this carries on until the water potential both inside and outside the cell reaches an equilibrium. How ever the water potential in this solution was to low that it caused all the water to be drained out of the cell and cause it to die, since equilibrium was still not reached.
At 0.8% x 10 concentration of nitrates, a deficiency of potassium and Magnesium could be detected, as the fronds were yellow in colour. Potassium is a cofactor that functions in protein synthesis, it also aids processes such as active transport and major solute functioning in water balance. The yellow colour obtained is because there was a shortage in chlorophylls which means that there is less light energy trapped due to fewer amounts of pigments; this is because of less magnesium – potassium complex being formed. Magnesium is a component of chlorophylls, it activates many enzymes. This yellow colouring of the fronds is known as Chlorosis. The fronds in 0.8%-2% x 10-3 concentration show a significant shortage in Nitrogen, which is a component of nucleic acids, proteins and hormones, so there was hardly any growth.
Principles and concepts
In the solutions where the uptake of nitrogen took place the fronds on the duckweeds grew. This is because nitrogen is an essential component for the plant’s growing process. Nitrogen is used in the manufacture of the nitrogenous co- enzyme NADP, it also in the energy used as ATP, as it contains the nitrogenous base Adenine. These two components need nitrogen to be taken in, in order to be produced. They are also the most important components for survival. NADP is used as a hydrogen accepter and transporters. The ATP molecule is used to transfer energy to metabolic places. So the solutions, which allowed the most uptake of nitrates, produced a greater number of ATP and NADP molecules, and their increased synthesis aided the growth of plant tissue.
In the thylakoid membranes of the plant, the light dependant part of photosynthesis took place. Here the light energy supplied by the constant light banks were absorbed by the chlorophyll and other pigments. The more nutrients that were taken up by the roots such as the magnesium and potassium meant that more pigments such as chlorophyll were manufactured. The lights are then harvested in photosystems so that maximum amount of light is taken inside. The light energy absorbed causes the electrons within the chlorophyll to become excited. The energy released synthesises ATP from ADP and an inorganic phosphate. Also during this stage the water absorbed by the roots in the solution, undergo photolysis. The H ions produced from this reduce the NADP into NADPH. These molecules produced are the essential components of the Calvin Cycle, this is water is also the reason why water is vital, as it provides the H ions, without these ions the Calvin Cycle cannot take place. This Light- independent reaction is where the main manufacture of sugars and carbohydrates takes place, with the help of the reduced NADP and energy providing ATP molecule. The light – independent reaction takes place in the stroma of the chloroplast, and the reaction needs energy and H ions to keep the cycle going.
B The fronds were in a constant environment, where each frond was exposed to the equal amount of CO2. The 5 carbon compound RuBP binds to the carbon dioxide, with the help of the enzyme Rubisco to produce another compound, GP. The ATP provides the energy for the synthesis of the synthesis of this compound into sugars such as sucrose. The NADP provides H+ ions for the reduction of organic compound to produce sugar. The Calvin cycle makes carbohydrates, lipids and protein via amino acids. The sugars produced ( mostly sucrose) are transported from the leaves to actively growing regions to provide energy for growth and respiration.
The nitrogen is also the component of proteins, which is the polymer of amino acids. Each amino acid contains the carboxyl group, R group and the nitrogen containing amine group. These amino acids link together by peptide bonds, forming a long chain of polypeptides. The chain leads to different structures of proteins. Two kinds of proteins can be made fibrous or globular proteins. The globular proteins that are made are like enzymes such as the Rubisco used in the Calvin cycle. Enzymes in plants are needed to make parts of the plants like chloroplasts and pigments. The membrane of these plant cells contains scattered proteins, which in the root cells allow the uptake of nitrates and other essential nutrients.
Proteins are vital components in a plants variety of metabolic pathways and processes. Proteins make up the molecular structure of DNA, RNA and host of other critical metabolic processes required for plant growth.
The plant grows using, mitosis as cell division, and therefore copies the previous cells DNA in order to divide and replicate. The cells therefore need to make many new DNA’s in each new cell. DNA is made up of 4 nitrogenous bases, adenine, guanine, cytosine and thymine. So the nitrates taken up by the roots are also used to manufacture the DNA, DNA carries the instructions for the cells in the form of codes to make particular proteins. The nitrogenous bases are attached to a 5 carbon sugar and a phosphate group, joined by a condensation reaction to form a nucleotide. Two strands of poly nucleotides join together to make the DNA, which is copied into every other new cells.
Nitrogen also stimulates the growth of roots, which enables efficient uptake of all other nutrients. Amino acids are made in the root tips and carried to growing areas in the plant to make proteins.
From the table that contains all the results pooled from my class, I will use the results to consider the hypothesis made earlier on. The reason I am using the pooled results and not my individual ones is because altogether there are 30 replicates for each concentration in the pooled results where as in my individual one there is only three. The greater the number of replicates means the more reliable and accuracy the results are likely to be. Using Trend A and Trend B I will firstly calculate the standard deviation, and using these results I will be able to carry out two t-tests, one for each of the trends. The outcomes of the t- test will allow me to conclude whether to accept the null hypotheses or the alternative hypotheses.
The Alternative Hypotheses of this experiment is : There will be a significant difference between the growth of the duckweeds fronds and the concentration of nitrates in the solution.
The Null Hypotheses of this experiment is : There will be no significant difference between the growth of the duckweed fronds and the concentration of the nitrates in solution.
To calculate the mean of each concentration I added all 30 replicates and divided by 30.
Mean Values of :
0% = 22.3
0.4% = 22
0.8% = 12.7
1.2% = 4.23
1.6% = 1.93
2% = 0.57
A t-test is carried out to compare the mean values in trend A and trend B. It also ensures that the difference between the two means is a genuine effect, which allows us to decide whether the difference is due to chance or not.
For each trend if I accept the null hypothesis, then I must reject the alternative, and vice versa. The alternative hypotheses can only be accepted if we are 95% or more sure that the null hypothesis is not correct.
The standard deviation formula used is
The standard deviation of
0% = 6.58
0.4% = 7.67
0.8% = 4.91
1.2% = 3.00
1.6% = 2.56
2% = 1.57
Looking at the standard deviation value, the o.4 % value is big so it means that the result values are quite spread out this could be the reason why the mean is smaller than the mean of 0%. As it is this spread out data that resulted in the average value of 0.4% to be smaller than the 0% average unlike in my individual results.
Trend A is between 0%- 0.4% x 10 concentrations of nitrates.
Trend B is between 0.4%- 2 % x 10 concentrations of nitrates.
I have decided not to use the values of 2% concentration in the t- test, as all the fronds had died, and using the 0 values will just increase the spread of data. So it will be more reliable not use them values, therefore the t- test carried out for trend B will be between 0.4% to 1.6%
The t- test formula that I am using is:
The t- test for trend B
The t-test for trend A
So the t value trend A is 0.124, and the t value in trend B is 13.6. The degrees of freedom for these t- tests carried out is 58. This is calculated as 30 x 2 replicates and minus 2 gives a total of 58. The standard error that will be used to compare these T-tests values is 5% since the critical value is 95%. Looking at the t- value table there is no degrees of freedom value for 58, so I will use the one before it which is 40. At 5 % level of significance the critical value is 2.021, so this means that my t value should be equal to or greater than this in order to be at least 95% confident that the difference between the two means is significant. However the value obtained by the t-test in trend A is 0.124 and this is lower than all the critical values in that degree of freedom. Therefore I am less than 80% confident that the difference is significant, this significance is too small, and so does not prove any difference between the two means in trend A is not by chance alone. So for this trend I will now have to reject the alternative hypotheses and accept the null hypotheses.
For trend B the critical value for 5% significance is also 2.021, the value obtained by the t-test is 13.5, and this is significantly greater than the critical value. This means that the probability that chance alone may have caused the difference between the two means in trend B is less than 0.01%. Therefore I am more than 99.9% confident that the difference between the two means for Trend B is significant. Therefore for this trend I can now reject the null hypotheses and accept the alternative hypotheses that there will be a significant difference between the effect of Nitrate concentration and the growth of duckweed fronds.
From my investigation I have found that the 0.4% is the most favoured environment on the growth of the duckweed fronds, as it is receiving the maximum amount of all nutrients, due to it’s favourable water potential solution.
Evaluation
The results obtained I found were reliable, because many replicates were carried out, for each of the nitrate concentration. This gave me a reasonable amount of data to work with and carry out statistical test. The result obtained from the t – test in Trend A did not provide enough significance in order to accept the alternative hypothesis. But the value in Trend B allowed me to accept the alternative hypotheses and reject the null. I think over all the results are reliable, but since the results were pooled from the class there may have been one or two anomalies. As the standard deviation in the 0.4% x 10-3 concentration of nitrates in trend A is more spread out because there were results that were unexpectedly small, such as 8 and 7 fronds, compared to 36 and 33fronds from the initial 8. So although there was the right increased amount of fronds in the concentration there was also a small amount of frond growth, which are anomalous results. This resulted in not a lot of difference between the mean values of 0% and 0.4% concentrations of nitrates.
On the other hand the results in trend B are very reliable, and show what was predicted to happen in the conclusions made earlier on due to osmosis effect.
In order to increase the reliability of the results factors such as the PH were kept constant. As the PH used was not too acidic or too alkaline, so that PH does not become a limiting factor for growth. The solutions used were dilute, so were a suitable environment for the duckweeds to grow. If the duckweeds were placed in a too acidic environment, then the duckweeds will not be able to grow properly as the Chlorosis process will take place, since the frond will not be able to get enough nutrients to make their pigments. To increase the reliability of the results 30 replicates were pooled together to allow me to carry out a statistical test, these 30 replicates all started and ended the investigation.
The major factors for survival of the plant were controlled as best as possible. The light banks were on all the way through the experiment which provided each duckweed with the maximum amount of light energy, so that they can photosynthesize as much as possible. Also since they were all exposed to the same light bank each duckweed in the experiment was exposed to the same quantity and quality of light. This increased the reliability of the results since each duckweed have equal chance of absorbing light and using the energy to grow. The temperature was controlled as there was an electrical heating system in the room which provided each replicate with the equal heat needed in order to carry out metabolic processes. Also this temperature was always kept constant through out the experiment and was controlled as best as possible. This increased the reliability of the results as an increase in temperature of will lead to an increase in the growth as processes such as the Calvin Cycle are enzyme controlled, so therefore more sugars and energy needed for growth will be supplied, and hence a decrease in temperature will slower the rate of growth, and therefore cause the results to be unreliable. The experiments were all held in the same room, so that other limiting factors such as carbon dioxide were controlled.
Each duckweed used was from the same pond, this increased the reliability of the results, because before staring the experiment the duckweeds all had the same nutrients and components inside the cells. As if they were all from different ponds, they may have been polluted and contained different nutrients inside them which could affect their growth rates.
The same tap water used increased the reliability of the results as tap water from different taps contain different amount of nutrients.
However to the low t- test value obtained in trend A means that there may be factors that affect the reliability of the results. So the factors that could affected the growth may be the size of the fronds, as even with the use of the magnifying glass it was not really possible to make sure that all the fronds were the same sizes accurately. Therefore if the fronds size were slightly bigger this would have affected the results because the plant would have carried out an increased photosynthesis so growth increased as there was more light energy available to make sugar and synthesize proteins for growth. And so a smaller frond meant less photosynthesis and energy provided for the plant to grow so this is a limitation to the equality in growth.
Another limitation was that the thickness in rootlets of the duckweeds was not considered, as they were too tiny to be able to measure with a ruler. This will affects the results obtained because a thicker rootlet meant that there was a bigger surface area for the root to absorb more water and uptake more nutrients, this therefore means that more nitrates are taken up and so increased growth. A thinner root would mean that there are fewer uptakes of nitrates and so decrease growth. This may be factor why in trend A the 0.4 % x 10 concentration of nitrates had the greatest spread of data, from its standard deviation.
Also another factor which could have affected the results is that the use of the mounted needle could have damaged the duckweeds, so therefore some duckweeds may not have photosynthesised and took up nitrogen as much as other duckweeds. This would have led to a decrease in frond growth.
Another major limitation was evaporation. Over the weekends evaporation would have occurred, and the plants were not watered then, this meant that the concentration of the solutes present inside the solution increased. This lead to a lower water potential of the solutions than usual, and so the results would have been affected, This is because not as much water entered the plant cells, so in more concentrated solution it would have led to dehydration of the cells. Therefore less growth of fronds takes place.
Another major limitation of the experiment was the growth of algae. Algae were present in some replicates of the 2% x 10 concentration of nitrates, so this would have affected the results. Algae are aquatic plants and so compete for the same factors of duckweeds, so they would have taken up nutrients in the solutions, leaving not as much for the duckweeds. And so the duckweeds were not able to grow as much.
Over all my results were reliable enough to show that the growth was increased by nitrogen if it was in the plant was surrounded by the correct water potential.
Basically this is the process that occurs in eutrophication in rivers and lakes near farms, where fertalizers containing nitrates leak in the water. The plants living in the water undergo the same process, as their growth increase due to the increased amount of nitrogen they receive.
If I were to carry out the experiment again I would use more replicates. And also use a more close range of nitrate concentration as this will give me a more reliable outcome.
Principles and concepts
In the solutions where the uptake of nitrogen took place the fronds on the duckweeds grew. This is because nitrogen is an essential component for the plant’s growing process. Nitrogen is used in the manufacture of the nitrogenous co- enzyme NADP, it also in the energy used as ATP, as it contains the nitrogenous base Adenine. These two components need nitrogen to be taken in, in order to be produced. They are also the most important components for survival. NADP is used as a hydrogen accepter and transporters. The ATP molecule is used to transfer energy to metabolic places. So the solutions, which allowed the most uptake of nitrates, produced a greater number of ATP and NADP molecules, and their increased synthesis aided the growth of plant tissue.
In the thylakoid membranes of the plant, the light dependant part of photosynthesis took place. Here the light energy supplied by the constant light banks were absorbed by the chlorophyll and other pigments. The more nutrients that were taken up by the roots such as the magnesium and potassium meant that more pigments such as chlorophyll were manufactured. The lights are then harvested in photosystems so that maximum amount of light is taken inside. The light energy absorbed causes the electrons within the chlorophyll to become excited. The energy released synthesises ATP from ADP and an inorganic phosphate. Also during this stage the water absorbed by the roots in the solution, undergo photolysis. The H ions produced from this reduce the NADP into NADPH. These molecules produced are the essential components of the Calvin Cycle, this is water is also the reason why water is vital, as it provides the H ions, without these ions the Calvin Cycle cannot take place. This Light- independent reaction is where the main manufacture of sugars and carbohydrates takes place, with the help of the reduced NADP and energy providing ATP molecule. The light – independent reaction takes place in the stroma of the chloroplast, and the reaction needs energy and H ions to keep the cycle going.
B The fronds were in a constant environment, where each frond was exposed to the equal amount of CO2. The 5 carbon compound RuBP binds to the carbon dioxide, with the help of the enzyme Rubisco to produce another compound, GP. The ATP provides the energy for the synthesis of the synthesis of this compound into sugars such as sucrose. The NADP provides H ions for the reduction of organic compound to produce sugar. The calvin cycle makes carbohydrates, lipids and protein via aminoacids. The sugars produced ( mostly sucrose) are transported from the leaves to actively growing regions to provide energy for growth and respiration.
The nitrogen is also the component of proteins, which is the polymer of aminoacids. Each amino acid contains the carboxyl group, R group and the nitrogen containing amine group. These amino acids link together by peptide bonds, forming a long chain of polypeptides. The chain leads to different structures of proteins. Two kinds of proteins can be made fiborous or globular proteins. The globular proteins that are made are like enzymes such as the Rubisco used in the Calvin cycle. Enzymes in plants are needed to make parts of the plants like chloroplasts and pigments. The membrane of these plant cells contains scattered proteins, which in the root cells allow theuptake of nitrates and other essential nutrients.
Proteins are vital components in a plants variety of metabolic pathways and processes. Proteins make up the molecular structure of DNA, RNA and host of other critical metabolic processes required for plant growth.
The plant grows using, mitosis as cell division, and therefore copies the previous cells DNA in order to divide and replicate. The cells therefore need to make many new DNA’s in each new cell. DNA is made up of 4 nitrogenous bases, adenine , guanine, cytosine and thymine. So the nitrates taken up by the roots are also used to manufacture the DNA, DNA carries the instructions for the cells in the form of codes to make particular proteins. The nitrogenous bases are attached to a 5 carbon sugar and a phosphate group, joined by a condensation reaction to form a nucleotide. Two strands of poly nucleotides join together to make the DNA, which is copied into every other new cells.
Nitrogen also stimulates the growth of roots, which enables efficient uptake of all other nutrients. Amino acids are made in the root tips and carried to growing areas in the plant to make proteins.
Evaluation
The results obtained I found were reliable, because many replicates were carried out, for each of the nitrate concentration. This gave me a reasonable amount of data to work with and carry out statistical test. The result obtained from the t – test in Trend A did not provide enough significance in order to accept the alternative hypothesis. But the value in Trend B allowed me to accept the alternative hypotheses and reject the null. I think over all the results are reliable, but since the results were pooled from the class there may have been one or two anomalies. As the standard deviation in the 0.4% of tren A is more spread out because there were results that were unexpectedly small.
A table to show the class results and average number of growth of fronds, using all the replicates.
The table above shows all the results obtained from the class, and have been pooled together. Each replicate shows the number fronds that were alive after the experiment had ended. These results are going to be used to calculate the t- test, in order to get a more reliable and accurate outcome to prove one of the hypotheses correct or wrong for each of the trends.
A table to show my individual results
I am using my individual results to plot the graph.