Index

 

                                                                                                                                   Pag.

Preface………………………………………………………………………………..2

 

Introduction…………………………………………………………………………...3

 

Main hypothesis………………………………………………………………………3

 

Experiment A “Photosynthesis in a coloured leaf”…………………………………..4

 

Experiment B “The making of oxygen”……………………………………………...6

 

Experiment D “Chromatography”…………………………………………………....9

 

Main conclusion……………………………………………………………………..11

 

Epilogue……………………………………………………………………………...11

 

Appendixs……………………………………………………………………………12
Preface

Leaves are like small factories that produce food for the plant. Different parts of the leaf have different jobs. The veins in a leaf are bundles of tiny tubes that carry water and minerals to the leaf and return food from the leaf to the rest of the plant. Veins also help with the support of the leaf.

On the underside of the leaf are small openings or pores called the stomata. The stomata serve as the lungs of the leaf allowing air to enter. The stomata allows the evaporation of water and the release of oxygen during the night.

The outer layers of the leaf are covered with a waxy layer, which prevents the leaf from drying out.

Leaves are green because they contain small bodies in the cells called chloroplasts. The chloroplasts contain a green pigment called chlorophyll. This green material gives the leaf its colour.

With the help of chlorophyll and energy from the sun, a leaf can change lifeless substances into food. This process is called photosynthesis. Plants need water (H₂O) and carbon dioxide (CO₂) to make food through the process of photosynthesis. The plant’s roots gather the water, and carbon dioxide is gathered from the air through the stomata.

The leaf uses chlorophyll and sunlight to change the water and carbon dioxide into oxygen and glucose (sugar). This sugar is mixed with water and sent to other parts of the plant to be used by the plant as food. The oxygen is released into the air through the stomata. This is written as:

6H₂O  +  6CO₂   ---------->  C₆H₁₂O₆   +  6O₂                                    (Netto)

This is read as carbon dioxide plus water in the presence of light and chlorophyll produces oxygen and sugar glucose.

Figure 1: Overview of photosynthetic processes as they occur in plants (and also in algae and cyanobacteria).

 

Introduction

To know some more about the phenomenon photosynthesis, we carried out some practical experiments. This project and these experiments were completed by Marianne Kreling and Wagma Alocozy.  This research took a lot of time. Every single experiment was being done on various days during the last two terms.  There were a total of four experiments, however, one of them was cancelled because it was already completed in the third class.

We started the first experiment (experiment A) on the 17^th of February and concluded it on the 19^th of February. This had to do with the photosynthesis in a coloured leaf.

On March 5^th, we carried out the second experiment.  We checked the experiment on March 7^th, however, no results were obtained.   It was not until March 10^th  that we had the results. Then we had experiment C, which we didn’t do.

Experiment D was started on April 23^rd and it consisted of the chromatography of leafs.

This report will describe all the experiments that were performed, the hypothesis, the needs of the experiment, the results and a conclusion relating to each one of the experiments. Lastly, the report will end with a general conclusion, summing up our project.

 

 Main hypothesis

There is talk of the phenomenon photosynthesis if a plant contains chloroplasts and when it receives sunlight. (water and carbon dioxide are indispensable)

 

Experiment A   “Photosynthesis in a coloured leaf”

 

Hypothesis:

If a part of a leaf doesn’t make contact with sunlight for 24 hours then that part will be uncoloured.

 

Needs:

-         Plant with coloured leafs, from which the leafs are partially covered with tin foil, and that has been in the light for 24 hours.

-         Water cooker with water, test tubes and test tube rack.

-         A pair of tweezers.

-         Ethanol or methylated spirit.

-         Petri plate.

-         Solution of iodine.

-         A leaf from the Tradescantia

 

Method:

On the first day we just covered one leaf from the plant partially with tin foil. We made a drawing of the covered leaf to be able to compare it with the leaf after the experiment[1]. Then, we placed the plant in front of the window.

The second time we worked on experiment A, we took the partially covered leaf from the plant. In the mean time we boiled the water. Then we took off the tin foil from the leaf. Next, we put the leaf for 180 seconds in the boiling water. The leaf became very soft. Then we used tweezers to take the leaf out of the water and placed it in a test tube. The water was starting to cool down, so filled half of the tube with alcohol, which already consisted of the leaf.  Then, we put the test tube in the boiling water in a fume-cupboard. The alcohol had also started to boil now.

When the leaf was uncoloured we took the test tube out of the water, took the leaf out of it and put it back in the boiling water for 180 seconds. Then, we put it in a petri plate and poured a solution of iodine over it, until it was totally under the liquid.

At the end we made a drawing from the leaf again[2].

 

Perception:

After boiling the leaf for the first time, it became very soft and vulnerable. In the fume-board, the leaf lost all of its colour and became white. The alcohol became green. Back in the boiling water the leaf stayed as it was, uncoloured.  After putting a solution of iodine over it the whole leaf became dark red. And gradually the colour changed to black.

 

Conclusion:

Our hypothesis is not fulfilled, because the leaf was black, opposite of what we had originally thought.                                                                                                                                 

 

Advice:

The reason why our experiment met with disaster is that we put it directly in the sunlight. Knowledge tells us when you want to carry out an experiment like this, you have to start with “a clean slate”. This means that there isn’t any “old” starch left anywhere in the leaf.

 

A better method to approaching this experiment is to place the leaf for 24 hours in the dark, before you set it in the sunlight.  When you first put it in the dark, the leaf will remove all the starch out of its spare parts. This is because the plant has to survive the dark. You can be sure that all the starch in the leafs will be consumed in those 24 hours. This way all the starch in the leaf will be vanished and there won’t be any starch under the tin foil either. Therefore, when you put it back in the sunlight, the plant has to build up new starch and now you can be sure it starts with “a clean slate”.

 

Another thing that could have improved our results was to use a verifiable leaf. So we had to cover another leaf totally. Afterwards we could compare both results to see if there was actually a utility to cover a part of the leaf with tin foil.

 

The third criticism is that we didn’t put the plant in the sunlight for a total of  24 hours. It had been staying there for almost three days. So the plant was also in the dark. That means that the leafs will remove all the starch out of its spare parts. And then the next morning the plant has to start with a clean slate again. This is not really advancing for the experiment. A better manner would be to put a plant in simulation light for a total 24 hours.

 

Summarised:

First we had to put two plants in a total dark room for 24 hours; one with a partially covered leaf with tin foil to do the experiment with and one with a total covered leaf with tin foil. After those 24 hours we had to put those two plant under a fake sun, who shines for a total of 24 hours.

                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  

 

Experiment B “The making of oxygen”

 

Hypothesis:

If a plant stays in front of the window for five days and another plant in total dark for five days, then the plant in front of the window will produce oxygen and the plant in the dark won’t.

 

Needs:

-         Plant from the water. We used  two pieces of 10 cm of the Cabomba

-         Erlenmeyer

-         Funnel

-         Test tube

-         Matches

-         Thin piece of wood

 

Method

We filled a test tube and an Erlenmeyer with water. Then, we put the plant into the Erlenmeyer under the funnel. After that, we put the test tube, filled with water, over the funnel.

 

 

 

 

Figure 2: experiment construction

 

We made two of these constructions. One of them we placed in front of the window and the other one in a total dark room (this is because of supervision). After two days we surveyed the plants. We gauged the quantity of the ‘air’ in the test tubes. Then, we placed the two constructions at their previous places for three days. After those three days our experiment was finished.

We had to prove that the ‘air’ in those two test tubes was oxygen. In order to prove this, we took a piece of wood glowing. Then we closed the first test tube with our thumb, so the gas couldn’t elude, and put the piece of wood into it. If the piece of wood kept on burning, that would mean the tube had oxygen in it.  However, if the fire died down then we would know that the tube did not consist of any oxygen. We also repeated this test with the tube that came from the dark. 

 

Results

 

	Plant in front of the window		Plant in the dark
	1st measuring (after 2 days)	last measuring (after 5 days)	1st measuring (after 2 days)	last measuring (after 5 days)
Quantity of ‘air’ (cm)	0,9	1,4	0,5	0,7

 

 

stock-taking:

Plant in front of the window:

1,4/ 5 = 0,28

This means that the quantity of air had an increase  of 0,28 cm a day.

 

Plant in the dark:

0,7/ 5 = 0,14

This means that the quantity of air had an increase of 0,14 cm a day.

 

Perception

When we were checking the air with the glowing piece of wood, it didn’t  burn again.

 

Conclusion

There was some gas in the test tubes, especially inside the one placed in front of the window, but we couldn’t verify that the originated air was oxygen. That’s why we can’t give an conclusion to our hypothesis and have to reject it.

 

Advice

We know from our knowledge that the gas has to be oxygen. So, there must be something wrong with the manner we did the experiment. We were thinking about that and perhaps we found the problem.

When we wanted to prove that the gas was oxygen, we closed the test tube with our thumb, so the gas couldn’t elude. But when we released the test tube, to put glowing piece of wood in it, the gas could have easily escaped. Another possibility is that outside air could have got inside the test tube. When this happened, the oxygen would have been diluted and then it wouldn’t have reacted with the glowing piece of wood.

 

We now have a better method. It is a lot easier to place a little hose, with a syringe on it, in the test tube when it is still under water.  This way you can easily suck out the gas. After that you have to squirt the glowing peace of wood with that gas in the syringe.

This way isn’t just much easier, but now you can also be sure that you have all of the gas and in a higher concentration, so it will be more effective. 

 

According to the theory, water and carbon dioxide are also indispensable by the process of photosynthesis.

In this research we only investigated the influence of sunlight, but to be sure about the working of photosynthesis it is important to investigat all the variables.

 

The other variable is the gas carbon dioxide.  This is the gas that is essential for the plant to build up this process. To research the importance of carbon dioxide in the photosynthesis, you have to accomplish the same experiment. Instead of putting one construction, as you can see in figure 2, in a total dark room, you have to put that one in a void place. To reach this you can use a bell jar. The construction has to be in the bell jar. After all this the air in it has to be sucked out.  This way you can be sure that the plant doesn’t make contact with carbon dioxide.

The other construction has to be in the same situation as in the first experiment. So you have one construction in a bell jar without any air (so without carbon dioxide) and one construction (the same as in experiment B).

Both constructions have to be put in front of the window.

Now you can see if carbon dioxide is really needed by the photosynthesis process and what the influence is on the production of oxygen.

 

To investigate what the influence of the temperature is on the photosynthesis you can use the same constructions as in experiment B in three different rooms. The first room has to be the normal room temperature. The others have to be extremely cold and extremely warm. But the other circumstances have to be the same, in order to be sure that the temperature is the only difference.  Now you have to measure the quantity of air in the test tubes again. Comparing the differences in quantity, you can discover what the influence of temperature is on the photosynthesis process.                                                                                

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Experiment D   “Chromatography”

 

 

Hypothesis:

Chlorophyll is not one chemical matter, but is composed of several chemical elements.

 

Needs:

-          Four different fresh leafs: Ligustrum vulgara  L., Castanea sativa L., Sambucus nigra L.  and Aegopodium podagraria L[3]. 

-          Mortar and pestle

-          Acetone

-          Test tube

-          Pipette

-          One slip of filtering paper

 

Method:

On this experiments, we worked in groups of four. Everyone in the group had a leaf, each leaf from a different plant.

We made the leaf in very little pieces by means of the mortar, the pestle, and acetone. After this we prepared the filtering paper: on the filtering paper, we put a line with a pencil at ca. 2  centimetres from the bottom. Using a pipette we put some concentrated chloroplasts solution on the pencil line of the paper. We waited till the acetone was evaporated. This was being repeated till we saw  a clear green dot.

When we had a clear green dot on the paper, we were ready to start with the chromatography experiment. We put the papers into a pail of a liquid. This was a liquid of 8% acetone and 92% petroleum ether . We set the papers in the liquid for about ten minutes, till the paper was covered with the liquid. After this we took the papers out of the of the liquid and let them dry. With a pencil, we marked the top of the liquid and also the boundary lines of the different colours on the paper.

After all this we compared the different leaves. First we compared the three Ligustrums , which were researched three times. After that we compared the four different leafs in our group (Ligustrum vulgara  L., Castanea sativa L., Sambucus nigra L.  and Aegopodium podagraria L).

 

Perception:

After we took the papers out of the liquid we could see that there were different colours on it[4]. In order, these were the colours on the paper (in this rank):

-          light green

-          green

-          yellow

-          orange

 

 

 

 

 

 

 

Results:

 

Ligustrum vulgara L.

 

 

The different leafs

 

Different leafs:	Distance between the spot and the different colours:
	Light green (chlorophyll A)	Green (chlorophyll B)	Yellow (xanthophylls)	Orange (carotene)
Ligustrum vulgara L.	3,40	4,40	5,60	8,10
Castanea sativa L.	3,10	3,70	5,10	8,10
Sambucus nigra L.	1,90	2,70	4,85	7,50
Aegopodium podagraria L.	1,10	1,80	4,10	5,70

 

As you can see in the tables, every leaf contains the same colours and in the same rank, but on the papers they reach different highs.

 

Conclusion:

When we look to the results of this experiment, we see that the hypothesis is quiet accurate. The different colours we see on the papers make us accept that chlorophyll is indeed not one chemical matter, but is composed of several chemical elements.

 

Because all the other circumstances are the same, the differences in highs are due to the amount of time the paper is set in the liquid.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Main conclusion

 

We can’t give a main conclusion, because our first two experiments failed. Why this experiments failed, you can read in the “advice”  of those experiments.

We were able to give a conclusion of the last experiment, but that is not sufficient for giving a main conclusion.

 

 

Epilogue

 

This was a very funny project and we learned a lot from it.  We did not procrastinate, which makes us feel that we accomplished what we had originally planned to do.  We met all of the goals that were required of us on this project.  Even though two of our experiments failed due to our poor methods, we still feel positive because we found out the reason why those experiments failed.  The reasons are listed under the “Advice” section of each experiment.  Therefore, if we had to do these experiments again, we believe that our first two experiments will be a success just like our third experiment. 

 

Appendix 3

 

 

a dehydrated Castanea sativa L.

a dehydrated Sambucus nigra L.

 

Appendix 4

 

 

 

 

 

a chromatogram of the Castanea sativa L.                                a chromatogram of  the Sambucus nigra L.