bio2

Anouk van Dijk

Monique v. d. Knaap

Naaldwijk - NL

AG5B

Index

Index....................................................................................................................................... 2

Introduction............................................................................................................................ 3

How does photosynthesis works?...................................................................................... 4

Practical work A: Photosynthesis in a coloured leaf......................................................... 6

Our central question is:.................................................................................................... 6

Hypothesis:........................................................................................................................ 6

Needs for lesson 1:.......................................................................................................... 6

To do for lesson 1:............................................................................................................ 6

Needs for lesson 2:.......................................................................................................... 7

To do for lesson 2:............................................................................................................ 7

The results......................................................................................................................... 7

Conclusion and questions............................................................................................... 8

Practical work B: The making of oxygen............................................................................ 9

Our central questions are:................................................................................................ 9

Hypotheses:...................................................................................................................... 9

Needs:............................................................................................................................... 9

To do:................................................................................................................................. 9

Results:.............................................................................................................................. 9

Conclusion:..................................................................................................................... 10

Practical work D: Chromatography from leafs............................................................... 11

Our central questions are:............................................................................................. 11

Hypothesis:..................................................................................................................... 11

Needs:............................................................................................................................. 12

To do:............................................................................................................................... 12

Results:............................................................................................................................ 12

Conclusion:..................................................................................................................... 14

Final Conclusion................................................................................................................. 15

Discussion.......................................................................................................................... 16

Practical work A: Photosynthesis in a coloured leaf................................................... 16

Practical work B: The making of oxygen...................................................................... 17

Practical work D: Chromatography from leafs............................................................ 17

Enclosure number 1……………………………………………………………………..18

Enclosure number 2……………………………………………………………………..19

Enclosure number 3……………………………………………………………………..20

Enclosure number 4……………………………………………………………………..21

Introduction

From week 8 until week 18 Anouk and Monique have been working at practical work for biology. This experiment was about photosynthesis.

In this report we are going to explain how photosynthesis works. First we are going to give some background information about the process, then we are going to explain the process with the three experiments we did.

The practical was split up in four parts. The first part (A) was to search for the difference in chloroplasts between covered leafs and uncovered leafs. The second part (B) we compared the making of oxygen from water thyme and American river weed. The third part (C) was an experiment with pencils about chromatography. But because we had already done this experiment at the third class, we’ve skip that part. So there isn’t anything about it in this account. The last part (D) was about the chromatography of leafs from four different kinds of plants. For this experiment we have worked with small group of four students (Wagma, Marianne, Anouk and Monique) and we exchanged our results afterwards.

At last we have a general conclusion and a discussion about the problems we encountered.

How does photosynthesis works?

All animals live on energy stored in the chemical bonds of organic molecules made by other organisms, which they take in as food. The molecules in food also provide the atoms that animals need to construct new living matter. Some animals obtain their food by eating other animals. But at the bottom of the animal food chain are animals that eat plants. The plants trap energy directly from sunlight. As a result, all of the energy used by animal cells is derived ultimately from the sun. In this article we will explain something about photosynthesis. How plants can make organic molecules out of only inorganic molecules.

Solar energy enters the living world through photosynthesis in plants and photosynthetic bacteria. Photosynthesis allows the electromagnetic energy in sunlight to be converted into chemical bond energy in the cell. Plants are able to obtain all the atoms they need from inorganic sources: carbon from atmospheric carbon dioxide, hydrogen and oxygen from water, nitrogen from nitrates in the soil, and other elements needed in smaller amounts from inorganic salts in the soil. They use the energy they derive from sunlight to build these atoms into sugars, amino acids, nucleotides, and fatty acids. These small molecules in turn are converted into the proteins, nucleic acids, polysaccharides, and lipids that form the plant. All of these substances serve as food molecules for animals, if the plants are eaten later.

The reactions of photosynthesis take place in chloroplasts in two stages. The first stage is called photophosphorylation. In this stage, energy from sunlight is captured by photosynthesis pigments who give the energy from the light to the electrons of the chlorophyll molecules. They will make a wider route around the kern of the molecule. With these electrons can happen two different things: They can hand over the energy by little quantities. This energy is used for active transport. The concentration difference on both sites of the membrane that arises by this, will be used as an energy source for the photosynthesis of ATP (energy molecules). After this the electron hasn’t any energy left and goes back to the chlorophyll molecule. In the other way the electrons (full of energy) will be hand over to electrons acceptors. Because the electrons have a negative charge the molecule who is left behind gets a positive charge. The electrons will be replaced by other electrons (without energy). These electrons are usually from water molecules. Molecular oxygen (O2) derived from the splitting of water by light is released as a waste product of this first stage.

In the second stage, the molecules that serve as energy carriers are used to help drive a carbon fixation process in which sugars are manufactured from carbon dioxide gas (CO2) and water (H2O), thereby providing a useful source of stored chemical bond energy and materials- both for the plant itself and for any animals that eat it. This reaction take place in the liquid of the chloroplasts. You can see the cycle of this reaction on the previous page.

The net result of the entire process of photosynthesis, can be summarized simply in the equation:

light energy + 6 CO2 + 6 H2O à sugar + 6 O2

The sugars produced are then used both as a source of chemical bond energy and as a source of materials to make the many other small and large organic molecules that are essential to the plant cell.

Practical work A: Photosynthesis in a coloured leaf

Like we explained before, sugars are manufactured from carbon dioxide gas (CO2) and water (H2O). Almost immediately these sugars are converted into starch. During the night, when there is no photosynthesis, the starch is put in other parts of the leafs.

In the first experiment we are going to investigate what the influence of photosynthesis pigments and light are on the formation of starch. We are going to use a plant with coloured leafs, from which the leafs are partially covered with tin foil. This way we can compare the parts with and without chloroplasts, (the green and the white parts), and the parts from the light and from the dark, (the covered parts and the uncovered parts). Starch can be showed by a solution of iodine.

Our central question is:

What is the influence of photosynthesis pigments and light on the formation of sugar?

Hypothesis:

We think we are not going to find starch on the white parts of the leaf, because there are no photosynthesis pigments. On the covered parts we are not going to find starch too, because photosynthesis needs light. So we think that we are only going to find starch on the green uncovered parts of the leaf.

Needs for lesson 1:

Ø Plant with coloured leafs, for example Clorophytum, Tradescantia, Hypoëstes sanguiolenta, Scindapsis aureus or the L.maculatum L.

Ø Some tin foil

To do for lesson 1:

Cover a part of the leaf of you plant with tin foil.
Draw your leaf true to nature.

24 hours later…

Needs for lesson 2:

Ø The plant from lesson 1

Ø Two pans with boiling water

Ø A pair of tweezers

Ø Ethanol in a closed test tube

Ø Test tube rack

Ø Petri plate

Ø Solution of iodine

To do for lesson 2:

1. Take the partially covered leaf from the plant.

Take the tin foil from the leaf.
Put the leaf in the pan with boiling water for 180 seconds. The leaf will be very soft then.
Take the leaf out of the water by means of the tweezers.
Put the leaf in the test tube with ethanol and close the test tube again.
Because you are working with ethanol, you’d better do the next step in a closed room with a cooker hood. (= fume-cupboard)
Put the test tube rack with the test tube in the other pan with boiling water. Pull the cork off of the test tube. Wait until your leaf is uncoloured.
Take the leaf from the test tube and put it again in the first pan with boiling water.
After 180 seconds you take the leaf out of the pan and put it in the petri plate.
Put iodine on it.
Make a drawing of the leaf again.

The results

Anouk van Dijk took the first lesson alone. So we have just one drawing from the first lesson. We took the second lesson with the two of us, so we have two drawings.

We chose the plant Hypoëstes sanguiolenta. It took about 9 minutes before the leaf was uncoloured. For the rest we don’t have that many results, just the drawings. They are enclosure 1, 2 and 3.

You can see that all the green parts and some of the white parts became black, because of the iodine.

Here you can see our leaf after the experiment.

Conclusion and questions

If you compare the parts of the leaf with chloroplasts to the ones without - the green parts and the white parts in our case - you’ll see that the green parts became black after the practical work and some white parts too. The other white parts remained white. If you compare the parts from the light to the ones from the dark, you won’t see any difference. The green parts under the tin foil are just as black as the uncovered parts. You can say the same for the white parts of the leaf.

So when we look at our results you can say there isn’t any difference between the covered and uncovered parts of the leaf and the parts with and without chloroplasts. .

Our practical work didn’t go exactly like we planned. We had expected another result. In the last part of our report, we’re going to discuss why this practical work didn’t turn out like we thought.

Practical work B: The making of oxygen

We’ve already told something about how photosynthesis works. And what kind of substances is necessary for this reaction, and which substances arise. We will repeat the reaction formula:

light energy + 6 CO2 + 6 H2O à sugar + 6 O2

In this experiment we are going to find out if this is correct and if there is a difference between the oxygen production of two different plants.

Our central questions are:

Which gas will arise during the experiment and is there a difference between the oxygen production of two different plants?

How can we make an experiment to show that carbon dioxide is needed and that the temperature of the surroundings is also very important for photosynthesis?

Hypotheses:

We think that oxygen arises during the experiment and that the plants won’t produce the same quantity of this gas. So it depends on the kind of plant how much oxygen have been produced.

Needs:

· Plants from the water: water thyme, American river weed.

· Erlenmeyer, funnel and test tube

· Matches and thin piece of wood

To do:

Fill the test tube and the Erlenmeyer with water.
Put the plant into the Erlenmeyer with the stem straight up.
Put the funnel and the test tube upside down into the Erlenmeyer.
Put the whole ‘construction’ into the light.
After two days the test tube will be filled with ‘air’.
Close the test tube ( with your thumb), make the piece of wood glowing and put it into the tube. This will burn again.

Results:

	length (cm) of the test tube filled with air:
datum:	water thyme:	American river weed:
5 March 2003 (begin)	0,05 cm	0,10 cm
7 March 2003	1,10 cm	0,90 cm
10 March 2003 (end)	1,40 cm	1,40 cm

At the end of this practical work we wanted to demonstrate what kind of gas was in the test tube. We followed the instructions, but the glowing piece of wood didn’t burn again. Why this didn’t happen we will discuss in the last part of this account.

Conclusion:

The gas in the tube we wanted to show with the burning piece of wood was oxygen. This appears from our extra information.

With this experiment we wanted to get to know the difference between the oxygen production of two different kind of plants. The water thyme produced the first few days more oxygen than the American river weed. We think that’s because the quantity of oxygen that was in the stem. The last couple of days the American river weed produced more oxygen than the water thyme. In the end both plants produced the same quantity of oxygen.

So we can say that there isn’t a big difference between the quantity of oxygen the both plants produced after a while, but there is a little difference between the speed the both plants produced oxygen.

If you want to investigate that carbon dioxide is needed for the photosynthesis, you have to make two framings. For one framing you use water that contains carbon dioxide and for the other framing you use water without carbon dioxide. You have to put both framings into the light. All other circumstances has to be similar as our experiment.

If you want to investigate that the temperature of the surroundings is very important for photosynthesis you have to make two framings again. Now you put one framing in a temperature that obviously difference from the temperature you put the other framing into. Both framings have to be in the light. All other circumstances has to be similar as our experiment.

Practical work D: Chromatography from leafs

Energy from sunlight is captured by photosynthesis pigments who direct the energy from the light to the electrons of the chlorophyll molecules. These electrons can release their energy and make the rest of the photosynthesis cycle possible.

The photosynthesis pigments exist within the chloroplasts.

There are four different kinds of pigments:

- Chlorophyll A

- Chlorophyll B

- Carotenoids

- Xanthophyll

White light or sunlight is a mixture of all colours of light. You can show all those colours of light with a prism. White light is broken into several weaves with each a different weave length. So you can see all the colours of the rainbow.

If light falls on a green leaf, the green light reflects and the other colours are absorbed. Every pigment absorbed a different weave length, a different colour. The advantage of having four kinds of pigment is that more light can be absorbed. Therefore the pigments can give more energy to the electrons. The photosynthesis pigments are mostly absorbing blue, red and violet light. You can see that in the diagram.

In the next experiment we are going to investigate what the difference is between the rapidity of the four photosynthesis pigments. And we are also going to investigate of there is a difference in the rapidity’s of the pigments of different plants.

Our central questions are:

What’s the difference in rapidity between the four photosynthesis pigments (Chlorophyll b, Chlorophyll a, Carotenoids and Xanthophylls)? And are the rapidity’s of the pigments the same by all plants?

Hypothesis:

We think that the speed of the pigments by every plant is the same and that only the quantity differs. We think the Xanthophylls is the fastest. The second fastest is Carotenoids. The slowest is Chlorophyll b and the second slowest is Chlorophyll a.

Needs:

· Fresh leafs from a plant, Ligustrum vulgare L., Aegopodium podagrarie L., Sambucus nigra L. and Castanea sativa L

· Mortar and pestle

· Some sand and aceton

· One slip of filtering paper

· A measure cylinders with a piece of cork or glass

· Some liquids, for example aceton (8%) and petroleum/paraffin (92%)

To do:

Make the leaf in very little pieces with help of the mortar, the pestle, some sand and aceton.
Make a concentrated solution of chloroplasts.
Put a line with a pencil at ca. 2 cm from the bottom on the filtering paper
Put some concentrated chloroplasts solution on the pencil line on the paper.
Wait till the aceton has been evaporated.

6. Repeat until you will see a clear green dot.

Put the papers into the cylinders with the liquids, filled for at about 1 cm. The liquids may not touch the dots.
Wait until the top of the liquids has reached ca. 2 cm from the top of the paper.
Mark on the paper this top of the liquid and mark the different coloured spots.

Results:

We made four chromatograms with the four of us. Two of them are in this account. They are enclosure number 4. The other two are in the account of Marianne and Wagma.

We compared four chromatograms of the Ligustrum vulgare L of three different groups. (The fourth one from Dirk is a failure) After this we compared the chromatograms of the four different kind of plants from our own group. We always measured from the middle of the spot to the top of one colour. The results are down here.

Ligustrum nr.	Chlorophyll b	Chlorophyll a	Carotenoids	Xanthophylls
1 (ours)	3,4	4,5	5,6	8,1
2 (wendy)	3,8	5,25	6,2	7,0
3 (sanne)	6,8	7,5	7,8	8,4

The last result we can’t compare, because that’s the point where the fluid is stopped. To compare this results right, we have to compare the relative rapidity’s of the pigments. We calculate this by divide the pigment by the end of the liquid. The end of the liquid is the same as the xanthophylls results. This is because we couldn’t finish the experiment because we hadn’t enough time. So the ends of the liquid aren’t all the same. For example: our chlorophyll b: 8,1/3,4 = 0,42

The relative results from all Ligustrum leafs:

Ligustrum nr.	Chlorophyll b	Chlorophyll a	Carotenoids	Xanthophylls
1 (ours)	0,42	0,56	0,69	1,00
2 (wendy)	0,54	0,75	0,89	1,00
3 (sanne)	0,81	0,89	0,93	1,00

The results of the different plants:

Plant nr.	Chlorophyll b	Chlorophyll a	Carotenoids	Xanthophylls
1. ligustrum	3,4	4,5	5,6	8,1
2. Aegopodium	1,1	1,8	4,1	5,7
3. Sambucus	1,9	2,7	4,85	7,5
4. Castanea	3,1	3,7	5,1	8,15

The relative results of the different plants:

Plant nr.	Chlorophyll b	Chlorophyll a	Carotenoids	Xanthophylls
1. ligustrum	0,42	0,56	0,69	1,00
2. Aegopodium	0,19	0,32	0,72	1,00
3. Sambucus	0,25	0,36	0,65	1,00
4. Castanea	0,38	0,45	0,63	1,00

Conclusion:

We already told that chloroplasts contains four different pigments: Chlorophyll b, Chlorophyll a, Carotenoids and Xanthophylls. Xanthophylls is the fastest. The second fastest is Carotenoids. The slowest is Chlorophyll b and the second slowest is Chlorophyll a. We can conclude this from our chromatogram.

As you can see from the relative results of the three Ligustrum vulgare L. chromatograms we can’t make a clear conclusion. The results are all very different in compare to each other. For example: The chlorophyll B from Sanne’s chromatogram is as twice as fast as ours. We can explain this by the differences in concentration of the solution of chloroplasts. Sanne and Wendy could have done less acetone in the solution than we did. There also can be a difference in the time we put the chromatogram into the acetone.

When we compare the chromatograms from the four different plants, you can see in the diagram that the plants aren’t exactly the same. Especially chlorophyll a and b differs more than carotenoids. But you can also see that the pigments of the Aegopodum podagrarie L. and the Sambucus nigra L. don’t differs very much.

The Ligustrum vulgare L. and the Castanea sativa L. don’t differs much either.

The chromatogram of the Aegopodum podagrarie L. fails a little bit, because the fluid lag behind if you compared it with the others. The time from these chromatograms was about the same. There can only be a difference in the concentrations of the solution of chloroplasts.

There are some results that don’t differs very much, but they aren’t exactly the same. So we can conclude that there are different rapidity’s of the same pigments of different plants.

Final Conclusion

We have proven oxygen, starch and pigments. We hope the process is explained properly. The tests didn’t all turn out the way we planned. The explanations about that follow.

In spite of the problems we had and the time there was between the different parts of the experiment (we did the practical work in 10 weeks, but we only need 6 lessons..), we liked the practical work. It was fun.

Making this account took a lot of work, because our results weren’t very clear and writing your account in English isn’t very easy. But we learned a lot from it.

a leaf (bottom), thylakoids within achloroplast (middle), and a photosystem in thylakoids (top).

Discussion

During our practical works we have had a couple of problems. In this part we will discuss these problems and recommend adjustments to the practical work, so the experiment can be done without many problems in the future. We will discuss the problems one by one. First the problems with practical work A, than B and at last D.

Practical work A: Photosynthesis in a coloured leaf

Like we said before in this account, experiment A didn’t go exactly like we thought it will. After we did the experiment we discussed the problems in the class and tried to explain the many problems. Here they are:

We used a solution of iodine to show starch. Our conclusion was: ‘there isn’t any difference between the covered and uncovered parts of the leaf.’ So there was starch everywhere in the leaf.
Starch caused by the process of photosynthesis, like we explained before. If you put a part of a leaf 24 hours in the dark, there isn’t taking place photosynthesis during that 24 hours. So if you are going to prove the presence of starch after that 24 hours, you don’t find any starch in the covered part. We did prove there was starch. So we did something wrong.
The starch we showed at the covered part of the leaf, was there before we start the experiment. So the experiment shows a wrong conclusion.
The next time you are going to do this practical work, you’d better put the plants 24 hours in the dark before you start the experiment. The starch in the leafs is than put in other parts of the plant and if you do the practical work then, you only show the starch which has caused by the process of photosynthesis. Then you conclusion is more reliable.
An other adjustment to the experiment is that you have to put the plants for the 24 hours of the practical work under a lamp. We didn’t and all the starch witch was caused by the photosynthesis during the day was put in other parts of the plant during the night. And under the lamp there arise more starch than there did with our experiment.
The leafs weren’t enough uncoloured. It takes about 9 minutes in our case and it wasn’t enough. So the leaf must be longer in the ethanol, until they are totally uncoloured and you don’t see a little bit of green anywhere. This will take a while.
At last we wanted to say you have to make sure there isn’t still a bit of ethanol on the leaf when you put the solution of iodine on it. Because if there is still a bit of ethanol on the leaf, the iodine can’t show the starch.

This practical work needs a lot of adjustments to get a good result. We hope it will with the adjustments we wrote about.

Practical work B: The making of oxygen

We had two main problems with this experiment.

We had a problem with making the framing. When we put the test tube upside down on the funnel, there came every time a little bit of air in the test tube. And because we had to prove how much oxygen arise during the experiment, this air was a little problem. We tried and tried to get no air into the test tube. After a few efforts we write down how much air there was in the test tube. It wasn’t much, but it was still too much. The next time you may can put the whole framing into a bucket. Than you don’t get air in the test tube. Or you can use a bigger Erlenmeyer, so that the funnel is completely under the water. That makes it easier to put the test tube upside down, without much water in the test tube.
The last part of this practical work didn’t work at all. When we put the glowing piece of wood in the test tube it extinguished. Part of this is, we think, to blame for the fact the glowing piece of wood was a match. A match can burn and it can extinguish, it can’t glowing. In the future you have to take a real glowing piece of wood instead of a match.
During the experiment there wasn’t arise much oxygen. So when you put a glowing piece of wood into the test tube, the little bit of oxygen is mixed with the air. So the glowing piece of wood won’t burn again. You can suck in the oxygen, for example with a squirt, when the test tube is still upside down in the water, like you see on the little drawing….. (*)
And then you can squirt the oxygen on the glowing piece of wood.

Practical work D: Chromatography from leafs

With this problem we didn’t have much big problems. We had a few little ones.

It was difficult to make a concentrated solution of chloroplasts which you can put on the filtering paper. We didn’t put the stem into this solution. But in the stem there are many chloroplasts, so if we look back we better put them in the solution. And we did need a lot of the liquid to make the solution a little liquid.
Another problem was the time. We had 50 minutes and the liquids didn’t reach ca. 2 cm from the top of the paper. It was just half the way. So the next time you need more time!

(*) Anouk and Monique forgot the drawing!