[THE PHOTOSYNTHESIS]{.underline}

**The students of the GLOBE section**

**Mentors: Suzana Kovač, Diana Matica, Andreja Belošević**

Elementary school Nikola Tesla, Zagreb, REPUBLIC OF CROATIA

## SUMMARY

The Questions that have lead us in the creation of this project were:
how photosynthesis of the water plants affects the concentration of the
dissolved oxygen and when is the photosynthesis the most intensive.

In the searching for our answer we have used some data of our GLOBE
measurements during the last two years, experiments in the laboratories,
results of the measurements during the 24 hours and data that were
available by Department of Geophysics, Faculty of Science, University of
Zagreb and "Jarun d.o.o."

The conclusions of this project are:

\- the water surfaces warm up slower than air, but at night they cold
down slower;

\- the water plants produce more oxygen when solar energy is the most
intensive, and that is in the summer between 11,00 a.m. and 13,00 p.m.
(local time);

\- the concentration of the dissolved oxygen in the water is increased
in the morning despite the increase of the temperature of the water and
decreased oxygen fusibility, because of the intensive photosynthesis;

\- in the afternoon and at night the concentration of the dissolved
oxygen decreases (even though temperature of the water decreases and
oxygen fusibility increases) because living creatures use it for
breathing.

In the future our research should be completed with data about the air
pressure and with speed of the wind.

We should study how the concentration of the dissolved oxygen changes
during the winter days when there are less water plants and in the
conditions of the decreased solar energy.

## RESEARCH QUESTION- HYPOTHESIS

Since 2001 a few times during the month we have been doing physical and
chemical analysis of the water in our hydrology study site: we were
taking certain measurements of the water temperature, pH, dissolved
oxygen, alkalinity, nitrate, nitrite. We were trying to explain and
connect the results of these measurements with the knowledge that is
learned as a part of biology, chemistry and physics at school.

We have learned that the concentration of the dissolved gases in the
water decreases with the increase of the water temperature, and it
increases with the increase of the air pressure. Oxygen in the water is
present because it is dissolved from the air and from the photosynthesis
of the water plants, and it is used for breathing of the water organisms
and for decomposition of dead organic matter.

We have analysed the results of our measurements and we have observed
different concentrations of dissolved oxygen that are measured with the
same temperature of the water. The concentrations of the nitrogen from
nitrate and nitrite were very low and they were not different from the
usual values. We have noticed that lower concentrations of the oxygen
are measured early in the morning and higher early in the afternoon. We
take these field measurements every second week at the same time because
of our school time-table.

We wanted to enrich our research so we decided to compare the amount of
the dissolved oxygen from three streams that flow near our school. The
results were unexpected. The concentration of nitrogen from nitrate and
nitrite were low and almost equal. In spite of that fact the highest
concentration of dissolved oxygen was measured in the stream with the
highest temperature.

We have tried to find out the explanation for these phenomenon and green
colour of the algae and the highest amount of the water plants in the
stream with the highest amount of oxygen has helped in the creation of
possible solution.

We have decided to check:

\- is it possible that the difference of the concentration of the
dissolved oxygen is the consequence of the highest amount of the water
plants

\- when is the photosynthesis the most intensive and when the plants
produce the highest amount of oxygen

## 3. RESEARCH METOD {#research-metod .unnumbered}

We have started the research with the introduction of the photosynthesis
on experiments in laboratories. We have proved that the plant for this
process needs water, carbon dioxide and solar energy and with this
process it produces oxygen and organic substance starch.

For the field research we have chosen our hydrology study site at the
lake Jarun. The surface that belongs to the lake Jarun is bigger than
200 hectares but 70 hectares is under the water. The lake Jarun is
former backwater channel of the river Sava. After the big flood it was
separated from it with big dike in 1964. The level of the water depends
on water level of the river Sava and on inflow of the underground water.
The water from the lake flow out by filtering into underground and by
overflow through drainpipes. The depth of the lake is between 4 - 6
metres, and the highest depth (13 metres) is measured in the Bog Lake
(Kerovec, 1990).

Hydrology study site is situated along the coast, and that place is not
sheltered (it is lightened whole day). Its coordinates are 4546\'28"N
and 1556\'29"E and they are measured by GPS Megalen.

We wanted to find out when did the plant produce the highest amount of
and we decided to take some measurements of the volume of oxygen each
hour during the day (from 8 a.m. 16th June, 2002 to 7 a.m. 17th July,
2002). At the same time we measured the water pH and temperature and the
concentration of the dissolved oxygen so that we can find out how does
the amount of the produced oxygen influence the concentration of the
dissolved oxygen in the water.

[**The experiments that we used for the research of the** photosynthesis
**in the lab. were:**]{.underline}

1\) The leaves of the *[Elodea canadensis]{.underline}* we covered with
the funnel and we fixed the test tubes filled with the water on it. The
produced gas from the leaves filled the test tubes and repressed the
water. With smouldering chip we proved that the product of the
photosynthesis is oxygen.

2\) We started with heating pelargonium leaves and alcohol in water
bath, and we removed the green colour - chlorophyll from the leaves. The
starch as a product of the photosynthesis was blue coloured after that
we added Lugol solution.

3\) This experiment was repeated, and we covered the part of the leaf
with the aluminium foil. We left it for a few hours on solar heating. We
didnt prove the presence of the starch in the part of the leaf which was
covered, and that was the proof that we need the light for the
photosynthesis.

4\) We repeated the same experiment with two plants. The first was
regularly watered and the second was not. The highest amount of the
starch was in the leaves that had more water.

5\) The need for the carbon dioxide we proved in the way that we put one
pelargonium leaf in the Erlenmeyer flask and it was filled with the
carbon dioxide and we left the another one in the air. The bigger amount
of the starch was formed in the leaf which had more carbon dioxide.

The volume of the oxygen that the plant produced each hour was measured
in the following way:

We covered the leaves of the plant with the glass funnel and the
straitened part we put in upside down turned graduated cylinder which
was filled with the water. We fixed it with the stand and with the
versatile clamps. We measured the volume of the gas that this plant
produced each hour.

**[The amount of the dissolved oxygen in the water]{.underline}** we
measured each hour and we used Dissolved oxygen test kit, HI 3810,
produced by "Hanna instruments". We used their kits also for
measurements of ammonium, nitrite and nitrate.

**[The temperature of the water and the air]{.underline}** we measured
with the mercury thermometer and pH of the water we measured with pH-pen
( 0,01 pH).

## 4. DATA SUMMARY {#data-summary .unnumbered}

TABLE 1. The results of the measurements of the physical - chemical
characteristics of the water in hydrology study site during one day
(16^th^- 17^th^ June 2002).

+------+-----------+-----------+-------+-------+-----------+---------+
| **t  | **air     | **water   | **clo | *     | **volume  | **di    |
| ime/ | te        | te        | uds** | *pH** | of the    | ssolved |
| hou  | mperature | mperature |       |       | produced  | oxygen  |
| rs** | (C)**     | (C)**     |       | **(pH | oxygen    | (       |
|      |           |           |       | p     | (ml)**    | mg/l)** |
|      |           |           |       | en)** |           |         |
+------+-----------+-----------+-------+-------+-----------+---------+
| 8,00 | 26        | 25,5      | clear | 7,98  |           | 7,00    |
+------+-----------+-----------+-------+-------+-----------+---------+
| 9,00 | 28        | 26        | clear | 7,98  |           | 7,5     |
+------+-----------+-----------+-------+-------+-----------+---------+
| 1    | 28        | 27        | clear | 8,03  | 0         | 8,0     |
| 0,00 |           |           |       |       |           |         |
+------+-----------+-----------+-------+-------+-----------+---------+
| 1    | 29,5      | 27,5      | clear | 8,09  | 4         | 8,1     |
| 1,00 |           |           |       |       |           |         |
+------+-----------+-----------+-------+-------+-----------+---------+
| 1    | 30        | 28        | scat  | 8,05  | 8         | 7,7     |
| 2,00 |           |           | tered |       |           |         |
+------+-----------+-----------+-------+-------+-----------+---------+
| 1    | 30        | 29        | scat  | 8,10  | 14        | 8,2     |
| 3,00 |           |           | tered |       |           |         |
+------+-----------+-----------+-------+-------+-----------+---------+
| 1    | 31,5      | 28        | scat  | 8,7   | 18        | 7,6     |
| 4,00 |           |           | tered |       |           |         |
+------+-----------+-----------+-------+-------+-----------+---------+
| 1    | 33        | 29        | scat  | 8,0   | 22        | 7,5     |
| 5,00 |           |           | tered |       |           |         |
+------+-----------+-----------+-------+-------+-----------+---------+
| 1    | \-        | \-        | scat  | 7,84  | 25,5      | 7,3     |
| 6,00 |           |           | tered |       |           |         |
+------+-----------+-----------+-------+-------+-----------+---------+
| 1    | 32        | 28        | scat  | 7,94  | \-        | \-      |
| 7,00 |           |           | tered |       |           |         |
+------+-----------+-----------+-------+-------+-----------+---------+
| 1    | 31        | 28        | scat  | 7,98  | \-        | \-      |
| 8,00 |           |           | tered |       |           |         |
+------+-----------+-----------+-------+-------+-----------+---------+
| 1    | 32        | 27        | scat  | 7,99  | 32        | 7,0     |
| 9,00 |           |           | tered |       |           |         |
+------+-----------+-----------+-------+-------+-----------+---------+
| 2    | 22        | 23        | clear | 7,65  | \-        | 7,0     |
| 4,00 |           |           |       |       |           |         |
+------+-----------+-----------+-------+-------+-----------+---------+
| 0    | 17        | 23        | clear | 7,94  | \-        | 5,6     |
| 5,00 |           |           |       |       |           |         |
+------+-----------+-----------+-------+-------+-----------+---------+
| 0    | 22        | 24        | clear | 7,91  | \-        | 7,7     |
| 7,00 |           |           |       |       |           |         |
+------+-----------+-----------+-------+-------+-----------+---------+

TABLE 2. The data from Department of Geophysics, Faculty of Science,
University of Zagreb (provided by prof. Zlatko Matica)

+-------------+---------------------+--------------+-------------------+
| time        | Intensity of solar  | time         | Intensity of      |
|             | radiation           |              | solar radiation   |
|             |                     |              |                   |
|             | (J/cm^2^)           |              | (J/cm^2^)         |
+-------------+---------------------+--------------+-------------------+
| 01:00       | \-                  | 17:00        | 67                |
+-------------+---------------------+--------------+-------------------+
| 02:00       | \-                  | 18:00        | 17                |
+-------------+---------------------+--------------+-------------------+
| 03:00       | \-                  | 19:00        | 7                 |
+-------------+---------------------+--------------+-------------------+
| 04:00       | \-                  | 20:00        | \-                |
+-------------+---------------------+--------------+-------------------+
| 05:00       | 5                   | 21:00        | \-                |
+-------------+---------------------+--------------+-------------------+
| 06:00       | 43                  | 22:00        | \-                |
+-------------+---------------------+--------------+-------------------+
| 07:00       | 99                  | 23:00        | \-                |
+-------------+---------------------+--------------+-------------------+
| 08:00       | 152                 | 24:00        | \-                |
+-------------+---------------------+--------------+-------------------+
| 09:00       | 208                 | 01:00        | \-                |
+-------------+---------------------+--------------+-------------------+
| 10:00       | 257                 | 02:00        | \-                |
+-------------+---------------------+--------------+-------------------+
| 11:00       | 276                 | 03:00        | \-                |
+-------------+---------------------+--------------+-------------------+
| 12:00       | 300                 | 04:00        | \-                |
+-------------+---------------------+--------------+-------------------+
| 13:00       | 302                 | 05:00        | 6                 |
+-------------+---------------------+--------------+-------------------+
| 14:00       | 274                 | 06:00        | 48                |
+-------------+---------------------+--------------+-------------------+
| 15:00       | 228                 | 07:00        | 105               |
+-------------+---------------------+--------------+-------------------+
| 16:00       | 133                 |              |                   |
+-------------+---------------------+--------------+-------------------+

![](media/image1.wmf)Figure 1. The relation of the volume of the
produced oxygen and the intensity of the solar heating

![](media/image2.wmf)

Figure 2. The relation of the volume of the produced oxygen and the
concentration of the dissolved oxygen.

## 5. ANALYSIS {#analysis .unnumbered}

a\) The temperature of the water followed daily increase and decrease of
the air temperature (Table 1.)

b\) The concentration of the dissolved oxygen increased until 1,00
p.m.(local time) (Figure 2.)

c\) The highest volume of the produced oxygen was noticed in the period
between noon and at 1,00 p.m. (Figure 2.)

d\) The highest concentration of the dissolved oxygen was noticed at
1,00 p.m. and the lowest at 5,00 a.m.

e\) The concentration of the dissolved oxygen increased from dawn till
1,00 p.m. and from 1,00 p.m. till the next morning it decreased (Table
1.)

f\) The increase in the volume of produced oxygen followed the increase
of solar radiation (Figure 1.)

g\) pH-value was higher during the day because the plants were under the
influence of the intensive photosynthesis, they removed carbon dioxide
from the water and in this way they decreased the acidity (Table 1.)

## 6. CONCLUSIONS {#conclusions .unnumbered}

While we were comparing the temperatures of the water and the air we
noticed that the water surfaces get warmer slowly than the air, but at
night they slowly get colder.

As the result of our data about the volume of produced oxygen and the
intensity of the solar heating our conclusion is that the water plants
produce more oxygen at time when the solar heating is the most intensive
and that is in summer between 11,00 a.m. and 1,00 p.m.(local time).

Our conclusion is that the concentration of the dissolved oxygen in the
water increases in the morning in spite of the increased water
temperature and decreased fusibility of the oxygen and the cause for
this is the most intensive photosynthesis and production of the oxygen.

The results show that in the afternoon and at night the concentration of
the dissolved oxygen decreases even the temperature of the water
decreases and fusibility of the oxygen in the water increases. The
explanation for this we found in the fact that the plants for the
photosynthesis need light and they produce less oxygen, while living
creatures spend it for breathing.

## 7. DISCUSSION {#discussion .unnumbered}

During the discussion about the results of these measurements engineer
Mirjana Pocuca from the organisation \'\'JARUN d.o.o\'\' helped us a
lot. Her work is very important because she takes some physical-chemical
measurements and microbiological analysis regularly. The purpose of her
work is to determine the quality of the water in the lake Jarun for
swimming. We compared these results and we noticed some differences in
the water temperature and in the concentration of the dissolved oxygen.
We tried to explain this with the fact that Mrs Pocuca took her samples
in the depth of one metre, while we took our measurements along the
coast at the depth of 10 cm.

Mrs Pocuca pointed out the fact that the concentration of the dissolved
oxygen may depend on influence of swimmers and waves in the lake. During
the summer there is also high supersaturation of water with oxygen. That
also indicates the eutrophication of the lake (the lake is relatively
shallow and it is lightened from the top to its bottom the great part of
the year) and after some time it will gradually turn into a pond.

This project also confirmed our assumptions and it helped us to use our
knowledge. It is very important because we learned to observe the
problem from different points of view and that we should collect
different informations and on that basis we should create our
conclusions.

Our conclusion is that the water temperature is not always the most
important parameter which has influence on the amount of the dissolved
oxygen. That amount depends on photosynthesis of the green plants which
produce oxygen, and photosynthesis depends on the intensity of the solar
energy. During the summer the greatest amount of direct solar heating
reach the plants at noon. That is the reason that the concentration of
the dissolved oxygen increases, and in the afternoon and at night it
decreases. It is also under the influence of other living creatures and
that continues at night. In this way we can explain different
concentrations of the oxygen at the same place and under the same
temperature of the water. Lower concentrations were measured early in
the morning when the photosynthesis was not very intensive, and higher
concentrations appeared early in the afternoon when the plants produce
more oxygen. Our assumption is that increased concentration of the
oxygen in the 2^nd^ stream was also the consequence of the increased
photosynthesis, and in this way this concentration was possible.

Our conclusion is that our research will be completed if we include in
it also the measurements of the air pressure and the speed of the wind.
They also can influence the concentration of the dissolved oxygen in the
water. It would also be very important to examine the concentration of
the dissolved oxygen which changes during the winter days, when there
are less water plants and the intensity of the solar heating is
decreased.

## 8. BIBLIOGAPHY {#bibliogaphy .unnumbered}

Kerovac, M. (1990) Living world of the Jarun Lake (in Croatian).
Ekološki glasnik 3-4, *57-59.*

### URL 1. http:// web.ukonline.co.uk

### GLOBE manual