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In the experiment we placed 2 pieces of Eloda (pondweed) into a syringe. We then filled the syringe with water up to the brim. The nozzle of the syringe was attached to a capillary tube. The barrel of the syringe was then put back on the syringe just enough to not allow any air to get into the apparatus. The syringe was pushed down to push all of the air out of the capillary tube and then pulled back up slowly to form a meniscus. The meniscus was then marked and a lamp placed 8cm away from the apparatus to produce the light needed for the plant to photosynthesise. The meniscus was then measured every 5 minutes for 30 minutes.

The process was then repeated but instead of using water in the syringe hydrocarbonate solution was used. These were 0.01, 0.0125, 0.0166, 0.025, 0.5 moles per dm3 .

The results we achieved were as a class and are below:

Group

Becky +Jo

Becky +Amy

Amy +Andy

Conc.

Water

Water

Water

Movement meniscus (mm)

5

1

3

46

10

6

9

120

15

19

15

160

20

33

21

220

25

63

27

255

30

113

315

Group

Robyn +Becky

Group

Tewy

Keri +Nicola

Becky +Robyn

Conc.

0.0100

Conc.

0.0166

0.0166

0.0166

Movement meniscus (mm)

Movement meniscus (mm)

5

0

5

2

3

59

10

0

10

4

7

148

15

0

15

6

13

282

20

1

20

8

19

392

25

1

25

11

26

482

30

2

30

572

Group

Amy +Lorna

Keri +Nicola

Becky +Jo

Conc.

0.0125

0.0125

0.0125

Movement meniscus (mm)

5

15

0

6

10

30

0

15

15

45

0

35

20

62

1

55

25

96

80

30

130

Group

Peter

Lorna +Amy

Becky +Jo

Conc.

0.025

0.05

0.05

Movement meniscus (mm)

5

3

6

1

10

4

20

6

15

7

65

19

20

9

125

33

25

12

218

63

30

113

Group

Ian

Andy +Amy

Keri +Nicola

Conc.

0.1

0.1

0.1

Movement meniscus (mm)

5

3

58

0

10

6

145

6

15

8

168

16

20

11

27

25

13

268

39

30

15

498

50

Average Results

Conc.

Water

0.025

0.01

0.0125

0.0166

0.5

0.1

Movement

5

16.7

3

0

7

21.3

3.5

20.3

10

45

4

0

15

53

13

52.3

15

64.7

7

0

26.7

100.3

42

64

20

91.3

9

1

39.3

139.7

79

?

25

115

12

1

88

173

140.5

106.6

30

214

2

130

572

113

187.6

The results for the same concentrations differ a lot from each other. There is a large range over which the meniscus has travelled for the same concentrations. One example of this is the Movement of the meniscus for the 0.0166M concentration of hydrogen carbonate. One group had a meniscus that moved a total of 482mm at 25 minutes but the other two groups measured 26mm and 11mm.

From the graphs as well as the tables it is evident that if more than one groups results are given that two of the groups are quite close to each other. This is evident in the 0.0166M solution as well as the water. This evidence indicates that some of the results may be anomalous.

If the anomalous results are left out of the graphs and tables a pattern would start to appear. The length that the meniscus moves increase with increased concentration of hydrocarbonate. However this does not work with all of the results. The results achieved for the water prove this. There is a large variation in distances travelled and they do not seem to correspond with the other results.

The results the class achieved for the 0.0100M concentration seem to also be anomalous; they do not fit into the pattern. These results were not clarified by the repetition of the concentration therefore we are fully aware of the effects of the 0.0100M concentration.

From the results a pattern emerges that the length of the meniscus increases with time. This can be explained by the plant photosynthesising and/or respiring and therefore producing gases. The gases will be released and rise to the top of the syringe and therefore push the meniscus down the capillary tube.

The anomalous results we achieved were probably due to mistakes in the experimental procedure and the set up of the experiment. Some of the results may also have been corrupted because of factors that were not considered when setting up the experiment.

The first assumption that was made in the experiment that may have affected the results is that we were measuring the effect of the hydrocarbonate in the solution. The movement of the meniscus could have occurred for a number of reasons. We may have been measuring the effect that the lamp had of the solution. The lamp was set up 8cm away form the plant and therefore the solution. Lamps as well as producing light emit heat. This heat form the lamp may have cause the particles in the water to expand and therefore would push the meniscus down with the force of expansion. Also the hat may have started slight water vapours to be produced at the top of the syringe therefore pushing the meniscus down. This expansion due to heat can also be looked at if hands or fingers were around the syringe or capillary tube. The heat from them may also have been enough to expand the solution as to affect the results.

The quality of the Eloda used may also have affected the results produced. If the Eloda in one experiment was of slightly better quality than of another’s it may have respired and photosynthesised at different rates. This would therefore have affected the amount of gaseous molecules produced and therefore the meniscus would have moved at different rates. The quality of the Eloda was not the only problem with the plant. The length of it could also of had an affect. If the plant in one experiment was larger it would probably have more chloroplast’s and therefore have more sites for photosynthesis.

It would probably have more mitochondria for sites of respiration as well. This means if more of he processes are occurring then more of the gases would be produced therefore making it an unfair test and producing anomalous results. One final factor about the Eloda that could also produce anomalous results is the acclimatisation period. This is how long it takes for the plant to adapt to its surroundings and how well it does this. If it takes one piece of plant longer than the other the acclimatise it may produce anomalous results. The acclimatisation may also be affected by the hydrocarbonate concentration.

The assumption that the gaseous molecules will reach the top of the syringe is another problem that could of produced anomalous results.. The solution would have to have gaseous molecules dissolved in it do that the plant can carry out its process that we are observing therefore some of the gases that the plant produces will therefore be reabsorbed into the solution ready for reuse. This could affect the results if one solution was dissolving more of the gaseous molecules than another’s.

One observation that I made during the experiment was that in the conical flasks containing the hydrocarbonate solutions sediment was in the bottom. This indicates that the solutions were not exact. This difference in molarity may have affected the results. The sediment also suggests that the solution may been saturated. This means that no more solid can be dissolved in the solution.

We have to take into account that the plant is limiting by CO2 concentration. This means that after a certain point the hydrocarbonate in the solution will not increase the rate of photosynthesis. This is because the plant needs a number of substances to carry out photosynthesis and carbon dioxide is one of the main reactants. This means that it will always become a limiting factor. The solution will probably have a steady amount of gaseous molecules dissolved in it but there will never be enough to keep increasing the rate of reaction. This will therefore cause the rate of reaction to level of and continue at a steady pace.

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