Measuring Rate of Rater Uptake by a Leafy Shoot


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Measuring Rate of Rater Uptake by a Leafy Shoot

The water uptake can be measured easily and because very high
proportion of the water taken up by a stem is lost in transpiration,
it enables the rate of transpiration to be measured.



Key Factors to be kept Constant: -
==================================

v Temperature - room temperature (approximately 25ºC)

v Wind speed - No artificial wind was produced to affect results

v Light intensity - Extra light was not used

v Humidity - it was not humid on the day experiments were conducted

The water uptake for the control Experiment.

Time (minutes)

Initial meniscus position of the air bubble (cm)

Final meniscus positionof the air bubble (cm)

Water uptake

(Distance moved) (cm)

Total water uptake (cm)

1

10.0

10.7

0.7

0.7

2

10.7

11.5

0.8

1.5

3

11.5

12.3

0.8

2.3

4

12.3

13.0

0.7

3.0

5

13.0

14.0

1.0

4.0

6

14.0

14.8

0.8

4.8

The water uptake when Vaseline is applied on the top surface of the
leaves.

Time (minutes)

Initial meniscus position of the air bubble (cm)

Final meniscus positionof the air bubble (cm)

Water uptake (Distance moved) (cm)

Total water uptake (cm)

1

6.0

6.6

0.6

0.6

2

6.6

7.2

0.6

1.2

3

7.2

7.9

0.7

1.9

4

7.9

8.5

0.6

2.5

5

8.5

9.2

0.7

3.2

6

9.2

9.7

0.5

3.7


Time (minutes)

Initial meniscus position of the air bubble (cm)

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Final meniscus positionof the air bubble (cm)

Water uptake

(Distance moved) (cm)

Total water uptake (cm)

1

5.2

5.6

0.4

0.4

2

5.6

6.0

0.4

0.8

3

6.0

6.5

0.5

1.3

4

6.5

6.9

0.4

1.7

5

6.9

7.4

0.5

2.2

6

7.4

7.9

0.5

2.7

[IMAGE]The water uptake when Vaseline is applied on both surfaces of
the leaves.


Gradient = m = Y1- Y2

X1 - X2

CONTROL EXPERIMENT = M = 1.5 - 0.7 = 0.8 = 0.8

2 - 1 1

VASELINE ON UPPER SURFACE = M = 1.2 - 0.6 = 0.6 = 0.6

2 -1 1

VASELINE ON BOTH SURFACES = M = 0.8 - 0.4 = 0.4 = 0.4

2 - 1 1

The graph shows that the results received for each experiment is very
consistent as the results are very close to the line of best fit. The
graph represents the water uptake per minute. For all the conditions,
the graph shows that the water uptake is increasing every minute.
Although the graph illustrates that this is the trend for the results
in each experiment, it also shows the variations between each
experiments. The graph shows that water uptake results were greater
during normal conditions, the water uptake was slightly lower when
Vaseline was applied on the upper surface of the leaf, and finally,
the water uptake was the lowest when Vaseline was applied on both
surfaces.

The conclusion that I can form from the graph and from having
calculated the gradient is that under normal conditions without having
altered factors such as temperature, light intensity, humidity, wind
speed, the water uptake is really fast. The application of the
Vaseline is very significant in affecting and altering the water
uptake by making it slower than it otherwise would be. The addition of
Vaseline is most affected when it is spread over the bottom of the
leaf, hence, covering the stomata.

The reason why this occurred is because, when the experiments were
conducted under normal conditions, there was nothing preventing
transpiration. It happened as it does normally. The upper surface of
the leaf has a layer of waxy cuticle, which reduces water loss. When I
applied Vaseline on the upper surface it meant that the leaf now had
two layers preventing water loss, so no doubt slightly reduced the
water uptake. In the final experiment, where Vaseline was covered on
both surfaces of the leaf, it considerably reduced transpiration
therefore, the water uptake. This is because a very high proportion of
water uptake is lost through transpiration.

Water is lost from the leaves, especially the bottom surface of the
leaf. This is because on the bottom surface, it lacks waxy cuticle and
usually has many more stomata. Stomata are pores surrounded by
specialized cells (guard cells). These pores allow water to escape by
diffusion into the air. As the water evaporates from the leaf by water
evaporating from the surface of the parenchyma and escaping out
through the stomata into the atmosphere, water from the xylem in the
leaf replaces it. As water leaves the xylem, more is sucked up from
below. A negative gradient in hydrostatic pressure forms, causing a
column of water to rise up the plant. This is known as the
transpiration pull. This means that transpiration directly affects the
rate of water uptake. If this did not occur, the plant will wilt, and
if water loss continues without being replaced, it will suffer
plasmolysis. (Biology 1 text book and 'Biology - AS in a week).

When both surfaces were covered with Vaseline, the Vaseline was
applied over the stomata as well. By covering the stomata it meant
that this would prevent water from escaping by diffusion, so this will
reduce transpiration, which then led to a decrease in water uptake.
The fact that both sides were now preventing any water from
evaporating from the leaves of the plant means that this experiment
had to have a lower water uptake, which it did.

The way in which water is transferred from the leaf to the atmosphere
is through transpiration. A mesophyll layer, which is the middle of
the leaf, is made of cells that are not tightly packed. This means
that they are spaces between the cells is filled with air. The
mesophyll walls are wet and some of the water from the mesophyll walls
evaporates into these air spaces. This means that the air within the
leaf is usually saturated with water vapour.

The air inside the spaces of the leaf has direct contact with the air
outside the leaf due to the plant containing stomata (small pores).
The potential gradient is significant because if there is a water
potential gradient between the air within the leaf with the air
outside the leaf, then this will result in the water vapour diffusing
out of the leaf down this gradient.

If there is an increase in the water potential gradient between the
air spaces in the leaf and the air outside the leaf, this will
increase the rate of reaction.

Other forces which move water up the xylem are root pressure and
cohesion. In root pressure, mineral ions are actively pumped into the
pericycle cells around the xylem from the adjacent endodermal cells.
This moves water into the xylem via osmosis and creates an upward
force.

Cohesion (tension theory) is also another way water moves up a plant.
Water molecules are polar and so both attract each other (cohesion)
and are attracted to the walls of the xylem (adhesion). These forces
draw up water.


T-tests
-------

T-tests compare exactly two groups



Results of T Test 1
===================

First Data Set 6 values

0.7

0.8

0.8

0.7

1.0

0.8

Second Data Set 6 values

0.4

0.4

0.5

0.4

0.5

0.5

Summary Statistics

n

sum

Mean

variance

std. dev.

Set 1

6

4.8

0.8000

0.0120

0.1095

Set 2

6

2.7

0.4500

0.0030

0.0548

T Test Results

t value

df

P value

7.0000

10

<0.0001

This shows the T-test results between the Control tests with the
results from the experiment with Vaseline on both surfaces of the
leaves.



Results of T Test 2
===================

First Data Set 6 values

0.7

0.8

0.8

0.7

1.0

0.8

Second Data Set 6 values

0.6

0.6

0.7

0.6

0.7

0.5

Summary Statistics

n

sum

Mean

variance

std. dev.

Set 1

6

4.8

0.8000

0.0120

0.1095

Set 2

6

3.7

0.6167

0.0057

0.0753

T Test Results

t value

df

P value

3.3786

10

0.0035

This shows the T-test results between the Control tests with the
results from the experiment with Vaseline on the upper surface of the
leaves.



Results of T Test 3
===================

First Data Set 6 values

0.4

0.4

0.5

0.4

0.5

0.5

Second Data Set 6 values

0.6

0.6

0.7

0.6

0.7

0.5

Summary Statistics

n

Sum

Mean

Variance

Std. dev.

Set 1

6

2.7

0.4500

0.0030

0.0548

Set 2

6

3.7

0.6167

0.0057

0.0753

T Test Results

T value

df

P value

-4.3853

10

0.0007

This shows the T-test results between the results from the experiment
with Vaseline on both sides of the leaves with the results from the
experiment with Vaseline on the upper surface of the leaves.

For all three T-tests, the pattern that is similar is that the
probabilities are all below the critical value, which is 0.05. This
means that I can reject the "null" hypothesis that there is no
difference between the means for each T-test and that the results only
occurred by chance. I can assume that there is a significant
difference between the means and the difference is real.

There is not a big difference between each individual reading either
which means that my results must be quite accurate.

From the tests I can also see that the mean for the control test is
greatest (0.8000), then the mean for the experiment with Vaseline on
top (0.6167) and the lowest mean was for the experiment with Vaseline
on both sides (0.4500).

The standard deviation also shows this trend 0.1095 for the control,
0.0753 for the Vaseline on top, and 0.0548 for the one with Vaseline
on both surfaces. The variance also supported this, 0.0120 for the
control experiment, 0.0057 for the Vaseline on top, and 0.0030 for the
one with Vaseline on both sides. The results from the T-tests support
the trend showed by the graph, and this is supported by the background
information.





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