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Transport in flowering plants- Dye Experiment 2. Aim: To find (a) the tissue responsible for the transport of water. (b) the rate of transport of water in a leafy shoot.

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1. Title: Transport in flowering plants- Dye Experiment

2. Aim: To find (a) the tissue responsible for the transport of water.

   (b) the rate of tran sport of water in a leafy shoot.

3. Principle of method:

When a branch of a plant is put in a coloured solution, the coloured solution will be absorbed by the plant tissue and transported up mainly by transpiration pull which is a suction pressure inside the xylem. By observing where the coloured stain is located in the stem, the tissue which responsible for water transport can be found. Moreover, the rate of water in the stem can also be determined by measuring the length of the coloured stain in the tissue responsible for water transport in a fixed time period.

4. Apparatus:

1 100ml beaker                      1 dropper

1 razor blade                        1 hand lens

1 ruler                              1 white title
1 forceps

5. Material:

Methylene blue solution
Stem of a flowering plant (Coleus)

6. Procedure:

1. The stem of the stem of the shoot provided under water was cut to remove any air bubble blocking the xylem tissue.

2. The shoot with its freshly cut end was placed in a 100 mL beaker containing some coloured water ( methylene blue).

3. The plant was left in a brightly lit and airy area for 30 minutes.

4. The shoot was removed and transverse sections of the stem were prepared at every 1 cm intervals. The presence of the coloured stain was recorded using a table.

5. The sections were observed using a hand lens in the same sequence as they were positioned in the stem. The position of the last section containing the stain was found out. The distance of water transported within 30 minutes was represented. The rate of transport of water in the stem was calculated.

6. The tissue containing the stain was identified. This is the tissue responsible for the transport of water in stem.

7. A low power drawing of a typical section was made to illustrate the distribution of the stained tissue.

7. Result:

Distance from the cut end of the stem        

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

Presence of stain

(+ or -)

+

+

+

+

+

+

+

+

+

-

-

-

-

-

-

-

-

-

Key: + represent the section stained blue

     - represent the section not stained blue

The ascent of the coloured solution is 9 cm

The rate of ascent: 9/0.5

                =18 cm/hour

8. Discussion:

In the stem of Coleus, the vascular bundles are separated and usually arranged in a ring at the periphery. The coloured solution was absorbed by the transpiration pull and the blue dye presented in the xylem. The rate of the absorption is different in the vascular bundles; it is because different vascular bundle has xylem with different size. The larger the size of the xylem, the lower the rate of the water transport. Therefore, the number of stain will decrease when the distance from the cut end of the stem increase.

There are some factors which affected the rate of the transportation of water in Coleus. The first factor is the light intensity. The rate of transpiration increase with an increase in light intensity. As the light intensity increases, the stomata open wider. More water vapour in the air space diffuses out through the stomata. In darkness, the stomata close, so that the rate of transpiration will decrease.
The second factor is the air movement. The rate of transpiration increases in windy conditions. In still air, the water vapour that diffuses out of the leaves accumulates around the stomata. Wind blows away the water vapour and prevents the decrease in the concentration gradient of water vapour between the air space in the leaves and the surrounding air. The rate of diffusion and therefore the rate of transpiration increases in windy conditions.
The third factor is the relative humidity. The rate of transpiration decrease with an increase in the relative humidity of the surrounding air. Since the air space in the leaves is saturated with water vapour, a higher relative humidity of the surrounding air will decrease the concentration gradient of water vapour between the air space and the surrounding air. Therefore, less water vapour from the air space will diffuse out through the stomata.

Moreover, my result is different from that of my neighbours due to some reasons. First, since the number and size of leaves on each leafy shoot are different from the others, this affects the surface area of leaves for evaporation which is directly related to the rate of transpiration and finally the rate of water transport. The larger the surface of the leaves, the more the stomata for transpiration, the faster the rate of water transport and thus the results are different.

Second, different leafy shoot has different number of vascular bundle and thus different number of xylem for transporting water. Therefore, the numbers of stain in different stem are different. Also, different vascular bundle has xylem with different size, the larger the size of the xylem, the lower the rate of the water transport, vice versa. The results are different.

Third, since we use the lamps to illuminate the leafy shoot, the light illumination to different leafy shoot may be uneven. Not all the leafy shoot is illuminated by the same amount of light. This affects the transpiration rate which eventually affects the rate of water transport and the result. Also, when the temperature rises, there will be an increase of the evaporation rate and the transpiration rate. There is variation in temperature on different leafy shoot because of the uneven light illumination. Therefore, the results are different.

A number of errors can be observed in the experiment. First, although the methylene blue is very sharp in colour, it is different to observe the water level due to the dilution of water. A measuring error may be resulted. Second, the size of the leafy shoots are different, the rate of water transport are also different. That’s unfair to measure the water transport. Third, the experiment is carried out in a slightly moving air condition. It is different to provide a still air condition in an open area. Therefore, the result may not be accuracy.

In order to increase the accuracy of the experiment, we can enclose the stem part of the Coleus with vastine to prevent water lose. The experiment should be carried out in a closed room where the air is still. Thus, it is easier to observe the water level use higher light intensity, so that the measuring error can be reduced. Furthermore, the size of the leafy shoot should be classified, choose the similar size one for the experiment.

Lastly, we can have some methods In order to increase the rate of water transport. We can increase the light intensity. As the light intensity increases, the stomata open wider. More water vapour in the air space diffuses out through the stomata. Besides, we can use a fan to increase the air moment so that it can blow away the water vapour and prevents the decrease in the concentration gradient of water vapour between the air space in the leaves and the surrounding air. The rate of diffusion, transpiration increase and thus the rate of water moment increase.

9. Conclusion:

When a branch of a plant is put in coloured solution, the coloured solution will be absorbed and transported by the xylem in vascular bundle by transpiration pull which is a suction pressure inside the xylem.

This student written piece of work is one of many that can be found in our GCSE Green Plants as Organisms section.

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