DESIGN PRACTICAL

Research Question: What is the effect of light intensity on the rate of transpiration?
Introduction:
Water is transported in plants from roots to the leaves. However, some water is lost in the air from the leaves and the stem. This process is known as Transpiration. This results in transpiration pull by creating diffusion pressure gradient between outside air and xylem. Therefore, tension exists in the water column extending from roots to leaves. The adhesive and the cohesive forces keep the column continues and this leads to water being continuously pulled upwards as it evaporates.
Therefore, in this experiment, the water absorbed from the container is noted to calculate the rate of transpiration.

Variables:
Independent variable:
Time:
Light intensity: The plant was subjected to different intensity of light.
Dependent variable:
Water loss: During the investigation, the loss of the water from was measured by using the decrease in the volume of the water from the measuring cylinder.
Controlled variable:
The plant: The same plant is used throughout the investigation.

Uncontrolled variable:
Room temperature: The room temperature is constant is not controlled.

Material required:
1. Potato plants
2. Measuring cylinder
3. Oil
4. Water
5. Lamp
Procedure
1. The leafy shoot of the potato has been immersed in a basin containing water, and its stem is cut diagonally. The leafy shoot was placed upright in the measuring cylinder filled with water upto 50ml.
2. Then, oil was added on top of water in measuring cylinder to reduce evaporation.
3. The apparatus was left for 30 minute with 3 minute interval basis.
4. After every 3 minute, the decrease in water level has been noted.
5. After that the plant is subjected to lamp and step 3 and 4 is repeated.
6. Graph has been plotted with time on the x-axis and water loss on the y- axis.

Data Table:
Since, we didn’t get the result; our teacher gave us the data. Following are the data for the potato plants at room temperature and when it was subjected to a higher intensity of light.

Potato -Room

Time (min) water loss (ml) 0
0.0
3
0.01
6
0.01
9
0.02
12
0.02
15
0.02
18
0.02
21
0.02
24
0.02
27
0.02
30
0.01

Potato- Lamp

Time (min) water loss (ml)
0
0.0
3
0.0
6
0.01
9
0.01
12
0.01
15
0.01
18
0.02
21
0.02
24
0.03
27
0.03
30
0.03

The above data are represented by the following graph

Figure Water loss with respect to time at Room environment for Potato
The gradient of the graph will give us the rate of the transpiration. As seen from the graph, the gradient is not same at all points as all the point does not lay on the same line. It differs from one point to another.
Rate of transpiration=
For the first controlled experiment, the surface area is 31 cm3.
Total loss of water =0.17ml
Total time= 30min
Therefore, average transpiration rate =
Transpiration rate= 1.83* 10-4ml/min/cm3 When the plant was subjected to higher intensity of light, the amount of water lost was different. The data are represented in the following graph.

Figure Water loss with respect to Time under Lamp condition for Potato
For this, the rate of transpiration differs from one to another. However, the total rate of transpiration is given by:
Rate of transpiration=
When it was subjected to higher intensity of light, the surface area is 15cm3.
Total loss of water =0.17ml
Total time= 30min
Therefore, transpiration rate =
Transpiration rate= 3.78*10-4ml/min/cm-3
This clearly shows that the average rate of transpiration has increased. However, the rate of transpiration is different from one point to another. Moreover, for the two experiment, even thought the plant taken is same, the surface area of the leave is different. If we consider 31cm3 as the base