CONCEPT OF BIOLOGY
1. To measure transpiration rates by using photometer.
2. To determine the factors that influences the rate of water loss from a plant through transpiration Introduction:
Most of the water a plant absorbs is not used for a plant’s daily functioning. It is instead lost through transpiration, the evaporation of water through the leaf surface and stomata, and through guttation, which is the loss of water from the vascular tissues in the margins of leaves. There are three levels of transport in plants: uptake and release of water and solutes by individual cells, short distance cell to cell transport at tissue and organ levels, and long distance transport of sap by xylem and phloem at the whole plant level. The transport of water is controlled by water potential. Water will always move from an area of high water potential to an area with low water potential. This water potential is affected by pressure, gravity, and solute concentration. Water moves into the plant through osmosis and creates a hydrostatic root pressure that forces the water upward for a short distance, however, the main force in moving water is the upward pull due to transpiration. This pull is increased by water’s natural properties such as adhesion and cohesion. Transpiration decreases the water potential in the stele causing water to move in and pull upward into the leaves and other areas of low water potential. Pressure begins to build in the leaves, so to prevent downward movement, guttation occurs. Guttation occurs through leaf openings on the leaf margins called hydrathodes. Loss of water through transpiration can be facilitated by the opening and closing of the stomata depending on environmental conditions.
Conical flask, capillary tubes, rubber tube, syringe, stopper, retort stand, stem section with leaf shoots of hibiscus plant.
Measuring transpiration rate using a potometer
1. Examine the prepared potometer.
2. Get a stem section with leaf shoots of suitable size and immediately place the cut section into some water. Leave the stem cut in the water until it is needed. 3. Make a fresh cut 1 inch from the original cut on the stem and do this under water just before placing the stem section into the rubber tube. 4. Insert the stem section into the rubber tube of the potometer that is filled with water. Supports stem section with a retort stand. Ensure that there are no leaks in the system. Wipe the wet leaves with tissue paper and place the potometer under bright light, no light, under fan with strong wind and without wind. 5. Determine the rate of transpiration by recording the distance of water movement in the capillary tube with time taken for a certain distance of water movement. Calculate the amount of water lost per unit time. 6. Determine the total surface area of transpiration.
Bright LightNo Light
Strong WindNo Wind
Data sheet for transpiration experiment
No.| Sample| Time| Distance Of Water Mark| Leaf Area| Amount of Water Lost (cm³)| Transpiration Rate (g/cm²/minute)| Notes| a.| Bright Light| 20 minute| 8cm| 560| 0.0628| 1.758| Lot of water loss| b.| No Light| 20 minute| 4cm| 560| 0.0314| 0.879| Water losses but slow| c.| Strong Wind| 20 minute| 6cm| 560| 0.0471| 1.319| Much water loss| d.| No Wind| 20 minute| 2cm| 560| 0.0157| 0.440| Water loss little|
Amount of water lost (cm³)= π r² h
1. Amount of water lost (a)=π r² h
=3.142 x 0.05² x 8
2. Amount of water lost (b)=π r² h
=3.142 x 0.05² x 4
3. Amount of water lost (c)=π r² h
=3.142 x 0.05² x 6
4. Amount of water lost (d)=π r² h
=3.142 x 0.05² x 2
Transpiration Rate=Amount of water lost X...