Mariano Marcos State University College of Arts and Sciences Batac City
MOVEMENT AND UPTAKE OF WATER IN PLANTS
Submitted by:
Rachelle Ann Ganal Rolando P. Luberio Jr. Jun Carlos R. Maruquin Jay Arr Paragoy BS BIOLOGY III
Submitted to: Dr. Shirley C. Agrupis Bot 131 Professor
September 2012
Introduction Water is very essential for plant growth, metabolism, transport, transpiration and guttation. As plants evolved, they have developed functional organs that would effectively suffice with their daily requirements, especially water and minerals. The roots mainly served this purpose, not only does it aid in anchoring the plant, but it also help in nutrient and water uptake. And from here on, when the roots have grown in search for water and nutrients, all this essential plant requirements must be equally distributed throughout the plant. Plants are composed of conducting vessels that efficiently transport water and minerals. For water conduction, plants have xylems. From the root hairs, water is absorbed by neighboring cells of the cortex to the endodermis then to the xylem tracheids or vessels. Absorbed water will then be transported into all parts of the plant body through the system of conductive tissues and distributed to leaves, flowers, fruits and growth apex. Potometer readings will typically vary according to factors in the environment, such as temperature, light, humidity, breeziness and the available supply of water for the plant (Slavík et al., 1974).Plant roots take up water and minerals from the soil and transport them up the stem to the leaves through specialized tissue known as xylem. Xylem consists of numerous tiny channels which run vertically all the way up the plant. When water reaches the leaves, it evaporates through openings called stomata. As water molecules tend to stick together, this evaporation from the top of the plant exerts an upward pull on the vertical columns of water in the xylem. By setting up a potometer experiment, transpiration rates can be measured when various environmental factors are changed. The Potometer does not measure the rate of transpiration accurately because not all of the water that is taken by the plant is used for transpiration (water taken might be used for photosynthesis or by the cells to maintain turgidity). The potometer measures the rate of uptake of water.
Objectives This experiment aims to familiarize with: The physiological processes involved in water uptake; Learn the factors affecting the rate of transpiration and evaporation by comparison. Understand the principle involved in the methods used to measure the process. Graphically show the differences in the transpiration of plant in varying conditions
Materials and Methods In this part of the experiment, the tissues concerned with water ascent in the stem were studied. Two leafy young shoots of Gardenia jasminoides (rosal) were secured. In one of the shoots, all leaves were detached. The bases of the shoots were cut under water and were immersed in separate test tubes which contained 2ml of 0.1% eosin. After 10 minutes, the shoots were removed from the tubes and were cut longitudinally. The length stained by the dye in each shoot was then measured. The free hand cross-sections of the shoots midway between the bases and the highest point reached by the stain were prepared. This was then observed under the microscope and the tissues stained were identified and labeled. The lifting power of transpiration was measured in this experiment. Two leafy shoots of Gardenia jasminoides (rosal) was secured. All the expanded leaves were removed from one of the shoot and a small amount of lanolin paste was applied on the exposed cuts. The other leafy branch was left intact. With a sharp knife, a clean cut was made on the base of both shoots. This was done under water. The basal portion of each shoot was connected separately to a capillary tube-rubber tubing assembly. It was made sure that the capillary tube-rubber (potometer) tubing assembly was completely filled with water prior to the placement of the shoot. The free end of each capillary tube was immersed into their respective test tube with mercury and the set-up was secured in a place against a support. The initial height of the mercury was noted and
the maximum height of mercury within 30 minutes time was also recorded in both defoliated and intact shoot. The mercury was returned in the test tube and the rate of ascent of mercury in the two set-ups was then computed. The next experiment dealt with the effect of light and wind on the rate of transpiration. For the first part, the Potometer method was used. An improvised photometer was set using a leafy shoot of the Gardenia jasminoides (rosal) plant. The base of the shoot was ringed for about 4cm and was inserted in a single holed
rubber stopper. It was made sure that there is a continuous column of water in the photometer. The distance it took the plant to cause movement into the pipet within 1 hour was recorded. Two replicate measurements were made for low light intensity and still air, and high light intensity and moderate wind. The rate of transpiration (volume of water lost per minute) was tabulated.
Results and Discussion Tissues concerned with water ascent in the stem As a mode of survival, plants evolved through time and developed vessels to suffice their water and nutrient requirements. The tracheary elements are the one responsible for water conduction. The distinguishing feature of vascular plants is the presence of vascular tissues, the xylem and phloem, which conduct water and nutrients between the various organs. Xylem tissue is responsible for the transport of water, dissolved minerals, and on occasion, small organic molecules upward throughout the plant from the root through the stem to aerial organs (Hopkins et al., 2009).Xylem consists of fibers, parenchyma cells and tracheary elements. The tracheary elements include both tracheids and vessel elements. Tracheary elements are the most highly specialized of the xylem cells and are the principal water-conducting cells. When mature and functioning, both tracheids and vessels form an interconnected network of nonliving cells, devoid of all protoplasm. The hollow, tubular nature of these cells together with their extensive interconnections facilitates the rapid and efficient transport of large volumes of water throughout the plant (Hopkins et al., 2009).
Species used: Gardenia jasminoides (rosal) Length of stained portion Defoliated 0.5cm Intact leaves 0.5cm b. Illustrate and label a cross-section of the stained portion of the stem and explain the above results Cross-section of Gardenia jasminoides (rosal)
In the experiment, the free hand cross-sections of the shoots midway between the bases and the highest point reached by the stain were viewed under the microscope. As shown in the picture above, the areas stained were the xylem and the cortex. The location to which the stain was seen is reasonable since conduction of water and nutrients from the roots to the stem going up is one of the xylem and phloem’s actions.
Lifting power of transpiration The ascent of xylem sap is explained by combining transpiration with the cohesive forces of water. The three most prominent are root pressure, capillarity and the cohesion theory. The most widely accepted theory for movement of water through plants is known as the cohesion theory. This theory depends on there being a continuous column of water from the tips of the roots through the stem and into the mesophyll cells of the leaf. According to this theory, the driving force for water movement in the xylem is provided by the evaporation of
water from the leaf and the tension or negative pressure that results (Hopkins et al., 2009). The cohesion theory proved to be the working mechanism in this experiment.
The effect of light and wind on the rate of transpiration st Table 1 (1 replicate) Condition Low Intensity Light
High Intensity
(10 watts)
Light (60 watts)
Quiet Air
Windy Air
Amount of Water Absorbed (ml) 10 minutes
0.3
0.9
0.4
0.3
20 minutes
0.2
0.3
0.3
0.2
30 minutes
0.15
0.3
0.2
0.25
40 minutes
0.15
0.3
0.3
0.15
50 minutes
0.17
0.2
0.3
0.15
60 minutes
0.13
0.5
0.2
0.07
Total Amount
1.1
2.5
1.7
1.1
Quiet Air
Windy Air
nd
Table 2 (2 replicate) Condition Time
Low Intensity Light
High Intensity
(10 watts)
Light (60 watts) Amount of Water Absorbed (ml)
10 minutes
0.1
0.1
0.2
0.1
20 minutes
0.1
0.2
0.2
0.1
30 minutes
0.1
0.05
0.2
0.1
40 minutes
0.1
0.05
0.1
0.1
50 minutes
0.1
0.1
0.2
0.08
60 minutes
0.1
0.1
0.2
0.1
Total Amount
0.6
0.6
1.1
0.58
Low Intensity Light (10 watts)
High Intensity Light (60 watts)
Quiet Air
Windy Air
st
1.1
2.5
1.7
1.1
nd
0.6
0.6
1.1
0.58
1.7
3.1
2.8
1.58
Table 2 (Average)
1 Replicate 2 Replicate
Average
Figure 1 Effect of Light and Wind in the rate of Transpiration Average
Effect of Light and Wind in the Rate of Transpiration r 3.5 u 3 o h 12.5 r o 2 f d e 1.5 b r o s 1 o b0.5 A r e 0 t a W
Low Intensity Light High Intensity Light (10 watts) (60 watts)
Quiet Air
Windy Air
Condition
Transpiration rate tends to be greatest under conditions of, high intensity light and quiet air because during these circumstances the stomates open up and carbon dioxide enters the plant and proceed to photosynthesis. When atmosphere is dry, then transpiration is more, because it receives water readily but when atmosphere becomes moist or saturated, then it can receive no more of water. The drier the atmosphere, the larger the driving force for water movement out of the plant, increasing the rates of transpiration. Light levels as low as one thousandth of the sun can cause stomata to open. A potometer sometimes known as a transpirometer is a device used for measuring the rate of water uptake of a leafy shoot. The causes of water uptake are photosynthesis and transpiration. A bubble is introduced to the capillary; as water is taken up by the plant, the bubble moves. By marking regular gradations on the tube, it is possible to measure water uptake (Slavík et al., 1974).
Conclusion There are several factors affecting the rate of transpiration. These are light, temperature, humidity, wind and soil water. The rate of transpiration is directly related to the evaporation of water molecules from plant surface, especially from the surface openings, or stoma, on leaves. Stomatic transpiration accounts for most of the water loss by a plant, but some direct evaporation also takes place through the cuticle of the leaves and young stems. The amount of water given off depends somewhat upon how much water the roots of the plant have absorbed (Martin et al., 1976) Transpiration is a process similar to evaporation. It is a part of the water cycle, and it is the loss of water vapor from parts of plants (similar to sweating), especially in leaves but also in stems, flowers and roots. Leaf surfaces are dotted with openings which are collectively called stomata, and in most plants they are more numerous on the undersides of the foliage. The stomata are bordered by guard cells that open and close the pore (Cummins, 2007). Leaf transpiration occurs through stomata, and can be thought of as a necessary "cost" associated with the opening of the stomata to allow the diffusion of carbon dioxide gas from the air for photosynthesis. Transpiration also cools plants and enables mass flow of mineral nutrients and water from roots to shoots. Mass flow of liquid water from the roots to the leaves is caused by the decrease in hydrostatic (water) pressure in the upper parts of the plants due to the diffusion of water out of stomata into the atmosphere. Water is absorbed at the roots by osmosis, and any dissolved mineral nutrients travel with it through the xylem (Swarthout et al., 2010).Despite the fact that transpiration accounts for water loss in plants; it is not simply a hazard of plant life. It is the engine that pulls water up from the roots to supply photosynthesis, bring minerals from the roots for biosynthesis within the leaf and also serves in cooling plants. The transpiration rate for low light and still air is lower as compared to high light and windy air. The entire set-up to which the experiment was performed measured 10-ml pipette was used. Windy air has a marked effect on transpiration because it modifies the effective length of the diffusion path for exiting water molecules. This is
due to the existence of the boundary layer introduced earlier. Before reaching the bulk air, water vapor molecules exiting the leaf must diffuse not only through the thickness of the epodermal layer, but also through the boundary layer. According to Fick’s law, this added length will decrease the rate of diffusion and, hence the rate of transpiration (Hopkins et al., 2009).The result presented above can be justified by the fact that the rate of transpiration is affected by light intensity. The rate of transpiration is directly proportional to light and wind. An increase in light and wind would also mean an increase in transpiration since during these conditions, the stomata tends to open. Light stimulates the stomata to open allowing gas exchange for photosynthesis,
and as a side effect this also increases transpiration. High temperature increases the rate of evaporation of water from the spongy cells,
and reduces air humidity, so transpiration increases. Wind blows away saturated air from around stomata, replacing it with drier air, so
increasing the water potential gradient thus increasing transpiration .
Other conclusions drawn were: If transpiration rates exceed water absorption rates the leaf cells loose turgor and show wilting,
due to this the physiological processes of plants are impaired Helps in sending out excessively absorbed water by plants Transpiration pull helps in ascent of sap.
Bibliography Benjamin Cummins (2007),Biological Science(3rded). Debbie Swarthout and C.Michael Hogan. (2010).Stomata . Encyclopedia ofEarth.National Council for Science and the Environment,Washington DC.
Martin, J.; Leonard, W.; Stamp, D. (1976).Principles of Field Crop Production (ThirdEdition), New York: Macmillan Publishing Co., Inc.
Goatley, James L.; Lewis, Ralph W. (March 1966)."Composition of Guttation Fluid from Rye, Wheat, and Barley Seedlings" . Plant Physiology 41(3): 373375.
Slavík, BohdanZ; Jarvis, Margaret Susan (1974). Methods of Studying Plant Water Relations. William G.;Huner, Norman P. A. (2009). ―Introduction to Plant Physiology(Fourth Edition), John Wiley & Sons, Inc
Documentation
Xylem and Cortex Stained
Low Intensity Light (10 w)
High Intensity Light (60w)
Quiet Air
Windy Air
