MEASURING RATE OF WATER UPTAKE BY A PLANT SHOOT USING A POTOMETER
All plants need salts minerals, water, CO2 and O2. To fulfill their requirements different plants use different ways. Lower plants use diffusion, however higher plants use vascular tissue that is located in the middle of the root and in the vascular bundles in the stem. The transpiration is the important process in the plant. The main reason is that transportation is the loss of water through vaporization and it helps to minerals and ions to be absorbed, also it helps water and minerals to flow from root to upper part of plant. Second important reason is that transpiration process helps to ‘cool’ the plants. Transpiration rate depends on 2 issues, first is the gradient in humidity from the leaf’s internal air spaces to the outside air and the diffusion resistance provided by the stomata pores. One way to measure the rate of transpiration in plants is by using a photometer. In this practical photometer will be used as device to measure the rate at which water enters a leaf shoot. The rate at which water enters a plant depends on the rate at which it evaporates from the leaves, for instance transpired into surrounding atmosphere. Also, in the shoot, the water could stay in the cells, or be used in photosynthesis and assimilated into carbohydrate, or it could be passed on up the xylem to the leaf tissue. Any external conditions which affect the rate of transportation will be expected to effect on the rate of water uptake. In this practical different effects of external conditions on rate of water uptake of plant. Factors affecting transpiration:
* High light intensity (bright sunlight)
* Increased/decreased temperatures (hot/ cold weather)
* Low humidity (dry conditions)
The aim of this practical is to assess the effect of different environmental conditions (e.g. temperature, wind speed, light intensity ) on transpiration rate of water uptake, by a shoot from a woody plant and using a photometer. Safety
* Some people find sap from plants irritating to the skin, inform your tutor if you have something * Take care when cutting the plant shoot.
* Take care when assembling and handling the glass potometer: it is easy to break the long glass tubes and cut or stab yourself with the broken ends. Be prepared with first aid for cuts from broken glass, and brief students how to deal with breakages
Methods and materials:
1. Apparatus was set up as in the diagram B in lab manual. 2. U- tube was placed on flat level surface, and water was added until it get meniscus on the top of both sides. Attention was pay that bubbles should not be inside the potometer 3. The stem of the leafy shoot was cut under water and then fit into the hole bung. The stem was tested to make sure the leafy twig will fit snug tightly into the top of the bung, because it may affect on results. Some amount of Vaseline was used to create a seal. 4. Second bung was place on the second tube of the potometer and inside the hole of this bung graduated pipette was placed. Excess water was released.
5. The potometer was put on the flat surface, by being not disturbed and moved. 6. The time was started to note and labeled by the meniscus of water in the scale, when different factors affected to transpiration of water such as temperature, wind and light. From 2 ways one was chosen to take measurements. 7. The stop clock was stopped after fixed minutes and the distance of water absorbed was noticed. 8. Light intensity. A lamp was used in this part to make different light conditions and try to lighten the plant shoot from different distances. 9. Wind speed. A fan was used to make a different wind conditions and try to blow from different distances. The wind speed was measure by anemometer. 10. Temperature. Water absorption was measured at different...