7c-Plants Transpiration Lab II, Study notes of Biology

Download 7c-Plants Transpiration Lab II and more Study notes Biology in PDF only on Docsity! Topic 7: Plants – 7c. Transpiration Lab Resources: Miller, K., Levine, J. (2004). Biology. Boston, MA: Pearson Prentice Hall. Ju, A. World's first synthetic tree is no giant redwood, but may lead to technologies for heat transfer, soil remediation [Internet]. Chronicle Online, Cornell University. 10 Sept. 2008. Available from: http://www.news.cornell.edu/stories/Sept08/stroock.trees.aj.html Building on: Transpiration is the evaporation of water from a plant. It occurs when the stomata of the leaves are open so that gas exchange (release of oxygen and the uptake of carbon dioxide) can occur to maximize photosynthesis. The water lost to transpiration also plays a role in the conduction of water from the roots of the plant to the leaves and chloroplasts where some of that water will be used in photosynthesis. An understanding of the movement of this water is critical to the transpiration flow theory, explaining how water moves through xylem. The connection between the stomata, the gas exchange, and the water loss is important to the understanding of photorespiration and why it occurs. Links to Chemistry: Polar molecules Properties of water Phase change Molecular movement Links to Physics: Pascal’s principle Atmospheric pressure Temperature Evaporation Energy and changes of phase Stories: Researchers at Cornell University have developed a synthetic tree. Actually, it isn’t a tree, but a synthetic model for plant transpiration. It has the equivalent of a root, a trunk, and a leaf. The trunk is made of an ultrathin tube. The roots and the leaves were the big breakthrough; they are made of a hydrogel, similar to what is found in soft contact lenses. This hydrogel has nanometer scale pores and microfluid channels that act like a wick to take up water by osmosis in the root. The water is held in a metastable state, which is a liquid on the verge of becoming a vapor. The negative pressure created by the water in the leaves, pulls the water up from the roots. This research is significant because it supports the transpiration pull theory, but it also proves that transpiration in plants is a physical process, not a biological process. That means that the movement of water through xylem requires no energy on the part of the plant. There are several placations for these findings. A larger model could be used to heat water by means of a solar collector on the roof of a building. The heated water could move through tubing down through the building, heating the building as it goes. When the water reaches the bottom of the building, the synthetic transpiration model would return water to the roof without the use of energy from electricity or burning of fossil fuels. Another benefit of this transpiration model would involve tapping water deep in the earth. In areas where the water table is very deep, extensive wells have to be constructed and pumps are used to bring the water to the surface. This new method would reduce the drilling and would eliminate the pumps. To read more about this go to: http://www.news.cornell.edu/stories/Sept08/stroock.trees.aj.html Materials for the Lab: • Celery stalks (one stalk for every two students; it is better to get celery with the leaves on the stalk.) • Beakers or cups • Razor blades • Red food color (Put enough in each cup to get the water quite red.) • Plastic wrap and Scotch tape • A fluorescent light (emits very little heat) • A box fan • A cabinet or box for the dark room • Clear plastic bags for the humidity • Digital balance • Stereo or dissecting microscopes that magnify about 100 times Instructions for the Teacher: This lab usually gets very good results. The wind (fan) usually has the greatest amount of transpiration and the humid condition has the least. Whether the light or dark will have more transpiration varies from year to year, and I think it has to do with how hydrated the celery is when the experiment begins. This lab will work with celery stalks with no leaves, which might be simpler with lower level kids. If you use celery stalks with leaves, the issue of how many and what size leaves are on different stalks may come up. With upper level kids, you can have them remove all of the leaves at the end of the lab and mass them. They can then cut 1 cm2 pieces of leaf and place them on the balance to find the mass of the leaves per cm2. A proportion equation can then be used to determine the cm2 of the leaves from each student’s stalk, and transpiration per cm2 can be calculated instead of % transpiration. Note, that depending on the sensitivity of your balance, you may need to put several sq. cm of leaves on it before you get a reading.