AP Biology
Lab Report
THE PROCESS
The movement of water from the roots to the leaves and flowers is due primarly to the differences in water potential between the two parts of the plant. Capillary action also aids in propelling the water upwards.
Transpiration is controlled by a variety of factors. Stomatol opening, which can be affected by the soil water quality and soil temperature, is one of these factors. Water is only able to leave the plant through these small openings found along the leaves of the plants. When there is little water supply, plants keep their stomata closed in order to keep water from evaporating. A closed stomata, however, reduces the amount of CO2 that can enter the plant in order for photosynthesis to occur. Environmental factors, such as wind, humidity, and sunlight, also have a role in the rate of transpiration.
Plant Transpiration
Plant transpiration deals with the vaporization of water from a plant that then enters the atmosphere. Moisture passes from the roots of a plant and onto the underside of leaves in order for transpiration to occur.
In the experimentation, there was a focus on the water quality-- the salinity of the water quality to be more specific. The diffusion of water across a membrane deals with the water potential and solute poptential. Because plants have cell walls, they are either turgid or very loose. When a plant is placed in a hypotonic solution, the cell wall and structure results in a turgid plant cell. This is due to the pulling of the cell wall. When a plant is placed in an isotonic solution, it is flacid because there is continuous movement of water. When it is placed in a hypertonic solution, however, it plasmolyzes. Because an influx of sodium chloride ions would make the water solution hypertonic to that of the plant cells, the plant will plasmolyze and transpiration will be compromised.
Plants have a variety of physiological and structural adaptations that prevent water loss. Structurally, plants can have fewer stomata in order to preserve water. Some plants also have smaller leaves, or no leaves at all, in order to have a smaller surface area where water can leave the plants. Plants sometimes also have thicker cuticles so that there is a slowing of water loss due to this waxy coating. In terms of physiology, some plants have developed into C4 plants and CAM pants in order to carry out photosynthesis without as much oxygen. These mechanisms all slow down transpiration because that involves water loss.
Transpiration is possible by a variety of plant mechanisms known by the acronym TACT. It is due to the forces of Transpiration, Adhesion, Cohesion, and Tenson that water is able to move from the roots of a plant and onto the surface of the plants where the water evaporates.
Transpiration itself is the process in which water is pulled through the xylem by the energy of evaporation and the tensile strength of water.
Adhesion is the attraction between water molecules and other molecules. The attraction that water and cellulose have, to each other, aids in the process of water moving upward because water molecules attract to the walls of the xylem capillary.
Cohesion is the attraction that water molecules have to each other. The cohesive force causes for a tensile strengh with also aids in the conduction of water through the plant.
Tension is the stress placed on an object by a pulling force. This pulling force is created by the surface tension which develops in the air spaces of the leaves.
These forces allow for the water to move throughout the plant and get pulled up into the leaves. The leaves hold the stomata which are controlled by gaurd cells. Stomatas are openings that are cused by the turgidness of gaurd cells. When the cells are turgid, the stomata are opened and secret water molecules. When the cells are flaccid, however, the stomata close up and no water is released. When the temperature around the plant goes up, there is a higher incidence of evaporation and therefore higher transpiration rates. The stomata, however, begins to close up as soon as this is detected. Gaurd cells take notice of the fact that there are environmental factors changing and therefore close the stomata in order to restrict water loss.