Transpiration
Leaves have a lot of small holes underneath, allowing gases to diffuse in and out. The hole is called the stomata. There are two guard cells around the stomata, and that changes shape in order to allow the gases to diffuse in and out. The stomata is usually open during the day and closed during the night, as photosynthesis can only take place during the day time.
Environmental Factors
If the rate of transpiration increases, then the root will absorb more water from the soil. The follow are a few environmental factors that can affect the rate of water uptake by a plant.
- When the temperature increases, more water will evaporate from the cell surface. This increases the rate of diffusion of water from the leaf.
- When there is low humidity, there is less of a concentration off water on the outside of the leaf. This increases the rate of diffusion of water from the leaf.
- When there is more air movement, water vapor is removed more quickly on the leaf surfaces. More water will diffuse off the surface.
- When the light intensity is higher, the rate of photosynthesis increases. The stomata will then open up so that water can diffuse out of the leaf.
Rate Calculations
The rate in which transpiration takes place can be measured by looking at either the decrease in mass of the plant due to water loss, or by looking at the volume of water that is absorbed. A potometer can be used. When the water moves through the plant as it is absorbed, the air bubble will move along the scale. This will allow you to measure the transpiration rate.
Translocation
Translocation is the name of the process when sugars are transported in the phloem. This is an active process. The phloem contains living cells, and its structure is made of sieve tubes and companion cells. Sieve tubes are needed for transport, and have no nuclei. Companion cells are attached to sieve tubes in order to provide energy for translocation. Sieve tubes and companion cells must work together in order for translocation to be successful.