Plant Transport

• The structure of root hair cells, xylem and phloem are adapted to their functions.
• The roots, stem and leaves form a plant organ system for transport of substances around the plant.
• Xylem vessels transport water and minerals from the roots to the stem and leaves.
• Xylem vessels are composed of hollow tubes strengthened by lignin, adapted for the transport of water in the transpiration stream.
• Phloem vessels transport food materials (mainly sucrose and amino acids) made by the plant from photosynthesising leaves to non-photosynthesising regions in the roots and stem.
• Xylem and phloem vessels are arranged throughout the root, stem and leaves in groups called vascular bundles.
• Osmosis causes water to pass into the root hair cells, through the root cortex and into the xylem vessels.
• Once the water gets into the xylem, it is carried up to the leaves where it enters mesophyll cells.
• Stomata (specifically the guard cells) control the diffusion of gases in and out of leaves, meaning stomata control the entry of carbon dioxide into leaves.
• Stomata open and close in a daily rhythm, even when the plant is kept in constant light or constant darkness, the daily rhythm of opening and closing of the stomata continues.
• Transpiration also serves to cool the plant down by converting water into water vapour as it leaves the cells and enters the airspace, using heat energy.
• Opening of stomata during the day maintains the inward diffusion of carbon dioxide and the outward diffusion of oxygen, allows the outward diffusion of water vapour in transpiration.
• Due to cohesion, the water in the xylem creates a continuous unbroken column, with each individual molecule ‘pulling’ on the one below it.
• The many interconnecting air spaces between the mesophyll cells and the stomata create a large surface area, allowing evaporation to happen rapidly when the stomata are open.
• Transpiration in plants has several functions, including transporting mineral ions, providing water to keep cells turgid, and providing water to leaf cells for photosynthesis.
• Water moves through the xylem vessels in a continuous transpiration stream from the roots to the leaves via the stem to replace the water that has been lost due to transpiration.
• Transpiration produces tension or ‘pulls’ on the water in the xylem vessels.
• Factors affecting the rate of water uptake include air movement, humidity, light intensity, and temperature.
• Evaporation of water occurs at the surfaces of the spongy mesophyll cells followed by diffusion of water vapour through the stomata.
• Transpiration is defined as the loss of water vapour from the parts of the plant that are above ground, including leaves, stem, and flowers.
• When all four factors are high, the rate of transpiration or water uptake is increased.
• Closing of stomata at night when photosynthesis cannot occur reduces the rate of transpiration, conserves water.
• When the guard cells are turgid the stoma is open, once the guard cells lose water by osmosis and become acid, the stoma closes.
• Transpiration is the process where water vapour is released from the leaves of a plant.
• As light intensity increases, the rate of transpiration increases.
• When working with practical investigations, remember to consider your CORMS evaluation.
• Cut the stem underwater and assemble equipment underwater to minimise opportunities for air bubbles to enter the xylem.
• Use the plant cuttings as soon as they have been cut, as transpiration rates may slow down when the cuttings are no longer fresh.
• The more stomata that are open, the more water can be lost by evaporation and diffusion through the stomatal pores.
• Transpiration rate increases with light intensity because more stomata tend to be open in bright light in order to maximise photosynthesis.
• The bubble moves a greater distance in the 30 minute time period when the lamp is placed closer to the leaf.
• Ensure that all equipment fits together rightly around the rubber bungs and assemble underwater to help produce a good seal.
• The plant cutting has a blockage.
• If testing the effect of light intensity, your evaluation should look something like this: Change - We will change the intensity of the light Organisms - The plants used in each repeat should be the same species, size, age, number of leaves Repeat - We will repeat the investigation several times to ensure our results are reliable Measurement 1 - We will measure the distance travelled by the bubble Measurement 2 - ...in 30 minutes (calculate the rate of transpiration ).
• Calculating the 'rate of transpiration' provides both M1 and M2 in the CORMS evaluation as the rate is calculated based on a distance (M1) and time period (M2).
• In this investigation, there are several different variations of the method depending on which environmental factor you are testing.
• We will control the temperature, wind speed and humidity of the environment.
• The potometer has shown no change during the experiment.
• The potometer equipment has a leak.
• There are two different types of potometer that could be used to investigate the effect of environmental conditions on transpiration: Apparatus Potometer (bubble or mass potometer).