Bubble And Mass Potometer Flashcards
How can we measure the rate of water uptake into a plant
Using a bubble potometer-consists of a fine capillary tube which is filled with water- connected to a plant which has been cut at the stem, tube also connected to a syringe filled with water
-use a needle to place a small air bubble at end of capillary tube.
-As water evaporates from the leaves of the plant, water is drawn into the stem, causes air bubble to move towards plant.
-By measuring how far the air bubble moves in a given time we can calculate the rate of water uptake into the plant
-can see how the rate of water uptake changes if we change the conditions.
-in between experiments we can reset the position of the air bubble by adding more water from the syringe.
Problem with potometer
Only measures water uptake into plant, not all this water will take part in transpiration
For example a small amount of water taken in will be a reactant in photosynthesis.
Things to consider when setting up a bubble potometer
-when we take our cutting from the parent plant, air will be sucked into the xylem vessels-these air gaps will prevent water from being taken up the stem.- place cut stem of our plant into water, cut off last 1cm- water will now flow into xylem and we will avoid any air gaps. Then place the potometer under the water and insert the cut end, again avoiding any air gaps.
-Potometer needs to be fully sealed, smear some petroleum jelly around the connection between the stem and the tube.
-need to allow the plant to adapt to its surroundings for ten minutes before starting experminents.
How do you use a mass potometer
Place our plant in its pot on a balance, as the plant loses water through transpiration, the total mass decreases.
-with this potometer we have to prevent evaporation of water from the soil, otherwise this would contribute to mass lost, giving a false reading for transpiration-cover soil with plastic wrap.
Two advantages to mass potometer
-directly measured the rate of transpiration rather than rate of water uptake
-much less disruptive to plant as it doesn’t involve cutting the stem.
