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Ganong's Potometer
Potometer

A potometer (from Greek ποτό = drunken, and μέτρο = measure) —sometimes known as a transpirometer— is a device used for measuring the rate of water uptake of a leafy shoot. The causes of water uptake are photosynthesis and transpiration.[1] Everything must be completely water tight so that no leakage of water occurs.

There are two main types of potometers used - the bubble potometer (as detailed below), and the mass potometer. The mass potometer consists of a plant with its root submerged in a beaker. This beaker is then placed on a digital balance; readings can be made to determine the amount of water lost by the plant. The mass potometer measures the water lost through transpiration of the plant and not the water taken up by the plant.

  • A potometer is a piece of apparatus used to measure the rate of water loss from a plant (transpiration). The rate of transpiration can be estimated in two ways:

1) Indirectly - by measuring the distance the water level drops in the graduated tube over a measured length of time. It is assumed that this is due to the cutting taking in water which in turn is necessary to replace an equal volume of water lost by transpiration. 2) Directly - by measuring the reduction in mass of the potometer over a period of time. Here it is assumed that any loss in mass is due to transpiration.

Design[edit]

Potometers come in a variety of designs, but all follow the same basic principle.

  • A length of capillary tube A bubble is introduced to the capillary; as water is taken up by the plant, the bubble moves. By marking regular gradations on the tube, it is possible to measure water uptake.
  • A reservoir. Typically a funnel with a tap; turning the tap on the reservoir resets the bubble. Some designs use a syringe instead.
  • A tube for holding the shoot. The shoot must be held in contact with the water; additionally, the surface of the water should not be exposed to the air. Otherwise, evaporation will interfere with measurements. A rubber bung greased with petroleum jelly suffices.

Preparation[edit]

  1. Cut a leafy shoot from a plant and plunge its base into water. This prevents the xylem from taking up any air. Wetting the leaves themselves will alter the rate of transpiration.
  2. Immerse the whole of the potometer into the sink. Move it about until all the air bubbles come out.
  3. Recut the shoot's stem underwater. Put it into the bung; grease the bung with plenty of petroleum jelly (Vaseline) if it doesn't stay and then put the bung into the potometer.
  4. Make sure the tap is closed, then lift the whole assembly out of the water.
  5. Leave the end of the capillary tube out of the water until an air bubble forms then put the end into a beaker of water.

Types of Potometers[edit]

  1. Bubble Potometer
  2. Mass potometer
  3. Ganong's Potometer
  4. Darwin's Potometer


Use[edit]

  1. Set up the conditions of the experiment. Alterations to lighting (placing the plant in bright light or shadow), wind (directing a fan at the plant), and humidity (placing the plant in a humid chamber) are typical.
  2. Let the bubble reach a "zero" point in the tube.
  3. Measure the movement of the bubble at regular intervals and record the results

Precautions[edit]

  1. When a twig is cut from a plant, it should be immediately put under water (only the cut portion). Then, a small part is cut under water. This prevents entry of air into the xylem vessels.
  2. The conditions of the potometer, other than the alteration that is being tested, should not be changed during a test, as outside conditions (for example, temperature) determine water uptake.

Limitations[edit]

  1. The Potometer does not measure the rate of transpiration accurately because not all of the water that is taken by the plant is used for transpiration (water taken might be used for photosynthesis or by the cells to maintain turgidity). The potometer measures the rate of uptake of water. To measure transpiration rate directly, rather than the rate of water uptake, utilize a scientific instrument which quantifies water transfer at the leaves.
    • The water retained by plant is so negligible that it can be neglected.
    • Introducing an air bubble may not be easy.
  2. A twig may not be active for a long time.

References[edit]

  1. ^ Slavík, BohdanZ. Methods of Studying Plant Water Relations.  |first2= missing |last2= in Authors list (help)

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Potometer — Please support Wikipedia.
This page uses Creative Commons Licensed content from Wikipedia. A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia.
1048 videos foundNext > 

Potometer

Instructions on how to set up a potometer that measures the rate of transpiration in a plant.

Crockett Science AS Biology Activity 15 Using a Potometer to measure Water Uptake

Its not Rocket Science its CROCKETT SCIENCE! My take on 'Using a Potometer to measure Water Uptake' Enjoy.

How to set up a potometer: by Simon and Lynn from the NSLC. First try! laurel poisonous don't eat!!

via YouTube Capture.

Using Potometer in a Lab

AP Biology Lab 9: Transpiration

Paul Andersen starts by defining transpiration as evaporation off of a leaf. He then describes how a potometer can be used to measure the rate of transpirati...

Setting up a potometer

The potometer is used to measure the rate of transpiration in plant stems.

Potometer Experiment: Measuring the rate of Water Uptake - Rainey Endowed School

Potometer Experiment: Measuring the rate of Water Uptake - Rainey Endowed School.

Instructions for Assembling a Potometer

Year 12 Biologists produced this instructional video to demonstrate how to set up a potometer for measuring water uptake in a plant.

Leaf transpiration in herbaceous plant (potometer)

Transpiration - How to set up a Potometer

Description.

1048 videos foundNext > 

3 news items

The Hindu

The Hindu
Mon, 10 Mar 2014 06:06:14 -0700

After which brave queen is the daily train running between Bangalore and Kolhapur named? 13. Which English Premier League club is nicknamed 'The Eagles'? 14. Of what use is a potometer to a botanist? 15. Which is the best known example of the 'G-type ...
 
Sciblogs (blog)
Sun, 04 Apr 2010 00:00:00 -0700

One of our first-year bio labs sees our students using potometers to determine how transpiration is affected by things like light, humidity, & wind movement. Those of my readers who are school students may well have done something similar, but for ...
 
What Digital Camera (press release)
Thu, 09 Sep 2010 08:35:44 -0700

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