Potometer

• What is the purpose of using a potometer in this context?

  To measure the uptake of water
• What is transpiration?

  Evaporation of water vapor from stomata
• How does transpiration affect water movement in plants?

  It draws up a continuous water column
• What are the four key factors affecting transpiration rate?

  Temperature, humidity, air movement, light intensity
• Why is it difficult to measure the rate of transpiration directly?

  Because it involves measuring water vapor evaporation
• What does a potometer measure?

  Water uptake by a plant over time
• Why is the plant shoot cut underwater?

  To prevent air from entering the xylem
• What happens if the plant is cut in the air?

  Air enters the xylem, breaking the water column
• Why must the potometer be filled with water underwater?

  To remove all air bubbles from the apparatus
• What is the purpose of covering joints with petroleum jelly?

  To prevent air entry and water leakage
• How is the air bubble introduced into the potometer?

  By lifting the capillary tube out of water
• What does the movement of the air bubble indicate?

  Water uptake by the plant
• How do you calculate the volume of water taken up?

  Using the formula for the volume of a cylinder
• What is the formula for the volume of a cylinder?

  Volume = $\pi r^2 h$
• If the radius of the capillary tube is $0.5 \text{ mm}$ and the air bubble moves $15.28 \text{ mm}$, what is the volume?


  Volume = $12 \text{ mm}^3$
• What must be controlled when comparing two different plant species?

  Surface area of the leaves
• What are the steps to set up a potometer?

  • Cut the plant shoot underwater
  • Fill the potometer with water underwater
  • Insert the plant shoot into the potometer
  • Seal joints with petroleum jelly
  • Introduce one air bubble
• What are the uses of a potometer in experiments?

  • Measure transpiration rate of one plant
  • Compare transpiration rates between different species
  • Assess effects of environmental variables
• What are the common exam questions related to potometers?

  1. Explain the setup process
  2. Why cut underwater?
  3. Importance of petroleum jelly
  4. Calculate water volume from measurements