transpiration + translocation

• What is the main topic covered in this video?

  Transpiration and the cohesion tension theory
• What is transpiration?

  Loss of water vapor from stomata
• Where are stomata mainly found?

  On the lower side of the leaf
• What are the four key conditions affecting transpiration rates?

  • Light intensity
  • Temperature
  • Humidity
  • Wind
• How does light intensity affect transpiration?

  Higher light intensity increases transpiration rate
• Why does temperature affect transpiration rates?

  Higher temperature increases water molecule kinetic energy
• What is the effect of humidity on transpiration?

  Higher humidity decreases transpiration rate
• Why does wind affect transpiration rates?

  Wind carries away water vapor, increasing evaporation
• What does the cohesion tension theory explain?

  How water moves up against gravity in plants
• What is cohesion in the context of water molecules?

  Sticking together of water molecules
• How does cohesion affect water movement in xylem?

  Creates a continuous water column in xylem
• What is adhesion in relation to water and xylem?

  Water molecules sticking to xylem walls
• How does capillarity relate to water movement?

  Narrow xylem increases water movement upward
• What is root pressure?

  Pressure from water entering roots by osmosis
• How does root pressure contribute to water movement?

  Pushes water upwards in the xylem
• What are the components of the cohesion tension theory?

  • Cohesion: water molecules stick together
  • Adhesion: water molecules stick to xylem walls
  • Root pressure: pushes water upwards
• How does transpiration create a pull on the water column?

  Evaporation lowers pressure, pulling water up
• What role do hydrogen bonds play in water movement?

  They create cohesion between water molecules
• How does tension affect the diameter of xylem?

  Tension pulls xylem walls inward, narrowing diameter
• What is the summary of transpiration and cohesion tension theory?

  • Transpiration: loss of water vapor from stomata
  • Affected by temperature, light, humidity, wind
  • Cohesion: water molecules stick together
  • Adhesion: water sticks to xylem walls
  • Root pressure: pushes water upwards
• What should students do to prepare for the next video?

  Subscribe for updates on new videos
• Who is the presenter of the A-level biology video?

  Miss Esther
• 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 instead of transpiration?

  The uptake of water by a plant
• Why is it necessary to cut the plant 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 from entering and water from leaking
• How is the air bubble introduced into the potometer?

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

  The amount of water taken up 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?


  12 mm³ per minute
• What must be controlled when comparing two different plant species?

  The surface area of the leaves
• What is the purpose of the reservoir of water in the potometer?

  To refill the potometer during the experiment
• Why is it important to close the tap during the experiment?

  To maintain a constant water level in the potometer