AP Biology Questions on Water Transport and Transpiration

📚 Quick Study Guide

• 💧 Water potential ($\Psi$) is the potential energy of water per unit volume relative to pure water at atmospheric pressure and room temperature.
• 🪴 Water moves from areas of high water potential to areas of low water potential. $\Psi = \Psi_p + \Psi_s$, where $\Psi_p$ is pressure potential and $\Psi_s$ is solute potential.
• ⬆️ Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves.
• 🍃 Stomata are pores in the epidermis of leaves that allow for gas exchange and transpiration.
• ☀️ Environmental factors like temperature, humidity, and wind affect the rate of transpiration.
• 🌳 Cohesion-tension theory explains how water moves up the xylem: water is pulled up due to transpiration, cohesion of water molecules, and adhesion to xylem walls.
• ⚙️ Guard cells regulate the opening and closing of stomata in response to environmental cues.

🧪 Practice Quiz

1. Which of the following environmental factors has the LEAST effect on transpiration rate?
   1. A) Light intensity
   2. B) Air Humidity
   3. C) Soil pH
   4. D) Wind Speed
2. What is the primary driving force for water transport in the xylem?
   1. A) Root pressure
   2. B) Guttation
   3. C) Transpiration
   4. D) Active transport
3. According to the cohesion-tension theory, what property of water is most important for its movement up the xylem?
   1. A) High specific heat
   2. B) High surface tension
   3. C) Cohesion
   4. D) Adhesion
4. Which of the following would cause stomata to close?
   1. A) Increased turgor pressure in guard cells
   2. B) High CO2 concentration in the leaf
   3. C) Low water potential in the soil
   4. D) Decreased abscisic acid (ABA) levels
5. If a plant cell has a pressure potential of 0.3 MPa and a solute potential of -0.45 MPa, what is the water potential?
   1. A) -0.75 MPa
   2. B) 0.15 MPa
   3. C) -0.15 MPa
   4. D) 0.75 MPa
6. What role do aquaporins play in water transport?
   1. A) Active transport of water against the water potential gradient
   2. B) Regulation of stomatal opening
   3. C) Facilitated diffusion of water across cell membranes
   4. D) Prevention of water loss through the cuticle
7. Which of the following best describes guttation?
   1. A) The loss of water vapor through stomata
   2. B) The exudation of water droplets from leaves due to root pressure
   3. C) The process of water moving up the xylem
   4. D) The regulation of water potential in guard cells