Transpiration 2/24
Flashcards: Transpiration & Water Balance in Plants
(Use these for quick study and review!)
Water Balance & Osmoregulation
Q: What is the difference between osmoconformers and osmoregulators?
A: Osmoconformers maintain internal osmolarity equal to their environment, while osmoregulators actively regulate their internal osmolarity.
Q: What is the difference between hypoosmotic and hyperosmotic conditions?
A:
Hypoosmotic: Lower solute concentration, higher free water concentration.
Hyperosmotic: Higher solute concentration, lower free water concentration.
Q: How do marine bony fish (e.g., cod) regulate water balance?
A:
Hypoosmotic to seawater.
Constantly lose water by osmosis and gain salt.
Drink seawater and actively excrete salt via gills.
Produce little urine to conserve water.
Q: How do freshwater fish (e.g., perch) regulate water balance?
A:
Hyperosmotic to their environment.
Constantly gain water by osmosis and lose salt.
Excrete dilute urine to remove excess water.
Actively absorb salts from surroundings.
Water Potential & Osmosis
Q: What is water potential (Ψ)?
A: A measure of water’s potential energy, determining the direction of water movement.
Q: How does water move in relation to water potential?
A: Water moves from higher water potential (Ψ) to lower water potential (Ψ).
Q: What happens when a plant cell is placed in a hypertonic solution (higher solute outside)?
A: Water leaves the cell, causing it to shrivel (plasmolysis).
Q: What happens when a plant cell is placed in a hypotonic solution (lower solute outside)?
A: Water enters the cell, increasing turgor pressure and making the cell firm.
Water Balance in Plants
Q: What are the three main reasons plants need water?
A:
Photosynthesis – Water provides electrons in light reactions.
Structural support – Water fills vacuoles for turgor pressure.
Nutrient transport – Minerals dissolve in water for uptake.
Q: What is the tradeoff between CO₂ uptake and water loss?
A: Stomata must open for CO₂ but this increases water loss.
Q: How much water is lost for every gram of CO₂ absorbed?
A: Up to 400 grams of water!
Transpiration Process
Q: What is transpiration?
A: The loss of water vapor from plants through stomata.
Q: What are the three main steps of transpiration?
A:
Water enters roots and moves to xylem.
Cohesion & adhesion help water form a continuous column.
Water evaporates from leaves and exits through stomata.
Q: What properties of water allow it to move up xylem?
A: Cohesion (water sticks to itself) and adhesion (water sticks to xylem walls).
Xylem & Water Transport
Q: What are the two types of xylem cells?
A: Tracheids (thin, slow transport) and vessel elements (wide, efficient transport).
Q: How do root hairs help water uptake?
A: Increase surface area for absorption.
Q: What role does adhesion play in xylem?
A: Water sticks to xylem walls, helping it move upward.
Cavitation (Air Bubbles in Xylem)
Q: What is cavitation?
A: Formation of an air bubble (embolism) in xylem, blocking water flow.
Q: What causes cavitation?
A:
High temperatures (midday water stress).
Freezing (gas comes out of solution when ice forms).
Q: How do plants minimize cavitation?
A:
Pits in xylem allow lateral water movement.
Xylem plates trap air bubbles.
Tracheids (narrower xylem cells) reduce bubble formation.
Water Potential & Transpiration
Q: How does water potential (Ψ) drive transpiration?
A: Water moves from higher to lower Ψ:
Soil → Roots → Stem → Leaves → Air.
Q: What happens if soil water potential is too low?
A: Water cannot move into the plant, leading to wilting.
Stomata & Water Regulation
Q: What are stomata?
A: Pores on the leaf surface that allow gas exchange and transpiration.
Q: Why do stomata close at night?
A: CO₂ uptake is not needed, so closing stomata prevents water loss.
Q: What are four conditions that cause stomata to open?
A:
Light – Blue light receptors trigger K⁺ uptake, making guard cells turgid.
Low CO₂ – Stomata open for gas exchange.
Circadian rhythm – Internal clock regulates daily cycles.
Drought stress – Hormone abscisic acid (ABA) signals closure.
Factors Increasing Water Loss
Q: What three factors increase transpiration?
A:
Open stomata.
Low humidity (higher evaporation rate).
Wind (removes moisture from leaf surface).
Plant Adaptations to Reduce Water Loss
Q: How do Ocotillo plants reduce water loss?
A:
Leafless most of the time.
Grow leaves only after rainfall.
Q: How do Old Man Cactus (Espostoa) survive dry conditions?
A:
Hair-like structures trap moisture.
Columnar shape reduces surface area.
Q: How does Oleander minimize water loss?
A:
Stomata are hidden in deep crypts.
Leaf hairs (trichomes) trap humidity.
Thick waxy cuticle prevents evaporation.
Final Review
Q: What is transpiration?
A: The loss of water vapor from plants through stomata.
Q: What forces help water move through xylem?
A: Cohesion, adhesion, and water potential gradients.
Q: What is the main tradeoff in plant water regulation?
A: CO₂ uptake vs. water loss—plants must open stomata for CO₂ but risk dehydration.
Q: How do plants regulate water loss through stomata?
A: They open during photosynthesis and close in response to drought or at night.
🌿 Study Tip! 🌿
Use these flashcards in quiz mode—test yourself, shuffle, and review the trickiest concepts! Let me know if you need more! 😊📚