Biology Revision and Quiz: Theme D: D2.3 Water Potential

Biology Revision and Quiz: Theme D: D2.3 Water Potential Remember: Each mark is approx. 90 seconds of time. Keep this in mind as you read the question, process the information, and provide your answer. The number of marks also ‘generally’ indicates the number of points you should be making in your answer. Multiple Choice Questions (20 Questions) [20 marks] What property of water makes it an effective solvent for charged and polar molecules? A) High pH B) High surface tension C) Polarity D) Low boiling point Which term describes the movement of water across a selectively permeable membrane? A) Diffusion B) Osmosis C) Active transport D) Phagocytosis What happens to a plant cell placed in a hypertonic solution? A) Turgid B) Flaccid C) Plasmolyzed D) Cytolyzed Which solution is considered isotonic to human blood? A) Distilled water B) 0.9% saline solution C) 5% salt solution D) 10% glucose solution What is the water potential of pure water at 20°C under standard atmospheric pressure? A) 1 kPa B) 0 kPa C) -1 kPa D) 100 kPa Which unit is used to measure water potential? A) J/mol B) kPa C) mol/L D) m/s What type of pressure contributes positively to the water potential in plant cells? A) Solute potential B) Osmotic pressure C) Turgor pressure D) Air pressure Which term refers to the relative concentration of solutes in a solution? A) Molarity B) Osmolarity C) Isotonicity D) Tonicity What happens to an animal cell placed in a hypotonic solution? A) It shrinks B) It bursts C) It becomes plasmolyzed D) It remains unchanged What type of solution causes water to leave a plant cell, resulting in plasmolysis? A) Hypotonic B) Hypertonic C) Isotonic D) Supersaturated What role does the contractile vacuole play in freshwater unicellular organisms? A) It regulates nutrient absorption B) It expels excess water C) It stores energy D) It prevents plasmolysis Which factor can only decrease the water potential of a cell? A) Solute concentration B) Air pressure C) Temperature D) Light intensity Which cell type can exhibit negative pressure potential? A) Guard cells B) Xylem vessels C) Root hair cells D) Phloem sieve tubes What is the effect of adding more solute to a solution on its water potential? A) Water potential increases B) Water potential decreases C) Water potential remains the same D) Solute potential becomes positive What happens to plant cells in a hypotonic solution? A) They shrink B) They burst C) They become turgid D) They remain plasmolyzed Why must intravenous fluids be isotonic to human blood? A) To avoid cell shrinkage or bursting B) To increase blood pressure C) To prevent dehydration D) To promote faster absorption of nutrients Which of the following describes water movement between isotonic solutions? A) No net movement B) Water moves in only one direction C) Water moves from hypertonic to hypotonic D) Rapid diffusion occurs What happens to water movement when the water potential on both sides of a membrane is equal? A) Water moves into the cell B) Water moves out of the cell C) No net movement occurs D) Osmosis stops completely Which of the following is the correct definition of osmolarity? A) Water potential per unit volume B) Concentration of solute per unit volume of solution C) The pressure exerted by water molecules D) The force required to move water across a membrane Which solution would have the highest water potential? A) Pure water B) Hypertonic saline solution C) Isotonic saline solution D) Sugar solution Short Answer Questions (5 Questions) Define osmosis and explain how it differs from diffusion. [2] Compare the effects of placing plant cells in hypertonic and hypotonic solutions. [2] State the formula for calculating water potential in a plant cell. [1] Explain why turgor pressure is important for plant cells. [1] Describe the process by which the contractile vacuole functions in freshwater organisms. [2] Matching Questions (10 Questions) Match the terms with their definitions: [10] Terms Water potential 1. 6. 2. 7. 3. 8. 4. 9. 5. 10. Osmosis Isotonic solution Hypertonic solution Hypotonic solution Solute potential Pressure potential Plasmolysis Turgor pressure Contractile vacuole Descriptions a. Movement of water across a selectively permeable membrane b. Equal concentration of solutes inside and outside the cell c. Net water movement out of the cell, causing it to shrink d. Net water movement into the cell, causing it to swell e. Contribution of solute concentration to total water potential f. Contribution of pressure to total water potential g. Shrinking of the cell membrane away from the wall h. Positive pressure within a plant cell due to water intake i. Expels excess water from unicellular organisms j. Potential energy of water per unit volume Explain the concept of water potential and its importance in plant physiology, using an example of water movement through a plant. [3] Calculate the solute potential of a plant cell given the concentration of solutes and interpret its impact on total water potential. [3] 0.3 mol/L (solute concentration) Analyze the relationship between osmolarity and water movement in cells by interpreting data from a tonicity experiment. [3] Data Provided: Solution Osmolarity (mol/L) Initial Mass (g) Final Mass (g) Pure Water 0.00 10.0 10.6 0.2 NaCl 0.20 10.0 9.8 0.5 NaCl 0.50 10.0 9.3 0.8 NaCl 0.80 10.0 8.9 Compare and contrast the impact of osmotic pressure on animal cells versus plant cells in hypertonic solutions. [3] Using a diagram, explain the role of guard cells and water potential in regulating stomatal opening and closing. [4] True or False Questions (10 Questions) [10] Osmosis is a type of active transport. True/False Turgor pressure increases when water leaves the plant cell. True/False Water potential is highest in pure water. True/False Animal cells can survive in hypertonic solutions without any damage. True/False Solute potential is always negative. True/False A contractile vacuole helps freshwater unicellular organisms expel excess water. True/False Isotonic solutions cause water to move into cells. True/False Pressure potential contributes negatively to water potential in cells. True/False Plasmolysis occurs in plant cells placed in a hypertonic solution. True/False Hypotonic solutions increase turgor pressure in plant cells. True/False Data Analysis Question (1 Question) Analyze the following data from an experiment involving plant tissue placed in solutions of varying solute concentrations. Calculate the water potential for each tissue sample. [ 3] Use these results to determine the concentration at which the tissue achieves equilibrium, and [2] interpret the biological significance. [3] Solute Concentration (mol/L) 0.0 0.2 0.4 0.6 0.8 Initial Mass (g) 5.0 5.0 5.0 5.0 5.0 Final Mass (g) 5.4 5.1 4.8 4.5 4.3 Answer Key Multiple Choice Questions C) Polarity Explanation: The polarity of water molecules makes it an effective solvent for charged and polar substances, as it can form hydrogen bonds with these molecules. Why others are incorrect: A) High pH is not a property of pure water and doesn't explain its solvent properties. B) Surface tension affects water's behavior at interfaces, not its solvent properties. D) Boiling point doesn't directly relate to water's ability to dissolve substances. B) Osmosis Explanation: Osmosis specifically refers to the movement of water across a selectively permeable membrane from an area of higher water potential to lower water potential. Why others are incorrect: A) Diffusion is a broader term for molecule movement and doesn't specifically refer to water. C) Active transport requires energy and isn't specific to water movement. D) Phagocytosis is a cellular eating process, not related to water movement. C) Plasmolyzed Explanation: In a hypertonic solution, water moves out of the cell, causing the cell membrane to pull away from the cell wall, resulting in plasmolysis. Why others are incorrect: A) Turgid occurs in hypotonic solutions. B) Flaccid is an intermediate state, not the extreme seen in hypertonic solutions. D) Cytolyzed refers to cell rupture, which doesn't occur in plant cells due to the cell wall. B) 0.9% saline solution Explanation: A 0.9% saline solution is isotonic to human blood, meaning it has the same solute concentration and doesn't cause net water movement into or out of blood cells. Why others are incorrect: A) Distilled water is hypotonic to blood. C, D) These are hypertonic solutions. B) 0 kPa Explanation: Pure water at standard conditions has a water potential of 0 kPa, as it's used as the reference point for water potential measurements. Why others are incorrect: A, C, D) These values would indicate the presence of solutes or pressure, which pure water doesn't have under standard conditions. B) kPa Explanation: Water potential is typically measured in units of pressure, with kilopascals (kPa) being the standard unit. Why others are incorrect: A) J/mol is used for energy, not water potential. C) mol/L is used for concentration, not water potential. D) m/s is a unit of velocity, not relevant to water potential. C) Turgor pressure Explanation: Turgor pressure is the positive pressure exerted by the cell contents against the cell wall, contributing positively to water potential. Why others are incorrect: A) Solute potential contributes negatively to water potential. B) Osmotic pressure is another term for solute potential, contributing negatively. D) Air pressure isn't typically considered in cellular water potential calculations. D) Tonicity Explanation: Tonicity refers to the relative concentration of solutes in a solution compared to another solution, typically the cell's interior. Why others are incorrect: A) Molarity is a measure of concentration, not relative concentration. B) Osmolarity is the total concentration of osmotically active particles. C) Isotonicity is a specific state of tonicity, not the general term. B) It bursts Explanation: In a hypotonic solution, water enters the animal cell. Without a cell wall, the cell can continue to take in water until it bursts (lyses). Why others are incorrect: A) Shrinking occurs in hypertonic solutions. C) Plasmolysis is a term used for plant cells, not animal cells. D) The cell will change due to water movement. B) Hypertonic Explanation: A hypertonic solution has a higher solute concentration than the cell, causing water to move out of the cell and leading to plasmolysis. Why others are incorrect: A) Hypotonic solutions cause water to enter the cell. C) Isotonic solutions don't cause net water movement. D) Supersaturated refers to solute dissolution, not osmotic effects. B) It expels excess water Explanation: The contractile vacuole in freshwater unicellular organisms pumps out excess water that enters the cell due to the hypotonic environment. Why others are incorrect: A) Nutrient absorption isn't the primary function of contractile vacuoles. C) Energy storage is typically a function of other organelles. D) Preventing plasmolysis isn't relevant in a hypotonic environment. A) Solute concentration Explanation: Increasing solute concentration always decreases water potential by making the solute potential more negative. Why others are incorrect: B, C) These factors can increase or decrease water potential. D) Light intensity doesn't directly affect water potential. B) Xylem vessels Explanation: Xylem vessels can experience negative pressure potential due to transpiration pull, creating tension in the water column. Why others are incorrect: A, C, D) These cell types typically maintain positive or zero pressure potential. B) Water potential decreases Explanation: Adding solutes decreases water potential by making the solute potential more negative. Why others are incorrect: A) More solutes decrease, not increase, water potential. C) Water potential changes with solute addition. D) Solute potential becomes more negative, not positive. C) They become turgid Explanation: In a hypotonic solution, water enters plant cells, increasing turgor pressure and making them turgid. Why others are incorrect: A) Shrinking occurs in hypertonic solutions. B) Plant cells don't burst due to their cell walls. D) Plasmolysis occurs in hypertonic solutions. A) To avoid cell shrinkage or bursting Explanation: Isotonic fluids prevent osmotic imbalances that could cause cell damage through shrinkage (if hypertonic) or bursting (if hypotonic). Why others are incorrect: B) Isotonic solutions don't significantly affect blood pressure. C) While important, preventing dehydration isn't the primary reason for isotonicity. D) Nutrient absorption isn't the main purpose of IV fluids. A) No net movement Explanation: In isotonic solutions, there's no net movement of water as the water potential is equal on both sides of the membrane. Why others are incorrect: B, C) These imply a concentration gradient, which doesn't exist between isotonic solutions. D) Rapid diffusion would occur if there was a concentration gradient. C) No net movement occurs Explanation: When water potential is equal on both sides of a membrane, there's no net movement of water, though individual water molecules may still cross the membrane. Why others are incorrect: A, B) These imply a water potential gradient, which doesn't exist in this scenario. D) While net movement stops, individual molecules can still move across the membrane. B) Concentration of solute per unit volume of solution Explanation: Osmolarity refers to the total concentration of osmotically active particles in a solution. Why others are incorrect: A) This describes water potential, not osmolarity. C) This is not a standard definition in osmosis. D) This describes osmotic pressure, not osmolarity. A) Pure water Explanation: Pure water has the highest water potential (0 kPa) as it has no solutes and is used as the reference point for water potential measurements. Why others are incorrect: B, C, D) These solutions all contain solutes, which lower their water potential compared to pure water. Short Answer Questions Define osmosis and explain how it differs from diffusion. Key points: Definition of osmosis Definition of diffusion Key differences Compare the effects of placing plant cells in hypertonic and hypotonic solutions. Key points: Definition of hypertonic and hypotonic Effects on plant cells in each solution Cellular processes involved Higher solute concentration outside the cell Water moves out of the cell Cell membrane pulls away from cell wall (plasmolysis) Cell becomes flaccid May impact cellular processes due to water loss Lower solute concentration outside the cell Water moves into the cell Cell swells, pressing against cell wall Cell becomes turgid Increased turgor pressure supports plant structure Direction of water movement Effect on cell volume and shape Impact on cellular functions State the formula for calculating water potential in a plant cell. Key points: Components of water potential Mathematical expression Solute potential (?s) is always negative or zero. Pressure potential (?p) is usually positive in turgid cells, zero in flaccid cells, and can be negative in xylem vessels. Explain why turgor pressure is important for plant cells. Key points: Definition of turgor pressure Structural support Cellular functions Plant growth and movement Maintains cell shape and rigidity Contributes to overall plant support, especially in non-woody plants Facilitates cell expansion during growth Influences the rate of cellular metabolic processes Enables rapid plant movements (e.g., Venus flytrap closing) Controls stomatal opening and closing Drives water uptake in roots through osmosis Influences water transport through the plant Allows plants to wilt in drought conditions, conserving water Describe the process by which the contractile vacuole functions in freshwater organisms. Key points: Purpose of the contractile vacuole Structure Mechanism of water expulsion Importance in osmoregulation Central vacuole Radiating channels (in some organisms) Pore in the cell membrane for water expulsion Excess water from the cytoplasm collects in the vacuole or radiating channels The vacuole contracts, pushing water towards the pore Water is expelled through the pore to the external environment The process continues to maintain proper cell volume Prevents cell lysis in hypotonic environments Allows organisms to thrive in freshwater habitats Demonstrates an evolutionary adaptation to specific environmental challenges Matching Questions j) Potential energy of water per unit volume a) Movement of water across a selectively permeable membrane b) Equal concentration of solutes inside and outside the cell c) Net water movement out of the cell, causing it to shrink d) Net water movement into the cell, causing it to swell e) Contribution of solute concentration to total water potential f) Contribution of pressure to total water potential g) Shrinking of the cell membrane away from the wall h) Positive pressure within a plant cell due to water intake i) Expels excess water from unicellular organisms Extended Response Questions Explain the concept of water potential and its importance in plant physiology, using an example of water movement through a plant. Key points: Definition of water potential Components of water potential Importance in plant physiology Example of water movement in plants Explanation: Water potential (?) definition: The potential energy of water per unit volume relative to pure water under standard conditions Measured in units of pressure (kPa) Drives water movement throughout the plant Influences cell growth and shape Affects nutrient uptake and transport Regulates stomatal opening and closing Contributes to overall plant structure through turgor pressure Higher water potential than roots Water moves into root hair cells by osmosis Lower water potential due to solutes Water moves from cell to cell towards the xylem Negative pressure potential due to transpiration pull Water moves up the xylem vessels Lower water potential than xylem Water moves from xylem into leaf cells Very low water potential Water evaporates from leaf surfaces, driving the process Calculate the solute potential of a plant cell given the concentration of solutes and interpret its impact on total water potential. Given: 0.3 mol/L (solute concentration) Calculation: ?s = -iCRT Where: ?s = Solute potential i = Ionization constant (assume 1 for non-ionizing solutes) C = Solute concentration in mol/L R = Gas constant (0.00831 L·MPa/mol·K) T = Temperature in Kelvin (assume 293 K, or 20°C) ?s = -(1)(0.3 mol/L)(0.00831 L·MPa/mol·K)(293 K) ?s ? -0.73 MPa or -730 kPa Interpretation: If the cell is flaccid, ?p ? 0, so ? ? -730 kPa If the cell is turgid, ?p will be positive, partially offsetting the negative solute potential Analyze the relationship between osmolarity and water movement in cells by interpreting data from a tonicity experiment. Data analysis: Pure Water (0.00 mol/L): Mass increased from 10.0g to 10.6g Cells gained water (hypotonic environment) 0.2 NaCl (0.20 mol/L): Mass decreased from 10.0g to 9.8g Cells lost water (hypertonic environment) 0.5 NaCl (0.50 mol/L): Mass decreased from 10.0g to 9.3g Cells lost more water (more hypertonic) 0.8 NaCl (0.80 mol/L): Mass decreased from 10.0g to 8.9g Cells lost even more water (most hypertonic) Interpretation: Relationship between osmolarity and water movement: As osmolarity of the external solution increases, net water movement out of the cells increases This is evidenced by the progressively greater mass loss in higher NaCl concentrations Isotonic point: Lies between 0.00 mol/L and 0.20 mol/L At this point, there would be no net water movement and no change in mass Cell osmolarity: Must be close to but slightly below 0.20 mol/L This explains why cells gain water in pure water but lose water in 0.20 mol/L NaCl Osmotic gradient: The greater the difference between cell osmolarity and solution osmolarity, the more pronounced the water movement This is shown by the increasing mass loss as NaCl concentration increases Compare and contrast the impact of osmotic pressure on animal cells versus plant cells in hypertonic solutions. Similarities: Water movement: Both animal and plant cells lose water in hypertonic solutions Solute concentration: Intracellular solute concentration increases in both cell types Volume change: Both types of cells experience a decrease in cell volume Cell shrinkage: Cells become smaller and irregularly shaped Crenation: Cell membrane forms irregular folds or projections Reversibility: Process is generally reversible if isotonic conditions are restored quickly Survival: Can survive moderate hypertonic conditions but may die in extreme cases Plasmolysis: Cell membrane pulls away from the cell wall Cell wall: Maintains overall cell shape despite loss of volume Turgor pressure: Loss of turgor pressure, cell becomes flaccid Reversibility: More easily reversible due to the rigid cell wall Wilting: Widespread plasmolysis leads to wilting in plant tissues Animal cells lack a cell wall, so the entire cell shrinks Plant cells maintain shape due to the cell wall, but the protoplast shrinks Animal cells are more vulnerable to osmotic stress Plant cells can withstand greater osmotic pressures Plants have evolved mechanisms to cope with water loss (e.g., stomatal closure) Using a diagram, explain the role of guard cells and water potential in regulating stomatal opening and closing. Explanation: Guard cell structure: Pair of specialized epidermal cells surrounding the stomatal pore Thickened inner walls, thinner outer walls Stomatal opening: Guard cells take up K+ ions actively Water potential in guard cells decreases Water enters guard cells by osmosis Cells become turgid Inner walls resist expansion more than outer walls Cells curve, opening the stomatal pore Stomatal closing: K+ ions are actively pumped out of guard cells Water potential increases Water leaves guard cells by osmosis Cells become flaccid Elastic forces in surrounding cells pull guard cells together Stomatal pore closes Role of water potential: Changes in solute concentration (mainly K+) alter water potential Water movement follows the water potential gradient This drives the physical changes in guard cell shape Factors influencing stomatal regulation: Light: Promotes opening by activating K+ uptake CO2 concentration: High levels promote closing Abscisic acid: Hormone that promotes closing during water stress Importance: Regulates gas exchange (CO2 uptake and water vapor loss) Balances photosynthesis needs with water conservation Allows plants to adapt to changing environmental conditions This mechanism demonstrates how changes in water potential at the cellular level can have significant impacts on whole-plant physiology and water relations. True or False Questions False - Osmosis is a type of passive transport, not active transport. Explanation: Osmosis is the movement of water across a selectively permeable membrane from an area of higher water potential to lower water potential, and does not require energy input. False - Turgor pressure decreases when water leaves the plant cell. Explanation: Turgor pressure is the force exerted by cell contents against the cell wall. When water leaves the cell, turgor pressure decreases, not increases. True - Water potential is highest in pure water. Explanation: Pure water has a water potential of 0 kPa, which is the highest possible water potential. Any addition of solutes or pressure changes will lower the water potential. False - Animal cells can survive in hypertonic solutions without any damage. Explanation: In hypertonic solutions, animal cells lose water and shrink, which can lead to crenation and potentially cell death if the conditions are extreme or prolonged. True - Solute potential is always negative. Explanation: Solute potential (?s) is always negative or zero because the presence of solutes lowers the water potential of a solution relative to pure water. True - A contractile vacuole helps freshwater unicellular organisms expel excess water. Explanation: Contractile vacuoles are organelles found in some unicellular organisms that actively pump out excess water, helping to maintain osmotic balance in hypotonic environments. False - Isotonic solutions cause water to move into cells. Explanation: Isotonic solutions have the same solute concentration as the cell interior, resulting in no net movement of water into or out of the cell. False - Pressure potential contributes negatively to water potential in cells. Explanation: In most plant cells, pressure potential (turgor pressure) contributes positively to water potential. However, in xylem vessels, it can be negative. True - Plasmolysis occurs in plant cells placed in a hypertonic solution. Explanation: In a hypertonic solution, water leaves the plant cell, causing the cell membrane to pull away from the cell wall, a process called plasmolysis. True - Hypotonic solutions increase turgor pressure in plant cells. Explanation: In a hypotonic solution, water enters the plant cell, increasing the turgor pressure as the cell contents push against the cell wall. Data Analysis Question Calculate the water potential for each tissue sample: (Assuming the initial mass represents equilibrium, and using the percent change in mass as an indicator of water potential) ? = (Final mass - Initial mass) / Initial mass × 100 0.0 mol/L: ? = (5.4 - 5.0) / 5.0 × 100 = +8% 0.2 mol/L: ? = (5.1 - 5.0) / 5.0 × 100 = +2% 0.4 mol/L: ? = (4.8 - 5.0) / 5.0 × 100 = -4% 0.6 mol/L: ? = (4.5 - 5.0) / 5.0 × 100 = -10% 0.8 mol/L: ? = (4.3 - 5.0) / 5.0 × 100 = -14% Determine the concentration at which the tissue achieves equilibrium: The equilibrium point is where there is no change in mass, which occurs between 0.2 mol/L and 0.4 mol/L. Interpolating: 0.2 mol/L gives +2% change 0.4 mol/L gives -4% change Assuming a linear relationship, the equilibrium point is approximately 0.3 mol/L. Interpret the biological significance: The plant tissue has a solute concentration equivalent to about 0.3 mol/L. In solutions less than 0.3 mol/L, the tissue gains water (becomes turgid). In solutions more than 0.3 mol/L, the tissue loses water (becomes flaccid or plasmolyzed). This demonstrates how plants maintain water balance in different environments. The ability to gain or lose water allows plants to respond to changing soil water conditions. Understanding this helps in agricultural practices, such as determining optimal irrigation or fertilizer concentrations.