Class 10 / Question Bank / Competency Based
Absorption by Roots Competency Based Questions on Absorption by Roots
Case Study 1:
A student sets up a potato osmoscope using strong sugar solution and water.
Identify the process responsible for the rise in the sugar solution level.
What acts as the semi-permeable membrane in this setup?
Answer: The living cytoplasmic lining of the potato cells.
Designing: What would happen if the potato was boiled?
Answer: No rise in level. Boiling kills the cells, destroying the semi-permeable nature of the membrane, making it freely permeable.
Analysis: Direction of water movement.
Answer: From Hypotonic (water in beaker) to Hypertonic (sugar solution in cavity).
If the beaker and cavity have the same concentration?
Answer: No net movement; level stays the same (Isotonic).
Case Study 2:
A farmer applies excessive chemical fertilizer and plants wilt.
6. Identify the condition.
Explain "Hypertonic solution" in this context.
Answer: The high concentration of fertilizer in the soil makes the soil water hypertonic compared to the cell sap of the root hairs.
Creating: Visual representation.
Answer: [Description: Plasmolysed cell shows shrunken protoplasm away from the cell wall].
Critical Thinking: How to reverse it?
Answer: Deplasmolysis by adding plenty of water to the soil to make it hypotonic.
Define "Exosmosis" and relate to wilting.
Answer: Exosmosis is the outward movement of water from the cell. Loss of turgidity leads to wilting.
Directions: (a) Both A/R true, R explains A; (b) Both true, R doesn't explain A; (c) A true, R false; (d) A false, R true.
Assertion (A): Roots absorb water by osmosis.
Reason (R): Cell sap has higher concentration than soil water.
Answer: (a) Both A and R are true and R is the correct explanation.
Assertion (A): Active transport requires energy (ATP).
Reason (R): It moves ions against concentration gradient.
Answer: (a) Both A and R are true and R is the correct explanation.
Assertion (A): A plant cell bursts if placed in distilled water.
Reason (R): Wall pressure counteracts turgor pressure.
Answer: (d) A is false but R is true. (Plant cells don't burst due to cell wall).
Assertion (A): Salt is a preservative.
Reason (R): Salt causes plasmolysis in bacteria.
Answer: (a) Both A and R are true and R is the correct explanation.
Assertion (A): Wooden doors swell in rainy season.
Reason (R): This is due to Imbibition.
Answer: (a) Both A and R are true and R is the correct explanation.
Designing: Root Pressure experiment.
Answer: Cut the stem of a potted plant near the base; attach a glass tube with a rubber connection. Water rises in the tube due to root pressure.
Creating: Metaphor for Semi-permeable membrane.
Answer: Like a sieve that allows water through but stops the noodles (solute).
Analysis: Diffusion vs Osmosis.
Answer: Osmosis is diffusion of solvent through a semi-permeable membrane.
Designing: Table TP vs WP.
Answer: TP (Turgor Pressure) is exerted by the cell contents against the wall. WP (Wall Pressure) is exerted by the wall against the contents. In turgid cell, TP = WP.
Visualisation: Root hair diagram.
Answer: [Description: Long extension of epiblema cell with large vacuole and thin wall]. Wall is freely permeable because it's cellulose.
Application: Saltwater gargle.
Answer: Hypertonic salt water causes exosmosis from the swollen tissues/bacteria, reducing inflammation.
Creating: Journey of a water molecule.
Answer: Soil -> Root Hair -> Cortex -> Endodermis -> Pericycle -> Xylem.
Analysis: Surface Area of root hairs.
Answer: Thousands of root hairs vastly increase the surface area available for absorption.
Designing: Test if tissue is alive.
Answer: Place in sugar solution; if it plasmolyses, it's alive.
Creating: Why plants "drink".
Answer: Plants use water to stand tall (turgidity) and to cook their food (photosynthesis).
DPD (Diffusion Pressure Deficit).
Answer: The thirst of a cell for water. DPD = OP - TP.
Scenario: Force at night.
Critical Thinking: Distilled water in IV?
Answer: No. It would cause RBCs to swell and burst (Haemolysis) because it's hypotonic to blood.
Application: Guttation.
Answer: Loss of liquid water from hydathodes. Dew is atmospheric condensation.
Apoplast vs Symplast.
Answer: Apoplast: Through cell walls. Symplast: Through cytoplasm/plasmodesmata.
Diagram Based: Turgid cell arrows.
Answer: TP outwards, WP inwards.
Cohesion and Adhesion.
Answer: Cohesion: Water-water attraction. Adhesion: Water-Xylem wall attraction.
Analysis: Fish osmoregulation.
Answer: Freshwater fish are hypertonic to water, so water enters by osmosis; they don't need to drink.
Competency: Endodermis checkpost.
Answer: Casparian strip forces water/minerals through the cell membrane (Symplast), allowing the cell to regulate entry.
Case: Cutting stem underwater.
Answer: Prevents air bubbles from entering the Xylem, which would break the water column.
Creating: Temp hypothesis.
Answer: Rate of absorption increases with temperature up to a certain point due to kinetic energy.
Designing: Passive vs Active Absorption.
Answer: Passive: Driven by transpiration pull (No ATP). Active: Driven by roots using energy (ATP).
Application: Killing weeds with salt.
Answer: Causes exosmosis from roots, leading to physiological drought and death.
Critical Thinking: Fully turgid absorption.
Answer: No more water can enter when Water Potential is zero (TP = OP).
Analysis: Hydrotropism movement.
Answer: Differential cell elongation on the side with more water.
Scenario: Water flow direction (DPD).
Answer: Cell A (DPD=4), Cell B (DPD=5). Water flows from lower DPD to higher DPD (A to B).
Designing: Imbibition model.
Answer: Soak dry seeds in a graduated cylinder. Measure the increase in volume.
Application: Importance of Turgidity.
Answer: Provides mechanical support to herbaceous plants and drives movements like stomatal opening.
Creating: Ascent of Sap graphic.
Answer: [Loop showing Root Pressure (push), Capillarity (minor), Transpiration Pull (main pull)].
Case Study: Transplanted plant death.
Answer: Loss of delicate root hairs means the plant cannot absorb enough water to replace what is transpired.
Isotonic Solution.
Answer: Solution with same concentration as cell sap; no net movement of water.
Critical Thinking: Fertilizer and soil OP.
Answer: More solutes increase the Osmotic Pressure of soil, making it harder for roots to absorb water.
Analysis: Plasmolysis vs Flaccidity.
Answer: Plasmolysis: Protoplasm shrunken. Flaccidity: Cell is not turgid but protoplasm still touches the wall.
Designing: Rate vs Soil Temp graph.
Answer: Rate is low at 0°C (viscous water), increases with temp, then drops at very high temp (membrane damage).
Creating: "Super Root".
Answer: Deep taproot, high concentration of solutes in sap, and thick mucilage coating.
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