Part 5 — Integrated Topics (Q101–125)

Part 5 — Integrated Topics (Q101–125)

Q101.

Wilting in plants occurs mainly due to:
A. Excessive imbibition
B. Loss of turgor due to high transpiration ✅
C. Increased root pressure
D. High mineral uptake

Explanation:

• A. Imbibition causes swelling, not wilting.
• B. (Correct) Excessive water loss by transpiration reduces turgor pressure → wilting.
• C. Root pressure promotes water entry, not wilting.
• D. Mineral uptake does not cause wilting.

Q102.

Which factor simultaneously influences both water absorption and transpiration?
A. Light ✅
B. Soil pH
C. Mineral concentration
D. Cuticle thickness

Explanation:

• A. (Correct) Light increases photosynthesis → stomatal opening (↑ transpiration) and root activity (↑ absorption).
• B. Soil pH mainly affects nutrient solubility.
• C. Minerals affect absorption, not transpiration.
• D. Cuticle thickness affects transpiration only.

Q103.

Which nutrient deficiency increases transpiration due to impaired stomatal regulation?
A. Calcium
B. Potassium ✅
C. Magnesium
D. Iron

Explanation:

• A. Ca = cell wall.
• B. (Correct) K⁺ regulates stomatal opening/closure; deficiency causes uncontrolled water loss.
• C. Mg = chlorophyll.
• D. Fe = enzymes and chlorophyll synthesis.

Q104.

If transpiration exceeds absorption, plant experiences:
A. Waterlogging
B. Temporary wilting ✅
C. Permanent wilting at once
D. Guttation

Explanation:

• A. Opposite case.
• B. (Correct) Temporary imbalance → temporary wilting, recovers in evening.
• C. Permanent wilting occurs if imbalance is prolonged.
• D. Guttation occurs under low transpiration.

Q105.

Which experiment demonstrates that phloem is responsible for translocation of sugars?
A. Pressure bomb
B. Girdling/ringing experiment ✅
C. Potometer
D. Hydathode study

Explanation:

• A. Water potential measurement.
• B. (Correct) Removal of phloem causes sugar accumulation above girdle.
• C. Potometer = transpiration rate.
• D. Hydathodes show guttation.

Q106.

In water-stressed conditions, which hormone closes stomata to reduce transpiration?
A. Auxin
B. Gibberellin
C. Abscisic acid (ABA) ✅
D. Cytokinin

Explanation:

• A/B/D. Not involved in stomatal closure.
• C. (Correct) ABA accumulates under stress → stomatal closure.

Q107.

Which factor decreases water absorption but increases transpiration?
A. Low humidity ✅
B. Cool soil temperature
C. Soil salinity
D. Low root hair density

Explanation:

• A. (Correct) Low humidity increases transpiration but does not enhance absorption much.
• B-D. These reduce absorption but not necessarily increase transpiration.

Q108.

When a plant cell is placed in hypotonic solution, it becomes turgid due to:
A. Osmotic water entry and increased pressure potential ✅
B. Active pumping of water into cell
C. Loss of solutes
D. Imbibition of water into wall

Explanation:

• A. (Correct) Water enters by osmosis, increasing pressure potential (turgor).
• B. Water uptake is passive.
• C. Solutes do not leave.
• D. Imbibition is wall swelling, not turgor.

Q109.

In xerophytes, transpiration is reduced by:
A. Stomata on upper surface
B. Sunken stomata and thick cuticle ✅
C. Large broad leaves
D. High stomatal density

Explanation:

• A. Upper stomata → higher loss.
• B. (Correct) Adaptations reduce water loss.
• C/D. Increase transpiration.

Q110.

Which factor provides the energy for translocation of sugars in phloem?
A. Root pressure
B. Sunlight directly
C. Osmotic gradient created by active loading ✅
D. Diffusion alone

Explanation:

• A. Root pressure affects xylem.
• B. Sunlight drives photosynthesis, not directly phloem flow.
• C. (Correct) Active loading creates osmotic gradient driving bulk flow.
• D. Diffusion too slow.

Q111.

If the Casparian strip were absent, what would happen?
A. Root hairs would die
B. Water would move freely into stele without selective uptake ✅
C. Mineral absorption would stop completely
D. Transpiration would cease

Explanation:

• A. Not related.
• B. (Correct) Casparian strip blocks apoplast → forces selective uptake. Without it, free flow.
• C/D. Incorrect.

Q112.

A plant placed in saline soil often wilts due to:
A. Increased imbibition
B. Low osmotic potential of soil solution (water potential more negative) ✅
C. High root pressure
D. Excess transpiration

Explanation:

• A. Not main reason.
• B. (Correct) Saline soil ψ < plant ψ → water leaves root cells → plasmolysis/wilting.
• C. Root pressure decreases in saline soil.
• D. Transpiration not sole cause.

Q113.

Which nutrient deficiency reduces photosynthesis and thus lowers transpiration indirectly?
A. Nitrogen ✅
B. Potassium
C. Calcium
D. Chlorine

Explanation:

• A. (Correct) N deficiency reduces proteins/enzymes → less photosynthesis → stomatal closure.
• B. K = stomata regulation.
• C. Ca = cell wall.
• D. Cl = ion balance.

Q114.

In phloem transport, water is essential because:
A. It hydrolyzes sucrose
B. It generates turgor pressure for bulk flow ✅
C. It provides energy for active loading
D. It reduces transpiration

Explanation:

• A. Hydrolysis not needed for transport.
• B. (Correct) Water entry creates hydrostatic pressure → drives flow.
• C. ATP, not water, provides energy.
• D. Not related.

Q115.

If stomata fail to open in the morning, which processes will be reduced first?
A. Respiration
B. Photosynthesis ✅
C. Mineral uptake
D. Protein synthesis

Explanation:

• A. Respiration occurs anyway.
• B. (Correct) Closed stomata reduce CO₂ entry → limits photosynthesis.
• C. Uptake less affected.
• D. Protein synthesis depends on photosynthesis, but indirectly.

Q116.

The water potential of a flaccid plant cell is:
A. Zero
B. Less than zero ✅
C. Greater than zero
D. Infinite

Explanation:

• A. Zero is pure water.
• B. (Correct) Solute potential is negative, pressure potential = 0 → ψ < 0.
• C/D. Not correct.

Q117.

Permanent wilting point occurs when:
A. Root pressure is maximum
B. Soil water potential becomes lower than plant water potential ✅
C. Transpiration ceases
D. Photosynthesis rate is maximum

Explanation:

• A. Opposite condition.
• B. (Correct) Soil too dry → ψsoil < ψplant → roots cannot absorb → permanent wilting.
• C. Transpiration may continue.
• D. Irrelevant.

Q118.

Which factor explains why stomata close at midday in many xerophytes?
A. High CO₂ concentration inside
B. Excessive transpiration and water stress ✅
C. High oxygen release
D. Low light intensity

Explanation:

• A. Not main cause.
• B. (Correct) To conserve water, midday closure reduces loss.
• C/D. Not major factors.

Q119.

What type of solution causes plasmolysis?
A. Hypotonic
B. Isotonic
C. Hypertonic ✅
D. Pure water

Explanation:

• A. Hypotonic → turgidity.
• B. Isotonic → flaccid.
• C. (Correct) Hypertonic → water leaves cell → plasmolysis.
• D. Pure water = hypotonic.

Q120.

Mineral ions absorbed by roots are mainly transported to aerial parts through:
A. Phloem
B. Xylem ✅
C. Cortex
D. Pith

Explanation:

• A. Phloem = organic solutes.
• B. (Correct) Minerals + water = transported in xylem.
• C/D. Storage, not transport.

Q121.

Which mineral is most directly linked to osmotic regulation in guard cells?
A. Calcium
B. Potassium ✅
C. Iron
D. Phosphorus

Explanation:

• A. Ca structural.
• B. (Correct) K⁺ accumulation controls stomatal turgor.
• C. Fe = enzymes.
• D. P = ATP.

Q122.

When a fully turgid cell is placed in pure water, what happens?
A. Water enters continuously
B. Water leaves the cell
C. No net movement of water ✅
D. Protoplast shrinks

Explanation:

• A. Already turgid.
• B. Not in pure water.
• C. (Correct) Cell ψ = water ψ, equilibrium, no net flow.
• D. Shrinking = plasmolysis.

Q123.

Why do minerals not move freely with water in apoplast across endodermis?
A. Endodermis lacks plasmodesmata
B. Casparian strip forces entry into symplast ✅
C. Cortex cells absorb all ions
D. Xylem is impermeable

Explanation:

• A. Plasmodesmata exist.
• B. (Correct) Casparian strip blocks apoplast → selective uptake.
• C. Not all absorbed.
• D. Xylem is permeable.

Q124.

Which type of transpiration is most important quantitatively?
A. Cuticular
B. Stomatal ✅
C. Lenticular
D. Hydathodal

Explanation:

• A. Minor.
• B. (Correct) Stomatal accounts for ~80–90%.
• C. Very minor.
• D. Guttation, not transpiration.

Q125.

Why is phloem transport bidirectional while xylem is unidirectional?
A. Xylem cells are living, phloem dead
B. Phloem can move solutes to multiple sinks, xylem only supplies upward ✅
C. Phloem has lignified walls
D. Phloem uses capillary action

Explanation:

• A. Reverse: xylem is dead, phloem living.
• B. (Correct) Source-sink relations vary; phloem flow can be both ways. Xylem always moves water upward.
• C/D. Not reasons.

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