Part 2 — Mechanism of Absorption, Root Physiology, Translocation in Xylem, Soil Nutrients (Q26–50)

Q26.

Passive absorption of mineral ions occurs mainly due to:
A. Root respiration
B. Osmotic and electrochemical gradients ✅
C. Active pumping of ATPases
D. Photosynthesis

Explanation:

A. Root respiration drives active absorption, not passive.
B. (Correct) Passive absorption happens along concentration/electrochemical gradients without energy expenditure.
C. Active transport depends on ATP.
D. Photosynthesis provides sugars, not direct ion uptake force.

Q27.

Which statement about active absorption is correct?
A. Does not require ATP
B. Requires ATP and carrier proteins ✅
C. Occurs only in dead cells
D. Independent of root metabolism

Explanation:

A. False, ATP is required.
B. (Correct) Active transport needs ATP hydrolysis (proton pumps) and specific transport proteins.
C. Requires living root cells.
D. Root metabolism provides the energy.

Q28.

Which structure in roots provides maximum surface area for mineral absorption?
A. Root cap
B. Root hairs ✅
C. Cortex
D. Pericycle

Explanation:

A. Root cap protects tip.
B. (Correct) Root hairs (epidermal outgrowths) increase surface area, directly contact soil solution.
C/D. Inner layers, not direct absorbers.

Q29.

Which path of water/mineral entry involves apoplastic movement up to endodermis?
A. Through cytoplasm of all cells
B. Through cell walls and intercellular spaces ✅
C. Through plasmodesmata only
D. Directly into xylem vessels only

Explanation:

A. That’s symplast.
B. (Correct) Apoplast = cell walls and intercellular spaces, blocked at Casparian strip.
C. Symplast, not apoplast.
D. Entry is regulated before xylem.

Q30.

Why does Casparian strip block apoplastic transport at endodermis?
A. It is rich in lignin
B. It is rich in suberin ✅
C. It has more cellulose
D. It contains plasmodesmata

Explanation:

A. Lignin strengthens xylem, not Casparian strip.
B. (Correct) Casparian strip contains suberin, a hydrophobic substance that blocks apoplastic flow.
C. Cellulose is not impermeable.
D. Plasmodesmata allow symplastic flow.

Q31.

Which condition favors active mineral absorption?
A. Low temperature
B. Lack of oxygen
C. High respiratory activity in roots ✅
D. Absence of ATP

Explanation:

A/B/D. Low temp, lack of O₂, or absence of ATP inhibit active absorption.
C. (Correct) Active uptake depends on energy supplied by respiration.

Q32.

Which element moves in the xylem along with transpiration stream?
A. Amino acids only
B. Sucrose
C. Mineral nutrients like nitrates ✅
D. Hormones exclusively

Explanation:

A/B. Organic solutes move via phloem.
C. (Correct) Nitrates, phosphates, calcium, and other minerals travel in xylem sap.
D. Some hormones also move, but minerals are major.

Q33.

The main driving force for long-distance transport of minerals in xylem is:
A. Root pressure
B. Transpiration pull ✅
C. Capillarity only
D. Diffusion

Explanation:

A. Root pressure operates short distances, in small plants.
B. (Correct) Transpiration creates negative pressure, pulling water + minerals upward.
C/D. Not sufficient for tall plants.

Q34.

Which factor most decreases active absorption of ions?
A. High ATP levels
B. Cyanide treatment ✅
C. Increased root respiration
D. Aerated soil

Explanation:

A/C/D. Favor active absorption.
B. (Correct) Cyanide inhibits respiration, reducing ATP, thus stopping active transport.

Q35.

Minerals absorbed by root hairs are loaded into xylem through:
A. Companion cells
B. Endodermis and pericycle ✅
C. Root cap
D. Cortex only

Explanation:

A. Companion cells are phloem-associated.
B. (Correct) Endodermis with Casparian strip and pericycle regulate entry into xylem.
C. Root cap is protective.
D. Cortex is transit zone.

Q36.

What is the role of ATPase pumps in root cells?
A. Pump water into xylem
B. Generate proton gradients for ion transport ✅
C. Break down minerals into ions
D. Transport sucrose into phloem

Explanation:

A. No direct water pumping.
B. (Correct) H⁺-ATPases pump protons out, generating gradients for symport/antiport transport of ions.
C. Minerals are absorbed as ions already.
D. That is phloem loading, not root uptake.

Q37.

Which mineral is absorbed by plants mostly in the cationic form?
A. Nitrate
B. Phosphate
C. Potassium ✅
D. Sulphate

Explanation:

A. Nitrate (NO₃⁻) is an anion.
B/D. Phosphate (H₂PO₄⁻), Sulphate (SO₄²⁻) are anions.
C. (Correct) Potassium is absorbed as K⁺ cation.

Q38.

Which is true for passive mineral absorption?
A. Depends on metabolic energy
B. Occurs down concentration gradient ✅
C. Requires oxygen
D. Is saturable

Explanation:

A/C. Passive absorption does not require ATP or O₂.
B. (Correct) Passive uptake is along electrochemical gradients.
D. Saturation is feature of active transport with carriers.

Q39.

Which part of soil holds most mineral ions available to plants?
A. Sand particles
B. Humus and clay particles ✅
C. Bedrock
D. Pure water in soil pores

Explanation:

A/C/D. Sand and rocks are poor in cation exchange capacity.
B. (Correct) Humus and clay have negative charges that adsorb cations (Ca²⁺, K⁺, Mg²⁺) → available for exchange and uptake.

Q40.

Which process releases mineral ions into soil solution making them available for roots?
A. Photosynthesis
B. Weathering of rocks ✅
C. Respiration
D. Pollination

Explanation:

A/C/D. Not related to mineral release.
B. (Correct) Weathering of rocks liberates minerals into soil solution.

Q41.

Soil solution contains ions mainly in which form?
A. Organic molecules only
B. Soluble ionic form (cations/anions) ✅
C. Insoluble crystals
D. Bound in DNA

Explanation:

A/D. Not correct.
B. (Correct) Plants absorb minerals from soil solution as ions like NO₃⁻, K⁺, Ca²⁺.
C. Insoluble minerals are not directly available.

Q42.

Which element is absorbed both as cation and anion?
A. Nitrogen ✅
B. Potassium
C. Calcium
D. Magnesium

Explanation:

B/C/D. Absorbed as cations only.
A. (Correct) Nitrogen is absorbed as nitrate (NO₃⁻), ammonium (NH₄⁺), and sometimes as nitrite (NO₂⁻).

Q43.

The ability of soil to hold cations against leaching is called:
A. Soil permeability
B. Soil aeration
C. Cation exchange capacity ✅
D. Field capacity

Explanation:

A/B/D. Different soil properties.
C. (Correct) Clay and humus hold cations, which can be exchanged with root H⁺ ions → cation exchange capacity.

Q44.

In acidic soils, which nutrient is most easily leached?
A. Calcium ✅
B. Iron
C. Boron
D. Sulphur

Explanation:

A. (Correct) Ca²⁺ is displaced by H⁺ in acidic soils, leaches readily.
B-D. Less susceptible compared to calcium.

Q45.

Translocation of minerals via xylem is supported by:
A. Phloem companion cells
B. Transpiration stream ✅
C. Casparian strip
D. Photosynthetic rate

Explanation:

A/C/D. Not directly responsible for long-distance transport.
B. (Correct) Minerals move with water in the transpiration stream through xylem vessels.

Q46.

Which pathway is fastest for mineral movement across root cortex?
A. Symplast
B. Apoplast ✅
C. Transmembrane
D. Phloem

Explanation:

A/C. Slower due to crossing membranes.
B. (Correct) Apoplastic movement through cell walls/intercellular spaces is faster, until blocked by Casparian strip.
D. Phloem = organic solute transport.

Q47.

In poorly aerated soils, active mineral uptake is reduced because:
A. CO₂ levels are high
B. Oxygen is limited, reducing ATP production ✅
C. Humus content is high
D. Sand particles are coarse

Explanation:

A. CO₂ accumulation is secondary.
B. (Correct) Active absorption depends on ATP from respiration, which requires oxygen.
C/D. Not direct causes.

Q48.

Which soil condition leads to micronutrient deficiencies?
A. Excess irrigation (waterlogging) ✅
B. High humus content
C. Slightly acidic pH
D. Adequate aeration

Explanation:

A. (Correct) Waterlogged soils reduce oxygen → lower solubility and uptake of micronutrients like Fe, Mn, Zn.
B-D. Favor nutrient availability.

Q49.

Which is the main form in which phosphorus is available to plants in soil?
A. ATP
B. Organic phosphate esters
C. Inorganic phosphate ions (H₂PO₄⁻, HPO₄²⁻) ✅
D. Pyrophosphate

Explanation:

A/B/D. Organic/complex forms not directly available.
C. (Correct) Plants absorb phosphorus as H₂PO₄⁻ and HPO₄²⁻ from soil.

Q50.

Why are clay soils generally more fertile than sandy soils?
A. They contain more oxygen
B. They have higher cation exchange capacity ✅
C. They lack capillarity
D. They leach nutrients easily

Explanation:

A. Not necessarily.
B. (Correct) Clay particles hold more nutrients due to greater surface area and negative charges.
C/D. Sandy soils leach more, not clay.

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Part 2 — Mechanism of Absorption, Root Physiology, Translocation in Xylem, Soil Nutrients (Q26–50)