Water Transport Practice Questions
20 free Water Transport practice questions for the NCERT Biology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which part of the root is primarily responsible for the absorption of water and minerals from the soil?
- A Root cap
- B Region of elongation
- C Root hairs
- D Mature zone without hairs
Correct answer: Root hairs
Root hairs are thin-walled slender extensions of root epidermal cells that greatly increase the surface area for absorption. They are in direct contact with soil water, facilitating efficient uptake via diffusion.
The movement of water through the intercellular spaces and the walls of the cells, without crossing any semi-permeable membrane, is called:
- A Plasmodesmata
- B Casparian strips
- C Lignified xylem vessels
- D Cytoplasmic streaming
Correct answer: Casparian strips
The endodermis contains a band of suberized matrix called the Casparian strip which is impervious to water. This forces water to cross the membrane and enter the symplastic pathway to reach the xylem.
What prevents the apoplastic movement of water into the vascular cylinder at the endodermis?
- A Movement through non-living cell walls
- B Movement through interconnected living protoplasts
- C Faster movement compared to the apoplast
- D Movement solely through the cell wall space
Correct answer: Movement through interconnected living protoplasts
The symplast consists of the living network of cells connected by plasmodesmata. Water travels through the cytoplasm, requiring it to cross cell membranes, which makes it relatively slower than apoplastic flow.
The symplastic system of water movement is characterized by:
- A Movement through non-living parts of the plant
- B Movement through the system of interconnected protoplasts
- C Faster movement compared to apoplast
- D Movement solely through the cell wall
Correct answer: Movement through the system of interconnected protoplasts
The symplast consists of the living network of cells connected by plasmodesmata. Water travels through the cytoplasm, requiring it to cross cell membranes, which makes it relatively slower than apoplastic flow.
Which of the following physical properties of water provides the 'tensile strength' required for the transpirational pull?
- A Transpiration from leaf surfaces
- B Guttation in herbaceous plants
- C Photosynthesis in mesophyll cells
- D Ascent of sap in tall trees
Correct answer: Guttation in herbaceous plants
Root pressure is a positive pressure developed due to active absorption of ions. In conditions of low transpiration, it causes 'guttation'—the loss of water in liquid form through hydathodes near the leaf tips.
Root pressure is primarily responsible for which of the following phenomena observed in small herbaceous plants?
- A Transpiration
- B Guttation
- C Photosynthesis
- D Ascent of sap in tall trees
Correct answer: Guttation
Root pressure is a positive pressure developed due to active absorption of ions. In conditions of low transpiration, it causes 'guttation'—the loss of water in liquid form through hydathodes near the leaf tips.
In the root, the symplastic movement of water is aided by which cellular process observable in Hydrilla or Elodea leaves?
- A Plasmolysis of cortical cells
- B Cytoplasmic streaming (cyclosis)
- C Endocytosis at root surface
- D Transcription of transport genes
Correct answer: Cytoplasmic streaming (cyclosis)
Cytoplasmic streaming (cyclosis) helps in the transport of materials within the cell and across the symplastic pathway. It is easily observed in the cells of the Hydrilla leaf.
In the root, the symplastic movement of water is aided by which cellular process in Hydra or Elodea leaves?
- A Pericycle layer
- B Root epidermis
- C Endodermis
- D Cortex parenchyma
Correct answer: Endodermis
The endodermis is the innermost layer of the cortex. It serves as a check-post for the entry of water and minerals into the vascular tissue due to the presence of the Casparian strip.
The inner boundary of the root cortex is occupied by the:
- A Cortical cells are loosely packed with many intercellular spaces
- B Symplastic transport is always faster and therefore preferred in the cortex
- C Casparian strips are absent in the epidermis
- D Cortical cells are dead and lack any selectively permeable plasma membrane
Correct answer: Cortical cells are loosely packed with many intercellular spaces
The cortical cells are loosely packed, offering little resistance to the mass flow of water through the cell walls and intercellular spaces (apoplast). This remains the preferred route until the endodermis is reached.
Water enters the root hair cell because its water potential is ______ than that of the soil water.
- A Higher
- B Lower
- C Equal
- D Zero
Correct answer: Lower
Water always moves from a region of higher water potential to a region of lower water potential. Root hair cells maintain a lower water potential by accumulating solutes, facilitating the inward osmosis of water.
Most of the water flow in the roots occurs via the apoplast because:
- A It drives water to the tops of very tall trees
- B It refills broken water columns in xylem vessels
- C It provides the main driving force for transpiration
- D It signals stomata to open and allow gas exchange
Correct answer: It refills broken water columns in xylem vessels
The main contribution of root pressure is not to push water to great heights, but to re-establish the continuous columns of water in the xylem which often break under the enormous tensions created by transpiration.
What is the primary role of root pressure in the ascent of sap?
- A It is slower than the symplastic pathway
- B It is blocked by the Casparian strip
- C It requires metabolic energy (ATP)
- D It involves only living protoplasts
Correct answer: It is blocked by the Casparian strip
While the apoplast is generally faster and easier, it is not continuous throughout the root. At the endodermis, the suberin layer (Casparian strip) blocks the wall-to-wall movement, forcing water into the symplast.
Which of the following is a limitation of the apoplastic pathway?
- A It is slow
- B It is blocked by the Casparian strip
- C It requires ATP
- D It involves living protoplasts
Correct answer: It is blocked by the Casparian strip
While the apoplast is generally faster and easier, it is not continuous throughout the root. At the endodermis, the suberin layer (Casparian strip) blocks the wall-to-wall movement, forcing water into the symplast.
The 'tensile strength' of water is its ability to:
- A Resist a pulling force without breaking
- B Rise in capillary tubes by adhesion
- C Evaporate rapidly at high temperatures
- D Dissolve and carry mineral salts
Correct answer: Resist a pulling force without breaking
Tensile strength is the property that prevents the water column from breaking when subjected to tension. Water's high tensile strength is due to strong cohesive forces between molecules.
Capillarity, the ability of water to rise in thin tubes, is aided by which characteristic of xylem elements?
- A Large diameter of vessels allows fast bulk flow
- B Small diameter of tracheary elements
- C Presence of living protoplasts in mature vessels
- D Thick secondary walls reinforced with lignin
Correct answer: Small diameter of tracheary elements
Capillarity is the rise of liquids in narrow tubes. In plants, the small diameter of tracheids and vessel elements facilitates this upward movement through adhesive and cohesive forces.
During transpiration, water evaporates from the ______ of the leaf into the intercellular spaces.
- A Xylem vessels near the leaf veins
- B Thin film on mesophyll cells
- C Phloem sieve tubes in vascular bundles
- D Guard cell chloroplasts facing the air space
Correct answer: Thin film on mesophyll cells
Transpiration starts with the evaporation of the thin film of water covering the mesophyll cells. This increases the concentration of solutes in those cells, lowering their water potential and pulling water from adjacent cells.
Which of the following statements about the 'Mass Flow Hypothesis' is correct?
- A Movement occurs due to concentration gradients only
- B Substances move in bulk due to pressure differences
- C Only water moves while solutes stay behind
- D It occurs only in the symplastic pathway
Correct answer: Substances move in bulk due to pressure differences
Mass flow (or bulk flow) is the movement of substances in bulk from 'source' to 'sink' as a result of pressure differences. Unlike simple diffusion, all substances (solutes and solvent) move at the same speed.
The value of the 'pull' generated by transpiration can create enough pressure to lift a size-equivalent column of water over how many meters high?
- A 10 meters
- B 50 meters
- C 130 meters
- D 500 meters
Correct answer: 130 meters
Measurements indicate that the forces generated by transpirational pull are sufficient to lift a column of water up to 130 meters high, which is enough to reach the top of the tallest trees.
Which pathway involves the movement of water through the plasmodesmata?
- A Apoplast
- B Symplast
- C Transmembrane
- D Root pressure
Correct answer: Symplast
In the symplastic pathway, water travels through the cells' cytoplasm; the intercellular movement is facilitated by plasmodesmata, which are cytoplasmic bridges connecting adjacent cells.
Which factor does NOT directly affect the rate of transpirational pull?
- A Ambient temperature of the air
- B Intensity of incoming light
- C Surrounding atmospheric pressure
- D Soil nitrogen content
Correct answer: Soil nitrogen content
Transpiration is affected by external factors like temperature, light, humidity, and wind speed. While soil nitrogen affects plant growth, it does not directly drive the physical mechanism of the transpirational pull.