biology : class11 Adsorption of Water : Definition, Mechanism, Examples, Importance : Imbibition MCQ Questions and Answers
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Adsorption of Water
MCQ questions and answers.
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MCQ Questions
1. In the initial stage of imbibition by a dry cell wall, water molecules are primarily held because they are:
A.
Chemically converted into solutes inside the wall
B.
Adsorbed onto hydrophilic surfaces of wall components
C.
Pushed into the wall by atmospheric pressure
D.
Drawn in only after the wall becomes completely saturated
Correct Answer:
Adsorbed onto hydrophilic surfaces of wall components
Explanation:
Dry cell-wall components such as cellulose and pectins possess hydrophilic groups that attract and hold water molecules on their surfaces. This surface attraction is adsorption and initiates imbibition.
2. Which molecular feature of cellulose most directly enables adsorption of water during imbibition?
A.
Hydroxyl groups capable of forming hydrogen bonds with water
B.
Hydrocarbon groups that repel polar molecules
C.
Peptide bonds that hydrolyse water molecules
D.
Phosphate groups that actively pump water inward
Correct Answer:
Hydroxyl groups capable of forming hydrogen bonds with water
Explanation:
Cellulose contains numerous hydroxyl groups. These polar groups form hydrogen bonds with water, allowing water molecules to be adsorbed onto the cellulose surface.
3. A dry seed imbibes water even when the surrounding solution has no solute concentration gradient. The immediate basis of this process is:
A.
Adsorption of water by hydrophilic seed constituents
B.
Active transport of water using ATP
C.
Evaporation of water from the seed surface
D.
Breakdown of all seed polymers into ions
Correct Answer:
Adsorption of water by hydrophilic seed constituents
Explanation:
Dry seed constituents, especially proteins, cellulose, and other hydrophilic materials, adsorb water onto their surfaces. This surface attraction can initiate imbibition without requiring an initial solute concentration gradient.
4. Which observation most clearly demonstrates that adsorption, rather than simple bulk absorption alone, contributes to imbibition?
A.
A hydrophilic solid swells while taking up water
B.
A liquid occupies the empty space in a glass container
C.
Water changes to vapour at its boiling point
D.
A salt dissolves after being stirred in water
Correct Answer:
A hydrophilic solid swells while taking up water
Explanation:
During imbibition, water is first adsorbed onto hydrophilic surfaces and causes expansion or swelling of the solid matrix. Swelling is therefore characteristic of adsorption-based water uptake by materials such as seeds and cell walls.
5. Why does the water potential of a dry hydrophilic matrix generally become more negative during the early stage of water uptake?
A.
Adsorption creates a strong matric attraction for water
B.
The matrix immediately releases large amounts of dissolved solute
C.
Water molecules lose all kinetic energy on contact with the matrix
D.
The surrounding air exerts a negative osmotic pressure on the matrix
Correct Answer:
Adsorption creates a strong matric attraction for water
Explanation:
The surfaces of a dry hydrophilic matrix bind water strongly by adsorption. This matric attraction lowers the matrix or water potential, often making it strongly negative and favouring water entry.
6. As a dry cell wall becomes progressively hydrated during imbibition, the rate of further water adsorption usually decreases because:
A.
The number of unoccupied high-affinity adsorption sites decreases
B.
Hydrogen bonds can no longer form with any water molecule
C.
Cellulose is converted into a hydrophobic polymer
D.
Water loses its polarity after entering the cell wall
Correct Answer:
The number of unoccupied high-affinity adsorption sites decreases
Explanation:
Initially, many hydrophilic sites on the dry matrix are available to adsorb water. As these sites become occupied and the matrix hydrates, the driving force for additional adsorption and imbibition declines.
7. Which pair correctly identifies a hydrophilic imbibant and the principal interaction responsible for its adsorption of water?
A.
Cellulose; hydrogen bonding through exposed hydroxyl groups
B.
Paraffin wax; ionic bonding with water
C.
Cholesterol; covalent bonding with water
D.
Silicone oil; peptide bonding with water
Correct Answer:
Cellulose; hydrogen bonding through exposed hydroxyl groups
Explanation:
Cellulose is a hydrophilic imbibant. Its exposed hydroxyl groups interact strongly with water through hydrogen bonding, causing adsorption and subsequent imbibition.
8. A dry biological material absorbs water and increases in volume, but the water remains associated mainly with its surface macromolecules at first. This process is best described as:
A.
Adsorption followed by swelling of a hydrophilic matrix
B.
Osmosis through a selectively permeable membrane
C.
Diffusion of solute into a concentrated solution
D.
Active absorption driven by cellular respiration
Correct Answer:
Adsorption followed by swelling of a hydrophilic matrix
Explanation:
In imbibition, water molecules initially adhere to the surfaces of hydrophilic macromolecules. The accumulating water causes the matrix to expand, producing swelling.
9. Which change would most directly reduce the adsorption of water by a dry cell-wall matrix?
A.
Replacing exposed polar groups with nonpolar groups
B.
Increasing the number of accessible hydroxyl groups
C.
Increasing the surface area of the dry hydrophilic matrix
D.
Increasing the polarity of the wall constituents
Correct Answer:
Replacing exposed polar groups with nonpolar groups
Explanation:
Water adsorption depends on attractive interactions between water and polar or charged groups on the matrix. Replacing such groups with nonpolar groups reduces the hydrophilicity and therefore decreases adsorption.
10. Why can a dry seed generate considerable imbibitional pressure while adsorbing water?
A.
Strong attraction between water and hydrophilic seed materials produces expansion against resistance
B.
Water is actively pumped into the seed by mature chloroplasts
C.
The seed produces atmospheric pressure by rapid respiration
D.
Water molecules chemically decompose the seed coat into gases
Correct Answer:
Strong attraction between water and hydrophilic seed materials produces expansion against resistance
Explanation:
Adsorption of water by hydrophilic seed constituents creates strong matric attraction. As these materials hydrate and swell, they can exert pressure against surrounding structures, called imbibitional pressure.
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