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1. By convention, the water potential ($\Psi_w$) of pure water at standard temperatures and no pressure is taken to be:
A. Zero
B. One
C. Less than zero
D. Infinite
Answer: A. Zero
Explanation: By convention, pure water at standard pressure and temperature has the maximum water potential, which is defined as zero.
2. The movement of water through the cell wall and intercellular spaces without crossing cell membranes is known as:
A. Apoplast pathway
B. Symplast pathway
C. Transmembrane pathway
D. Vacuolar pathway
Answer: A. Apoplast pathway
Explanation: The apoplast is the system of adjacent cell walls that is continuous throughout the plant, except at the Casparian strips of endodermis.
3. The Casparian strip in root endodermis is impervious to water due to the deposition of:
A. Suberin
B. Lignin
C. Cutin
D. Pectin
Answer: A. Suberin
Explanation: The endodermis is impervious to water because of a band of suberized matrix called the Casparian strip, forcing water into the symplast.
4. The loss of water in the form of liquid droplets from hydathodes near leaf margins is called:
A. Guttation
B. Transpiration
C. Evaporation
D. Bleeding
Answer: A. Guttation
Explanation: Guttation occurs when high root pressure pushes liquid water out through specialized openings called hydathodes in herbaceous plants.
5. According to the pressure flow hypothesis, phloem translocation moves sugars from source to sink driven by a gradient in:
A. Turgor pressure / Hydrostatic pressure
B. Transpiration pull
C. Osmotic potential only
D. Electrical potential
Answer: A. Turgor pressure / Hydrostatic pressure
Explanation: Active loading of sucrose at the source creates a hypertonic condition, water enters, raising hydrostatic (turgor) pressure, driving mass flow to the sink.
6. Water molecules are attracted to each other in the liquid phase more than in the gas phase due to:
A. Cohesion
B. Adhesion
C. Surface tension
D. Imbibition
Answer: A. Cohesion
Explanation: Cohesion is the mutual attraction between water molecules, providing high tensile strength to the column of water in xylem.
7. When a plant cell is placed in a hypertonic solution, the cell membrane shrinks away from its cell wall. This phenomenon is called:
A. Plasmolysis
B. Imbibition
C. Deplasmolysis
D. Turgidity
Answer: A. Plasmolysis
Explanation: Water moves out of the cell into the hypertonic external solution, causing the protoplast to shrink away from the cell wall (plasmolysis).
8. The swelling of dry seeds when soaked in water is a classical example of:
A. Imbibition
B. Active transport
C. Facilitated diffusion
D. Guttation
Answer: A. Imbibition
Explanation: Imbibition is a special type of diffusion where water is absorbed by solids (colloids) causing an enormous increase in volume.
9. Which of the following transport mechanisms requires ATP energy and moves substances against a concentration gradient?
A. Active transport
B. Simple diffusion
C. Facilitated diffusion
D. Osmosis
Answer: A. Active transport
Explanation: Active transport uses energy (ATP) to pump molecules against a concentration gradient across the cell membrane.
10. Water channel proteins that facilitate the rapid transport of water molecules across biological membranes are known as:
A. Aquaporins
B. Porins
C. Carrier proteins
D. Symporters
Answer: A. Aquaporins
Explanation: Water channels are made up of eight different types of aquaporins that facilitate rapid water movement across membranes.
11. A Symport system moves two types of molecules across a membrane in:
A. The same direction simultaneously
B. Opposite directions simultaneously
C. Independent steps randomly
D. One direction only when energy is released
Answer: A. The same direction simultaneously
Explanation: In symport, both molecules cross the membrane in the same direction, whereas in antiport, they move in opposite directions.
12. Solute potential ($\Psi_s$) is always:
A. Negative
B. Positive
C. Zero
D. Variable depending on temperature
Answer: A. Negative
Explanation: The addition of solutes lowers the free energy of pure water; hence, solute potential ($\Psi_s$) is always a negative value.
13. The relationship between water potential ($\Psi_w$), solute potential ($\Psi_s$), and pressure potential ($\Psi_p$) is expressed as:
A. $\Psi_w = \Psi_s + \Psi_p$
B. $\Psi_w = \Psi_s - \Psi_p$
C. $\Psi_s = \Psi_w + \Psi_p$
D. $\Psi_p = \Psi_w + \Psi_s$
Answer: A. $\Psi_w = \Psi_s + \Psi_p$
Explanation: Water potential ($\Psi_w$) of a cell is determined by the sum of its solute potential ($\Psi_s$) and pressure potential ($\Psi_p$).
14. When a cell is fully turgid, its water potential ($\Psi_w$) becomes equal to:
A. Zero
B. Its solute potential
C. Its pressure potential
D. Infinity
Answer: A. Zero
Explanation: In a fully turgid cell, $\Psi_p = -\Psi_s$, so $\Psi_w = \Psi_s + \Psi_p = 0$, halting net water influx.
15. Root pressure is positive pressure developed in xylem vessels due to active transport of ions into root cells. It helps mainly in:
A. Re-establishing continuous chains of water molecules in xylem
B. Pulling water up tall trees over 100 meters high
C. Stomatal closure during midday heat
D. Increasing photosynthesis rate
Answer: A. Re-establishing continuous chains of water molecules in xylem
Explanation: Root pressure cannot push water to great heights, but it plays a key role in re-establishing broken water columns in xylem vessels.
16. The driving force for the Cohesion-Tension-Transpiration Pull model of xylem ascent of sap is provided by:
A. Transpiration from leaves
B. Root pressure
C. Active transport in phloem
D. Imbibition in roots
Answer: A. Transpiration from leaves
Explanation: Water loss through transpiration creates a negative pressure (tension) in mesophyll cells, which pulls water up through the xylem column.
17. Which guard cell feature facilitates the opening of stomata during daytime?
A. Radially arranged cellulose microfibrils in cell walls
B. Thick outer walls and thin inner walls
C. Lack of chloroplasts in guard cells
D. Decreased turgor pressure inside guard cells
Answer: A. Radially arranged cellulose microfibrils in cell walls
Explanation: Radial orientation of cellulose microfibrils makes it easier for guard cells to bulge outward when turgid, opening the stoma.
18. Attraction of water molecules to polar surfaces like tracheary elements is referred to as:
A. Adhesion
B. Cohesion
C. Surface tension
D. Tensile strength
Answer: A. Adhesion
Explanation: Adhesion is the attraction of water molecules to polar non-water surfaces, such as the lignified cell walls of xylem elements.
19. In mycorrhizal association, fungal hyphae absorb water and mineral ions (especially phosphorus) for the host plant in exchange for:
A. Sugars and N-containing compounds
B. Structural proteins
C. Growth hormones
D. Oxygen gas
Answer: A. Sugars and N-containing compounds
Explanation: Fungi provide high surface area for absorption of water and minerals, while roots provide organic compounds like sugars to the fungus.
20. Seeds of which tree cannot germinate and establish without the presence of a mycorrhizal association?
A. Pinus
B. Cycas
C. Mango
D. Wheat
Answer: A. Pinus
Explanation: Pinus seeds have an obligate association with mycorrhizae and fail to germinate or establish without them.
21. Most mineral ions enter the root epidermal cells by active transport because:
A. Concentration of minerals in soil is lower than inside root cells
B. Minerals are non-polar molecules
C. Cell membrane is completely permeable to ions
D. Water potential of soil is always lower than root cells
Answer: A. Concentration of minerals in soil is lower than inside root cells
Explanation: Minerals exist as charged ions in soil at low concentration, requiring active transport against a gradient into roots.
22. Chief sinks for mineral elements in plants are:
A. Apical and lateral meristems and developing fruits
B. Mature leaves preparing to drop
C. Suberized root endodermis
D. Non-growing heartwood tissues
Answer: A. Apical and lateral meristems and developing fruits
Explanation: Growing regions like shoot and root tips, young leaves, flowers, seeds, and storage organs are the major mineral sinks.
23. Elements that are mobilized easily from senescent (aging) plant parts to younger leaves include:
A. Nitrogen, Potassium, and Phosphorus
B. Calcium and Structural sulfur
C. Iron and Lead
D. Silicon and Lignin
Answer: A. Nitrogen, Potassium, and Phosphorus
Explanation: Remobilized elements include N, P, K, and S. Calcium, being a structural component of cell walls, is not remobilized.
24. Classic girdling experiments on trees demonstrated that phloem is responsible for the transport of:
A. Organic food (sugars)
B. Water and inorganic minerals
C. Oxygen to roots
D. Nitrogenous waste products
Answer: A. Organic food (sugars)
Explanation: Removing a ring of bark down to the phloem causes swelling above the ring due to accumulated food, proving downward phloem transport.
25. Phloem sap is composed primarily of water and:
A. Sucrose
B. Glucose
C. Starch
D. Cellulose
Answer: A. Sucrose
Explanation: Phloem sap is mainly water and sucrose, though other sugars, amino acids, and plant hormones are also translocated.
This page contains a chapter-wise objective practice set. Try the questions without checking the answer first, then use the explanation to understand the point you missed. The current page contains 25 questions, so you can practise in smaller sets when you are revising.
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