Q.47 Two plant cells M and N are lying side by side making direct contact. “M” has osmotic potential (𝚿𝒔)
of -10 bar and pressure potential ( 𝚿 p) of 4 bar. On the other hand, ” 𝑵 ” has osmotic potential (𝚿𝒔) of
-12 bar and pressure potential ( 𝚿 p) of 5 bar.
Based on these data, what would be the direction of movement of water between M and N?
(A) M to N
(B) N to M
(C) There will be no movement
(D) In both directions
water potential gradient between the two adjacent plant cells,
a concept frequently tested in CSIR NET Life Sciences and
related competitive exams.
Water Potential Formula
Water potential (Ψw) determines the direction of
water movement in plants and is given by:
Ψw = Ψs + Ψp
- Ψs = osmotic (solute) potential (always negative)
- Ψp = pressure potential (positive due to turgor)
Water moves from a region of higher water potential
(less negative value) to lower water potential
(more negative value).
Calculations for Cells M and N
For cell M:
ΨwM = Ψs + Ψp
= (−10) + 4 = −6 bar
For cell N:
ΨwN = Ψs + Ψp
= (−12) + 5 = −7 bar
Since −6 bar > −7 bar, water moves from
cell M to cell N.
Option Analysis
- (A) M to N: Correct, because Ψw of M (−6 bar)
is higher than Ψw of N (−7 bar). - (B) N to M: Incorrect, since N has a lower water potential.
- (C) No movement: Incorrect, because the water potentials differ.
- (D) Both directions: Incorrect, as net water flow is always
unidirectional down the water potential gradient.
Key Concepts for Exams
- Osmotic potential (Ψs) becomes more negative with higher solute concentration.
- Pressure potential (Ψp) is positive in turgid plant cells.
- Pure water has Ψw = 0 bar.
- Water always moves from higher (less negative) to lower (more negative) Ψw.
Exam Relevance
Questions on the direction of water movement between plant cells
are common in CSIR NET and GATE Life Sciences. Quickly calculating
Ψw for each cell and comparing values ensures accurate answers
in time-limited exams.
SEO Keywords
direction of water movement between plant cells, water potential Ψw,
osmotic potential and pressure potential, plant cell osmosis CSIR NET,
water movement plant physiology
