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Question 23 of 29

Q.In a fully turgid cell:

(a) DPD = 0 atm; OP = 5 atm; TP = 10 atm;
(b) DPD = 10 atm; OP = 5 atm; TP = 10 atm;
(c) DPD = 20 atm; OP = 20 atm; TP = 10 atm;
(d) DPD = 0 atm; OP = 10 atm; TP = 10 atm;
Tamil Nadu DgeTamil Nadu HSC First Year (DGE) Board 2025MCQ· 1mImportance★★★★★
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DPD (also called suction pressure, SP) equals OP minus TP. In a fully turgid cell, TP has risen to equal OP exactly, so DPD = 0 — which is only consistent with OP = TP = 10 atm.

The relationship among these water-relations quantities is:

DPD (or Suction Pressure, SP) = OP − TP

where OP is the osmotic pressure of the cell sap (which draws water in) and TP is the turgor/wall pressure (which pushes back and resists further water entry).

As a cell absorbs water by osmosis, its turgor pressure (TP) rises. When the cell becomes FULLY turgid, TP has risen until it exactly equals OP — at this point there is no further net tendency to absorb water, so DPD = OP − TP = 0.

Now check the options for internal consistency with DPD = OP − TP:

(a) DPD = 0, OP = 5, TP = 10 → OP − TP = 5 − 10 = −5, not 0. Inconsistent. …

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