  Question

Study the following table showing the components of water potential of four cells of an actively transpiring plant. CellSolute potentialPressure potential(MPa)(MPa)A−0.680.42B−0.750.36C−0.830.47D−0.570.29 Identify the four cells as root hair, cortical cell, endodermal cell (lacking casparian strips) and pericycle cell respectively in the young root (assuming symplastic water flow through them).

A

B, D, C, A  B

D, A, C, B  C

A, D, C, B  D

A, C, B, D  Solution

The correct option is C A, D, C, B The movement of water from one cell to another cell through the plasmodesmata is called the symplast pathway. It occurs in the following sequence: Root hair → Epidermis → Cortex → Endodermis → Pericycle → Xylem Solute potential (ψs) and pressure potential (ψp) are two components of water potential. Water potential can be calculated using the formula: (ψw=ψs+ψp) Water always flows from higher potential to lower potential. The water potential values of the four given cells are: A → - 0.68 + 0.42 = - 0.26 B → -0.75 + 0.36= - 0.39 C → - 0.83 + 0.47 = - 0.36 D → - 0.57 + 0.29 = - 0.28 So, the correct sequence of the flow of water is A → D → C → B. Thus, A, D, C and B respectively are the root hair, cortical cell, endodermal cell and pericycle cell. Biology

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