Gce Model Questions Vol1 2025 Biology Question 32

Practice objective / multiple choice question 32 from the 2025 Gce Model Questions Vol1 Biology examination.

Gce Model Questions Vol1 2025 Biology Objective / Multiple Choice Medium Difficulty
Question 32 GCE_MODEL_QUESTIONS_VOL1 • 2025 • BIOLOGY • objective

Water moves through a plant xylem according to the hydraulic analogue of Ohm's law: flow \(F = \Delta\Psi / R\). The water potential in the roots is \(-0.2\ \text{MPa}\) and in the leaves is \(-0.8\ \text{MPa}\). The total hydraulic resistance of the pathway is \(4 \times 10^{9}\ \text{MPa\,s\,kg}^{-1}\). (a) Calculate the initial flow rate (in kg s\(^{-1}\)). (b) If stomatal closure makes the leaf water potential rise to \(-0.6\ \text{MPa}\), what is the new flow rate? (c) What is the percentage change in flow rate between the two states (to the nearest whole percent)?

Answer Options

A. New flow = 9.0 × 10⁻¹¹ kg s⁻¹; the flow decreases by about 25 %.
Correct Answer B. New flow = 1.0 × 10⁻¹⁰ kg s⁻¹; the flow decreases by about 33 %.
C. New flow = 1.5 × 10⁻¹⁰ kg s⁻¹; the flow decreases by about 20 %.
D. New flow = 8.0 × 10⁻¹¹ kg s⁻¹; the flow decreases by about 40 %.
Correct Answer
B
Correct Option:
New flow = 1.0 × 10⁻¹⁰ kg s⁻¹; the flow decreases by about 33 %.

About This Question

This is Gce Model Questions Vol1 2025 Biology Question 32. It is one of the objective questions from the 2025 Gce Model Questions Vol1 Biology examination.

Difficulty level: Medium .

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