Q6 - Nernst Potentials and Ion Transport Direction in Root Epidermal Cells

Theoretical 1 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Mineral Nutrition & Nutrient Uptake Plasma Membrane Structure & Transport

For the growth of plants, the supply of nutrient inorganic ions is essential. A certain crop was grown in two different soils (X, Y). The concentrations of nutrients (potassium ions and chloride ions) in each type of soil are shown in the table. The estimated cytosolic concentrations of each ion in the root epidermal cells of this crop are also shown. When the membrane potential of the epidermal cell is -150 mV, how is each ion transported into the cell? Ion movement is determined by electrical and concentration gradients. The membrane potential which would counterbalance the concentration gradient is given by the Nernst equilibrium potential equation. The direction of ion transport is determined by comparing the Nernst equilibrium potential with the membrane potential of the cell. Here, transport against the electrochemical gradient of each ion is called “active transport” and transport according to the electrochemical gradient of each ion is called “passive transport.”

Using the information and data, determine which of the statements are true or which are false.

A. In soil X, potassium ions are absorbed by the active transport system.

B. In soil Y, potassium ions are absorbed by the active transport system.

C. In soil X, chloride ions are absorbed by the passive transport system.

D. In soil Y, chloride ions are absorbed by the passive transport system.

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Question reproduced from IBO 2020, Theoretical Exam 1, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)