Active transport of ions across the membrane of a root hair can be assumed to be taking place if:
A. The cell produces more glutathione
B. The cell has mitochondria
C. The uptake of ions stops when cyanide is added
D. The uptake of ions is against the concentration gradient.
Show Hint
Active transport is characterized by:
1. Movement against a electrochemical/concentration gradient (uphill transport).
2. Direct dependence on metabolic energy (ATP), meaning it is inhibited by respiratory poisons like cyanide or 2,4-DNP.
Step 1: Understanding the Concept:
Ion absorption by plant root hairs occurs via two mechanisms: passive transport (no energy required) and active transport (requires energy).
Active transport utilizes metabolic energy (ATP) generated by cellular respiration to pump ions across the membrane. Step 3: Detailed Explanation:
To prove that ion transport is active, the following physiological criteria must be met:
- Uptake against a concentration gradient (D): Transporting ions from a region of lower concentration (soil solution) to a region of higher concentration (inside root cells) requires work and metabolic energy.
- Sensitivity to metabolic inhibitors (C): Active transport depends on ATP produced during aerobic respiration. If a respiratory inhibitor like cyanide (which blocks cytochrome c oxidase in the mitochondrial electron transport chain) is added, respiration stops, ATP production ceases, and active uptake is halted.
The presence of mitochondria (B) is a general cellular feature and does not prove that a specific transport process is active. Glutathione production (A) is related to antioxidant defense, not directly to active ion transport. Step 4: Final Answer:
The correct combination is (C) and (D) only, making option (B) the correct answer.
