Chemiosmotic phosphorylation is dependent upon :

Options

A. the ability of ADP to join with P even in the absence of a supply of energy
B. the establishment of an electrochemical hydrogen ion `(H^(+) ) `gradient
C. an outside supply of phosphate and other chemicals
D. the diffusion of waste across a differentially permeable membrane

Explanation

**Step-by-Step Solution:**

1. **Understanding Chemiosmosis**: Chemiosmosis is a process that explains how ATP is synthesized in both chloroplasts during photosynthesis and mitochondria during cellular respiration. This concept was proposed by Peter Mitchell.

2. **Identifying the Role of Proton Gradient**: The key to chemiosmotic phosphorylation is the establishment of a proton gradient (H⁺ ions) across a membrane. This gradient is crucial for ATP synthesis.

3. **Formation of Proton Gradient**: The proton gradient is formed by:
- The splitting of water molecules, which releases H⁺ ions into the thylakoid lumen.
- The activity of photosystems (PS1 and PS2) that facilitate the movement of electrons and the removal of protons from the stroma, contributing to the accumulation of H⁺ ions in the lumen.
- The action of NADP reductase, which also contributes to the accumulation of protons in the lumen.

4. **ATP Synthesis Mechanism**: The accumulated H⁺ ions in the thylakoid lumen create a potential energy difference across the membrane. As H⁺ ions flow back into the stroma through ATP synthase (the enzyme responsible for ATP production), this flow drives the conversion of ADP and inorganic phosphate (Pi) into ATP.

5. **Conclusion**: Therefore, chemiosmotic phosphorylation is dependent upon the establishment of an electrochemical hydrogen ion gradient.

**Final Answer**: Chemiosmotic phosphorylation is dependent upon the establishment of an electrochemical hydrogen ion gradient.

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