Question

Which of the following are spontaneous processes? Explain your answer for each process. (a) The hydrolysis of ATP to ADP and \(P_{i}\) (b) The oxidation of glucose to \(\mathrm{CO}_{2}\) and \(\mathrm{H}_{2} \mathrm{O}\) by an organism (c) The phosphorylation of ADP to ATP (d) The production of glucose and \(\mathrm{O}_{2}\) from \(\mathrm{CO}_{2}\) and \(\mathrm{H}_{2} \mathrm{O}\) in photosynthesis

Short answer

Processes (a) and (b) are spontaneous, while processes (c) and (d) are non-spontaneous.

Step-by-step solution

- Determine the nature of the hydrolysis of ATP

Hydrolysis of ATP to ADP and inorganic phosphate (Pi) is known to be a highly exergonic process, meaning it releases energy. Since this process releases energy, it is considered spontaneous.

- Assess the oxidation of glucose

The oxidation of glucose to carbon dioxide (CO_2) and water (H_2O) is a catabolic process, which releases energy as heat and is an exergonic reaction. Due to the release of energy, this process is also spontaneous.

- Evaluate the phosphorylation of ADP

The phosphorylation of ADP to ATP is an endergonic process, meaning it requires an input of energy. Because energy must be consumed to drive this reaction, it is non-spontaneous.

- Analyze the production of glucose in photosynthesis

The production of glucose and oxygen from carbon dioxide and water in photosynthesis is an endergonic process that requires energy from sunlight. Thus, this reaction is non-spontaneous.

Key concepts

ATP Hydrolysis

ATP hydrolysis is a crucial reaction in biochemistry. ATP (adenosine triphosphate) breaks down into ADP (adenosine diphosphate) and an inorganic phosphate (\text{\texttt{\(P_i\)}}). This process releases energy, making it highly exergonic.

The main reason ATP hydrolysis is spontaneous is because it liberates a significant amount of energy. Cells harness this energy to perform many functions, such as muscle contraction, nerve impulse propagation, and chemical synthesis.

Thus, when ATP hydrolyzes, it moves to a lower energy state, releasing energy the cell can use. This release of energy is why ATP hydrolysis is classified as a spontaneous process.

• ATP → ADP + \(P_i\) + Energy Release

Glucose Oxidation

Glucose oxidation is a vital energy-releasing process. During this reaction, glucose is broken down into carbon dioxide (\text{\texttt{\(CO_2\)}}) and water (\text{\texttt{\(H_2O\)}}). This catabolic reaction is exergonic, meaning it releases energy.

The energy released during glucose oxidation is harnessed by cells to produce ATP, which is essential for various cellular activities. Since energy is released, glucose oxidation is considered spontaneous.

• Glucose + \(O_2\) → \(CO_2\) + \(H_2O\) + Energy Release

The spontaneity of glucose oxidation is a critical component in cellular respiration, a process that powers our cells and, consequently, our bodies.

ADP Phosphorylation

ADP phosphorylation is the process of adding a phosphate group to ADP, forming ATP. Unlike ATP hydrolysis, this reaction requires energy input, making it an endergonic process.

Because it needs energy to proceed, ADP phosphorylation is non-spontaneous. This energy usually comes from cellular respiration or photosynthesis.

• ADP + \(P_i\) + Energy Input → ATP

The creation of ATP from ADP is essential for storing and transferring energy within the cell, but it cannot happen spontaneously without an energy source.

Photosynthesis Energy Requirement

Photosynthesis involves the conversion of carbon dioxide (\text{\texttt{\(CO_2\)}}) and water (\text{\texttt{\(H_2O\)}}) into glucose and oxygen (\text{\texttt{\(O_2\)}}) using energy from sunlight. This reaction is endergonic, meaning it requires an input of energy.

Because photosynthesis needs sunlight to drive the reaction, it is non-spontaneous. Plants use chlorophyll to capture sunlight, which then powers the conversion process.

• \(CO_2\) + \(H_2O\) + Sunlight Energy → Glucose + \(O_2\)

Photosynthesis is essential for life on Earth as it produces oxygen and organic compounds needed by most organisms for survival.