Question

Which of these represents an endergonic reaction? a. \(\mathrm{ADP}+\mathrm{P}_{\mathrm{i}} \rightarrow \mathrm{ATP}\) b. \(\mathrm{ATP} \rightarrow \mathrm{ADP}+\mathrm{P}_{\mathrm{i}}\) c. glucose \(+\mathrm{O}_{2} \rightarrow \mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}\) d. \(\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O} \rightarrow\) glucose e. both \(a\) and \(d\) f. both \(b\) and \(c\)

Short answer

The short answer is: e. both \(a\) and \(d\).

Step-by-step solution

Option a: \(\mathrm{ADP}+\mathrm{P}_{\mathrm{i}} \rightarrow \mathrm{ATP}\)

The reaction converts adenosine diphosphate (ADP) and inorganic phosphate (Pi) into adenosine triphosphate (ATP). This reaction is endergonic because it requires an input of energy to form the high-energy phosphate bond in ATP. In this process, ΔG is positive, indicating an endergonic reaction. #Step 2: Analyze option b#

Option b: \(\mathrm{ATP} \rightarrow \mathrm{ADP}+\mathrm{P}_{\mathrm{i}}\)

The reaction breaks down adenosine triphosphate (ATP) into adenosine diphosphate (ADP) and inorganic phosphate (Pi). This reaction releases the stored energy in the high-energy phosphate bond of ATP, which means it is an exergonic reaction with a negative ΔG. #Step 3: Analyze option c#

Option c: glucose \(+\mathrm{O}_{2} \rightarrow \mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}\)

In this reaction, glucose reacts with oxygen to form carbon dioxide and water, which is a process known as cellular respiration or glucose oxidation. This reaction releases energy, hence it is exergonic, and ΔG is negative. #Step 4: Analyze option d#

Option d: \(\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O} \rightarrow\) glucose

In this reaction, carbon dioxide and water form glucose, which is a process known as photosynthesis. This reaction requires an input of energy (in the form of sunlight) to produce glucose, making it an endergonic reaction. In this process, ΔG is positive. #Step 5: Evaluate given options based on the analysis#

Considering the analyses of each option

Based on our analysis, we find that options a and d represent endergonic reactions. Therefore, the correct answer is option e (both a and d).

Key concepts

ATP Synthesis

ATP synthesis is a fundamental process for energy storage in biological systems. It involves the formation of adenosine triphosphate (ATP) from adenosine diphosphate (ADP) and inorganic phosphate (\(\text{Pi}\)). This reaction is endergonic, meaning it requires an input of energy to occur.
The energy is needed to form a new phosphate bond, which is a high-energy bond.

• This energy is usually provided by cellular processes like respiration.
• The synthesis of ATP is crucial for storing energy that cells can use immediately or at a later stage.
• It's a reversible reaction, with the reverse being exergonic where ATP is broken down, releasing energy.

Thus, ATP synthesis functions much like a cellular "battery", storing and releasing energy when needed.

Photosynthesis

Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy in the form of glucose.
This process occurs mainly in the chloroplasts of plant cells and requires carbon dioxide (\(\text{CO}_2\)) and water (\(\text{H}_2\text{O}\)) as reactants.
Being an endergonic reaction, photosynthesis requires an external energy source, which is provided by sunlight.

• During the light-dependent reactions, sunlight is captured by chlorophyll and used to generate ATP and NADPH.
• The ATP and NADPH are then used in the Calvin cycle to convert \(\text{CO}_2\) into glucose.
• This process not only supports plant growth but also forms the foundation of Earth's food chain.

Photosynthesis effectively transforms solar energy into a storable form, sustaining not just plants but also the animals and humans that consume them.

Energy in Biological Systems

Energy plays a pivotal role in all biological systems as it drives the various biochemical reactions necessary for life.
Energy is stored, transferred, and transformed within organisms to carry out essential processes like metabolism, growth, movement, and reproduction.

• In cells, energy is typically stored in the form of ATP, a molecule that can easily release or absorb energy.
• Biological systems constantly convert energy from one form to another, such as during cellular respiration where chemical energy in glucose is converted into usable ATP.
• This energy transformation is indispensable for homeostasis, the maintenance of stable internal conditions in an organism.

Overall, energy flow in biological systems is a dynamic process, ensuring that life continues effectively despite changing external conditions.