Question

In biochemistry, the exergonic process of converting glucose and oxygen to carbon dioxide and water in aerobic metabolism can be considered the reverse of photosynthesis, in which carbon dioxide and water are converted to glucose and oxygen. Do you expect both processes to be exergonic, both endergonic, or one exergonic and one endergonic? Why? Would you expect both processes to take place in the same way? Why?

Short answer

Aerobic metabolism is exergonic and photosynthesis is endergonic. They do not occur in the same way due to different cellular conditions and locations.

Step-by-step solution

Understand the Definitions

First, it's important to know what exergonic and endergonic reactions are. Exergonic reactions release energy, whereas endergonic reactions require the input of energy.

Analyze Aerobic Metabolism

In aerobic metabolism, glucose and oxygen are converted to carbon dioxide and water. This process releases energy, so it is exergonic.

Analyze Photosynthesis

In photosynthesis, carbon dioxide and water are converted to glucose and oxygen using energy from sunlight. This process requires an input of energy, making it endergonic.

Compare the Two Processes

Since aerobic metabolism releases energy (exergonic) and photosynthesis requires energy (endergonic), they are opposite types of reactions.

Evaluate Process Similarity

Both processes do not take place in the same way because they occur under different conditions and in different cellular organelles. Aerobic metabolism occurs in mitochondria, while photosynthesis occurs in chloroplasts.

Key concepts

Exergonic Reactions

Exergonic reactions are chemical reactions where energy is released to the surroundings. These reactions are characterized by a negative change in free energy (ΔG < 0). In other words, the products of the reaction have less free energy than the reactants. Some key points to remember are:

• Exergonic reactions occur spontaneously.
• Since they release energy, they can provide power for other cellular activities.
• A common example of an exergonic reaction is the cellular respiration process where glucose is broken down into carbon dioxide and water, releasing energy in the form of ATP.

Aerobic metabolism, where glucose and oxygen are converted to carbon dioxide and water, is a quintessential exergonic reaction. It powers various cellular activities by releasing energy.

Endergonic Reactions

Endergonic reactions are the opposite of exergonic reactions. They require an input of energy to proceed and are not spontaneous. These reactions have a positive change in free energy (ΔG > 0), meaning that the products have more free energy than the reactants. Important to note:

• Endergonic reactions absorb energy from their surroundings.
• They are essential for processes that build complex molecules.
• Photosynthesis is a prime example, where water and carbon dioxide are converted to glucose and oxygen using the energy from sunlight.

During photosynthesis, energy from sunlight is captured and used to drive the synthesis of glucose, making this process endergonic.

Aerobic Metabolism

Aerobic metabolism is the process of producing cellular energy involving oxygen. Cells break down food in the mitochondria in a long, multistep process that produces roughly 36 ATP (the energy currency of the cell) for every glucose molecule. Key points include:

• This process begins with glycolysis, where glucose is broken down in the cytoplasm into pyruvate.
• The pyruvate is then transported into the mitochondria where it enters the Krebs cycle.
• Finally, the electron transport chain uses oxygen and produces water and ATP.

The overall chemical reaction for aerobic metabolism is: \[ \text{C}_6\text{H}_{12}\text{O}_6 + 6 \text{O}_2 \rightarrow 6 \text{CO}_2 + 6 \text{H}_2\text{O} + 36 \text{ATP} \] This process is crucial for the energy needs of complex organisms.

Photosynthesis

Photosynthesis is the process where plants, algae, and some bacteria convert light energy, usually from the sun, into chemical energy stored in glucose. This process can be summarized in three major steps:

• Light-dependent reactions, where sunlight is captured to make ATP and NADPH.
• The Calvin cycle (light-independent reactions), where ATP and NADPH are used to convert carbon dioxide and water into glucose.
• Oxygen is released as a byproduct.

Photosynthesis can be represented by the following equation: \[ 6 \text{CO}_2 + 6 \text{H}_2\text{O} + light \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6 \text{O}_2 \] This is an endergonic process because it requires the input of energy from light.

Energy Transformation

Energy transformation is a fundamental concept in both biochemical reactions discussed: aerobic metabolism and photosynthesis.
In every exergonic and endergonic reaction, energy is transformed from one type to another. For instance:

• In aerobic metabolism, chemical energy stored in glucose is transformed into ATP, which cells use for their energy needs.
• In photosynthesis, light energy is transformed into chemical energy stored in glucose molecules.

These energy transformations are essential for life processes. They allow organisms to grow, reproduce, and maintain their structures. Understanding these transformations helps explain how cells manage energy efficiently through different cellular pathways.