Question

Starting with glucose \(\left(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\right),\) write the overall equation for glucose breakdown in the presence of oxygen, compare this to the overall equation for photosynthesis, and explain how the energy components of the equations differ.

Short answer

The overall equation for glucose breakdown (cellular respiration) in the presence of oxygen is: \[\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6} + 6 \mathrm{O}_{2} \rightarrow 6 \mathrm{H}_{2} \mathrm{O} + 6 \mathrm{CO}_{2} + \text{Energy}\] In contrast, the overall equation for photosynthesis is: \[6 \mathrm{H}_{2} \mathrm{O} + 6 \mathrm{CO}_{2} + \text{Energy (light)} \rightarrow \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6} + 6 \mathrm{O}_{2}\] These equations are essentially reverse processes. The main difference in their energy components is that cellular respiration releases energy by breaking down glucose, while photosynthesis stores energy by synthesizing glucose and oxygen using light energy, water, and carbon dioxide.

Step-by-step solution

Identify the overall equation for glucose breakdown in the presence of oxygen

The overall equation for the breakdown of glucose (cellular respiration) in the presence of oxygen is called cellular respiration, which can be written as: \[\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6} + 6 \mathrm{O}_{2} \rightarrow 6 \mathrm{H}_{2} \mathrm{O} + 6 \mathrm{CO}_{2} + \text{Energy}\] This equation represents the breakdown of glucose into carbon dioxide and water, releasing energy in the process.

Identify the overall equation for photosynthesis

Photosynthesis is the process by which plants and other organisms convert sunlight, carbon dioxide, and water into glucose and oxygen. The overall equation for photosynthesis can be written as: \[6 \mathrm{H}_{2} \mathrm{O} + 6 \mathrm{CO}_{2} + \text{Energy (light)} \rightarrow \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6} + 6 \mathrm{O}_{2}\] This equation represents the synthesis of glucose and oxygen from water and carbon dioxide, using light energy.

Compare the two equations

When comparing the two equations, we can observe that they are essentially the reverse of each other. Cellular respiration breaks down glucose and produces carbon dioxide, water, and energy, while photosynthesis uses carbon dioxide, water, and light energy to produce glucose and oxygen. Cellular Respiration: \[\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6} + 6 \mathrm{O}_{2} \rightarrow 6 \mathrm{H}_{2} \mathrm{O} + 6 \mathrm{CO}_{2} + \text{Energy}\] Photosynthesis: \[6 \mathrm{H}_{2} \mathrm{O} + 6 \mathrm{CO}_{2} + \text{Energy (light)} \rightarrow \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6} + 6 \mathrm{O}_{2}\]

Explain the difference in energy components

The key difference between the energy components of the two equations lies in the fact that cellular respiration releases energy while photosynthesis stores energy. In cellular respiration, the breakdown of glucose results in the release of energy, which is then utilized by the cells for performing various metabolic activities. The energy is usually stored in the form of ATP (adenosine triphosphate). On the other hand, photosynthesis requires an input of energy in the form of light to convert carbon dioxide and water into glucose and oxygen. This energy is stored in the glucose molecules, which can be later broken down by the cells during cellular respiration to release the stored energy. In summary, cellular respiration and photosynthesis are complementary processes that are involved in the energy transformation within living organisms. While cellular respiration releases energy by breaking down glucose, photosynthesis stores energy by synthesizing glucose and oxygen using light energy, water, and carbon dioxide.

Key concepts

Photosynthesis

Photosynthesis is a crucial process carried out by plants, algae, and certain bacteria. Using chlorophyll, the green pigment found in plants, they harness sunlight to transform carbon dioxide and water into glucose and oxygen. This complex process consists of two main stages: the light-dependent reactions and the light-independent reactions.
- **Light-dependent reactions**: These occur in the thylakoid membranes of the chloroplasts where sunlight is absorbed and used to split water molecules (\(H_2O\)), releasing oxygen (\(O_2\)) and generating energy-rich compounds such as ATP and NADPH.
- **Light-independent reactions**: Also known as the Calvin cycle, these reactions use ATP and NADPH produced in the light-dependent reactions to convert carbon dioxide into glucose (\(C_6H_{12}O_6\)). This glucose can be utilized by the plant for growth and development, or it can be stored for future use.
Overall, photosynthesis not only provides the necessary organic matter for plant life but also plays a foundational role in providing oxygen and organic compounds for all living organisms.

Glucose Metabolism

Glucose metabolism is a fundamental biological process that organisms use to extract energy from glucose. This process begins with glycolysis in the cytoplasm, where glucose is broken down into two molecules of pyruvate. Glycolysis generates a small amount of ATP and NADH, which are energy carriers. Following glycolysis, depending on the presence of oxygen, glucose metabolism proceeds via two different pathways:
- **Aerobic Pathway (Cellular Respiration)**: If oxygen is available, pyruvate enters the mitochondria, where it undergoes the Krebs cycle and the electron transport chain. These stages further break down pyruvate, releasing more ATP and transforming energy-rich carriers into ATP, the primary energy currency of cells. - **Anaerobic Pathway (Fermentation)**: In the absence of oxygen, cells can still obtain energy by converting pyruvate through fermentation, resulting in lactic acid or ethanol, depending on the organism. This pathway yields much less ATP compared to aerobic respiration.
Glucose metabolism is vital as it ensures that cells have the necessary energy to function efficiently under various conditions, supporting life at the cellular level.

Energy Transformation

Energy transformation is a fundamental aspect of life, encompassing the conversion of energy from one form to another in living organisms. This process is pivotal not only in cellular respiration and photosynthesis but also in all biological activities.
- **In Photosynthesis**: Light energy is transformed into chemical energy in the form of glucose. Plants capture sunlight and convert it into chemical bonds in glucose molecules, which store the energy until needed.
- **In Cellular Respiration**: The stored chemical energy in glucose is transformed into ATP. As cells break down glucose during cellular respiration, they convert the energy from glucose into ATP, providing a readily usable energy form for cellular processes like muscle contraction and molecule transport.
This balance of energy transformation ensures that living organisms can effectively utilize the energy derived from their environment. It highlights how interconnected processes like photosynthesis and respiration sustain life by continuously providing and cycling the energy necessary for survival.