Principles and Applications of Cellular Respiration

Section 3: Principles and Applications of Cellular Respiration

Yeast is a type of single-cell fungus closely associated with human life. Making steamed buns, bread, brewing alcohol, and other processes utilize yeast respiration.

Essence of Respiration

Respiration essentially involves the oxidative breakdown of organic substances within cells, releasing energy. Hence, it is also called cellular respiration.

Modes of Cellular Respiration

Does cellular respiration always require oxygen? Can organisms perform cellular respiration under both aerobic and anaerobic conditions?

Yeast can undergo cellular respiration under both aerobic and anaerobic conditions. Under aerobic conditions, yeast produces large amounts of carbon dioxide and water through cellular respiration. Under anaerobic conditions, yeast produces alcohol through cellular respiration, along with small amounts of carbon dioxide.

Based on extensive experimental results, scientists have concluded that cellular respiration can be categorized into aerobic respiration and anaerobic respiration.

Aerobic Respiration

For most organisms, aerobic respiration is the primary form of cellular respiration, requiring the involvement of oxygen. The mitochondria are the main sites for aerobic respiration. Mitochondria have inner and outer membranes, with folds in the inner membrane called cristae, greatly increasing the surface area of the inner membrane (see Figure 5-8). The space around the cristae is filled with liquid matrix. Many enzymes related to aerobic respiration are present on the inner membrane and in the matrix of mitochondria. Glucose is the most commonly utilized substance in aerobic respiration, and its chemical reaction can be simplified as:

C6H12O6 + 6O2 + 6H2O + enzymes → 6CO2 + 12H2O + energy

Aerobic respiration is a highly complex process, summarized into three stages, each catalyzed by specific enzymes (see Figure 5-9). The first stage involves the breakdown of one molecule of glucose into two molecules of pyruvic acid, releasing a small amount of [H] and energy in the cytoplasm, without requiring oxygen.

The second stage involves the complete breakdown of pyruvic acid and water into carbon dioxide, [H], and a small amount of energy in the mitochondrial matrix, without direct oxygen participation.

The third stage involves [H] generated from the previous stages combining with oxygen through a series of chemical reactions on the inner mitochondrial membrane to form water, releasing a large amount of energy. This stage requires oxygen and occurs on the inner mitochondrial membrane.

In summary, aerobic respiration refers to the process where cells, with the participation of oxygen and catalysis by various enzymes, completely oxidize and break down organic substances such as glucose, producing carbon dioxide and water, releasing energy, and generating a large amount of ATP. Compared to combustion of organic matter outside biological organisms, aerobic respiration is characterized by its gentle process and gradual release of energy through a series of chemical reactions, with a significant portion of this energy stored in ATP.

Anaerobic Respiration

Apart from yeast, many bacteria (e.g., lactic acid bacteria) can perform anaerobic respiration. Additionally, cells in plant organs like potato tubers, rice roots, apple fruits, and animal skeletal muscle cells can undergo anaerobic respiration when oxygen is limited. Generally, glucose is also the most commonly utilized substance in anaerobic respiration.

The entire process of anaerobic respiration can be summarized into two stages, catalyzed by different enzymes, both occurring in the cytoplasm. The first stage is identical to the second stage of aerobic respiration. The second stage involves pyruvic acid breaking down into alcohol and carbon dioxide, or converting into lactic acid under the catalysis of enzymes different from those in aerobic respiration. Regardless of whether it breaks down into alcohol and carbon dioxide or converts into lactic acid, anaerobic respiration only releases a small amount of energy in the first stage, generating minimal ATP. Most of the energy in the glucose molecule remains stored in alcohol or lactic acid.

The chemical reactions of anaerobic respiration can be summarized into the following two types:

C6H12O6 + enzymes → 2C2H5OH (alcohol) + 2CO2 + minimal energy

C6H12O6 + enzymes → 2CH3CH(OH)COOH (lactic acid) + minimal energy

The anaerobic respiration of microorganisms such as yeast and lactic acid bacteria is also referred to as fermentation. The process of releasing a small amount of energy through incomplete decomposition of organic substances like glucose without the involvement of oxygen is called anaerobic respiration.

Both aerobic and anaerobic respiration fall under the category of cellular respiration. Cellular respiration refers to the process where organic substances undergo a series of oxidative decompositions within cells, generating carbon dioxide or other products, releasing energy, and producing ATP. The survival of all organisms depends on the energy released by cellular respiration.

In addition to providing energy for organisms, cellular respiration is also central to metabolism. For instance, intermediate products generated during cellular respiration can be converted into non-sugar substances such as glycerol and amino acids. Metabolism of non-sugar substances produces certain products similar to intermediate products of cellular respiration, which can further form glucose. The metabolism of proteins, carbohydrates, and lipids is interconnected through the process of cellular respiration.

Applications of Cellular Respiration Principles

Please analyze the following information to understand the applications of cellular respiration principles in life and production.

The principles of cellular respiration have been widely applied in life and production. In daily life, the production of traditional foods such as steamed buns, bread, and fermented vegetables, as well as modern fermentation industries producing products like penicillin and monosodium glutamate, are all based on the utilization of microbial cellular respiration principles. In agricultural production, many measures taken are also related to regulating the intensity of respiration. For example, deep plowing and timely drainage improve oxygen supply to promote root respiration in crops, aiding their growth. When storing fruits and vegetables, measures such as lowering temperatures and reducing oxygen content are often taken to reduce the respiratory activity of fruits and vegetables, thereby minimizing the consumption of organic matter.