Respiration

Basic Process

Respiration is a biochemical process in which living organisms obtain energy from organic substances (like glucose). It involves the breakdown of food molecules to release energy, which is then used for various life processes. This process occurs continuously in all living cells.

Word Equation:

Glucose + Oxygen → Carbon Dioxide + Water + Energy

The Three Stages of Cellular Respiration

Cellular respiration is a complex process that can be divided into three main stages: glycolysis, the Krebs cycle, and the electron transport chain.

1. Glycolysis

• Location: Cytoplasm of the cell.
• Process: The breakdown of a single glucose molecule into two molecules of pyruvate. This process does not require oxygen.
• Products: 2 ATP (net), 2 NADH, and 2 pyruvate molecules.

2. Krebs Cycle (Citric Acid Cycle)

• Location: Mitochondrial matrix.
• Process: Before entering the cycle, pyruvate is converted into acetyl-CoA. The acetyl-CoA then enters the cycle and is oxidized through a series of reactions.
• Products (per glucose molecule): 2 ATP, 6 NADH, 2 FADH₂, and 4 CO₂.

3. Electron Transport Chain (ETC)

• Location: Inner mitochondrial membrane.
• Process: NADH and FADH₂ donate their high-energy electrons to the ETC. As electrons move through the chain, energy is released and used to pump protons, creating a proton gradient. This gradient drives ATP synthase to produce a large amount of ATP. Oxygen is the final electron acceptor, forming water.
• Products: Approximately 34 ATP molecules.

Respiration in Plants

Plants also respire, taking in oxygen and releasing carbon dioxide, just like animals. Respiration in plants can be of two types:

1. Aerobic Respiration

• Basic Concept: Occurs in the presence of oxygen. It is a complete breakdown of glucose into carbon dioxide and water, releasing a large amount of energy.
• Word Equation: Glucose + Oxygen → Carbon Dioxide + Water + Energy (large amount)
• Examples: Most plants and animals perform aerobic respiration.

2. Anaerobic Respiration

• Basic Concept: Occurs in the absence or limited supply of oxygen. It is an incomplete breakdown of glucose, releasing a smaller amount of energy compared to aerobic respiration.
• Word Equation (in plants/yeast - alcoholic fermentation): Glucose → Ethanol + Carbon Dioxide + Energy (small amount)
• Examples: Some bacteria, yeast, and plant tissues under waterlogged conditions (e.g., roots in waterlogged soil).

Respiration and Photosynthesis in Plants

These two processes are complementary and vital for plant life, but they are distinct.

Difference in Both Processes