Cellular Respiration & Fermentation

Overview of Energy Flow in Cells

Cells require energy to perform work, and this energy is primarily supplied by ATP, which is generated through the breakdown of food molecules. The processes of photosynthesis and cellular respiration are central to the flow of energy in biological systems.

• Photosynthesis uses light energy to convert CO2 and H2O into organic molecules (such as glucose) and O2.

• Cellular respiration occurs in mitochondria and breaks down organic molecules, generating ATP and releasing CO2 and H2O as waste products.

• ATP produced powers most cellular work, and some energy is lost as heat.

Anabolic vs. Catabolic Processes

Metabolic pathways are classified as either anabolic or catabolic, depending on whether they build up or break down molecules.

• Anabolic processes (e.g., photosynthesis) build complex molecules from simpler ones, requiring energy input.

• Catabolic processes (e.g., cellular respiration) break down complex molecules into simpler ones, releasing energy.

• Photosynthesis is anabolic because it synthesizes organic molecules from CO2 and H2O.

• Cellular respiration is catabolic because it breaks down organic molecules to release energy.

Metabolic Pathways and Energy Yield

Cells obtain energy by oxidizing fuels through metabolic pathways. The energy enters ecosystems as light and exits as heat.

• Photosynthesis: CO2 + H2O + light energy → organic molecules + O2

• Cellular respiration: organic molecules + O2 → ATP + CO2 + H2O

Types of Cellular Respiration and Fermentation

Cells can generate ATP through different processes, depending on the availability of oxygen.

• Fermentation: Partial degradation of sugars without oxygen.

• Aerobic respiration: Consumes organic molecules and oxygen, yielding ATP.

• Anaerobic respiration: Consumes compounds other than oxygen as electron acceptors.

Comparison of ATP-Producing Pathways

Key Terms and Definitions

• ATP (Adenosine Triphosphate): The primary energy currency of the cell.

• Photosynthesis: The process by which plants, algae, and some bacteria convert light energy into chemical energy.

• Cellular Respiration: The process of breaking down organic molecules to produce ATP.

• Fermentation: An anaerobic process that allows cells to produce ATP without oxygen.

• Aerobic Respiration: Respiration that requires oxygen.

• Anaerobic Respiration: Respiration that does not require oxygen and uses other molecules as electron acceptors.

Example: Energy Flow in Ecosystems

In a plant cell, photosynthesis captures light energy to produce glucose and oxygen. In an animal cell, cellular respiration uses glucose and oxygen to produce ATP, which powers cellular activities.

Equations

• Photosynthesis:

• Cellular Respiration:

Additional info:

• Fermentation is important in food production (e.g., yogurt, bread, alcohol) and in muscle cells during intense exercise when oxygen is limited.

• ATP is regenerated from ADP and phosphate through cellular respiration.