what reactants are needed for respiration

Cellular Respiration: Fuel and Oxidant

The Core Process

Cellular respiration is a metabolic process that converts biochemical energy from nutrients into adenosine triphosphate (ATP), and then releases waste products. ATP is used by the cell for energy. This process typically involves a series of chemical reactions.

Required Substrates

Organic molecules are the primary sources of energy. These include:

  • Glucose: A simple sugar that is a major energy source for many organisms.
  • Fatty Acids: Lipids broken down into smaller components, which enter pathways such as beta-oxidation.
  • Amino Acids: Proteins broken down to provide carbon skeletons, though this is less common under normal circumstances.

The Crucial Oxidizer

The primary agent responsible for extracting energy from these substrates is:

  • Molecular Oxygen (O2): Serves as the final electron acceptor in the electron transport chain, a critical component of oxidative phosphorylation, which generates the majority of ATP. In its absence, some organisms can perform anaerobic respiration using other inorganic molecules.

Byproducts

The process also generates specific outputs. These include:

  • Carbon Dioxide (CO2): A waste product that is exhaled or otherwise removed from the organism.
  • Water (H2O): Another byproduct formed during the electron transport chain.

Alternative Oxidative Pathways

While molecular oxygen is the most common and efficient oxidizing agent, some organisms utilize alternative substances in anaerobic respiration. These alternatives include:

  • Sulfate (SO42-): Used by certain bacteria and archaea as a terminal electron acceptor.
  • Nitrate (NO3-): Another alternative electron acceptor for some bacteria, leading to denitrification.
  • Iron (Fe3+): Utilized by some bacteria to accept electrons, reducing it to Fe2+.