What reactants are needed for cellular respiration

Cellular respiration primarily requires the following reactants:

1. Glucose: This is the main source of energy for the process. It can come from food sources rich in carbohydrates.
2. Oxygen gas (O₂): This is necessary for aerobic respiration, which is the most efficient form of cellular respiration.

The products of cellular respiration are water (H₂O) and carbon dioxide (CO₂), but these are not reactants.

In summary, the main reactants needed for cellular respiration are glucose and oxygen gas.

If one of the key reactants for cellular respiration—glucose or oxygen—is not available, the cell's ability to break down glucose will be significantly affected:

1. If Glucose is Not Available:

   • Without glucose, the cell cannot undergo aerobic respiration. This means that the primary energy source (ATP) derived from breaking down glucose will be unavailable. Cells may utilize other energy sources, such as fats or proteins, but these pathways are less efficient, and the overall energy yield will be lower. The metabolic pathways would shift towards gluconeogenesis or the use of alternative substrates, but overall energy production will be limited.

2. If Oxygen is Not Available:

   • In the absence of oxygen, cells cannot perform aerobic respiration, which is the most efficient way to generate ATP from glucose. Instead, cells may switch to anaerobic respiration or fermentation to produce ATP. For example, in human muscle cells, this can result in lactic acid fermentation, leading to less ATP production (only 2 ATP molecules per glucose molecule compared to the 36-38 ATP produced by aerobic respiration). In yeast, alcoholic fermentation occurs, producing ethanol and CO₂.

In summary, the absence of glucose limits the substrate available for energy production, while the absence of oxygen limits the efficiency of ATP generation and may increase byproducts like lactic acid or ethanol, dependent on the organism and conditions.