During respiration, food materials are (oxidized / reduced)

Explanation

**Step-by-Step Solution:**

1. **Understanding Respiration**: Respiration is a physiological process that involves both physical and chemical components. The physical part includes breathing, which is the exchange of gases between the body and the environment.

2. **Chemical Process of Respiration**: In the chemical aspect of respiration, the food we consume is digested and broken down into simpler substances at the cellular level. This breakdown releases energy, primarily in the form of ATP (adenosine triphosphate).

3. **Respiratory Substrates**: The most common respiratory substrate is glucose. Although proteins and fats can also be used, glucose is the primary source of energy during respiration.

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