The function of the Simple Past Tense is to indicate an action is completed and belongs to the past; for example, actions that occurred yesterday and were completed should be in this tense. Besides this, the simple past tense is mainly indicated by the verb because this should be in past form; this in most cases means the verb needs to end in -ed (suffix that indicates past) as in the verbs talked, called, or watched. However, in the case of irregular verbs, this rule does not apply, this includes verbs in past such as wrote (write), ran (run), or bought (buy). Thus, the formula used to indicate the simple past in most cases is verb+ed.
Our cells need glucose to function, which is gained from the nutrients in the food. Oxygen is gained from breathing, so it has nothing to do with food.
