Question: what is a substrate in a chemical reaction
[{'answer': 'the chemical species being observed', 'provenance': [{'wikipedia_id': '8526433', 'title': 'Substrate (chemistry)', 'start_paragraph_id': 1, 'start_character': 39, 'end_paragraph_id': 1, 'end_character': 74, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'provenance': [{'wikipedia_id': '8526433', 'title': 'Substrate (chemistry)', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 485, 'bleu_score': 0.895369351620473, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 18054839441098042932}, 'section': 'Section::::Abstract.'}]}]