Final answer:
Oxygen is the by-product of the chemical reactions involved in making glucose and is necessary for animal life.
Step-by-step explanation:
The by-product of the chemical reactions involved in making glucose, as well as necessary for animal life, is oxygen. During photosynthesis, plants produce glucose as a result of capturing sunlight energy and combining carbon dioxide and water. Oxygen is released as a waste product during this process and is essential for animals to perform cellular respiration, where glucose is broken down to release energy.
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