Identify the open-ended question from among the following :

The correct answer is: What would happen if humans could digest cellulose ?

Explanation:

An open-ended question is a question that requires more than a simple one-word answer, factual statement, or predetermined list. It encourages critical thinking, reasoning, hypothetical analysis, and elaboration.

Let us analyze each of the given options:

1. "Why can humans not digest cellulose ?" – This is a closed factual question with a specific scientific explanation (humans lack the enzyme cellulase needed to break down cellulose).

2. "What is cellulose made of ?" – This is a factual closed-ended question asking for a specific answer (beta-glucose units).

3. "What would happen if humans could digest cellulose ?" – This is a hypothetical, open-ended question. It prompts reflection on human diet, evolution, agriculture, energy production, and digestive physiology, allowing for multiple creative and analytical perspectives without a single fixed answer.

4. "Name any five organisms that can digest cellulose." – This is a direct recall question requiring a simple list of specific examples (such as cows, termites, goats, horses, and sheep).

Therefore, "What would happen if humans could digest cellulose ?" is the correct open-ended question.