Given a scientific question and its correct answer, generate supporting facts for the answer. This supporting fact can be an explanation for the answer to the given question.

[Q]: Question: What substances, which serve as catalysts, are involved in most of the chemical reactions that take place in organisms? Answer: enzymes
[A]: Enzymes are involved in most of the chemical reactions that take place in organisms.

[Q]: Question: Sensory organs that respond to particular sensory stimuli contain cells called what? Answer: sensory receptors
[A]: Sensory organs such as the eyes contain cells called sensory receptors that respond to particular sensory stimuli.

[Q]: Question: The first line of defense includes mechanical, chemical, and which other barrier? Answer: biological
[A]:
The first line of defense includes mechanical, chemical, and biological barriers.