The digestive and respiratory systems are both responsible for taking in useful molecules into the body. When taken in by these systems, where do the molecules go first?

• A. The muscular system.
• B. The cardiovascular system.
• C. The endocrine system.
• D. The urinary system.

Answer: (B)

Verified step by step guidance

1. Identify the primary function of the digestive and respiratory systems: the digestive system breaks down food into nutrients, and the respiratory system facilitates the exchange of gases (oxygen and carbon dioxide).
2. Understand that once nutrients and oxygen are absorbed, they need to be transported to various cells in the body where they are needed.
3. Recognize that the cardiovascular system, which includes the heart and blood vessels, is responsible for transporting substances throughout the body.
4. Consider how the cardiovascular system circulates blood, which carries oxygen from the lungs and nutrients from the digestive tract to cells.
5. Conclude that the molecules absorbed by the digestive and respiratory systems are first transported by the cardiovascular system to reach their target destinations in the body.