An example of an in vitro experiment is one performed where?

• A. In living organisms
• B. Using a questionnaire to survey opinion
• C. Using glass syringes to collect blood
• D. In a test tube

Answer: (D)

An in vitro experiment is done outside a living organism in a controlled, artificial environment. The classic setting is a test tube or similar container where researchers can observe chemical or biological processes without the complexities of a whole organism. This is different from an in vivo approach, which occurs inside a living being.

A questionnaire is a data-collection method, not a lab experiment. Collecting blood with a glass syringe is a sampling step, not an experimental setup conducted to study a process in a controlled environment. Therefore, performing an experiment in a test tube best fits the definition of in vitro.