The chapter deals with questions and answers related to biotic organisms that derive energy from food to sustain life. The nature of the questions is very diversified and includes multiple-choice questions (MCQs), true or false statements, fill in the blanks, and match the correct statements that are widely used in entrance tests, competitive examinations, and at some places, in certifying examinations. These questions are important for self-study and self-assessment and will also be useful to test the knowledge, understanding, and application ability of the student in the relevant field of specialization.