Correct Answer: B

Rationale: Mitochondria are the organelles responsible for producing energy in the cell through a process called cellular respiration. They are often referred to as the powerhouses of the cell due to their role in generating ATP, the cell's energy currency. The nucleus is not involved in energy production but houses the cell's genetic material. Ribosomes are responsible for protein synthesis, not energy production. The Golgi apparatus is involved in processing and packaging proteins for secretion, not energy production.

Correct Answer: B

Rationale: The medulla oblongata, located in the brainstem, plays a crucial role in controlling vital functions such as breathing, heart rate, and blood pressure. It serves as the control center for automatic functions necessary for survival, making it the correct choice in this scenario. The cerebrum is responsible for higher brain functions like thinking and voluntary movements, so it does not control basic physiological functions like breathing and heart rate. The cerebellum is mainly involved in coordination and balance, while the hypothalamus regulates body temperature, hunger, and thirst, but not specifically breathing and heart rate.

Correct Answer: D

Rationale: The pinna, also known as the auricle, is the most visible part of the ear. Its external shape and location make it easily noticeable on the side of the head. The pinna helps in capturing sound waves and directing them into the ear canal, where the sound transmission process begins. The other structures listed, the Organ of Corti, Cochlea, and Ear canal, are essential parts of the ear involved in hearing and sound processing, but they are not as visibly prominent as the pinna. Therefore, the correct answer is the pinna because of its external visibility and role in capturing sound waves.

Correct Answer: B

Rationale: The correct answer is the Hyoid bone. The hyoid bone is distinctive as it does not directly articulate with any other bone in the body. Instead, it is held in place by muscles and ligaments, playing a crucial role in supporting the tongue and providing attachment points for various muscles involved in swallowing and speech. The other choices, Femur, Radius, and Tibia, all articulate with other bones in the body. The femur articulates with the hip bone, the radius articulates with the ulna and other bones in the wrist, and the tibia articulates with the femur and fibula.

Correct Answer: B

Rationale: The correct answer is B: 'To break down food.' The stomach's primary function in digestion is to break down food mechanically and chemically. It accomplishes this by mixing food with gastric acid and digestive enzymes, resulting in the formation of chyme, a semi-liquid mixture that moves on to further digestion in the small intestine. Choice A is incorrect because the absorption of nutrients occurs mainly in the small intestine, not in the stomach. Choice C is incorrect because while the stomach does secrete digestive enzymes like pepsin, its primary role is not just limited to enzyme secretion. Choice D is incorrect because the storage of glucose primarily occurs in the liver and muscles, not in the stomach.