What is the main function of the digestive system?

Correct Answer: A

Rationale: The main function of the digestive system is to break down food into nutrients through the process of digestion. Once the food is broken down, the nutrients are absorbed into the bloodstream and utilized by the body for various functions. Choice B, regulating body temperature, is incorrect as it is the function of the body's thermoregulatory system, not the digestive system. Choice C, transporting nutrients, is incorrect as the digestive system primarily focuses on breaking down and absorbing nutrients rather than transporting them. Choice D, producing hormones, is also incorrect as hormone production is mainly carried out by endocrine glands and not the digestive system.

Correct Answer: C

Rationale: Mitochondria are commonly referred to as the powerhouses of the cell as they are primarily responsible for generating energy through cellular respiration. This process involves converting nutrients into adenosine triphosphate (ATP), which is the main energy currency of the cell. The nucleus is responsible for storing the cell's genetic material, the ribosome is involved in protein synthesis, and the Golgi apparatus is responsible for packaging and distributing molecules produced by the cell; therefore, they are not directly involved in energy generation.

Correct Answer: B

Rationale: The primary function of the skin in the integumentary system is to protect the body from external damage. The skin acts as a barrier against pathogens, UV radiation, and physical trauma. While the skin does help regulate body temperature by sweating and vasodilation, its main role is protection. Skin does not produce red blood cells; this is the function of the bone marrow. Hormones are primarily produced by endocrine glands, not the skin.

Correct Answer: B

Rationale: The lens of the eye is responsible for focusing light onto the retina. It plays a crucial role in adjusting the focus to allow for clear vision. After the light passes through the lens, it reaches the retina where it is converted into neural signals for the brain to interpret. The cornea is the transparent outer layer of the eye that helps in focusing light, but its main function is to protect the eye. The pupil is the opening in the center of the iris that regulates the amount of light entering the eye. The iris is the colored part of the eye that controls the size of the pupil.

Correct Answer: C

Rationale: The pineal gland, located in the brain, is responsible for regulating sleep and wakefulness by secreting the hormone melatonin. Melatonin plays a crucial role in controlling the sleep-wake cycle, with higher levels at night inducing sleepiness. The hypothalamus (Choice A) regulates various physiological processes but is not primarily responsible for sleep-wake cycles. The thalamus (Choice B) is involved in relaying sensory information but not specifically in regulating sleep. The cerebellum (Choice D) plays a role in coordination and motor control rather than sleep regulation.