What is the primary function of the cardiovascular system?

Correct Answer: A

Rationale: The correct answer is A: "To transport oxygen and nutrients." The primary function of the cardiovascular system is to transport oxygen, nutrients, and hormones to cells throughout the body and remove waste products. This system plays a crucial role in maintaining homeostasis by delivering essential substances to tissues and organs while eliminating metabolic waste. Choices B, C, and D are incorrect because although the cardiovascular system indirectly helps in removing waste products through circulation, its primary function is focused on transporting essential substances and not on regulating body temperature or fighting infections.

Correct Answer: A

Rationale: The correct answer is A: 'To filter waste from the blood.' The primary function of the kidneys in the urinary system is to filter waste products and excess substances from the blood, forming urine, which is then excreted from the body. This process helps maintain the body's internal environment by regulating the balance of electrolytes, fluid levels, and eliminating metabolic waste products. Choices B, C, and D are incorrect because while the kidneys do produce urine, regulate blood pressure, and maintain fluid balance, their primary function within the urinary system is the filtration of waste from the blood.

Correct Answer: A

Rationale: The correct answer is the Pineal gland. This gland is responsible for producing melatonin, a hormone that helps regulate the sleep-wake cycle. Melatonin production is influenced by exposure to light, with levels typically rising in the evening to promote sleep and falling in the morning to aid wakefulness. The Thyroid gland (choice B) produces hormones that regulate metabolism, the Adrenal gland (choice C) produces hormones like adrenaline and cortisol, and the Pituitary gland (choice D) controls several other glands in the endocrine system.

Correct Answer: B

Rationale: The primary function of the digestive system is to break down food into smaller molecules and absorb nutrients such as vitamins, minerals, carbohydrates, proteins, and fats. These nutrients are then utilized by the body for energy, growth, and repair. The digestive system plays a crucial role in the process of extracting essential components from food and distributing them to the body's cells through the bloodstream. Choices A, C, and D are incorrect because transporting oxygen, producing hormones, and transporting blood are functions associated with other body systems like the respiratory system, endocrine system, and circulatory system, respectively, not the digestive system.

Correct Answer: B

Rationale: The primary function of the skin is to protect the body from external damage. While the skin also helps regulate body temperature and produces vitamin D in response to sunlight, its main role is to act as a barrier against harmful external factors, such as pathogens and physical injuries. Choices A, C, and D are incorrect because although the skin does play a role in regulating body temperature and producing vitamin D, its primary function is providing protection against external threats.