Which structure in the eye is responsible for focusing light on the retina?

Correct Answer: B

Rationale: The lens of the eye is responsible for focusing light onto the retina. It plays a crucial role in bending light rays to ensure that they converge on the retina, enabling clear vision. The cornea helps in focusing light, but the final adjustment and fine-tuning occur through the lens. The retina receives the focused light and converts it into neural signals for the brain to interpret. The pupil, on the other hand, controls the amount of light entering the eye by dilating or constricting.

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: B

Rationale: The alveoli in the lungs are tiny air sacs responsible for the exchange of oxygen and carbon dioxide during breathing. Oxygen from inhaled air diffuses into the bloodstream through the alveoli, while carbon dioxide produced by cells is removed from the blood and exhaled out of the body through the alveoli. This gas exchange process is essential for the body to obtain oxygen and get rid of carbon dioxide, supporting cellular functions and maintaining overall health. Choices A, C, and D are incorrect because the alveoli do not filter blood, transport nutrients, or store oxygen. Their main function is gas exchange.

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.