What is the primary role of hemoglobin in red blood cells?

Correct Answer: A

Rationale: The correct answer is A: Carrying oxygen. Hemoglobin's primary function in red blood cells is to bind with oxygen in the lungs and transport it to the body's tissues and cells. This process is crucial for cellular respiration and the overall oxygenation of the body. Choices B, C, and D are incorrect because hemoglobin primarily carries oxygen, not nutrients, carbon dioxide, or waste products.

Correct Answer: A

Rationale: The glomerulus is the correct answer. It is a vital structure in the kidney responsible for filtering blood. The glomerulus is a network of capillaries that filters waste products and excess substances from the blood to form urine. While the Bowman's capsule, Loop of Henle, and Collecting duct are also essential components of the nephron, the primary site of blood filtration occurs at the glomerulus. The Bowman's capsule surrounds the glomerulus and collects the filtered fluid, the Loop of Henle reabsorbs water and important ions, and the Collecting duct further concentrates the urine, but none of these structures are primarily responsible for filtering blood as the glomerulus is.

Correct Answer: B

Rationale: The correct answer is B: Absorbing nutrients. The small intestine plays a crucial role in digestion by absorbing nutrients. It is where the majority of nutrient absorption occurs, allowing digested food to pass into the bloodstream for distribution to the body's cells. Choice A (Breaking down fats) is incorrect because the breakdown of fats primarily occurs in the small intestine with the help of bile from the liver and enzymes from the pancreas. Choice C (Secreting digestive enzymes) is incorrect because while the small intestine does produce some digestive enzymes, its primary role is absorption. Choice D (Storing bile) is incorrect as the storage of bile occurs in the gallbladder, not the small intestine.

Correct Answer: C

Rationale: Vitamin D is essential for the absorption of calcium in the intestines, aiding in the maintenance of strong bones and teeth. It helps regulate calcium and phosphorus levels in the body, supporting bone health and preventing conditions like osteoporosis. Vitamin A (Choice A) is important for vision and immune function, not specifically for calcium absorption. Vitamin C (Choice B) is crucial for collagen synthesis and immune function but is not directly involved in calcium absorption. Vitamin K (Choice D) plays a role in blood clotting and bone health, but it is not primarily responsible for calcium absorption.

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.