Correct Answer: B

Rationale: The primary function of the kidneys in the urinary system is to filter blood to remove waste products and excess fluids, which are then excreted as urine. Kidneys act as a filtration system, removing waste like urea, excess salts, and toxins. While the kidneys do play a role in regulating blood pressure by secreting renin and maintaining electrolyte balance by adjusting the levels of sodium, potassium, and other ions in the blood, their main and essential function is filtration and waste removal, making choice B the correct answer.

Correct Answer: B

Rationale: The Golgi apparatus is an organelle responsible for packaging and distributing proteins and lipids within the cell. It modifies, sorts, and packages these molecules into vesicles for transportation to their final destinations, either within the cell or outside of it. The Golgi apparatus plays a crucial role in the secretory pathway of cells, ensuring that proteins are properly processed and directed to where they are needed. Ribosomes are responsible for protein synthesis, not packaging and distributing proteins. The endoplasmic reticulum is involved in protein synthesis and folding but not primarily in packaging and distributing proteins. Mitochondria are known as the powerhouse of the cell and are responsible for generating energy in the form of ATP through cellular respiration, not packaging and distributing proteins.

Correct Answer: A

Rationale: The larynx, also known as the voice box, is a crucial structure in the respiratory system. It is located in the upper part of the trachea and houses the vocal cords. The larynx plays a key role in producing sound and protecting the trachea by closing during swallowing to prevent food from entering the airway. This makes the larynx the correct answer in this context. The trachea (Choice B) is a respiratory structure that connects the larynx to the lungs, allowing air to pass through. The pharynx (Choice C) is a shared pathway for both air and food, located at the back of the throat. The esophagus (Choice D) is part of the digestive system, responsible for transporting food from the mouth to the stomach. Therefore, Choices B, C, and D are not located in the respiratory system.

Correct Answer: B

Rationale: The primary function of the immune system is to fight infections. It identifies and destroys pathogens like bacteria and viruses, protecting the body from harmful substances. While oxygen transportation is carried out by the respiratory system, energy production is mainly the role of the metabolic system, and body temperature regulation is managed by the thermoregulatory system. These functions are separate from the immune system's primary role of defending the body against infections.

Correct Answer: B

Rationale: The urethra is the correct answer because it is a tube that is part of both the male reproductive system and the urinary system. It allows urine to pass out of the body as part of the urinary system and also transports semen as part of the male reproductive system. The bladder (Choice A) is solely part of the urinary system, storing urine. The prostate (Choice C) is part of the male reproductive system, secreting fluids that nourish and protect sperm. The seminal vesicle (Choice D) is also part of the male reproductive system, producing seminal fluid that mixes with sperm to form semen.