Correct Answer: B

Rationale: The aortic semilunar valve is the correct answer as it prevents the backflow of blood into the left ventricle once it has been pumped into the aorta. The pulmonary semilunar valve prevents backflow into the right ventricle, the tricuspid valve controls blood flow between the right atrium and ventricle, and the mitral valve regulates blood flow between the left atrium and ventricle. Therefore, option B is the correct choice for this question.

Correct Answer: B

Rationale: The correct answer is B: Kidneys. The kidneys are vital organs in the human body responsible for filtering blood to remove waste products and excess substances, producing urine as a result. The liver plays a role in detoxification and metabolism. The pancreas is involved in digestion and blood sugar regulation. The heart pumps blood throughout the body but does not filter blood or produce urine.

Correct Answer: A

Rationale: The correct answer is A: Arteries, veins, capillaries. Arteries carry blood away from the heart, veins carry blood to the heart, and capillaries facilitate the exchange of gases and nutrients between the blood and tissues. Choice B is incorrect because bronchioles are not blood vessels but part of the respiratory system. Choice C is incorrect as it lists veins before arteries, which is not the standard order in anatomy. Choice D is incorrect as alveoli are small air sacs in the lungs, not blood vessels.

Correct Answer: B

Rationale: The corrected answer is B: 'Vulva: external structures of the female genitalia.' The vulva includes external structures such as the labia, clitoris, and vaginal opening. These structures play roles in sexual arousal and protection of the internal genital organs. Choices A, C, and D are incorrect because they are internal reproductive organs. The ovaries produce eggs, the uterus houses the developing fetus, and the vagina serves as the birth canal. Hence, they are not components of the female external genitalia.

Correct Answer: B

Rationale: The correct answer is B: Proteins. Proteins are the only macromolecules that always contain nitrogen in their amino acid structure. Nitrogen is a key element found in the amino groups of amino acids, which are the building blocks of proteins. Fatty acids (Choice A), lipids (Choice C), and carbohydrates (Choice D) do not always contain nitrogen in their structure. Fatty acids are composed of long hydrocarbon chains and do not contain nitrogen. Lipids consist mainly of carbon, hydrogen, and oxygen, with some classes of lipids containing phosphorus but not nitrogen. Carbohydrates are made up of carbon, hydrogen, and oxygen, forming structures like sugars and starches, but they do not contain nitrogen.