Correct Answer: C

Rationale: Option C, 'It helps cushion the heart against jarring motions,' is NOT a major function of the respiratory system in humans. The primary functions of the respiratory system include gas exchange, regulation of blood pH, and vocalization. The respiratory system does not play a role in cushioning the heart; that function is primarily carried out by the pericardium and other protective structures around the heart. Choices A, B, and D are major functions of the respiratory system in humans. Choice A refers to the respiratory system's role in gas exchange, Choice B highlights its involvement in regulating blood pH, and Choice D points out its responsibility for vocalization.

Correct Answer: A

Rationale: Cytokinesis is the correct term for the division of the cytoplasm during cell division. It is the final stage of cell division, following either mitosis or meiosis, where the cytoplasm of a parent cell is divided into two daughter cells. Mitosis is the process of nuclear division, while meiosis is a type of cell division that results in four daughter cells with half the number of chromosomes of the parent cell. Apoptosis, on the other hand, is programmed cell death and not the division of the cytoplasm.

Correct Answer: C

Rationale: The correct answer is C: 'Blood would not be pumped to the body.' When tissue in the left ventricle loses blood flow due to a heart attack, the ability of the left ventricle to pump oxygenated blood to the body is compromised. This can lead to serious consequences for the patient's overall health and organ function. Choices A, B, and D are incorrect because a heart attack affecting the left ventricle does not directly impact blood flow from the lungs, cause blood to back up in the legs, or prevent blood from being oxygenated. The primary concern is the compromised ability of the left ventricle to pump blood to the rest of the body, affecting overall circulation and organ perfusion.

Correct Answer: A

Rationale: Totipotent stem cells possess the unique ability to differentiate into any cell type, including forming an entire organism. These cells have the highest potency level and can give rise to both embryonic and extraembryonic cell types, allowing them to develop into a complete organism. Multipotent stem cells (Choice B) can differentiate into a limited range of cell types within a specific tissue or organ. Pluripotent stem cells (Choice C) can differentiate into any cell type in the body except for those needed to support and develop a fetus. Hematopoietic stem cells (Choice D) are a type of multipotent stem cell that can differentiate into various blood cell types.

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.