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Which of the following chemicals is released by one type of immune cell to directly activate another type of immune cell?
- A. Cytokines
- B. Granzymes
- C. Lysozymes
- D. Perforin
Correct Answer: A
Rationale: The correct answer is A: Cytokines. Cytokines are signaling molecules released by immune cells to directly activate and regulate the activity of other immune cells. They play a crucial role in coordinating the immune response. Granzymes, lysozymes, and perforin have different functions in the immune system. Granzymes are enzymes that induce apoptosis in target cells, lysozymes have antimicrobial properties, and perforin is involved in the destruction of infected cells.
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Which of the following is an efferent neuron responsible for releasing a neurotransmitter that stimulates a muscle?
- A. Neuron
- B. Motor neuron
- C. Nephrons
- D. Neurotransmitter
Correct Answer: B
Rationale: The correct answer is B, 'Motor neuron.' Motor neurons are efferent neurons that carry signals from the central nervous system to muscles or glands. These neurons release neurotransmitters, such as acetylcholine, at the neuromuscular junction to stimulate muscle contraction. Choice A, 'Neuron,' is a broad term for a nerve cell and does not specifically describe the function mentioned. Choice C, 'Nephrons,' are structural components of the kidney and are not related to muscle stimulation. Choice D, 'Neurotransmitter,' refers to the chemical messenger released by neurons to communicate with other cells and is not the specific neuron type responsible for muscle stimulation.
Lithium has an atomic number of 3 and a mass number of 7. What is the number of protons in a lithium atom?
- A. 7
- B. 4
- C. 12
- D. 3
Correct Answer: D
Rationale: The number of protons in an atom is equal to its atomic number. In this case, lithium has an atomic number of 3, so it contains 3 protons. The mass number (7) includes both protons and neutrons, with the difference between the mass number and atomic number representing the number of neutrons. Therefore, the correct answer is 3 protons in a lithium atom.
Which of the following statements best describes the function of a buffer?
- A. It permanently binds hydrogen ions.
- B. It causes the pH of a solution to become neutral.
- C. It decreases the pH of the solution.
- D. It enables resistance to a change in pH.
Correct Answer: D
Rationale: The correct answer is D: 'It enables resistance to a change in pH.' Buffers function by resisting changes in pH when small amounts of acid or base are added to a solution, thereby maintaining a stable pH. Option A is incorrect because buffers do not permanently bind hydrogen ions; they can release or absorb them as needed to maintain pH. Option B is incorrect because buffers do not necessarily cause a solution's pH to become neutral; they stabilize the pH at a specific value. Option C is incorrect; buffers can increase or decrease pH depending on the conditions to maintain stability. Therefore, the best description of a buffer's function is its ability to resist changes in pH.
Which of the following tissues lines the interior surfaces of the heart?
- A. Epicardium
- B. Myocardium
- C. Endocardium
- D. Pericardium
Correct Answer: C
Rationale: The correct answer is C, Endocardium. The endocardium is the innermost layer of tissue that lines the interior surfaces of the heart, providing a smooth surface for blood flow. This smooth lining helps reduce friction as blood passes through the heart chambers. The epicardium is the outermost layer of the heart, the myocardium is the middle muscular layer responsible for the heart's contractions, and the pericardium is the protective sac surrounding the heart and providing support to the heart's structures.
To accurately measure the density of a series of small irregular solids made of plastic, wood, fiberglass, and glass, which of the following laboratory tools will a student need?
- A. Graduated cylinder, water, weighing balance
- B. Weighing balance, Bunsen burner, metric ruler
- C. Graduated cylinder, spectrophotometer, water
- D. Graduated beaker, metric ruler, water
Correct Answer: A
Rationale: To accurately measure the density of irregular solids made of various materials, a student needs specific laboratory tools. Firstly, a graduated cylinder is required to measure the volume of the irregular solids using the water displacement method, which allows for precise volume determination. Secondly, a weighing balance is necessary to measure the mass of the irregular solids accurately. Density is calculated by dividing the mass by the volume, hence the need for both mass and volume measurements. Therefore, the essential tools for this task are a combination of a graduated cylinder, water, and weighing balance (Choice A). These tools together provide the necessary measurements for calculating the density of the irregular solids accurately.