Nokea
An atom has 17 protons, 20 neutrons, and 17 electrons. What is its mass, in amu?
- A. 17
- B. 20
- C. 37
- D. 54
Correct Answer: C
Rationale: The atomic mass of an atom is the sum of the protons and neutrons in its nucleus. In this case, the atom has 17 protons and 20 neutrons, totaling 37 particles in the nucleus. Electrons are not considered in the atomic mass calculation as their mass is negligible compared to protons and neutrons. Therefore, the mass of the atom in atomic mass units (amu) is 37.
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A person wakes up with a fever. The body begins its response to locate the origin of the problem and fix it. What type of feedback mechanism is this?
- A. Equal
- B. Negative
- C. Neutral
- D. Positive
Correct Answer: B
Rationale: This scenario describes a negative feedback mechanism. When the body detects a fever, it initiates responses to lower the temperature back to normal levels. Negative feedback mechanisms work to counteract changes and maintain homeostasis in the body. Choice A ('Equal') is incorrect as feedback mechanisms aim to restore balance, not maintain an equal state. Choice C ('Neutral') is incorrect as it does not describe the corrective nature of negative feedback. Choice D ('Positive') is incorrect as it would amplify the fever rather than regulate it.
How do killer T cells recognize infected cells?
- A. The B cells flag the infected cells with amino acids.
- B. Tiny bits of the virus's RNA are left around the cell.
- C. Macrophages show up to help consume the infected cell.
- D. The T cells have receptors that recognize the proteins the virus leaves on the surface of the cell.
Correct Answer: D
Rationale: Killer T cells recognize infected cells by detecting viral proteins displayed on the surface of these cells. The T cells possess receptors specifically designed to identify these viral proteins, allowing them to target and eliminate the infected cells. Choice A is incorrect because B cells are not directly involved in the recognition process of infected cells by killer T cells. Choice B is incorrect because tiny bits of the virus's RNA being left around the cell is not how killer T cells primarily recognize infected cells. Choice C is incorrect because while macrophages play a role in immune responses, they do not directly assist in the recognition of infected cells by killer T cells.
How many electrons are typically found in each shell of a neutral aluminum atom with 13 electrons in its electron cloud?
- A. 6 in the first shell, 7 in the second shell
- B. 2 in the first shell, 11 in the second shell
- C. 2 in the first shell, 8 in the second shell, 3 in the third shell
- D. 3 in the first shell, 5 in the second shell, 5 in the third shell
Correct Answer: C
Rationale: In a neutral aluminum atom with 13 electrons, the electron distribution typically follows the electron shell filling order based on the Aufbau principle. The first shell can hold a maximum of 2 electrons, the second shell can hold up to 8 electrons, and the third shell can hold up to 8 electrons as well. Therefore, the distribution would be 2 electrons in the first shell, 8 electrons in the second shell, and 3 electrons in the third shell, totaling 13 electrons. Choice A is incorrect as it exceeds the maximum number of electrons the shells can hold. Choice B is incorrect as it does not distribute the electrons correctly among the shells. Choice D is incorrect as it also does not distribute the electrons correctly among the shells.
Which structure do cells rely on for movement?
- A. Flagellum
- B. Microtubule
- C. Pili
- D. Vesicle
Correct Answer: A
Rationale: The correct answer is A: Flagellum. Cells rely on flagella for movement, which are whip-like structures that propel the cell forward through their whipping motion. Flagella provide motility to single-celled organisms and certain cells in multicellular organisms. Microtubules, on the other hand, provide structural support to the cell and play a role in intracellular transport. Pili are short, hair-like structures used for attachment to surfaces or other cells, not for movement. Vesicles are membrane-bound sacs involved in intracellular transport, aiding in the movement of substances within the cell, but not in the movement of the cell itself.
At what stage is urine formed in the kidney?
- A. After fluid reaches the bladder.
- B. When fluid fills the collecting duct.
- C. Before blood enters the glomerulus.
- D. During fluid transport to the urethra.
Correct Answer: B
Rationale: Urine is formed when fluid fills the collecting duct in the kidney. The collecting duct is where the final concentration of urine occurs after the filtration process in the nephron. Choice A is incorrect because urine formation happens before fluid reaches the bladder. Choice C is incorrect because urine formation occurs after blood has been filtered in the glomerulus. Choice D is incorrect because urine formation happens before fluid is transported to the urethra for elimination.