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Which of the following atoms is most likely to become a cation?
- A. Potassium, atomic number 19
- B. Oxygen, atomic number 8
- C. Fluorine, atomic number 9
- D. Helium, atomic number 2
Correct Answer: A
Rationale: Among the options provided, Potassium is the most likely atom to become a cation. Atoms tend to form cations by losing electrons to achieve a stable electron configuration. Potassium has 19 electrons and only needs to lose one electron to attain an electron configuration similar to the nearest noble gas, argon. This loss of an electron leads to the formation of a potassium cation with a +1 charge.
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Which laboratory method is most useful to separate genomic DNA fragments by size?
- A. Titration
- B. Spectrophotometry
- C. Electrophoresis
- D. Filtration
Correct Answer: C
Rationale: Electrophoresis is the most suitable laboratory method for separating genomic DNA fragments by size. It works by subjecting DNA fragments to an electric field, causing them to migrate through a gel matrix based on size differences. Smaller fragments move faster and travel farther than larger ones, allowing for separation and analysis based on size. Titration is a technique used to determine the concentration of a solution, not to separate DNA fragments by size. Spectrophotometry is used to measure the amount of light absorbed by a substance at different wavelengths, not for DNA fragment size separation. Filtration is a method used to separate solid particles from a liquid or gas by passing it through a filter medium, not for separating DNA fragments by size.
In a phase diagram, what term is used for a substance held at a temperature and pressure where solid, liquid, and gaseous states of a substance exist simultaneously?
- A. critical temperature
- B. triple point
- C. absolute zero
- D. critical point
Correct Answer: B
Rationale: The point described in the question is called the triple point. At the triple point, all three phases of a substance (solid, liquid, and gas) coexist in equilibrium. The critical temperature is the highest temperature at which a distinct liquid phase can form, while absolute zero is the lowest possible temperature. The critical point is the point on a phase diagram that represents the highest temperature and pressure at which a distinct liquid and gas phase can coexist. Therefore, the correct answer is the triple point, where all three phases coexist.
Which of the following types of cells stimulates other immune cells to attack and destroy foreign agents?
- A. Cytotoxic T-cells
- B. Natural killer cells
- C. Helper T-cells
- D. Plasma cells
Correct Answer: C
Rationale: Helper T-cells play a crucial role in coordinating the immune response by activating and directing other immune cells, such as cytotoxic T-cells and macrophages, to attack and eliminate foreign invaders. They achieve this through the release of signaling molecules called cytokines, which regulate the immune system's response to infections and other challenges. Helper T-cells are also involved in activating B-cells to produce antibodies. Natural killer cells, on the other hand, are part of the innate immune system and can directly kill infected or abnormal cells without prior activation.
Which of the following skin layers lacks blood vessels?
- A. Hypodermis
- B. Reticular papillary
- C. Epidermis
- D. Dermis
Correct Answer: C
Rationale: The correct answer is C, Epidermis. The epidermis is the outermost layer of the skin and is avascular, lacking blood vessels. Nutrients are received through diffusion from the underlying dermis. In contrast, the hypodermis, dermis, and reticular papillary layers contain blood vessels that provide nutrients and oxygen to the skin. Understanding the avascular nature of the epidermis is crucial in grasping its functions and how it receives nourishment. Remember, the epidermis acts as a protective barrier and relies on the underlying layers for its blood supply.
Which of the following chemicals is released by one type of immune cell to directly activate another immune cell?
- A. lysozymes
- B. cytokines
- C. perforin
- D. granzymes
Correct Answer: B
Rationale: The correct answer is B: cytokines. Cytokines are signaling molecules released by immune cells to regulate the immune response. They play a crucial role in coordinating and communicating between different immune cells. By releasing cytokines, immune cells can directly activate other immune cells, enhancing the immune response. Lysozymes are enzymes that break down bacterial cell walls, perforin is a protein involved in cell-mediated immune responses, and granzymes are enzymes that induce apoptosis in target cells, mainly used by cytotoxic T cells and natural killer cells, not for directly activating other immune cells.