Nokea
The triple point of a substance is the temperature and pressure at which the substance exists as which of the following?
- A. As a gel with solid and liquid trapped in gas
- B. Simultaneously in sol, gel, and plasma phases
- C. Simultaneously in solid, liquid, and gas phases
- D. As a sol with gas and solid trapped in liquid
Correct Answer: C
Rationale: The triple point is a specific condition where a substance can exist simultaneously in all three phases: solid, liquid, and gas. The other options do not accurately describe this state.
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Among the following molecules, which one contains the fewest covalent bonds?
- A. Water molecule (H2O)
- B. Methane molecule (CH4)
- C. Chlorine molecule (Cl2)
- D. Ammonia molecule (NH3)
Correct Answer: C
Rationale: The correct answer is C. The chlorine molecule (Cl2) contains the fewest covalent bonds as it consists of two chlorine atoms sharing a single covalent bond. Water (H2O), methane (CH4), and ammonia (NH3) involve multiple atoms bonded together, leading to more covalent bonds compared to the chlorine molecule. Hence, among the options provided, the chlorine molecule has the least number of covalent bonds.
What distinguishes endocrine and exocrine glands from one another?
- A. The biochemistry of their secretions
- B. The presence or absence of ducts
- C. The presence or absence of nerve innervation
- D. The effect their secretions have on the target cell
Correct Answer: B
Rationale: The correct answer is B. The presence or absence of ducts is the key factor that distinguishes endocrine and exocrine glands. Endocrine glands secrete hormones directly into the bloodstream without ducts, while exocrine glands secrete substances through ducts to the external environment or onto a surface. Choice A is incorrect because both types of glands can have different biochemistries in their secretions. Choice C is incorrect because both types of glands can receive nerve innervation. Choice D is incorrect as it does not differentiate between endocrine and exocrine glands based on the effect of their secretions on target cells.
Which of the following statements is correct regarding the pH scale?
- A. A substance with a pH of 3 is more acidic than a substance with a pH of 4.
- B. A substance with a pH of 3 is two times more alkaline than a substance with a pH of 4.
- C. A substance with a pH of 3 is 10 times more alkaline than a substance with a pH of 4.
- D. A substance with a pH of 3 is 10 times more acidic than a substance with a pH of 4.
Correct Answer: D
Rationale: The correct answer is D. The pH scale measures the acidity or basicity of a substance on a scale of 0 to 14. Each whole pH value below 7 is ten times more acidic than the next higher value. Therefore, a substance with a pH of 3 is 10 times more acidic than a substance with a pH of 4. The difference in pH values indicates the concentration of hydrogen ions in the substance, with lower pH values representing higher acidity and higher pH values representing higher basicity.
When an organism with an unknown genotype is crossed with another organism displaying the recessive trait (aa), the Punnett square shown above illustrates the outcomes. What is the unknown genotype?
- A. a
- B. Aa
- C. AA
- D. aa
Correct Answer: B
Rationale: In the provided Punnett square, the recessive trait (aa) is displayed. This means the known organism must be homozygous recessive (aa). When crossed with the unknown genotype, which is represented by a capital letter (A), it results in a 50% chance of producing heterozygous offspring (Aa). As the recessive trait is expressed in the outcomes, the unknown genotype must carry the dominant allele (A) alongside the recessive allele (a), making it heterozygous (Aa). Therefore, the correct answer is B, Aa.
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.