Nokea
The innate immune system provides a non-specific first line of defense. What are some physical barriers that contribute to the innate immune system?
- A. Antibodies
- B. Phagocytes
- C. Skin and mucous membranes
- D. Memory B cells
Correct Answer: C
Rationale: Physical barriers such as the skin and mucous membranes are crucial components of the innate immune system's first line of defense. These barriers act as physical obstacles that prevent pathogens from entering the body. Antibodies (option A) are produced by the adaptive immune system in response to specific pathogens and do not serve as physical barriers. Phagocytes (option B) are cells that engulf and digest pathogens, playing a role in the innate immune response but not as physical barriers. Memory B cells (option D) are part of the adaptive immune system and aid in mounting a faster and more effective immune response upon subsequent exposure to a specific pathogen, but they are not physical barriers against initial pathogen entry.
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Through what tubes does urine travel from the kidneys to the bladder?
- A. Urethra
- B. Ureters
- C. Renal arteries
- D. Renal veins
Correct Answer: B
Rationale: The correct answer is 'Ureters.' The ureters are the tubes that transport urine from the kidneys to the bladder. The urethra, not a choice in this question, is the tube responsible for carrying urine from the bladder out of the body. Renal arteries and veins are blood vessels that respectively supply and drain the kidneys, not involved in the transport of urine to the bladder.
Elements tend to gain or lose electrons to achieve stable electron configurations like those of noble gases. Their group number often indicates the number of electrons gained/lost and the resulting ionic charge, providing a good starting point for prediction.
- A. Ionic bonds involve electron sharing, while metallic bonds involve electron transfer.
- B. Ionic bonds are weak and directional, while metallic bonds are strong and non-directional.
- C. Ionic bonds exist between metals and non-metals, while metallic bonds exist only between metals.
- D. Ionic bonds form discrete molecules, while metallic bonds form extended structures.
Correct Answer: C
Rationale: Ionic bonds typically form between metals and non-metals, where one atom donates electrons (cation) and the other accepts electrons (anion). This results in the transfer of electrons. Metallic bonds, on the other hand, occur between metal atoms where electrons are shared among a sea of delocalized electrons, leading to the characteristic properties of metals like malleability and conductivity. Choice A is incorrect because ionic bonds involve electron transfer, not sharing. Choice B is incorrect as ionic bonds are strong, not weak, and are non-directional, while metallic bonds are strong and non-directional. Choice D is incorrect as ionic bonds do not form discrete molecules but rather a lattice structure, whereas metallic bonds form extended structures.
What is the primary function of the strong nuclear force?
- A. Binding electrons in atomic orbitals
- B. Binding protons and neutrons within the nucleus
- C. Mediating the attractive force between opposite charges
- D. Mediating the repulsive force between like charges
Correct Answer: B
Rationale: The strong nuclear force primarily functions to bind protons and neutrons within the nucleus. It is responsible for overcoming the electrostatic repulsion between positively charged protons, holding the nucleus together. Choices A, C, and D are incorrect because the strong nuclear force specifically acts on nucleons (protons and neutrons) within the nucleus, not on electrons in atomic orbitals or charges outside the nucleus.
If you compare a 1 M solution of NaCl to a 1 M solution of glucose (C6H12O6) in water, which solution would have the higher boiling point?
- A. The NaCl solution
- B. The glucose solution
- C. They would have the same boiling point
- D. It depends on the temperature
Correct Answer: A
Rationale: 1. Boiling point elevation: When a solute is added to a solvent, it raises the boiling point of the solution compared to the pure solvent. This phenomenon is known as boiling point elevation.
2. Van't Hoff factor: The extent of boiling point elevation depends on the number of particles the solute dissociates into in the solution. NaCl dissociates into two ions (Na+ and Cl-) in water, while glucose does not dissociate into ions. Therefore, NaCl has a higher Van't Hoff factor than glucose.
3. Colligative properties: Boiling point elevation is a colligative property, meaning it depends on the concentration of the solute particles, not the identity of the solute. Since both NaCl and glucose are 1 M solutions, the NaCl solution will have a higher boiling point due to its higher Van't Hoff factor.
4. Conclusion: The NaCl solution
Decomposers in an ecosystem play a vital role by:
- A. Photosynthesizing and producing organic matter
- B. Breaking down dead organisms and returning nutrients to the environment
- C. Preying on herbivores and controlling their populations
- D. Fixing nitrogen from the atmosphere and making it available to plants
Correct Answer: B
Rationale: Decomposers are organisms that break down dead organic matter, such as dead plants and animals, into simpler substances. By doing so, they help to recycle nutrients back into the environment, making them available for other organisms to use. This process is essential for the functioning of ecosystems, as it ensures that nutrients are not lost but instead are continuously cycled through the ecosystem. Photosynthesis (option A) is the process by which plants and some other organisms convert light energy into chemical energy in the form of glucose, and it is not a role of decomposers. Preying on herbivores (option C) is a role typically carried out by predators, not decomposers. Fixing nitrogen from the atmosphere (option D) is a process carried out by nitrogen-fixing bacteria, not decomposers.