Nokea
What are fingernails and toenails primarily made of?
- A. Collagen (Collagen is found in the dermis)
- B. Keratin
- C. Melanin (Melanin provides pigment, not structure)
- D. Sebum (Sebum is an oily substance)
Correct Answer: B
Rationale: Fingernails and toenails are primarily made of a protein called keratin. Keratin is a tough, fibrous protein that provides structure and strength to nails, hair, and the outer layer of skin. Collagen, as mentioned, is found in the dermis and is not the primary component of nails. Melanin provides pigment to the skin and hair, not the structure of nails. Sebum is an oily substance produced by the skin's sebaceous glands and is not a structural component of nails.
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What is the process of combining two or more substances to form a heterogeneous mixture called?
- A. Dissolving
- B. Diluting
- C. Mixing
- D. Reacting
Correct Answer: C
Rationale: The correct answer is 'Mixing.' When substances are combined, a heterogeneous mixture is formed where the components are physically distinguishable. 'Dissolving' (Choice A) is the process of a solute becoming uniformly dispersed in a solvent to form a solution, not a heterogeneous mixture. 'Diluting' (Choice B) refers to reducing the concentration of a solute in a solution. 'Reacting' (Choice D) involves a chemical change where substances interact to form new products, rather than just physically mixing to form a heterogeneous mixture.
Which element is used in fire extinguishers to smother flames by displacing oxygen?
- A. Nitrogen
- B. Carbon dioxide
- C. Helium
- D. Argon
Correct Answer: B
Rationale: Carbon dioxide is the correct answer. It is used in fire extinguishers because it displaces oxygen, which is necessary for combustion. When carbon dioxide is released onto a fire, it reduces the oxygen concentration around the flames, effectively smothering the fire. This disruption of oxygen availability interrupts the chemical reaction that sustains the fire. Nitrogen (Choice A), helium (Choice C), and argon (Choice D) are not typically used in fire extinguishers for smothering flames by displacing oxygen. Nitrogen is an inert gas that can displace oxygen but is not as effective as carbon dioxide in fire suppression.
Which of the following is NOT a function of the muscular system?
- A. Movement
- B. Maintaining posture
- C. Generating heat
- D. Regulating blood sugar levels
Correct Answer: D
Rationale: The muscular system is responsible for movement, maintaining posture, and generating heat. Regulating blood sugar levels is not a function of the muscular system. This function is primarily carried out by the endocrine system, specifically the pancreas and its production of insulin and glucagon. Choices A, B, and C are all correct functions of the muscular system as they involve the contraction and relaxation of muscles to produce movement, support the body's structure, and generate heat as a byproduct of muscle activity.
How do vaccines work?
- A. By directly killing pathogens
- B. By introducing weakened or inactive versions of pathogens to trigger an immune response
- C. By stimulating the immediate production of specific antibodies
- D. None of the above
Correct Answer: B
Rationale: Vaccines work by introducing weakened or inactive versions of pathogens to trigger an immune response in the body. This exposure helps the immune system recognize and remember the pathogen, enabling a faster and more effective response upon future exposure. Vaccines do not directly kill pathogens but prepare the immune system for a potential encounter, enhancing protection. They also do not stimulate the immediate production of specific antibodies as the immune response takes time to develop upon vaccination. Choice A is incorrect because vaccines do not kill pathogens directly; they prime the immune system to recognize and respond to them. Choice C is incorrect because while vaccines lead to the production of specific antibodies, it is not immediate, as it takes time for the immune response to develop and produce these antibodies.
Which of these pairs represents an example of convergent evolution?
- A. Humans and chimpanzees
- B. Bats and birds
- C. Dolphins and sharks
- D. Snakes and earthworms
Correct Answer: B
Rationale: Convergent evolution refers to the process by which different species independently evolve similar traits or characteristics due to similar environmental pressures. In the case of bats and birds, both have evolved wings for flight despite not sharing a recent common ancestor with wings. Bats are mammals, while birds are avians, yet they both have wings adapted for flight, which is a classic example of convergent evolution.
A) Humans and chimpanzees share a common ancestor and have not independently evolved similar traits.
C) Dolphins and sharks are not closely related, and their similarities are due to adaptations to their aquatic environment rather than convergent evolution.
D) Snakes and earthworms belong to different classes (reptiles and annelids, respectively) and do not share recent common ancestors, making their similarities not a result of convergent evolution.