Nokea
Photons, the basic unit of light, are:
- A. Charged particles
- B. Packets of energy with wave-particle duality
- C. Electromagnetic waves only
- D. Always absorbed by matter
Correct Answer: B
Rationale: Photons are not charged particles; they are packets of energy that exhibit wave-particle duality, meaning they can behave as both particles and waves. While photons are part of the electromagnetic spectrum, they are not electromagnetic waves themselves but rather discrete energy packets. They are not always absorbed by matter; they can be reflected, transmitted, or scattered.
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A symbiotic relationship where one organism benefits and the other is not harmed is called:
- A. Mutualism
- B. Commensalism
- C. Parasitism
- D. Predation
Correct Answer: B
Rationale: B) Commensalism: In commensalism, one organism benefits while the other is neither helped nor harmed. This is the relationship described in the question. The correct answer is Commensalism because it specifically fits the scenario where one organism benefits without affecting the other. A) Mutualism: In mutualism, both organisms involved benefit from the relationship. C) Parasitism: In parasitism, one organism benefits at the expense of the other organism, which is harmed. D) Predation: In predation, one organism (predator) kills and consumes another organism (prey) for food.
Which of the following properties is NOT characteristic of a covalent bond?
- A. Sharing of electrons between atoms
- B. High melting and boiling points
- C. Low electrical conductivity in solid state
- D. Directional bonding
Correct Answer: B
Rationale: Covalent bonds are formed by the sharing of electrons between atoms, leading to the formation of molecules with directional bonding. This means that the atoms are held together in a specific orientation. Covalent compounds generally exhibit low melting and boiling points compared to ionic compounds due to the weaker intermolecular forces present in covalent compounds. Furthermore, covalent compounds do not conduct electricity in the solid state because the electrons are localized between the atoms and are not free to move and carry charge. Hence, high melting and boiling points are not characteristic of covalent bonds. The correct answer is 'B' because high melting and boiling points are typically associated with ionic compounds due to their strong electrostatic interactions, while covalent compounds have lower melting and boiling points. Choices A, C, and D are all characteristics of covalent bonds, making them incorrect answers for this question.
Myelin sheath is a fatty substance that insulates and protects the long extensions of some nerve cells. It is produced by:
- A. Schwann cells
- B. Astrocytes
- C. Neurons
- D. Oligodendrocytes
Correct Answer: A
Rationale: Schwann cells are indeed responsible for producing the myelin sheath in the peripheral nervous system. These cells wrap around axons to form the myelin sheath, which enhances the speed of nerve impulse conduction. In the central nervous system, oligodendrocytes are responsible for producing the myelin sheath. Astrocytes provide support and maintenance functions for neurons, while neurons are the nerve cells themselves and do not produce myelin. Therefore, the correct answer is Schwann cells as they are specifically involved in myelin production in the peripheral nervous system.
According to Newton's third law of motion, if you push against a wall with a certain force, the wall will push back with:
- A. A smaller force
- B. An equal force
- C. A greater force
- D. No force at all
Correct Answer: B
Rationale: According to Newton's third law of motion, for every action, there is an equal and opposite reaction. When you push against a wall with a certain force, the wall will push back on you with an equal force in the opposite direction. Choice A is incorrect because the wall exerts an equal force back. Choice C is incorrect as it suggests a greater force, which goes against Newton's third law. Choice D is incorrect as the wall does exert a force back in response to your push.
Which radioactive isotope is commonly used in medical imaging techniques such as PET scans?
- A. Uranium-235
- B. Plutonium-239
- C. Potassium-40
- D. Fluorine-18
Correct Answer: D
Rationale: Fluorine-18 is the radioactive isotope commonly used in medical imaging techniques such as PET scans. It is frequently used in the form of fluorodeoxyglucose (FDG) to locate areas of heightened metabolic activity in the body, such as in cancer cells. Uranium-235 and Plutonium-239 are not typically employed in medical imaging, and Potassium-40, while a naturally occurring radioactive isotope found in the human body, is not commonly used in medical imaging techniques.