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What is the half-life of a radioactive isotope, and how does it relate to its decay rate?
- A. The time it takes for half of the initial sample to decay.
- B. The time it takes for all of the sample to decay.
- C. The rate at which new isotopes are created.
- D. The energy released during decay.
Correct Answer: A
Rationale: The half-life of a radioactive isotope is the time it takes for half of the initial sample to decay. After one half-life, half of the radioactive atoms have decayed. The decay rate, however, refers to the rate at which radioactive atoms decay, which is not directly related to the half-life. Choice B is incorrect because it does not correctly define the half-life. Choice C is incorrect as it refers to the creation of new isotopes, not the decay process. Choice D is incorrect as it describes the energy released during decay, which is not the same as the concept of half-life.
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What is the primary function of B cells in the immune system?
- A. Directly attacking and engulfing pathogens
- B. Producing antibodies specific to a pathogen
- C. Destroying infected body cells
- D. All of the above
Correct Answer: B
Rationale: B cells are a type of white blood cell that primarily functions by producing antibodies specific to a pathogen. These antibodies play a crucial role in marking pathogens for destruction by other immune cells. While B cells are essential for the immune response, they do not directly attack and engulf pathogens or destroy infected body cells. These functions are carried out by other immune cells like macrophages and cytotoxic T cells. Therefore, the correct answer is B, as it accurately reflects the primary role of B cells in the immune system.
When an atom gains or loses electrons, it becomes a(n):
- A. Molecule
- B. Isotope
- C. Ion
- D. Compound
Correct Answer: C
Rationale: When an atom gains or loses electrons, it becomes an ion. Gaining or losing electrons alters the atom's electron count and charge, creating a positively or negatively charged ion. A molecule is formed when two or more atoms are chemically bonded. An isotope is a variation of an element with a different number of neutrons. A compound consists of two or more different elements chemically bonded together.
Where is the heart located within the human body cavities?
- A. Dorsal cavity
- B. Ventral cavity
- C. Thoracic cavity
- D. Abdominal cavity
Correct Answer: C
Rationale: The heart is located within the thoracic cavity, specifically in the mediastinum, which is the central compartment of the thoracic cavity. The thoracic cavity is part of the ventral cavity, which also includes the abdominal cavity. The dorsal cavity refers to the posterior side of the body and does not contain the heart. The heart is situated in the thoracic cavity between the lungs and above the diaphragm, making option C the correct choice. Therefore, the correct answer is the thoracic cavity (option C). The ventral cavity (option B) includes the thoracic and abdominal cavities, but the heart is specifically situated in the thoracic cavity. The dorsal cavity (option A) is located on the posterior side of the body, not where the heart is positioned. The abdominal cavity (option D) is below the thoracic cavity and houses organs such as the stomach, liver, and intestines, but it does not contain the heart.
During which phase of the cardiac cycle do the atria contract, pushing blood into the ventricles?
- A. Atrial diastole
- B. Ventricular systole
- C. Atrial systole
- D. Ventricular diastole
Correct Answer: C
Rationale: Atrial systole is the phase of the cardiac cycle during which the atria contract, pushing blood into the ventricles. This occurs after the atria have been filled during atrial diastole. Ventricular systole refers to the phase when the ventricles contract to push blood out of the heart, not when the atria contract. Ventricular diastole is the phase when the ventricles relax and fill with blood, not when the atria contract. Therefore, the correct answer is atrial systole as it specifically describes the atrial contraction phase.
What is the definition of the term 'momentum' in physics?
- A. Force exerted on an object
- B. Speed of an object in motion
- C. Mass in motion
- D. Distance traveled per unit time
Correct Answer: C
Rationale: Momentum in physics is the product of an object's mass and its velocity. It is a vector quantity that describes the motion of an object and is given by the formula p = mv, where p is momentum, m is mass, and v is velocity. Therefore, momentum is best described as the mass of an object in motion. Choice A, 'Force exerted on an object,' is incorrect because force is not equivalent to momentum. Choice B, 'Speed of an object in motion,' is incorrect because speed only considers the rate of motion and not the mass aspect. Choice D, 'Distance traveled per unit time,' is incorrect as it relates to speed and not momentum, which involves both mass and velocity.