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What is the momentum of a car with a mass of 1500 kg moving at a speed of 20 m/s?
- A. 30,000 kg m/s
- B. 1500 kg m/s
- C. 20 kg m/s
- D. Momentum cannot be determined without knowing the direction of motion.
Correct Answer: A
Rationale: The momentum of an object is calculated by multiplying its mass by its velocity. In this case, the momentum of the car can be determined using the formula momentum = mass x velocity. Substituting the given values, momentum = 1500 kg x 20 m/s = 30,000 kg m/s. Therefore, the correct answer is A, 30,000 kg m/s. Choice B (1500 kg m/s) is incorrect because that value represents the mass of the car, not its momentum. Choice C (20 kg m/s) is incorrect as it only represents the speed of the car, not its momentum. Choice D (Momentum cannot be determined without knowing the direction of motion) is incorrect because momentum is a vector quantity and can be determined using magnitude and direction, but in this case, only the magnitude is required.
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How does RNA polymerase differ from DNA polymerase?
- A. Both enzymes are identical in function and structure.
- B. RNA polymerase does not require a primer to initiate RNA synthesis.
- C. RNA polymerase can synthesize both RNA and DNA.
- D. RNA polymerase can only synthesize RNA, unlike DNA polymerase.
Correct Answer: B
Rationale: Rationale:
A) This statement is incorrect. RNA polymerase and DNA polymerase are not identical in function and structure. They have different roles in the cell.
B) This statement is correct. Unlike DNA polymerase, RNA polymerase does not require a primer to initiate RNA synthesis. RNA polymerase can start the synthesis of RNA de novo.
C) This statement is incorrect. RNA polymerase is specialized for synthesizing RNA, not DNA. DNA polymerase is responsible for synthesizing DNA.
D) This statement is correct. RNA polymerase can only synthesize RNA, while DNA polymerase is responsible for synthesizing DNA.
What is the difference between a pure substance and a mixture?
- A. Pure substances have a fixed composition, mixtures don't.
- B. Mixtures have a fixed composition, pure substances don't.
- C. Pure substances can be in any state, mixtures are not always solids.
- D. Pure substances are always elements, mixtures are always compounds.
Correct Answer: A
Rationale: Pure substances have a definite and constant composition, meaning they are made up of only one type of atom or molecule with fixed proportions. This composition does not vary. On the other hand, mixtures are composed of two or more substances physically combined. The components of a mixture can be present in varying proportions, leading to a variable composition. Choice A is correct as it accurately distinguishes between pure substances and mixtures based on the fixed composition of pure substances and the variable composition of mixtures. Choice B is incorrect because mixtures, not pure substances, have variable compositions. Choice C is incorrect as both pure substances and mixtures can exist in different states. Choice D is incorrect because pure substances can be compounds as well, not exclusively elements, and mixtures can contain elements and compounds.
Which hormone plays a key role in stimulating the release of milk from breast tissue after childbirth?
- A. Follicle-stimulating hormone (FSH)
- B. Luteinizing hormone (LH)
- C. Prolactin
- D. Estrogen
Correct Answer: C
Rationale: Prolactin is the hormone responsible for stimulating the release of milk from breast tissue after childbirth. It is produced by the pituitary gland and plays a crucial role in lactation. Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are involved in the menstrual cycle and reproductive processes, not milk production. Estrogen is a female sex hormone with various functions but is not directly involved in milk production.
The neutral theory of molecular evolution proposes that:
- A. Most mutations in DNA are selectively neutral and do not affect an organism's fitness.
- B. All mutations are beneficial and contribute to the adaptation of a population.
- C. The rate of evolution is primarily driven by strong directional selection pressures.
- D. Genetic drift plays a negligible role in shaping genetic variation within populations.
Correct Answer: A
Rationale: Rationale:
A) The neutral theory of molecular evolution, proposed by Motoo Kimura in the 1960s, suggests that the majority of mutations that occur in DNA are selectively neutral, meaning they do not have a significant impact on an organism's fitness. These neutral mutations are not subject to natural selection and are allowed to accumulate in populations over time. This theory helps explain the high levels of genetic variation observed within populations.
B) Option B is incorrect because not all mutations are beneficial. Mutations can be neutral, harmful, or beneficial, and the neutral theory specifically focuses on the idea that many mutations are neutral in their effects.
C) Option C is incorrect because the neutral theory suggests that evolution is not primarily driven by strong directional selection pressures. Instead, it emphasizes the role of genetic drift and the accumulation of neutral mutations in shaping genetic variation.
D) Option D is incorrect because
Which of the following is the main function of the skin?
- A. To protect the body from harm
- B. To regulate body temperature
- C. To produce hormones
- D. To sense touch, temperature, and pain
Correct Answer: A
Rationale: Rationale:
A) To protect the body from harm: The skin acts as a physical barrier that protects the body from external threats such as pathogens, UV radiation, and physical injuries. It helps prevent infections and dehydration, making it a crucial function of the skin.
B) To regulate body temperature: While the skin does play a role in regulating body temperature through processes like sweating and vasodilation/vasoconstriction, its primary function is protection.
C) To produce hormones: Hormone production is primarily carried out by endocrine glands such as the pituitary gland, thyroid gland, and adrenal glands, not the skin.
D) To sense touch, temperature, and pain: The skin contains sensory receptors that allow us to perceive touch, temperature, and pain, but this function is secondary to its main role of protecting the body from harm.