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What is the primary function of lymph nodes, small, bean-shaped structures found along lymphatic vessels?
- A. To store excess lymph fluid
- B. To produce red blood cells
- C. To filter lymph and fight infection
- D. To transport lymph to the heart
Correct Answer: C
Rationale: Lymph nodes primarily function to filter lymph and fight infection. They contain immune cells that help to remove pathogens and foreign particles from the lymph fluid as it passes through the nodes. This process helps to activate the immune response and defend the body against infections. Choice A is incorrect as lymph nodes do not store excess lymph fluid; they filter lymph. Choice B is incorrect as the production of red blood cells primarily occurs in the bone marrow, not in lymph nodes. Choice D is incorrect as lymph nodes do not transport lymph to the heart; they filter and process lymph to remove impurities and activate the immune response.
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In the cardiovascular system, what does the term 'double circulation' refer to?
- A. The separation of oxygenated and deoxygenated blood flow within the heart.
- B. The regulation of blood pressure through vasoconstriction and vasodilation.
- C. The cyclic contraction and relaxation of the heart muscle.
- D. The existence of two separate circulatory pathways, one for the lungs and one for the body.
Correct Answer: D
Rationale: The term 'double circulation' in the cardiovascular system refers to the existence of two separate circulatory pathways, one for the lungs (pulmonary circulation) and one for the body (systemic circulation). Oxygen-poor blood is pumped from the heart to the lungs for oxygenation, and then oxygen-rich blood is pumped from the lungs back to the heart to be circulated to the rest of the body. Choices A, B, and C are incorrect as they do not accurately describe the concept of 'double circulation.' Choice A refers to the separation of oxygenated and deoxygenated blood within the heart, choice B relates to blood pressure regulation mechanisms, and choice C describes the cardiac muscle's contraction and relaxation, none of which define 'double circulation' in the context of the cardiovascular system.
What happens to the frequency of a wave if its wavelength decreases while the speed remains constant?
- A. Frequency decreases
- B. Frequency increases
- C. Frequency remains constant
- D. Frequency becomes zero
Correct Answer: B
Rationale: The correct answer is B: Frequency increases. Frequency and wavelength are inversely proportional in a wave with a constant speed. When the wavelength decreases while the speed remains constant, the frequency must increase to maintain the constant speed of the wave. This relationship is governed by the equation: speed = frequency x wavelength. Choice A is incorrect as frequency increases when wavelength decreases. Choice C is incorrect as the frequency changes in this scenario. Choice D is incorrect as the frequency does not become zero but increases when the wavelength decreases.
Which of the following is NOT a factor affecting the rate of a chemical reaction?
- A. Concentration of reactants
- B. Temperature
- C. Presence of a catalyst
- D. Color of the reaction mixture
Correct Answer: D
Rationale: The color of the reaction mixture is not a factor affecting the rate of a chemical reaction. Factors such as the concentration of reactants, temperature, and the presence of a catalyst can influence the rate of a chemical reaction by affecting the frequency of collisions between reactant molecules and the energy of those collisions. The color of the reaction mixture is a physical property and does not directly impact the kinetics or speed of the reaction process. It is a qualitative observation that does not alter the reaction rate or mechanisms involved.
What is the role of RNA interference in silencing genes?
- A. Increases protein production
- B. Promotes gene mutation
- C. Inhibits the expression of specific genes
- D. Repairs damaged DNA
Correct Answer: C
Rationale: RNA interference (RNAi) is a biological process that involves the silencing of gene expression by inhibiting the translation of mRNA or by degrading mRNA molecules. This mechanism plays a crucial role in regulating gene expression and can be used to selectively silence specific genes. By interfering with the expression of specific genes, RNAi can downregulate protein production from those genes. Therefore, option C, 'Inhibits the expression of specific genes,' is the correct role of RNA interference in silencing genes. Options A, B, and D are incorrect because RNA interference does not increase protein production, promote gene mutation, or repair damaged DNA; its primary function is to inhibit gene expression by degrading or interfering with mRNA.
Which type of waves require a medium (solid, liquid, or gas) to propagate?
- A. Transverse waves
- B. Longitudinal waves
- C. Electromagnetic waves
- D. Surface waves
Correct Answer: B
Rationale: Longitudinal waves require a medium (solid, liquid, or gas) to propagate because the particles in the medium move parallel to the direction of the wave. As a result, they rely on the medium for transmission. Transverse waves, on the contrary, do not need a medium and can travel through a vacuum, making choice A incorrect. Electromagnetic waves, represented by choice C, do not require a medium as they consist of oscillating electric and magnetic fields that can propagate through a vacuum. Surface waves, the option in D, involve a combination of both longitudinal and transverse motion and do require a medium to travel, but longitudinal waves are the ones that strictly depend on a medium for propagation.