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How does the body maintain a relatively constant blood pH level, even with changes in blood carbon dioxide concentration?
- A. Cellular respiration
- B. Gas exchange
- C. Buffering system
- D. Deoxygenation
Correct Answer: C
Rationale: The correct answer is C: Buffering system. The buffering system is responsible for maintaining a relatively constant blood pH level by minimizing changes in pH when acids or bases are added to the blood. This system consists of chemical compounds that can donate or accept protons to help stabilize the pH. Choice A, Cellular respiration, and Choice B, Gas exchange, are processes involved in gas exchange within the body, not specifically related to maintaining blood pH. Choice D, Deoxygenation, refers to the removal of oxygen from a substance and is not directly related to the regulation of blood pH.
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What is the name for the smallest amount of an element that can exist independently and retain its chemical properties?
- A. Atom
- B. Molecule
- C. Compound
- D. Mixture
Correct Answer: A
Rationale: The correct answer is 'Atom.' An atom is the fundamental unit of an element that can exist independently and retain its unique chemical properties. It consists of a nucleus containing protons and neutrons, surrounded by electrons. Choice B, 'Molecule,' is incorrect because a molecule is a combination of two or more atoms bonded together. Choice C, 'Compound,' is incorrect as a compound is a substance formed by the chemical combination of two or more different elements. Choice D, 'Mixture,' is incorrect since a mixture is a blend of two or more substances physically combined, but the individual components retain their properties.
Through which structure do the kidneys reabsorb water, salts, and nutrients and return them to the body?
- A. Renal artery
- B. Renal vein
- C. Nephron
- D. Glomerulus
Correct Answer: C
Rationale: The question has been corrected to specify the structure responsible for reabsorbing water, salts, and nutrients in the kidneys. The correct answer is the nephron, which is the functional unit of the kidney that performs filtration and reabsorption processes. The renal artery brings blood into the kidney for filtration, the renal vein carries filtered blood away from the kidney, and the glomerulus is a part of the nephron where filtration occurs. Therefore, the nephron is the structure that reabsorbs substances and returns them to the body.
What is the primary function of red blood cells?
- A. To transport nutrients
- B. To transport oxygen
- C. To fight infection
- D. To produce antibodies
Correct Answer: B
Rationale: The correct answer is B: To transport oxygen. Red blood cells play a crucial role in carrying oxygen from the lungs to all the tissues and organs in the body. This oxygen transport is essential for cellular respiration, where oxygen is used in the production of energy. Red blood cells do not primarily transport nutrients, fight infection, or produce antibodies. Choice A is incorrect because while red blood cells do carry some nutrients, their primary function is to transport oxygen. Choice C is incorrect because immune cells, not red blood cells, are responsible for fighting infections. Choice D is incorrect as antibody production is mainly carried out by specialized white blood cells, not red blood cells.
In a single displacement reaction, one element takes the place of another element in a compound. Which of the following is an example?
- A. 2H2 + O2 -> 2H2O
- B. Zn + 2HCl -> ZnCl2 + H2
- C. CaCO3 -> CaO + CO2
- D. CH4 + 2O2 -> CO2 + 2H2O
Correct Answer: B
Rationale: Option B demonstrates a single displacement reaction where zinc (Zn) displaces hydrogen (H) in hydrochloric acid (HCl) to produce zinc chloride (ZnCl2) and hydrogen gas (H2). This reaction exemplifies the concept of one element (Zn) replacing another element (H) in a compound (HCl), which is characteristic of single displacement reactions. Choices A, C, and D do not involve a single element displacing another in a compound, making them incorrect. In choice A, hydrogen and oxygen combine to form water, which is not a single displacement reaction. In choice C, calcium carbonate decomposes into calcium oxide and carbon dioxide, not involving displacement of elements. In choice D, methane reacts with oxygen to form carbon dioxide and water, which is a combustion reaction, not a single displacement reaction.
What is the building block of DNA?
- A. Amino acid
- B. Nucleotide
- C. Phosphate group
- D. Fatty acid
Correct Answer: B
Rationale: - Amino acids are the building blocks of proteins, not DNA.
- Nucleotide is the correct building block of DNA. A nucleotide consists of a sugar (deoxyribose in DNA), a phosphate group, and a nitrogenous base (adenine, thymine, cytosine, or guanine).
- The option 'C) Phosphate group' is incorrect as it is only part of a nucleotide, not the complete building block of DNA.
- Fatty acids are not the building blocks of DNA; they are a type of lipid molecule.