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Why do chloride ions have a negative charge?
- A. It lost a proton.
- B. It gained a proton.
- C. It gained an electron.
- D. It lost an electron.
Correct Answer: C
Rationale: Chloride ions (Cl-) have a negative charge because they gained an electron. When an atom gains an electron, it increases the number of negative charges relative to positive charges, resulting in a net negative charge, as seen in chloride ions. In the case of chloride ions, a chlorine atom gains an extra electron to achieve a stable electron configuration, turning it into a chloride ion with a negative charge.
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Which of the following tools can be used to measure the turbidity of a liquid by assessing the transmission of light through the sample?
- A. Spectrophotometer
- B. Microdensitometer
- C. Electrophoresis apparatus
- D. Centrifuge
Correct Answer: A
Rationale: A spectrophotometer is an instrument commonly employed to determine the amount of light absorbed by a substance in a liquid sample. Turbidity, the cloudiness or haziness of a liquid due to suspended particles, can be quantified using a spectrophotometer by analyzing the transmission of light through the sample. In contrast, a microdensitometer measures optical density, an electrophoresis apparatus separates macromolecules based on size and charge, and a centrifuge isolates substances according to density or size via centrifugal force. None of the alternative tools directly relate to assessing turbidity through light transmission, making option A, the spectrophotometer, the correct choice.
In a plant in which fuzzy leaves (F) are dominant over smooth leaves (f), which of the following crosses will reproduce only offspring with smooth leaves?
- A. FF by ff
- B. ff by ff
- C. Ff by Ff
- D. FF by FF
Correct Answer: B
Rationale: The correct answer is B: 'ff by ff.' When a plant with fuzzy leaves (Ff) is crossed with another plant with smooth leaves (ff), all the offspring will inherit one smooth leaf allele from the smooth-leaved parent, resulting in only smooth leaves. The genotype of the offspring will be ff, leading to the expression of smooth leaves. This cross ensures that both alleles for leaf texture are the recessive smooth allele (f), resulting in all offspring having smooth leaves.
The breakdown of lactose in the small intestine is mediated by the enzyme lactase, and the products are galactose and glucose. Galactose and glucose are which of the following?
- A. Disaccharides
- B. Oligosaccharides
- C. Polysaccharides
- D. Monosaccharides
Correct Answer: D
Rationale: Galactose and glucose are both simple sugars consisting of single sugar units. Therefore, they are classified as monosaccharides. This makes option D the correct answer.
Which laboratory method is most useful to separate genomic DNA fragments by size?
- A. Titration
- B. Spectrophotometry
- C. Electrophoresis
- D. Filtration
Correct Answer: C
Rationale: Electrophoresis is the most suitable laboratory method for separating genomic DNA fragments by size. It works by subjecting DNA fragments to an electric field, causing them to migrate through a gel matrix based on size differences. Smaller fragments move faster and travel farther than larger ones, allowing for separation and analysis based on size. Titration is a technique used to determine the concentration of a solution, not to separate DNA fragments by size. Spectrophotometry is used to measure the amount of light absorbed by a substance at different wavelengths, not for DNA fragment size separation. Filtration is a method used to separate solid particles from a liquid or gas by passing it through a filter medium, not for separating DNA fragments by size.
The triple point of a substance is the temperature and pressure at which the substance exists as which of the following?
- A. As a gel with solid and liquid trapped in gas
- B. Simultaneously in sol, gel, and plasma phases
- C. Simultaneously in solid, liquid, and gas phases
- D. As a sol with gas and solid trapped in liquid
Correct Answer: C
Rationale: The triple point is a specific condition where a substance can exist simultaneously in all three phases: solid, liquid, and gas. The other options do not accurately describe this state.