Nokea
Which of the following nucleotides is only found in RNA?
- A. Adenine
- B. Uracil
- C. Guanine
- D. Thymine
Correct Answer: B
Rationale: The correct answer is B: Uracil. Uracil is a nucleotide base that is specifically found in RNA. In DNA, thymine replaces uracil. Adenine, guanine, and cytosine are nucleotides present in both RNA and DNA. Understanding the unique nucleotide composition of RNA and DNA is essential in molecular biology to comprehend the genetic information flow and transcription processes accurately. RNA uses uracil instead of thymine, which is a key distinction between the two nucleic acids.
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What causes osteoporosis?
- A. An increase in osteocyte activity while osteoclast activity continues at expected levels
- B. A decline in osteoblast activity while osteoclast activity continues at expected levels
- C. An increase in osteocyte activity while osteoblast activity continues at expected levels
- D. A decline in osteoclast activity while osteoblast activity continues at expected levels
Correct Answer: B
Rationale: Osteoporosis is a condition characterized by reduced bone density and mass, leading to brittle bones. Osteoblasts are cells responsible for forming new bone tissue, while osteoclasts break down old or damaged bone. In osteoporosis, there is a decrease in osteoblast activity, causing a net loss of bone as the breakdown surpasses formation. Meanwhile, osteoclast activity remains relatively stable. This imbalance between bone formation (osteoblast activity) and bone resorption (osteoclast activity) contributes to the development of osteoporosis by reducing bone strength and increasing susceptibility to fractures.
In pea plants, green pod color (G)is dominant to yellow pod color (g). A cross was done between a plant with green pods and plant with yellow pods. Of the resulting offspring. 50% had green pods and 50% had yellow pods. Which of the following we the genotypes of both present plants?
- A. GG X GG
- B. Gg × gg
- C. Gg × gg
- D. Gg × Gg
Correct Answer: D
Rationale: The 50% green and 50% yellow offspring suggests that one parent was heterozygous (Gg) and the other was homozygous recessive (gg), leading to a 1:1 ratio of green to yellow.
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.
Which of the following is used to determine a person's DNA sequence?
- A. hormones
- B. enzymes
- C. blood types
- D. genes
Correct Answer: D
Rationale: Genes are the correct choice for determining a person's DNA sequence. Genes carry genetic information that dictates various traits and characteristics in individuals. A person's unique DNA sequence is determined by the specific arrangement of nucleotides within their genes. Scientists can analyze genes to decode the DNA sequence that represents an individual's genetic composition.
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.