Ribosomes associated with cells or organelles have a certain size, which is expressed in Svedberg units. Which associations are incorrect?

Correct Answer: A

Rationale: The correct answer is A because cyanobacteria have ribosomes measured in 70s, not 80s. Ribosomes in prokaryotes are either 70s (composed of 50s and 30s subunits) or 80s in eukaryotes (60s and 40s subunits). Choices B, C, and D are incorrect because chloroplasts, photosynthetic bacteria, and green algal cytoplasm all have ribosomes measured in 70s or 80s, consistent with their cell types.

Correct Answer: A

Rationale: The correct answer is A: XHâ‚‚, Y. This is because the reduction potential of -50 mV for X/XHâ‚‚ indicates that X is more likely to lose electrons compared to Y with a reduction potential of +75 mV. Therefore, electrons would be removed from XHâ‚‚ (X) to reduce Y. Choice B is incorrect because Y has a higher reduction potential than XHâ‚‚, so electrons would not be removed from Y to reduce XHâ‚‚. Choices C and D are also incorrect as they do not consider the relative reduction potentials of X/XHâ‚‚ and Y/YHâ‚‚.

Correct Answer: C

Rationale: The correct answer is C, Cancer of the bone marrow. Autoimmune diseases occur when the immune system mistakenly attacks healthy cells. Rheumatoid arthritis, multiple sclerosis, and insulin-dependent diabetes are autoimmune diseases where the immune system targets specific tissues or organs. Cancer of the bone marrow, on the other hand, is a result of uncontrolled cell growth and division, not a malfunction of the immune system attacking the body's own tissues. Therefore, it is not considered an autoimmune disease.

Correct Answer: C

Rationale: The correct answer is C: Chromosomal DNA. Chromosomal DNA refers to the DNA found in the chromosomes of an organism's nucleus, carrying the majority of its genetic information. In molecular biology, the annotation C typically refers to the chromosomal DNA of the organism being studied. Plasmid DNA (choice B) and vector DNA (choice A) are extrachromosomal DNA elements that are separate from the chromosomal DNA. Recombinant DNA (choice D) is a DNA molecule formed by combining DNA from different sources, which can include chromosomal, plasmid, or vector DNA. Therefore, the correct choice is C as it specifically refers to the chromosomal DNA component.

Correct Answer: B

Rationale: The correct answer is B: Mg2+. Mg2+ is an essential cofactor for restriction endonuclease enzymes because it stabilizes the enzyme-substrate complex, promotes proper binding of the enzyme to DNA, and facilitates the catalytic activity of the enzyme. Mg2+ ions help in the coordination of the active site residues and the phosphate backbone of DNA, which is crucial for the cleavage of DNA strands. Zn2+, Co2+, and Ca2+ do not provide the necessary coordination and stabilization required for restriction endonuclease enzyme activity, making them incorrect choices.