Who accidentally identified the antimicrobial action of penicillin?

Correct Answer: C

Rationale: The correct answer is C: Alexander Fleming. Fleming discovered the antimicrobial action of penicillin in 1928 through his experiment with Staphylococcus bacteria. He noticed that mold from a contaminated petri dish inhibited the growth of the bacteria. Robert Koch (A) is known for his work in identifying specific bacteria causing diseases. Richard Petri (B) is not a known figure in the field of microbiology. Louis Pasteur (D) is famous for his germ theory and pasteurization, but he did not discover penicillin's antimicrobial action. Therefore, based on historical evidence and Fleming's specific contribution to microbiology, choice C is the correct answer.

Correct Answer: D

Rationale: The Calvin cycle is a series of biochemical reactions that take place in the stroma of chloroplasts during photosynthesis. It occurs in the dark phase (without direct light requirement), making choice D correct. Choice A is incorrect because the Calvin cycle is a C3 pathway, not C5. Choice B is incorrect because not all photoautotrophic microorganisms use the Calvin cycle; some use alternative pathways. Choice C is incorrect because C4 pathway is a different photosynthetic pathway that occurs in certain plants to minimize photorespiration.

Correct Answer: A

Rationale: Step-by-step rationale: 1. During an allergic reaction, allergens trigger the release of IgE antibodies. 2. The allergen binds with IgE antibodies, leading to the activation of mast cells. 3. Activated mast cells release histamine and other inflammatory mediators. 4. This cascade of events causes allergic symptoms. Therefore, option A is correct as it accurately describes the initial binding of allergen with IgE antibodies. Option B is incorrect as mast cells are activated, not deactivated. Option C is incorrect as the body is hypersensitive, not immunodeficient. Option D is incorrect as it is mast cells, not Helper T cells, that release histamine.

Correct Answer: B

Rationale: DNA ligase catalyzes the formation of phosphodiester bonds between the sugar-phosphate backbone of DNA strands. The correct answer is B because DNA ligase specifically acts on these phosphodiester bonds to seal nicks in the DNA molecule during processes like DNA replication and repair. Option A, ester bonds, are not formed by DNA ligase. Option C, phosphohydroxyl bonds, is not a recognized type of bond in DNA ligation. Option D, amide bonds, are not formed by DNA ligase either. Thus, the correct answer is B as it aligns with the known function of DNA ligase.

Correct Answer: B

Rationale: The correct answer is B: increased yield. If the amount of template in a PCR falls significantly below the optimal amount, it would be expected to result in a decreased yield rather than an increased yield. The template is essential for DNA amplification in PCR, and a lower amount would lead to fewer copies being produced. Non-specific amplification (choice A) can occur if there is too much template or incorrect primer annealing. Allelic drop-out (choice C) is likely to happen if there is insufficient template present to amplify all alleles. Longer targets amplifying poorly or failing (choice D) is also a common outcome when template concentration is low. Therefore, the least expected outcome would be an increased yield as that goes against the principle of PCR amplification.