The main structure components of Viruses are:

Correct Answer: C

Rationale: The correct answer is C: Nucleic acid and proteins. Viruses contain genetic material in the form of nucleic acids (DNA or RNA) surrounded by a protein coat. This genetic material carries instructions for viral replication. Proteins are also essential components of viruses, serving various functions like facilitating viral entry into host cells. Option A is incorrect as lipids are not main components of viruses. Option B is incorrect as lipids are not typically found in the main structure of viruses. Option D is incorrect as lipids are not primary components of viruses, and glycoproteins are not always present in the main structure of viruses.

Correct Answer: A

Rationale: The correct answer is A: Streptococcus pyogenes. Rationale: 1. Gram-positive cocci in pairs suggest Streptococcus species. 2. Catalase-negative rules out Staphylococcus. 3. Beta-hemolytic indicates Streptococcus pyogenes due to its beta-hemolytic properties. Summary: B: Streptococcus pneumoniae is catalase-negative but not beta-hemolytic. C: Enterococcus faecalis is not typically beta-hemolytic. D: Staphylococcus aureus is catalase-positive and not typically in pairs.

Correct Answer: A

Rationale: The correct answer is A (25-37 °C) because mesophilic bacteria thrive best at moderate temperatures typical of most environments, making 25-37 °C their optimum range. This range allows for optimal enzyme activity and growth. Choice B (55-65 °C) is incorrect as it is more suitable for thermophilic bacteria. Choice C (15-18 °C) is too low for mesophiles to thrive efficiently. Choice D (38-45 °C) is too high and is more suitable for thermophiles. Ultimately, the correct answer aligns with the typical temperature range where mesophilic bacteria are most active and abundant.

Correct Answer: A

Rationale: The correct answer is A: Clostridia. Fusiform spore-forming microorganisms that stain violet-blue with Gram's stain are characteristic of Clostridia. Clostridia are anaerobic, rod-shaped bacteria known for their ability to form spores and cause diseases such as tetanus and botulism. Summary of other choices: B: Streptococci are spherical, not fusiform, and typically do not form spores. C: Spirochaete are spiral-shaped bacteria and do not typically form spores. D: Actinomycete are filamentous bacteria that do not typically form spores and do not stain violet-blue with Gram's stain.

Correct Answer: C

Rationale: The correct answer is C: gram-negative bacteria have an outer membrane that acts as an extra barrier. This outer membrane in gram-negative bacteria contains lipopolysaccharides and porins, which restrict the entry of antibiotics like penicillin. The outer membrane acts as an additional layer of protection, making it harder for penicillin to penetrate and reach its target, the peptidoglycan layer. Choices A, B, and D do not directly address the specific mechanism of resistance seen in gram-negative bacteria. Choice A focuses on transpeptidase enzyme quantity, which is not the primary reason for penicillin resistance. Choice B refers to β-lactamase enzymes in the periplasmic space, which are actually enzymes that degrade penicillin and contribute to resistance, but this is not unique to gram-negative bacteria. Choice D mentions a thicker cell wall, which is a characteristic of gram-positive bacteria, not gram-negative bacteria.