Correct Answer: B

Rationale: The correct answer is B: mycorrhizae. Mycorrhizae are symbiotic fungi that form a mutualistic relationship with plant roots, aiding in the absorption of minerals and water. They enhance the plant's nutrient uptake capacity, promoting plant growth and health. Decomposers (A) break down dead organic matter, yeasts (C) are single-celled fungi used in fermentation, and molds (D) are fungi that grow in multicellular filaments. These options do not specifically assist plant roots in mineral and water absorption like mycorrhizae do.

Correct Answer: A

Rationale: The correct answer is A: Gram-positive rod-shaped bacterium. Campylobacter fetus is actually a Gram-negative bacterium. This is because it has a thin peptidoglycan layer in its cell wall, which does not retain the crystal violet stain used in the Gram-staining technique. It appears red or pink under a microscope after counterstaining with safranin. Therefore, statement A is incorrect. B: Optimal temperature for cultivation 35-37C - Correct, as Campylobacter fetus thrives at this temperature range. C: Opportunistic pathogen causes infections usually in newborns, immunocompromised patients, and cancer - Correct, as Campylobacter fetus can cause infections in these populations. D: Fastidious, microaerophile - Correct, as Campylobacter fetus is fastidious and requires specific growth conditions, including low oxygen levels.

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: 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.

Correct Answer: A

Rationale: Correct Answer: A Rationale: 1. Enteropathogenic E. coli (EPEC) attach to enterocytes via a type III secretion system. 2. Once attached, they form attaching and effacing lesions on the microvilli, leading to microvillus destruction. 3. This mechanism allows EPEC to cause diarrhea by disrupting the normal absorptive function of the intestines. Summary: - B (They are invasive and produce enterotoxin) is incorrect because EPEC are non-invasive and do not produce enterotoxins. - C (Cause disease clinically similar to bacterial) is vague and does not provide specific information about EPEC pathogenesis. - D (None of the above) is incorrect as A is the correct explanation for EPEC pathogenicity.