A patient with diarrhea had stool microscopy revealing large, oval protozoa with a single nucleus and four flagella. What is the most likely causative agent?

Correct Answer: A

Rationale: Step 1: Large, oval protozoa with a single nucleus and four flagella indicate Giardia lamblia. Step 2: Giardia lamblia is a flagellated protozoan causing diarrhea. Step 3: It has a distinct appearance under microscopy. Step 4: Entamoeba histolytica causes dysentery with no flagella. Step 5: Balantidium coli is a ciliated protozoan with a larger size. Step 6: Trichomonas vaginalis lacks a cyst stage and causes genitourinary infections.

Correct Answer: C

Rationale: The correct answer is C: Staphylococcus. Staphylococcus is a common bacteria that can cause neonatal conjunctivitis, also known as "sticky eye." Staphylococcal conjunctivitis presents with symptoms like eye redness, discharge, and swelling. Streptococcus (choice A) typically causes throat infections, herpes simplex (choice B) causes genital or oral sores, and Escherichia (choice D) is a bacteria commonly found in the gastrointestinal tract and is not typically associated with neonatal conjunctivitis. Therefore, the most likely pathogen causing "sticky eye" in newborns is Staphylococcus.

Correct Answer: D

Rationale: Bacteriophages are viruses that infect bacteria, not living organisms. They do not reproduce through division, mitosis, or meiosis because they lack the cellular machinery for these processes. Instead, bacteriophages replicate by inserting their genetic material into a host bacterium and hijacking its cellular machinery to produce new viral particles. Therefore, the correct answer is D - None of them. Division and mitosis involve cellular division in living organisms, while meiosis is a specialized process for sexual reproduction in eukaryotic organisms, none of which apply to bacteriophages.

Correct Answer: B

Rationale: The correct answer is B: intravenous administration. This route bypasses the first-pass metabolism, allowing the drug to directly enter the bloodstream for immediate distribution. In contrast, on the skin (A) and sublingual (D) routes have slower absorption rates due to barriers like skin layers or mucous membranes. Intramuscular (C) absorption is slower than intravenous due to slower perfusion rates in muscle tissues. Overall, intravenous administration provides the fastest and most direct route for drug absorption, making it the most rapid method.

Correct Answer: B

Rationale: The correct answer is B: homeostasis. Homeostasis refers to the process by which living organisms maintain a stable internal environment despite external changes. It involves various biological processes and mechanisms that regulate factors such as temperature, pH, and nutrient levels within narrow limits. This is crucial for the proper functioning of cells, tissues, and organs. Now, let's analyze the other choices: A: Infection - Infection refers to the invasion and multiplication of harmful microorganisms in the body, leading to illnesses. It is not the correct answer as it does not encompass the overall maintenance of internal conditions. C: Immunity - Immunity is the body's ability to resist and fight off infections. While immunity is related to defense against foreign agents, it does not fully capture the concept of maintaining internal stability. D: Commensalism - Commensalism is a type of symbiotic relationship between different species where one benefits without harming the other. It is not related to the overall regulation of