MCQs

The correct option is Granulomatous lesions resulting from hypersensitivity reactions to remaining spirochetes. Gummas are soft, non-cancerous granulomatous growths that characterize tertiary syphilis. They are essentially a destructive delayed hypersensitivity immune response to localized persistent spirochete antigens.

The correct option is Latent stage. Following the disappearance of secondary stage symptoms, syphilis enters a latent phase where the patient is asymptomatic but retains the spirochetes in tissues, maintaining positive blood tests for antibodies.

The correct option is Neisseria gonorrhoeae. When a newborn passes through a birth canal infected with gonorrhea, the pathogen can infect the eyes, causing ophthalmia neonatorum. Routine prophylactic eye drops (e.g., erythromycin) are given to prevent this.

The correct option is CD4+ T-helper lymphocytes. HIV uses the CD4 receptor to enter and eventually destroy T-helper cells. The loss of these orchestrator cells severely impairs both humoral and cell-mediated immune responses, leading to AIDS.

The correct option is The HSV ulcer is preceded by painful fluid-filled vesicles. Genital herpes begins as painful vesicles (blisters) that rupture to form painful, shallow ulcers. The syphilitic chancre is a single, painless, firm (indurated) ulcer without a vesicular stage.

The correct option is Neonatal exposure to the virus during passage through the birth canal. Genital herpes is generally not transmitted across the placenta (unlike syphilis). Neonatal herpes is acquired via direct contact with infectious lesions in the birth canal, which a C-section bypasses.

The correct option is Herpes Simplex Virus type 2 (HSV-2). HSV-2 infects epithelial cells and then travels retrogradely up sensory nerve fibers to reside latently in the sacral ganglia. Stress or immunosuppression can trigger anterograde transport and recurrent painful blisters.

The correct option is Secondary stage. The secondary stage of syphilis is characterized by systemic spread of the spirochetes, leading to widespread mucocutaneous rashes, classically involving the palms and soles, along with systemic symptoms like fever and lymphadenopathy.

The correct option is Spirochete. Treponema pallidum is a thin, tightly coiled spirochete with endoflagella (axial filaments) that allow a corkscrew motion, enabling it to penetrate intact mucous membranes. Neisseria is a diplococcus.

The correct option is Syphilis. The primary stage of syphilis is characterized by a hard, painless ulcer known as a chancre at the site of infection. Genital herpes presents with painful blisters/ulcers. Gonorrhea typically presents with discharge, not an ulcer.

The correct option is Pelvic inflammatory disease (PID). In females, gonorrhea is often asymptomatic initially but can ascend to the uterus and fallopian tubes, causing PID. This leads to scarring, infertility, and ectopic pregnancy. Ulcers are typical of syphilis; blisters of herpes; cervical cancer is associated with HPV.

The correct option is Neisseria gonorrhoeae. The clinical presentation of purulent discharge and dysuria, combined with the microscopic finding of intracellular Gram-negative diplococci (coffee-bean shape), is the classic diagnostic hallmark of gonorrhea. Treponema is a spirochete, while HSV and HIV are viruses.

The Modern Synthesis integrated Darwinian natural selection with Mendelian genetics, mathematical population genetics, and chromosome theory to explain evolution at the molecular and population levels.

Evolution is the broader phenomenon (descent with modification), whereas natural selection is one of the primary mechanisms (alongside drift, gene flow, mutation) that drive it.

The selective pressure (predation) favors one extreme of the phenotypic spectrum (dark fur), causing a directional shift in the population's average fur color over time.

Disruptive selection splits the population's phenotypic profile into two distinct groups by selecting against the average/intermediate phenotype.

Speciation occurs gradually as populations diverge genetically and phenotypically in response to different selective pressures, eventually leading to reproductive isolation.

The HMS Beagle voyage (1831–1836) exposed Darwin to diverse ecosystems and fossil beds, particularly in South America and the Galapagos, which inspired his thinking on evolution.

Evolutionary fitness is defined solely by reproductive success; it is a measure of how many copies of its genes an individual passes on to subsequent, reproducing generations.