NEET Zoology - MCQ Practice Questions

# Diagnosis of Vaginal Bleeding in Third Trimester with Previous Cesarean Deliveries

This clinical scenario involves a pregnant woman at 32 weeks gestation with vaginal bleeding and a significant obstetric history of three prior cesarean deliveries—key risk factors that guide differential diagnosis.

Step 1: Analyze the Clinical Presentation

Third trimester vaginal bleeding (after 20 weeks) narrows the differential to three main conditions:

The patient presents with vaginal bleeding without mention of abdominal pain or contractions, suggesting painless hemorrhage.

Step 2: Evaluate Risk Factors for Placenta Previa

Placenta previa risk increases with:

This patient has multiple strong risk factors for placenta previa.

Step 3: Distinguish from Other Conditions

The absence of pain and the classic risk factors point away from abruption and accreta.

Step 4: Clinical Diagnosis

Placenta previa—where the placenta partially or completely covers the internal cervical os—is the most common cause of painless third-trimester bleeding and is strongly associated with maternal age, multiparity, and prior uterine surgery.

Answer: Placenta previa (Option B)

The combination of painless vaginal bleeding at 32 weeks, advanced maternal age (35 years), and three previous cesarean deliveries makes placenta previa the most likely diagnosis. Confirmation requires transvaginal ultrasound to visualize placental location.

Elevated basal FSH (>10 IU/L on day 3) indicates reduced ovarian reserve, meaning fewer eggs remain in the ovaries, affecting fertility prognosis.

IVF is the gold standard for endometriosis-related infertility as it bypasses tubal and peritoneal factors. IUI has lower success rates in endometriosis. GIFT is rarely used now.

Cystic fibrosis typically results in congenital bilateral absence of vas deferens (CBAVD), leading to azoospermia with normal seminal fluid parameters (obstructive azoospermia).

In unexplained infertility, IVF allows multiple sperm-egg interactions and can overcome subtle defects in gamete interaction that cannot be detected by standard testing.

This law states that two species competing for identical resources in the same habitat cannot coexist; one will be outcompeted.

Understanding ecological terms and their definitions

Step 1: Analyze each option

Step 2: Match the key phrase "varies in different environmental contexts"

The question emphasizes that a species' role CHANGES depending on conditions — this is the ability to adapt and shift function, not a fixed characteristic. This is plasticity/versatility.

Step 3: Example confirmation

A generalist species like a crow eats different foods in different habitats (urban vs. rural) — demonstrating ecological plasticity, not fixed niche breadth.

Answer: (D) Ecological plasticity or ecological versatility

Biomagnification causes toxic substances like DDT and heavy metals to accumulate in higher concentrations as they move up the food chain, affecting apex predators most severely.

Himalayan glaciers are melting at accelerated rates due to climate change, threatening water supplies for millions in northern India and affecting downstream agriculture.

The tragedy of the commons occurs when individuals act in self-interest to exploit shared resources (like fisheries or forests), leading to overall depletion and collective loss.

While multiple factors contribute to ocean health, addressing single-use plastic directly tackles the primary source of marine plastic pollution through policy and behavioral change.

Inverted pyramids occur when individual organisms at lower trophic levels are larger (e.g., one tree supporting many insects).

Energy pyramids always show decreasing energy upward and cannot be inverted, making them the most reliable representation.

Biological control using natural enemies provides sustainable, long-term management without ecological disruption.

Agriculture accounts for ~70% of water use in India and will face severe stress due to changing precipitation patterns and increased evapotranspiration.

High biodiversity ecosystems typically show Shannon index values between 2.5-4.0, reflecting greater species diversity and evenness.

Niche partitioning allows different predator species to exploit different resources or hunting strategies, reducing direct competition.

Lotka-Volterra cycles show predator population lags behind prey by approximately 90 degrees, peaking after prey abundance increases.

Rising sea temperatures are the primary trigger for coral bleaching, causing symbiotic algae expulsion. Climate-induced warming of coastal waters around India's coral reefs (Andaman, Lakshadweep) directly causes bleaching events.

Small, isolated populations experience increased genetic drift, loss of genetic diversity, and inbreeding depression, reducing fitness and adaptive capacity, making them highly vulnerable to extinction from random events.