NEET Zoology - MCQ Practice Questions

IUDs have failure rates of less than 1% in typical use, making them one of the most effective contraceptive methods available, with effectiveness approaching that of sterilization.

The notochord develops from cells of the primitive node (primitive pit) during gastrulation and serves as the primary organizer for embryonic development.

Trichomoniasis, caused by Trichomonas vaginalis, presents with greenish-yellow, frothy vaginal discharge and is the most common non-viral STI worldwide.

Endometriosis is characterized by ectopic endometrial tissue outside the uterus, causing dysmenorrhea, pelvic pain, and infertility due to inflammation and mechanical obstruction.

Maternal obesity, advanced age (>35 years), family history of diabetes, and previous gestational diabetes are significant risk factors for GDM.

Meiosis II is similar to mitosis; sister chromatids separate at anaphase II, resulting in four haploid cells from the two haploid cells formed after meiosis I.

Klinefelter syndrome (47,XXY) is the most common male chromosomal abnormality, presenting with azoospermia, hypogonadism, gynecomastia, and infertility.

Folic acid supplementation (400 mcg minimum, higher for high-risk women) during the periconceptional period reduces neural tube defects by 50-70%.

Ovulation typically occurs 14 days before the next menstruation. In a 28-day cycle, this corresponds to day 14 of the cycle, marking the middle of the proliferative phase.

An empty uterus with positive hCG indicates an ectopic pregnancy (implantation outside the uterus), which may present with vaginal bleeding, abdominal pain, and hemodynamic instability.

Levonorgestrel prevents or delays ovulation when given within 72 hours of unprotected intercourse and may also alter cervical mucus to impede sperm transport.

PCOS is characterized by elevated LH levels relative to FSH (typically LH:FSH ratio >3:1), along with hyperandrogenism and insulin resistance.

Oxytocin triggers the milk ejection reflex (letdown reflex), while prolactin stimulates milk production. Both hormones are essential for successful lactation.

# 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.

CMV is the most common congenital infection, affecting 0.5-1% of live births and causing microcephaly, hearing loss, and developmental delays if acquired in utero.

Spermatids undergo spermiogenesis (morphological changes) to transform into mature spermatozoa. This is the final stage of spermatogenesis.

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

The LNG-IUD releases levonorgestrel directly into the uterine cavity, causing endometrial atrophy and thickened cervical mucus, with effectiveness lasting 3-7 years.

LH acts on Leydig cells in the testes to stimulate testosterone synthesis and secretion. Low LH indicates secondary hypogonadism.

FSH directly stimulates Sertoli cells in seminiferous tubules to initiate spermatogenesis. While LH and testosterone support the process, FSH is the primary initiator.