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NEET Zoology

Zoology questions for NEET UG — Animal Kingdom, Human Physiology, Genetics, Evolution.

540 Q 6 Topics Take Test
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Difficulty: All Easy Medium Hard 191–200 of 540
Topics in NEET Zoology
During in vitro fertilization (IVF), what is the purpose of using GnRH agonists in the downregulation phase?
A To increase FSH levels for superovulation
B To suppress endogenous GnRH, preventing premature LH surge
C To directly stimulate ovarian follicles
D To increase progesterone production
Correct Answer:  B. To suppress endogenous GnRH, preventing premature LH surge
EXPLANATION

GnRH agonists cause initial stimulation followed by desensitization, suppressing endogenous LH and FSH to prevent premature ovulation during controlled ovarian hyperstimulation.

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Q.192 Medium Reproductive Health
A 32-year-old woman presents with amenorrhea and galactorrhea. Pregnancy test is negative. Which investigation would be MOST diagnostic?
A Serum prolactin levels
B FSH and LH levels
C Thyroid function tests
D Estrogen level estimation
Correct Answer:  A. Serum prolactin levels
EXPLANATION

Galactorrhea with amenorrhea strongly suggests hyperprolactinemia. Serum prolactin >200 ng/mL indicates pituitary adenoma, while TSH should also be checked for secondary hyperprolactinemia.

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Q.193 Medium Reproductive Health
What is the primary advantage of Copper-T (Cu-IUD) over hormonal IUDs in terms of side effects?
A No hormonal side effects and longer duration of action
B Heavier menstrual bleeding compared to hormonal IUDs
C Higher expulsion rates
D Requires replacement every 2 years
Correct Answer:  A. No hormonal side effects and longer duration of action
EXPLANATION

Cu-IUDs work non-hormonally, avoiding systemic hormonal side effects. They are effective for 10 years, longer than some hormonal variants.

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Which hormone is essential for maintaining the corpus luteum during the first 8 weeks of pregnancy?
A Estrogen
B Human Chorionic Gonadotropin (hCG)
C Human Placental Lactogen (hPL)
D Follicle Stimulating Hormone (FSH)
Correct Answer:  B. Human Chorionic Gonadotropin (hCG)
EXPLANATION

hCG produced by trophoblastic cells maintains the corpus luteum until week 8-10, after which placental progesterone takes over luteal function.

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A couple has been trying to conceive for 2 years without success. The male partner has normal semen analysis. What is the next appropriate investigation for the female partner?
A Hysterosalpingography (HSG)
B Laparoscopy
C Hormone level assessment (Day 3 FSH, LH)
D Pelvic ultrasound for ovarian assessment
Correct Answer:  A. Hysterosalpingography (HSG)
EXPLANATION

HSG is the first-line radiological investigation for assessing tubal patency and uterine cavity in suspected secondary infertility after normal male factor evaluation.

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Q.196 Medium Reproductive Health
Which of the following STIs can be VERTICAL transmitted (from mother to child)?
A Chlamydia trachomatis only
B Syphilis and HIV
C Gonorrhea and Chlamydia only
D All STIs can be vertically transmitted
Correct Answer:  B. Syphilis and HIV
EXPLANATION

Syphilis (causes congenital syphilis), HIV, Hepatitis B, and HSV can be vertically transmitted. Chlamydia and gonorrhea cause neonatal infections but are acquired during delivery.

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What is the correct chronological order of events during the menstrual cycle?
A Menstruation → Proliferative phase → Ovulation → Secretory phase
B Proliferative phase → Menstruation → Ovulation → Secretory phase
C Menstruation → Proliferative phase → Secretory phase → Ovulation
D Ovulation → Proliferative phase → Secretory phase → Menstruation
Correct Answer:  A. Menstruation → Proliferative phase → Ovulation → Secretory phase
EXPLANATION

The menstrual cycle begins with menstruation (days 1-5), followed by proliferative phase (days 5-14), ovulation (day 14), and secretory/luteal phase (days 15-28).

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Q.198 Medium Reproductive Health
Which stage of spermatogenesis is most sensitive to radiation damage?
A Spermatogonial stage
B Primary spermatocyte stage
C Secondary spermatocyte stage
D Spermatid stage
Correct Answer:  A. Spermatogonial stage
EXPLANATION

Spermatogonial stem cells are most radiosensitive. Damage here affects all subsequent stages. Recovery takes 74 days (duration of spermatogenesis).

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A 28-year-old female reports irregular menstrual cycles with excessive bleeding. Laboratory tests show elevated FSH and normal prolactin levels. What could be the likely diagnosis?
A Hyperprolactinemia
B Premature Ovarian Insufficiency (POI)
C Thyroid dysfunction
D Polycystic Ovary Syndrome
Correct Answer:  B. Premature Ovarian Insufficiency (POI)
EXPLANATION

Elevated FSH with irregular cycles indicates diminished ovarian reserve characteristic of POI. PCOS typically shows normal or low FSH with hyperandrogenism.

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Q.200 Medium Reproductive Health
What is the primary mechanism of action of levonorgestrel as an emergency contraceptive?
A Prevents implantation of blastocyst
B Inhibits or delays ovulation when taken before LH surge
C Causes uterine contractions to expel fertilized ovum
D Damages sperm motility in female reproductive tract
Correct Answer:  B. Inhibits or delays ovulation when taken before LH surge
EXPLANATION

Levonorgestrel primarily works by inhibiting or delaying ovulation, especially effective within 72 hours before ovulation. It does not act as an abortifacient.

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