The single trap that costs marks in menstrual cycle questions: swapping which hormone dominates which phase. FSH and progesterone sound equally "hormonal," and under pressure aspirants assign them to the wrong half of the 28-day cycle.
The menstrual cycle averages 28 days and divides into four overlapping events (NCERT Class 12 Biology Chapter 2, page 40):
Menstrual phase (Days 1–5): Endometrium sheds. Progesterone and estrogen are at their lowest. FSH begins rising.
Follicular (proliferative) phase (Days 6–13): FSH from the anterior pituitary stimulates growth of ovarian follicles. The growing follicle secretes estrogen, which rebuilds the endometrium and inhibits FSH via negative feedback — but also primes the hypothalamus for positive feedback at high concentrations.
Ovulation (Day 14): A sharp LH surge (triggered by peak estrogen via positive feedback on GnRH/LH) ruptures the Graafian follicle, releasing the secondary oocyte.
Luteal (secretory) phase (Days 15–28): The ruptured follicle transforms into the corpus luteum, which secretes progesterone (dominant hormone) and some estrogen. Progesterone maintains the thickened endometrium and inhibits GnRH/FSH/LH. If no fertilisation occurs, the corpus luteum degenerates → progesterone drops → endometrium sheds → cycle resets.
The high-frequency trap: Questions give you a day number (e.g., "Day 20") and ask which hormone is dominant. Map it: Days 1–13 = follicular = FSH-driven (estrogen rising). Day 14 = LH peak. Days 15–28 = luteal = progesterone-dominant. Confusing LH surge with FSH dominance, or placing progesterone in the follicular phase, is the mark-losing error NTA exploits.
Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.
Which hormone is primarily responsible for the proliferation of endometrium during the follicular phase of the menstrual cycle?
Answer: B. Estrogen secreted by the developing follicle stimulates endometrial proliferation during the follicular phase (NCERT Class 12 Biology Chapter 2, page 40).
Why A is wrong: A is wrong because progesterone is the dominant hormone of the luteal phase (Days 15–28), not the follicular phase. (trap: phase-hormone swap)
Why C is wrong: C is wrong because LH surges briefly on Day 14 to trigger ovulation; it does not drive endometrial proliferation. (trap: phase-hormone swap)
Why D is wrong: D is wrong because FSH stimulates follicle growth in the ovary, but it is estrogen (from the follicle) that acts on the endometrium. (trap: confusing upstream signal with effector)
On approximately which day of a typical 28-day menstrual cycle does ovulation occur?
Answer: B. Ovulation occurs around Day 14 of the 28-day cycle, triggered by the LH surge (NCERT Class 12 Biology Chapter 2, page 40).
Why A is wrong: A is wrong because Day 5 is still within the menstrual phase (Days 1–5). (trap: phase-day mismatch)
Why C is wrong: C is wrong because Day 10 is mid-follicular phase when the follicle is still growing. (trap: premature ovulation assumption)
Why D is wrong: D is wrong because Day 21 falls in the luteal phase, well after ovulation. (trap: confusing luteal phase with ovulation)
The corpus luteum secretes which of the following hormones to maintain the endometrium during the luteal phase?
Answer: C. The corpus luteum primarily secretes progesterone along with some estrogen, maintaining the secretory endometrium (NCERT Class 12 Biology Chapter 2, page 40).
Why A is wrong: A is wrong because FSH and LH are anterior pituitary hormones, not products of the corpus luteum. (trap: confusing source gland)
Why B is wrong: B is wrong because FSH is from the anterior pituitary; while estrogen is partially correct, the pairing with FSH is incorrect. (trap: mixing pituitary and ovarian hormones)
Why D is wrong: D is wrong because GnRH is released by the hypothalamus, not the corpus luteum. (trap: confusing hypothalamic with ovarian secretion)
During the menstrual cycle, a high concentration of estrogen near the end of the follicular phase triggers a surge of LH via:
Answer: D. At high concentrations, estrogen switches from negative to positive feedback on the hypothalamus, stimulating GnRH release which drives the pre-ovulatory LH surge (NCERT Class 12 Biology Chapter 2, page 40).
Why A is wrong: A is wrong because negative feedback SUPPRESSES LH/FSH; the LH surge requires positive feedback — the opposite mechanism. (trap: confusing positive vs negative feedback)
Why B is wrong: B is wrong because progesterone receptor inhibition is not the mechanism for the LH surge; progesterone is low during the late follicular phase. (trap: fabricated mechanism)
Why C is wrong: C is wrong because the corpus luteum does not exist yet at this point — it forms only after ovulation. (trap: temporal sequence error)
If the corpus luteum degenerates without fertilisation, which sequence of events follows?
Answer: C. Degeneration of the corpus luteum causes progesterone to fall, which removes endometrial support, leading to shedding (menstruation) and the start of a new cycle (NCERT Class 12 Biology Chapter 2, page 40).
Why A is wrong: A is wrong because corpus luteum degeneration LOWERS progesterone; rising progesterone would maintain the endometrium, not lead to a new cycle. (trap: reversing the hormonal direction)
Why B is wrong: B is wrong because this describes the pre-ovulatory positive feedback loop, not the post-luteal event sequence. (trap: placing ovulatory events after corpus luteum degeneration)
Why D is wrong: D is wrong because FSH actually rises (not falls) after corpus luteum degeneration removes inhibition, recruiting new follicles. Amenorrhea does not result from a normal luteal regression. (trap: inverting feedback outcome)
A woman's blood sample taken on Day 22 of her cycle shows a high level of progesterone and low FSH. This hormonal profile indicates she is in the:
Answer: A. Day 22 falls in the luteal phase (Days 15–28), characterised by high progesterone from the corpus luteum and suppressed FSH due to negative feedback (NCERT Class 12 Biology Chapter 2, page 40).
Why B is wrong: B is wrong because the late follicular phase has rising estrogen and FSH activity, not high progesterone. (trap: assigning progesterone dominance to the wrong phase)
Why C is wrong: C is wrong because the ovulatory phase is a brief event (Day ~14) marked by an LH surge, not sustained high progesterone. (trap: confusing LH peak with progesterone peak)
Why D is wrong: D is wrong because the menstrual phase (Days 1–5) has LOW progesterone and RISING FSH — the opposite of the profile described. (trap: phase-hormone swap)
During the follicular phase, FSH promotes follicle growth. The growing follicle produces estrogen, which at moderate levels inhibits further FSH secretion. This is an example of:
Answer: A. Estrogen at moderate levels inhibits FSH release from the anterior pituitary — a classic negative feedback loop where the product suppresses its own upstream stimulus (NCERT Class 12 Biology Chapter 2, page 40).
Why B is wrong: B is wrong because positive feedback amplifies the stimulus (as estrogen does at HIGH levels before the LH surge); moderate-level inhibition is negative feedback. (trap: confusing the two estrogen feedback modes)
Why C is wrong: C is wrong because a neurohumoral reflex involves neural stimulation triggering hormonal release (e.g., suckling reflex); this is purely hormonal feedback. (trap: mis-categorising mechanism type)
Why D is wrong: D is wrong because autocrine signalling means a cell acts on itself via its own secretion; FSH comes from the pituitary and acts on follicular cells — this is endocrine, not autocrine. (trap: confusing signalling types)
Consider a 28-day menstrual cycle. The endometrium is at its maximum thickness and glandular activity on Day 24. Which TWO conditions must both be true for this to occur?
I. Corpus luteum is functional
II. FSH levels are at their cycle peak
III. Progesterone is maintaining the secretory endometrium
IV. LH surge is occurring
Answer: D. On Day 24 (luteal phase), the corpus luteum must be functional (secreting hormones) AND progesterone must be maintaining the secretory endometrium. These two conditions together explain maximum endometrial thickness (NCERT Class 12 Biology Chapter 2, page 40).
Why A is wrong: A is wrong because FSH levels are LOW (not at peak) during the luteal phase — progesterone-mediated negative feedback suppresses FSH. (trap: placing FSH peak in the wrong phase)
Why B is wrong: B is wrong because while III is correct, IV is not — the LH surge is a Day-14 event, not a Day-24 event. (trap: confusing ovulatory trigger with luteal maintenance)
Why C is wrong: C is wrong because BOTH statements are incorrect for Day 24: FSH is suppressed and the LH surge occurred 10 days earlier on Day 14. (trap: double temporal error)
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Given
A woman on Day 18 of her menstrual cycle shows a thickened, glandular endometrium with increased blood supply.
Required
Identify the dominant hormone responsible for this endometrial state and the ovarian structure producing it.
Concept
The menstrual cycle phases map hormones to days: follicular phase (Days 1–13, FSH/estrogen-driven), ovulation (Day 14, LH surge), luteal phase (Days 15–28, progesterone-dominant from corpus luteum).
Formula/Rule
Day number → Phase → Dominant hormone → Source structure.
Day 18 falls in Days 15–28 → Luteal phase → Progesterone → Corpus luteum.
Substitution
Day 18 ∈ [15, 28] → Luteal phase confirmed.
Endometrial maintenance + glandular secretion = hallmark of progesterone action.
Source = corpus luteum (transformed from ruptured Graafian follicle post-Day 14).
Calculation
No numerical calculation. Logical mapping:• Phase identification: 18 > 14 → post-ovulatory → luteal ✓• Hormone: progesterone (not estrogen, which drives proliferation in follicular phase) ✓• Structure: corpus luteum (not follicle — follicle already ruptured) ✓
Final answer
The dominant hormone is progesterone, secreted by the corpus luteum.
Common trap
Aspirants confuse the proliferative effect of estrogen (rebuilding endometrium in follicular phase) with the secretory/maintenance effect of progesterone (glandular transformation in luteal phase). Both thicken the endometrium — but the mechanism and phase differ. NEET exploits this by describing "thickened endometrium" and offering estrogen as a distractor for luteal-phase questions.
Similar NEET-style question
"On Day 25, a blood test shows high progesterone and low LH. Which ovarian structure is responsible for this hormonal profile? (A) Graafian follicle (B) Corpus luteum (C) Primary follicle (D) Corpus albicans."
Answer: B — the corpus luteum secretes progesterone during the luteal phase; corpus albicans is the degenerated remnant that no longer secretes hormones.
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28-day cycle with 4 phases: menstrual (1-5), follicular/proliferative (6-13), ovulatory (14 — LH surge), luteal/secretory (15-28). FSH → follicle growth, LH → ovulation + corpus luteum (progesterone). Estrogen + progesterone feedback.
-- NCERT Class 12 Biology, Ch. 2, p. 35These are the exact patterns that cause wrong answers in NEET. Each trap includes when it triggers and how to avoid it.
Category: Similar Terms
FSH dominant follicular phase; LH surge triggers ovulation Day 14; progesterone dominant in luteal phase.
Question gives day or phase and asks dominant hormone.
Follicular = FSH. Day 14 = LH peak. Luteal = progesterone (corpus luteum).
More in Reproduction: 9 exam traps and mistakes · 1 question pattern from its other lessons.
3 questions from NEET 2023, 2025, 2026. Answers verified against NTA official keys.
The first menstruation is called :
Page numbers are the ones printed in the current NCERT textbook (2023 rationalised edition), unless marked pre-2023. The books are free at ncert.nic.in.
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