Fertilization Pregnancy

8 MCQs9-step worked example
Source: NCERT Anatomy of Flowering PlantsPYQ coverage: NEET 2020, 2021, 2022, 2023, 2024, 2025Official key: NTA-verifiedLast reviewed: May 2026

Lesson

The trap: NEET repeatedly tests whether you confuse the hormonal trigger of parturition with the hormone that maintains pregnancy. Progesterone maintains pregnancy — it does NOT trigger labour. Oxytocin triggers uterine contractions via positive feedback. Getting this backward costs you marks under negative marking.

Fertilisation and early development. Fertilisation occurs in the ampulla (ampullary-isthmic junction) of the fallopian tube (NCERT Class 12 Biology Chapter 2, page 45). The zygote undergoes cleavage divisions during its transit through the oviduct, forming a blastocyst. Implantation occurs approximately 6–7 days after fertilisation, when the blastocyst embeds in the uterine endometrium. The trophoblast layer establishes contact with the endometrium for nutrient exchange.

Pregnancy. After implantation, the chorion develops finger-like villi that interdigitate with uterine tissue to form the placenta. The placenta secretes human chorionic gonadotropin (hCG) — not the anterior pituitary. hCG maintains the corpus luteum during the first trimester so that progesterone production continues. Later, the placenta itself produces progesterone, oestrogen, and human placental lactogen (hPL).

Parturition. At term (~9 months), signals from the foetus (foetal cortisol) initiate a cascade. Oxytocin from the posterior pituitary stimulates uterine smooth muscle contractions. These contractions stimulate more oxytocin release — a positive feedback loop (neuroendocrine reflex). Prostaglandins amplify contractions. Progesterone levels fall before parturition; it does not drive contractions.

Lactation. Prolactin (anterior pituitary) stimulates milk production. Oxytocin triggers milk ejection (let-down reflex). Colostrum, the first secretion, contains antibodies (IgA) providing passive immunity to the newborn.

Watch-out: hCG source = placenta (not pituitary). Parturition trigger = oxytocin (not progesterone). Implantation timing = day 6–7 post-fertilisation.

Practice MCQs

Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.

MCQ 1Easy RecallPractice

Where does fertilisation normally occur in the human female reproductive tract?

MCQ 2Easy RecallPractice

Implantation of the human blastocyst in the uterine endometrium occurs approximately:

MCQ 3Easy RecallPractice

Human chorionic gonadotropin (hCG) is secreted by:

MCQ 4Direct ApplicationPractice

Which hormone is primarily responsible for triggering uterine contractions during parturition?

MCQ 5Direct ApplicationPractice

During parturition, oxytocin release increases progressively because of:

MCQ 6Direct ApplicationPractice

The function of hCG during early pregnancy is to:

MCQ 7Concept TrapPractice

A student claims that progesterone triggers labour. Which of the following corrections is accurate?

MCQ 8Easy RecallPractice

Which of the following statements about lactation is correct?

Worked Example

  1. 1

    Given

    - Early pregnancy (week 6) - Corpus luteum removed surgically - Placenta not yet fully functional for steroid production

  2. 2

    Required

    Predict the consequence of corpus luteum removal at this stage.

  3. 3

    Concept

    During weeks 1–8 of pregnancy, the corpus luteum is the primary source of progesterone. hCG (from the placenta) maintains the corpus luteum. Progesterone maintains the endometrium and suppresses uterine contractions. If progesterone supply ceases before the placenta assumes production (~week 8–12), the endometrium cannot be maintained.

  4. 4

    Key relationships

    - hCG → maintains corpus luteum → progesterone secretion - Progesterone → maintains endometrium → sustains pregnancy - Remove corpus luteum at week 6 → progesterone drops → endometrium degenerates

  5. 5

    Reasoning chain

    Corpus luteum removed → no progesterone source (placenta not ready) → endometrial breakdown → spontaneous abortion (miscarriage).

  6. 6

    Conclusion

    The most likely consequence is spontaneous abortion due to progesterone withdrawal, since the placenta has not yet taken over progesterone production at week 6.

  7. 7

    Final answer

    Removal of corpus luteum at week 6 leads to **spontaneous abortion** because the placenta cannot yet sustain adequate progesterone levels to maintain the endometrium.

  8. 8

    Common trap

    Students may say "hCG levels drop" — but hCG is from the placenta, not the corpus luteum. Removing the corpus luteum does not directly reduce hCG; it removes the TARGET of hCG. The consequence is progesterone loss, not hCG loss. Also, confusing this with late pregnancy (when the placenta is self-sufficient) leads to the wrong answer — after week 12, corpus luteum removal has minimal effect.

  9. 9

    Similar NEET-style question

    "If hCG secretion were blocked during week 4 of pregnancy, what would be the expected outcome?" (Answer: corpus luteum degenerates → progesterone falls → miscarriage — same reasoning chain but triggered one step earlier.) ---

Before solving, remember these

Key Fact

Pregnancy & lactation

Fertilization → zygote → cleavage → blastocyst → implantation (~6-7 days). hCG maintains corpus luteum first 3 months. Placenta develops; oxytocin → parturition. Prolactin → milk; oxytocin → milk ejection. Colostrum rich in IgA antibodies.

-- NCERT Class 12 Biology, Ch. 2, p. 45

Exam Traps & Common Mistakes

These are the exact patterns that cause wrong answers in NEET. Each trap includes when it triggers and how to avoid it.

Trap

Contraceptive method category confusion

Category: Similar Terms

Hormonal: pills, implants. Barrier: condom, diaphragm. IUD: Cu releasing (CuT), hormonal (LNG-20). Surgical: vasectomy/tubectomy.

When it triggers

Question asks which category a specific method falls in.

How to avoid

Map by mechanism: hormone → pill/implant; physical block → barrier; uterine → IUD; permanent → surgical.

Trap

Implantation day confusion

Category: Negative Marking

Fertilisation in ampulla; cleavage during journey; implantation occurs ~6-7 days after fertilisation in uterine endometrium.

When it triggers

Question on day of implantation, location of fertilisation.

How to avoid

Fertilisation = ampulla. Implantation = day 6-7 post-fertilisation in uterus.

Trap

Menstrual cycle phase hormones swapped

Category: Similar Terms

FSH dominant follicular phase; LH surge triggers ovulation Day 14; progesterone dominant in luteal phase.

When it triggers

Question gives day or phase and asks dominant hormone.

How to avoid

Follicular = FSH. Day 14 = LH peak. Luteal = progesterone (corpus luteum).

Trap

Spermatogenesis vs oogenesis product confusion

Category: Similar Terms

Spermatogenesis: 1 spermatogonium → 4 sperm (all functional). Oogenesis: 1 oogonium → 1 functional ovum + 3 polar bodies.

When it triggers

Question on number of functional gametes per primary cell.

How to avoid

Sperm: 4. Ovum: 1 (with 3 polar bodies discarded).

Mistake

Says oogenesis produces 4 ova per oogonium.

Root cause: term confusion

Correction

Oogenesis yields ONLY 1 functional ovum + 3 (or 1 + 2) polar bodies that degenerate. Asymmetric cytokinesis preserves cytoplasm in the egg.

Past Year Questions

48 questions from NEET 2020, 2021, 2022, 2023, 2024, 2025. Answers verified against NTA official keys.

NEET 2025

Consider the following : A. The reductive division for the human female gametogenesis starts earlier than that of the male gametogenesis. B. The gap between the first meiotic division and the second meiotic division is much shorter for males compared to females. C. The first polar body is associated with the formation of the primary oocyte. D. Luteinizing Hormone (LH) surge leads to disintegration of the endometrium and onset of menstrual bleeding. Choose the correct answer from the options given below:

1B and C are true
2A and B are true
3A and C are true
4B and D are true
NTA Answer: Option 2(final)
NEET 2025

Given below are two statements : One is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : Both wind and water pollinated flowers are not very colourful and do not produce nectar. Reason (R) : The flowers produce enormous amount of pollen grains in wind and water pollinated flowers. In the light of the above statements, choose the correct answer from the options given below:

1A is false but R is true
2Both A and R are true and R is the correct explanation of A
3Both A and R are true but R is NOT the correct explanation of A
4A is true but R is false
NTA Answer: Option 3(final)
NEET 2025

Given below are two statements: Statement I: In a floral formula stands for zygomorphic nature of the flower, and G stands for inferior ovary. Statement II: In a floral formula stands for actinomorphic nature of the flower and G stands for superior ovary. In the light of the above statements, choose the correct answer from the options given below:

1Statement I is incorrect but Statement II is correct
2Both Statement I and Statement II are correct
3Both Statement I and Statement II are incorrect
4Statement I is correct but Statement II is incorrect
NTA Answer: Option 1(final)
NEET 2024

Identify the set of correct statement: A. The flowers of Vallisneria are colourful and produce nectar. B. The flowers of waterlily are not pollinated by water. C. In most of water-pollinated species, the pollen grains are protected from wetting. D. Pollen grains of some hydrophytes are long and ribbon like. E. In some hydrophytes, the pollen grains are carried passively inside water. Choose the correct answer from the options given below.

1C, D and E only
2A, B, C and D only
3A, C, D and E only
4B, C, D and E only
NTA Answer: Option 4(final)
NEET 2024

Identify the correct description about the given figure:

1Wind pollinated plant inflorescence showing flowers with well exposed stamens.
2Water pollinated flowers showing stamens with mucilaginous covering.
3Cleistogamous flowers showing autogamy.
4Compact inflorescence showing complete autogamy
NTA Answer: Option 1(final)
NEET 2024

Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R : Assertion A : FSH acts upon ovarian follicles in female and Leydig cells in male. Reason R : Growing ovarian follicles secrete estrogen in female while interstitial cells secrete androgen in male human being. In the light of the above statements, choose the correct answer from the options given below :

1Both A and R are true and R is the correct explanation of A
2Both A and R are true but R is NOT the correct explanation of A
3A is true but R is false
4A is false but R is true
NTA Answer: Option 4(final)
NEET 2023

Given below are two statements: one is labelled as Assertion A and other is labelled as Reason R. Assertion A : Amniocentesis for sex determination is one of the strategies of Reproductive and Child Health Care Programme. Reason R : Ban on amniocentesis checks increasing menace of female foeticide. In the light of the above statements, choose the correct answer from the options given below.

1Both A and R are true and R is NOT the correct explanation of A.
2A is true but R is false.
3A is false but R is true.
4Both A and R are true and R is the correct explanation of A.
NTA Answer: Option 3(final)
NEET 2023

Which of the following statements are correct regarding female reproductive cycle? A. In non-primate mammals cyclical changes during reproduction are called oestrus cycle. B. First menstrual cycle begins at puberty and is called menopause. C. Lack of menstruation may be indicative of pregnancy. D. Cyclic menstruation extends between menarche and menopause. Choose the most appropriate answer from the options given below.

1A and B only
2A, B and C only
3A, C and D only
4A and D only
NTA Answer: Option 3(final)
NEET 2023

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R. Assertion A: Endometrium is necessary for implantation of blastocyst. Reason R: In the absence of fertilization, the corpus luteum degenerates that causes disintegration of endometrium. In the light of the above statements, choose the correct answer from the options given below:

1Both A and R are true but R is NOT the correct explanation of A.
2A is true but R is false.
3A is false but R is true.
4Both A and R are true and R is the correct explanation of A.
NTA Answer: Option 1(final)
NEET 2022

Identify the incorrect statement related to Pollination :

1Moths and butterflies are the most dominant pollinating agents among insects
2Pollination by water is quite rare in flowering plants
3Pollination by wind is more common amongst abiotic pollination
4Flowers produce foul odours to attract flies and beetles to get pollinated
NTA Answer: Option 1(final)
NEET 2022

Given below are two statements : Statement I : Cleistogamous flowers are invariably autogamous Statement II : Cleistogamy is disadvantageous as there is no chance for cross pollination In the light of the above statements, choose the correct answer from the options given below :

1Statement I is incorrect but Statement II is correct
2Both Statement I and Statement II are correct
3Both Statement I and Statement II are incorrect
4Statement I is correct but Statement II is incorrect
NTA Answer: Option 2(final)
NEET 2022

Given below are two statements: Statement I : The release of sperms into the seminiferous tubules is called spermiation. Statement II : Spermiogenesis is the process of formation of sperms from spermatogonia. In the light of the above statements, choose the most appropriate answer from the options given below :

1Statement I is incorrect but Statement II is correct
2Both Statement I and Statement II are correct
3Both Statement I and Statement II are incorrect
4Statement I is correct but Statement II is incorrect
NTA Answer: Option 4(final)
NEET 2021

Match List-I with List-II.

1(iv) (ii) (i) (iii)
2(iv) (i) (iii) (ii)
3(iii) (i) (iv) (ii)
4(ii) (iii) (iv) (i)
NTA Answer: Option 3(final)
NEET 2021

Which of the following statements of incorrect? 148. Match List-I with List-II.

1Oxidation-reduction reactions produce proton List-I List-II gradient in respiration (a) Protein (i) C = C double bonds
2During aerobic respiration, role is oxygen is (b) Unsaturated (ii) Phosphodiester limited to the terminal state fatty acid bonds (c) Nucleic acid (iii) Glycosidic bonds
3In ETC (Electron Transport Chain), one molecule of NADH + H+ gives rise to 2 ATP molecules, (d) Polsyaccharide(iv) Peptide bonds and one FADH gives rise to 3 ATP molecules 2 (a) (b) (c) (d)
4ATP is synthesized through complex V (1) (iv) (iii) (i) (ii)
NTA Answer: Option 3(final)
NEET 2021

Which of the following is not a step in Multiple (4) (b) and (c) only Ovulation Embryo Transfer Technology (MOET)?

1Fertilized eggs are transferred to surrogate Answer (4) mothers at 8-32 cell stage 197. Following are the statements about prostomium of
2Cow is administered hormone having LH like earthworm. activity for super ovulation (a) It serves as a covering for mouth.
3Cow yields about 6-8 eggs at a time (b) It helps to open cracks in the soil into which it
4Cow is fertilized by artifical insemination can crawl.
NTA Answer: Option 2(final)
NEET 2020

¬ÊŒ¬ ∑§Ê fl„ ÷ʪ ∑§ÊÒŸ-‚Ê „Ò Á¡‚◊ ŒÊ ¬Ë…∏Ë - ∞∑§ ¬Ë…∏Ë 92. The plant parts which consist of two generations - one within the other : ŒÍ‚⁄ U ∑ § •ãŒ⁄U „Ê ÃË „Ò? (a) Pollen grains inside the anther (a) ¬⁄Uʪ∑§Ê ‡Ê ∑ § •ãŒ⁄U ¬⁄Uʪ∑§áÊ (b) ŒÊ Ÿ⁄U ÿÈÇ◊∑§Ê flÊ‹Ë • ∑ȧÁ⁄Uà ¬⁄Uʪ∑§áÊ (b) Germinated pollen grain with two male gametes (c) »§‹ ∑ § •ãŒ⁄U ’Ë¡ (d) ’Ë¡Êá«U ∑ § •ãŒ⁄U ÷Í˝áÊ-∑§Ê (c) Seed inside the fruit

1(a) •Ê⁄Ò U (d) (d) Embryo sac inside the ovule
2∑ §fl‹ (a) (1) (a) and (d)
3(a), (b) •ÊÒ⁄U (c) (2) (a) only
4(c) •ÊÒ⁄U (d) (3) (a), (b) and (c) (4) (c) and (d)
NTA Answer: Option 1(final)
NEET 2020

ÿÊÒŸ ‚ øÁ⁄Uà ⁄UÊ ªÊ ∑ § ‚„Ë Áfl∑§À¬ ∑§Ê øÿŸ ∑§⁄UÊ – 99. Select the option including all sexually transmitted

1∑Ò §‚⁄U, AIDS, Á‚Á»§Á‹‚ diseases.
2‚È¡Ê∑§, Á‚Á»§Á‹‚, ¡ŸÁŸ∑§ ¬Á⁄U‚¬¸ (1) Cancer, AIDS, Syphilis
3‚È¡Ê∑§, ◊‹ Á⁄UÿÊ, ¡ŸÁŸ∑§ ¬Á⁄U‚¬¸ (2) Gonorrhoea, Syphilis, Genital herpes
4AIDS, ◊‹ Á⁄UÿÊ, »§Êß‹ Á⁄UÿÊ (3) Gonorrhoea, Malaria, Genital herpes (4) AIDS, Malaria, Filaria
NTA Answer: Option 2(final)
NEET 2020

ÁŸêŸ ⁄UÊ ªÊ ∑§Ê ©Ÿ∑ § ¬ÒŒÊ ∑§⁄UŸ flÊ‹ ¡ËflÊ ∑ § ‚ÊÕ Á◊‹ÊŸ ∑§⁄U 109. Match the following diseases with the causative organism and select the correct option. ‚„Ë Áfl∑§À¬ ∑§Ê øÿŸ ∑§⁄UÊ – Column - I Column - II Sà ÷ - I Sà ÷ - II (a) ≈UÊß»§ÊÚß«U (i) flÈø ⁄ UÁ⁄UÿÊ (a) Typhoid (i) Wuchereria (b) ãÿÍ◊Ê ÁŸÿÊ (ii) å‹Òí◊Ê Á«Uÿ◊ (b) Pneumonia (ii) Plasmodium (c) »§Êß‹ Á⁄U∞Á‚‚ (iii) ‚ÊÀ◊Ê Ÿ ‹Ê (c) Filariasis (iii) Salmonella (d) ◊‹ Á⁄UÿÊ (iv) „Ë◊Ê Á»§‹‚ (d) Malaria (iv) Haemophilus (a) (b) (c) (d) (a) (b) (c) (d)

1(iv) (i) (ii) (iii) (1) (iv) (i) (ii) (iii)
2(i) (iii) (ii) (iv) (2) (i) (iii) (ii) (iv)
3(iii) (iv) (i) (ii) (3) (iii) (iv) (i) (ii)
4(ii) (i) (iii) (iv) (4) (ii) (i) (iii) (iv)
NTA Answer: Option 3(final)

How NEET usually asks this

Recurring question shapes from past papers. Each pattern shows why wrong options look tempting.

Sources

NCERT refs: Class 12 Biology Chapter 2, p.45

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