📖 Chapter BN05 · NDA Class 11–12 Level🎯 NDA Level : High Priority
Reproduction is one of the highest-yield Biology chapters in NDA. Questions appear on methods of asexual reproduction with organism examples, flower structure and whorls, pollination types, double fertilisation in angiosperms (unique to flowering plants), male and female human reproductive organ functions, menstrual cycle phases and controlling hormones, and embryo development stages. Diagram-based and example-matching formats are especially common.
📌 What to expect in NDA (based on 2022–2025 pattern): (1) Asexual reproduction methods — binary fission, budding, fragmentation, spore formation, vegetative propagation + organism examples; (2) Flower structure — name each of the four whorls and every part within them; (3) Double fertilisation (unique to angiosperms) — what fuses with what to form embryo vs endosperm; (4) True fruit vs false fruit; ovule vs ovary after fertilisation; (5) Male and female reproductive anatomy — organ to function matching; (6) Menstrual cycle — four phases, day ranges, dominant hormones (FSH, LH, oestrogen, progesterone); (7) Fertilisation site, implantation site, hCG function, and embryo development stages.
Definition + specific organism examples — both are tested in NDA MCQs
Asexual reproduction involves a single parent, produces genetically identical offspring (clones), requires no gametes, and is rapid. It generates no genetic variation. All major methods are listed below with their NDA-tested examples.
🔴 Binary Fission
Amoeba, Paramecium, Euglena, Bacteria
Parent cell divides into two equal halves
Most common in prokaryotes and unicellular organisms
Amoeba: irregular fission (any plane)
Paramecium: transverse binary fission
Bacteria: amitotic — no spindle formed; very rapid (every 20 min in E. coli)
🌿 Budding
Yeast, Hydra, Sponge
Small outgrowth (bud) forms on parent, grows, then detaches
Yeast: unicellular fungus; bud pinches off
Hydra: multicellular; bud develops tentacles before detaching
Offspring is genetically identical to parent
🔷 Fragmentation
Spirogyra, Planaria, Starfish, Ulva
Parent body breaks into fragments; each regenerates into new organism
Spirogyra (filamentous alga): classic NDA example
Planaria: even a small cut piece regenerates
Starfish: single arm can regenerate entire body
★ Spore Formation
Rhizopus (bread mould), Mucor, Ferns, Mosses
Spores = tiny, resistant reproductive units produced in sporangia
Dispersed by wind, water, or animals; germinate into new organism
Survive harsh conditions (drought, heat)
Conidia = asexual spores in Penicillium, Aspergillus
🌿 Vegetative Propagation
Potato, Ginger, Onion, Bryophyllum, Strawberry
New plant grows from vegetative (non-reproductive) part
Stem tuber: Potato — eyes = axillary buds at nodes
Leaf buds: Bryophyllum — plantlets on leaf margin notches
🔴 Parthenogenesis
Honeybee drones, aphids, some lizards
Development of egg without fertilisation
Drone honeybees: develop from unfertilised eggs → haploid (n)
Workers and queens → fertilised eggs → diploid (2n)
Haplo-diploid sex determination system in bees
Fig. 1 — Binary fission in Amoeba (left): parent cell elongates, DNA doubles, a constriction forms at the equator, and two genetically identical daughter cells result. Budding in Hydra (right): a bud grows from the body wall, develops tentacles, and pinches off as a new complete organism.
Q1. In which of the following organisms does budding occur as a method of asexual reproduction?
A. Amoeba
B. Spirogyra
C. Hydra
D. Planaria
Answer: C — Hydra. Hydra reproduces by budding — a small outgrowth (bud) forms on the body wall, grows, develops its own tentacles, and detaches as a new individual. Amoeba: binary fission. Spirogyra: fragmentation. Planaria: regeneration from body fragments.
Q2. Vegetative propagation through leaf margins is characteristic of:
A. Potato
B. Ginger
C. Bryophyllum
D. Onion
Answer: C — Bryophyllum (Kalanchoe). Bryophyllum produces adventitious buds along the notches of its leaf margins. Each bud can drop off and develop into a complete new plant. Potato = stem tuber; Ginger = rhizome (horizontal underground stem); Onion = bulb. All three are stem-based, not leaf-based.
Q3. The male honeybee (drone) develops by:
A. Fragmentation
B. Parthenogenesis
C. Budding
D. Binary fission
Answer: B — Parthenogenesis. Drone honeybees develop from unfertilised eggs and are haploid (n). Worker bees and the queen develop from fertilised eggs and are diploid (2n). This haplo-diploid sex determination is characteristic of Hymenoptera (bees, wasps, ants).
TRICKY🧐 Asexual Reproduction Traps
⚠️ "Potato reproduces through its roots." True or False?
False. Potato is a stem tuber — a modified underground stem. Key evidence: it has nodes (eyes with axillary buds), internodes, scale leaves, and apical buds. Sweet potato is a root tuber (storage root with no buds/nodes). Ginger/turmeric = rhizome (stem). Dahlia = root tuber. The distinction node = stem, no node = root is the definitive test. NDA 2024 directly tested this.
⚠️ "Drone honeybees are diploid like the queen." True or False?
False. Drones are haploid (n) — they develop from unfertilised eggs via parthenogenesis. The queen and all worker bees are diploid (2n). Because drones are haploid, all their sperm are genetically identical (no meiosis needed!). NDA may ask: "How many chromosomes does a drone have compared to the queen?" → Half.
2. Sexual Reproduction in Plants
2.1
Structure of a Flower — Four Whorls, Parts and Functions
Only egg cell and polar nuclei participate in fertilisation
🍀 Double Fertilisation — Unique to Angiosperms (Nawaschin, 1898):
Two male gametes released simultaneously by pollen tube into embryo sac: Fusion 1 (Syngamy): Male gamete 1 (n) + Egg cell (n) → Zygote (2n) → develops into Embryo (the future plant) Fusion 2 (Triple fusion): Male gamete 2 (n) + 2 Polar nuclei (n + n = 2n) → Primary Endosperm Nucleus, PEN (3n, triploid) → develops into Endosperm (food store for developing embryo)
This double fertilisation is the definitive characteristic of angiosperms only — gymnosperms have simple fertilisation with no endosperm formed this way.
Structure before fertilisation
Becomes (after fertilisation)
Role
Egg cell (n)
Part of Zygote (2n) → Embryo
Future plant
Polar nuclei (n+n) + 2nd gamete
Endosperm (3n)
Food reserve in seed
Ovule
Seed
Contains embryo + endosperm + testa
Ovary wall
Fruit (pericarp)
Protects seeds; aids dispersal
Integuments of ovule
Testa (seed coat)
Outer protective covering of seed
📌 True Fruit vs False Fruit & Coconut (NDA Traps): True fruit (from ovary only): Mango (mesocarp edible), Tomato, Grape, Orange False fruit / Pseudocarp (ovary + other parts): Apple (fleshy part = swollen receptacle/thalamus), Strawberry (receptacle), Cashew (peduncle), Pineapple (multiple fruits fused on axis) Coconut water = liquid endosperm; White coconut flesh = solid cellular endosperm. The whole coconut with husk is the fruit; husk = pericarp (mesocarp = fibrous coir; endocarp = hard shell).
PYQTopic-Wise PYQs — Plant Sexual Reproduction
Q4. Double fertilisation is a characteristic feature of:
A. Gymnosperms
B. Pteridophytes
C. Angiosperms
D. Bryophytes
Answer: C — Angiosperms. Double fertilisation involves two simultaneous fusions in the embryo sac: male gamete 1 + egg → zygote (embryo) and male gamete 2 + 2 polar nuclei → triploid endosperm. First described by Nawaschin (1898). Gymnosperms have simple fertilisation only; Pteridophytes and Bryophytes have no endosperm formed this way.
Q5. After fertilisation in a flowering plant, the ovule develops into the:
A. Fruit
B. Pericarp
C. Seed
D. Endosperm only
Answer: C — Seed. Ovule → seed; Ovary → fruit. A common NDA confusion is reversing this. The seed contains: embryo (from zygote) + endosperm (from PEN) + testa (from integuments). The endosperm is just one component of the seed, not the whole seed.
Q6. The edible fleshy part of an apple is derived from the:
A. Ovary wall (mesocarp)
B. Thalamus (receptacle)
C. Endocarp
D. Seed coat
Answer: B — Thalamus (receptacle). Apple is a false fruit (pseudocarp). The fleshy, sweet part we eat is the greatly swollen thalamus (receptacle). The actual true fruit (ovary wall) is the central core with the seeds. Mango is a true fruit — its edible fleshy part IS the mesocarp (ovary wall). This comparison is one of NDA's most repeated biology tricks.
TRICKY🧐 Plant Reproduction Traps
⚠️ "Coconut water is the fruit juice of coconut." True or False?
False. Coconut water is the liquid endosperm — the food reserve of the developing seed. As the coconut matures, liquid endosperm solidifies into the white flesh (solid cellular endosperm). Both are endosperm. The whole green coconut = fruit. Husk = pericarp. Hard shell = endocarp. NDA has directly asked: "Coconut water represents ___?" → Liquid endosperm.
⚠️ "The pollen tube enters the ovule through the style." True or False?
False (partially). The pollen tube grows through the style to reach the ovary, but it enters the ovule itself through the Micropyle — a small pore in the ovule's integuments. After entering, it discharges the two male gametes into the embryo sac. NDA asks: "The entry point of pollen tube into the ovule is called ___?" → Micropyle.
3. Sexual Reproduction in Humans
3.1
Male Reproductive System — Organs and Functions
Sperm pathway sequence + each organ function — both directly tested in NDA
Fig. 3 — Schematic of the male reproductive system. Sperm is produced in the seminiferous tubules of the testes (in scrotum, 2–3°C below body temp), matures in epididymis, transported via vas deferens, mixed with seminal vesicle (fructose) and prostate (alkaline) secretions to form semen, then ejaculated through the urethra.
📒 Male Organs — Functions
Testes: in scrotum (2–3°C below body temp; essential for spermatogenesis); produce sperm + testosterone
Seminiferous tubules: actual site of sperm production inside testis; Sertoli cells nourish developing sperm
Leydig (interstitial) cells: between tubules; secrete testosterone
Epididymis: coiled tube on testis; sperm maturation and temporary storage (~3 weeks)
Vas deferens: muscular tube; transports sperm from epididymis to urethra
Seminal vesicle: secretes fructose-rich fluid + prostaglandins (energy for sperm)
Sperm structure: head (nucleus + acrosome) + midpiece (mitochondria for energy) + tail (flagellum for motility)
Acrosome: contains hydrolytic enzymes to penetrate egg
3.2
Female Reproductive System — Organs and Functions
Ovary, fallopian tube, uterus, cervix, vagina — location and function of each is NDA-testable
Fig. 4 — Schematic of the female reproductive system. Ovaries produce eggs and hormones. Fimbriae sweep the released ovum into the fallopian tube. Fertilisation occurs in the ampulla of the fallopian tube. The zygote travels and develops into a blastocyst that implants in the endometrium ~7 days after fertilisation.
📓 Female Organs — Functions
Ovaries: produce oocytes (oogenesis) + oestrogen + progesterone; almond-shaped, one pair
Fallopian tube (Oviduct): conducts ovum from ovary to uterus; site of fertilisation (ampulla region)
Fimbriae: finger-like projections at open end of fallopian tube; sweep released ovum in
Corpus luteum: remnant of ruptured Graafian follicle; secretes progesterone
3.3
Menstrual Cycle, Fertilisation & Embryo Development
Four phases with day ranges + controlling hormones — the complete NDA menstrual cycle format
Menstrual Phase Day 1–5
Endometrial lining sheds (menstruation/period). Cause: fall in oestrogen and progesterone when corpus luteum degenerates (no fertilisation). All hormones at lowest. Bleeding lasts 3–5 days. Day 1 of menstruation = Day 1 of the cycle.
Follicular Phase Day 1–13
FSH (from anterior pituitary) stimulates Graafian follicle maturation. Follicle secretes oestrogen → endometrium thickens (proliferative phase). Rising oestrogen → positive feedback → LH surge. This phase is variable in length (accounts for cycle-to-cycle differences between women). Dominant hormone: Oestrogen.
Ovulation Day 14
LH surge (from anterior pituitary) triggers rupture of Graafian follicle and release of secondary oocyte into fallopian tube. Most fertile period. LH surge is the single most reliable ovulation marker. If viable sperm are present in the fallopian tube within ~24 hours, fertilisation may occur.
Luteal Phase Day 15–28
Ruptured follicle → Corpus luteum (yellow body). Corpus luteum secretes progesterone (dominant) + some oestrogen → maintains thick, vascular endometrium ready for implantation. If no fertilisation → corpus luteum degenerates ~Day 26–28 → progesterone falls → menstruation begins again. Dominant hormone: Progesterone.
Fig. 5 — Hormone changes during the 28-day menstrual cycle. FSH rises to stimulate follicle growth; oestrogen peaks in the follicular phase (endometrium proliferates). The sharp LH surge at Day 14 triggers ovulation. Progesterone dominates the luteal phase (secreted by corpus luteum; maintains endometrium). Both oestrogen and progesterone fall if no fertilisation → endometrium sheds → menstruation.
💔 Fertilisation & Implantation
Fertilisation site: ampulla of fallopian tube
Acrosomal reaction: sperm releases enzymes (acrosin) to penetrate zona pellucida of egg
Fertilisation completes meiosis II of secondary oocyte → Zygote (2n) formed
Zygote undergoes cleavage (mitosis) while moving toward uterus
Implantation: blastocyst embeds in endometrium ~Day 7 post-fertilisation
hCG: secreted by trophoblast (blastocyst/placenta); maintains corpus luteum; basis of pregnancy test; appears in urine ~Day 10
🐱 Embryo Development Stages
Zygote: single fertilised cell (2n)
Cleavage: rapid mitosis; no growth; produces blastomeres
Morula: solid ball of 16–32 blastomeres
Blastocyst: hollow ball; inner cell mass (embryo) + trophoblast (placenta)
Q7. Fertilisation in humans normally takes place in the:
A. Ovary
B. Uterus
C. Fallopian tube
D. Cervix
Answer: C — Fallopian tube (ampulla region). Fertilisation occurs in the ampulla — the widest part of the fallopian tube, nearest the ovary. The zygote then undergoes cleavage as it moves toward the uterus and implants as a blastocyst in the endometrium ~7 days after fertilisation.
Q8. The hormone responsible for triggering ovulation is:
A. FSH
B. Oestrogen
C. LH
D. Progesterone
Answer: C — LH (Luteinising Hormone). The sharp LH surge from the anterior pituitary at ~Day 14 directly triggers rupture of the Graafian follicle and release of the secondary oocyte (ovulation). FSH stimulates follicle maturation; oestrogen builds the endometrium; progesterone maintains the endometrium in the luteal phase. LH surge = ovulation trigger.
Q9. One primary oocyte produces how many functional ova?
A. 4
B. 2
C. 3
D. 1
Answer: D — 1 functional ovum. Oogenesis (unequal cytokinesis): 1 primary oocyte → 1 ovum + 3 polar bodies (which degenerate). This conserves cytoplasm for the one large egg. Contrast with spermatogenesis: 1 primary spermatocyte → 4 functional sperms (equal division). NDA directly compares these two numbers.
Q10. Pregnancy tests detect which hormone in urine?
A. Progesterone
B. LH
C. hCG
D. FSH
Answer: C — hCG (human Chorionic Gonadotropin). hCG is secreted by the trophoblast cells of the blastocyst after implantation (~Day 10 post-fertilisation). It appears in maternal urine and is detected by home pregnancy tests. hCG also maintains the corpus luteum so it continues secreting progesterone, preventing menstruation during early pregnancy.
TRICKY🧐 Human Reproduction Traps
⚠️ "Meiosis II in the oocyte is completed at the time of ovulation." True or False?
False. The secondary oocyte is arrested at Metaphase II at the time of ovulation. Meiosis II is completed only after penetration by a sperm. If fertilisation does not occur, the secondary oocyte degenerates without completing meiosis. Technically the structure released at ovulation is a secondary oocyte, not yet a mature ovum. NDA has asked: "At what stage is the oocyte released at ovulation?" → Secondary oocyte (arrested at Metaphase II).
⚠️ "Progesterone is the dominant hormone in the follicular phase." True or False?
False. Progesterone is dominant in the luteal phase (Days 15–28), secreted by the corpus luteum. Oestrogen is the dominant hormone in the follicular phase (Days 1–13), secreted by the growing Graafian follicle. Easy way to remember: Follicular = F = oestrogen builds the Floor (endometrium); Luteal = L = corpus Luteum makes Progesterone to maintain it.
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