BC05 — Reproduction

📖 BC05 · CDS General Knowledge — Biology CDS Level

Reproduction is the biological process that ensures the continuation of a species. CDS questions focus on distinguishing asexual methods, the structure of the flower (for plant reproduction), and key events in human reproductive biology like fertilisation and the menstrual cycle.

📌 CDS Focus: Binary fission = bacteria and Amoeba; budding = Hydra and yeast; fragmentation = Spirogyra; vegetative propagation (potato = stem modification); fertilisation in plants = double fertilisation (unique to angiosperms); in humans — fertilisation occurs in fallopian tube (oviduct); implantation in uterus.

1. Asexual Reproduction Methods

MethodMechanismOrganism Binary fissionCell splits into two equal halves; fast; no gametesBacteria, Amoeba, Paramoecium BuddingSmall outgrowth (bud) forms on parent and detachesHydra (animal), Yeast (fungus) FragmentationBody breaks into pieces; each piece regeneratesSpirogyra (algae), Planaria (flatworm) Spore formationSpores produced; dispersed by wind; germinate in good conditionsFern, Fungi (Rhizopus), Moss Vegetative propagationNew plant from vegetative parts of parent plantPotato (stem tuber), Ginger (rhizome), Onion (bulb), Rose (cutting) RegenerationA whole organism develops from a fragmentStarfish, Planaria, Hydra

2. Sexual Reproduction in Flowering Plants

Fig. 1 — Structure of a Flower: Four Whorls and Their Reproductive Roles

Double Fertilisation (Unique to Angiosperms — direct CDS question):

When a pollen tube delivers 2 male gametes to the embryo sac:
● First fertilisation: One male gamete (n) + Egg cell (n) → Zygote (2n) → develops into embryo
● Second fertilisation: Other male gamete (n) + Polar nuclei (2n) → Endosperm (3n) → provides nutrition to embryo

This double fertilisation is found ONLY in flowering plants (angiosperms). It was discovered by Nawaschin (1898).

📝 CDS PYQs — Reproduction

Q1. In humans, fertilisation takes place in the: CDS PYQ

(a) Uterus(b) Cervix(c) Fallopian tube (Oviduct)(d) Vagina

✔ Answer: (c) Fallopian tube (Oviduct)

Fertilisation (fusion of sperm and ovum) occurs in the fallopian tube (oviduct), specifically in its upper third (ampullary-isthmic junction). The sperm travels from the vagina through the uterus into the fallopian tube. The fertilised egg (zygote) then travels to the uterus and implants in the uterine wall (endometrium) after about 7 days. Implantation in any other location = ectopic pregnancy (dangerous). This is a direct CDS question.

Q2. Which of the following reproduces by budding? CDS PYQ

(a) Amoeba(b) Spirogyra(c) Hydra(d) Fern

✔ Answer: (c) Hydra

Hydra reproduces by budding — a small outgrowth (bud) forms on the parent's body, grows, develops tentacles, and eventually pinches off to become an independent individual. Yeast (a fungus) also reproduces by budding. Amoeba = binary fission; Spirogyra = fragmentation; Fern = spore formation. The CDS question almost always asks to match organism to reproduction method.

Q3. Double fertilisation is a characteristic of: CDS PYQ

(a) Gymnosperms(b) Pteridophytes(c) Bryophytes(d) Angiosperms

✔ Answer: (d) Angiosperms

Double fertilisation is the defining feature of angiosperms (flowering plants). Two male gametes are involved: one fertilises the egg to form the embryo; the other fuses with the polar nuclei to form the endosperm (food for the developing embryo). Gymnosperms, pteridophytes, and bryophytes do NOT have double fertilisation. This is consistently asked in CDS as a direct factual question.

🧠 Quick Memory Chart — BC05

🔂 Asexual Methods

Binary fission: Amoeba, Bacteria
Budding: Hydra, Yeast
Fragmentation: Spirogyra, Planaria
Spore: Fern, Rhizopus
Vegetative: Potato (stem tuber), Ginger

🌸 Flower Parts

Calyx (sepals): protection
Corolla (petals): attract pollinators
Androecium (stamens): male; pollen
Gynoecium (carpel): female; ovule
Ovary → fruit; Ovule → seed

👪 Human Reproduction

Fertilisation: fallopian tube
Implantation: uterine wall
Double fertilisation: angiosperms only
Menstrual cycle: ~28 days
Ovulation: day 14 (approx)

📝 Practice Exercise

E1. Potato is an example of vegetative propagation through:

(a) Root tuber(b) Bulb(c) Stem tuber(d) Rhizome

E2. The male reproductive organ in a flower is called:

(a) Calyx(b) Androecium(c) Gynoecium(d) Corolla

E3. Menstruation occurs due to:

(a) Fertilisation of the egg(b) Release of the egg from the ovary(c) Shedding of the uterine lining when fertilisation does not occur(d) Implantation

Answers:
E1 → (c) Stem tuber [potato = modified underground stem; "eyes" are buds; sweet potato = root tuber] | E2 → (b) Androecium [stamens (filament+anther); anther produces pollen (male gametes)] | E3 → (c) Shedding of uterine lining [if no fertilisation occurs, progesterone drops, endometrium sheds as menstrual blood]

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