📌 Key Points
- Asexual: One parent, no gamete fusion, genetic clones, fast (fission, budding, fragmentation, spores)
- Sexual: Two parents, gamete fusion, genetic variation, slower but adaptive
- Spermatogenesis: Testes produce 4 functional sperm continuously via meiosis. ~74-day cycle
- Oogenesis: Ovaries produce 1 functional ovum per cycle. Arrests in Meiosis I, resumes at ovulation
- Menstrual cycle: 28 days: Menstruation (1-5) → Follicular (5-13, FSH, estrogen) → Ovulation (14, LH) → Luteal (14-28, progesterone)
- Ovulation: Release of egg from follicle triggered by LH surge around day 14. Egg viable 12-24 hours
- Fertilization: Sperm fuses with egg in oviduct forming zygote (2n, 46 chromosomes)
- Implantation: Blastocyst embeds in uterine lining days 6-10 post-fertilization
- Pregnancy: 280 days (40 weeks). Trimester 1: organs form; Trimester 2: growth; Trimester 3: final development
- Placenta: Connects fetus to uterus. Functions: nutrient/oxygen exchange, waste removal, hormone production
- Umbilical cord: 2 arteries (deoxygenated to placenta) + 1 vein (oxygenated from placenta)
- Double fertilization (plants): Sperm1 + Egg → Embryo; Sperm2 + Polar nuclei → Endosperm
- Gametogenesis: Formation of gametes (sperm and egg) through meiosis. Reduces 2n to n
- Male system: Testes → Epididymis → Vas deferens → Seminal vesicles/Prostate → Urethra → Penis
- Female system: Ovaries → Oviduct → Uterus → Cervix → Vagina
- Pollination: Transfer of pollen (wind, insect, water). Self or cross-pollination
- Seed dispersal: Wind (wings), water (floating), animals (burrs, attractive fruit)
- Vegetative propagation: Runners (strawberry), rhizomes (ginger), bulbs (onion), cuttings
- Advantages sexual reproduction: Genetic diversity, adaptation, disease resistance, evolution
- Advantages asexual: Speed, efficiency, no mate needed, genetic uniformity in stable environments
📘 Important Definitions
⚠️ Common Mistakes
✗ Wrong: Asexual reproduction produces variation.
✓ Correct: Asexual produces genetic clones (no variation). Sexual produces variation through different gamete combinations.
✗ Wrong: Oogenesis produces 4 functional gametes like spermatogenesis.
✓ Correct: Oogenesis produces 1 functional ovum (egg) + polar bodies due to unequal meiotic division.
✗ Wrong: Ovulation occurs at start of menstrual cycle.
✓ Correct: Ovulation occurs around day 14 (middle) of menstrual cycle, not at start.
✗ Wrong: Fetal blood mixes directly with maternal blood in placenta.
✓ Correct: Placental barrier separates maternal and fetal blood. Oxygen and nutrients diffuse across, but blood doesn't mix.
✗ Wrong: Menstruation occurs when estrogen is high.
✓ Correct: Menstruation occurs when progesterone drops (corpus luteum degenerates). Low hormone levels trigger lining shedding.
✗ Wrong: Pregnancy lasts about 9 months (270 days).
✓ Correct: Pregnancy lasts ~280 days (40 weeks, 9 months 10 days) from fertilization.
📝 Exam Focus
These questions are frequently asked in CBSE exams:
🎯 Last-Minute Recall
Close your eyes and try to recall: Key definitions, formulas, and 3 common mistakes. If you can recall 80% without looking, you're exam-ready!