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Reproduction

Subject: Biology
Topic: 9
Cambridge Code: 0610 / 0970 / 5090

Two Types of Reproduction​

Sexual Reproduction​

  • Gametes: Two parents produce sex cells (sperm, egg)
  • Fertilization: Fusion of gametes
  • Meiosis: Produces haploid (n) gametes
  • Diploid offspring: Same genetic info as parents (not clones)
  • Genetic variation: Different alleles in offspring

Asexual Reproduction​

  • Single parent: No gametes needed
  • Mitosis: Produces identical daughter cells
  • Offspring: Clones of parent
  • No meiosis: No genetic variation
  • Quick: Faster than sexual reproduction

Meiosis​

Meiosis - Two divisions producing four haploid cells

Meiosis I (First Division)​

Prophase I:

  • Homologous chromosomes pair (bivalents)
  • Crossing over exchanges genetic material

Metaphase I:

  • Bivalents line up at equator

Anaphase I:

  • Homologous chromosomes separate
  • Bivalents pull apart

Telophase I:

  • Two nuclei form
  • Cell divides (cytokinesis)
  • Result: Two haploid cells

Meiosis II (Second Division)​

Similar to mitosis:

  • Sister chromatids separate
  • Four haploid cells formed
  • Each is genetically different

In Males vs Females​

Spermatogenesis (males):

  • Produces 4 functional sperm from each cell
  • Continuous from puberty

Oogenesis (females):

  • Produces 1 egg and 3 polar bodies
  • Cyclical (monthly)

Human Male Reproductive System​

Testes​

  • Produce: Sperm and testosterone
  • Structure: Seminiferous tubules
  • Temperature: Must be 34°C (below body temp)

Sperm Production​

  • From spermatogonia (stem cells)
  • ~74 days to maturity
  • Millions produced daily

Sperm Structure​

  • Head: Nucleus with DNA, acrosome (enzymes)
  • Midpiece: Mitochondria (energy)
  • Tail: Flagellum (movement)

Path of Sperm​

Seminiferous tubule → Epididymis (storage) → Vas deferens → Urethra → Penis

Semen​

  • Sperm + Seminal fluid
  • Prostate gland: Alkaline fluid
  • Seminal vesicles: Fructose (energy)
  • Bulbourethral gland: Mucus

Human Female Reproductive System​

Ovaries​

  • Produce: Eggs and hormones (estrogen, progesterone)
  • Follicles: Cells surrounding egg

Ovum (Egg) Structure​

  • Nucleus: DNA
  • Cytoplasm: Nutrients (yolk in other species)
  • Zona pellucida: Protective layer
  • Larger: Than sperm

Menstrual Cycle​

28-day cycle (average)

Menstruation (Days 1-5):

  • Uterine lining shed
  • Bleeding for 3-5 days

Follicular Phase (Days 1-14):

  • FSH stimulates follicle development
  • Estrogen increases
  • Uterine lining rebuilds

Ovulation (Day 14):

  • LH surge triggers egg release
  • Ovary ruptures
  • Egg enters fallopian tube

Luteal Phase (Days 15-28):

  • Corpus luteum produces progesterone
  • Uterine lining prepared for implantation
  • If no fertilization: Lining sheds

Fertilization and Development​

Fertilization​

  • Location: Fallopian tube
  • Process: Sperm nucleus fuses with egg nucleus
  • Result: Diploid zygote (46 chromosomes)
  • Time: Must occur within 12-24 hours of ovulation

Early Development​

Mitosis in zygote:

  • Zygote → 2 cells → 4 cells → 8 cells
  • Blastocyst forms (days 3-5)
  • Arrives in uterus (day 6-7)

Implantation (day 7-12):

  • Blastocyst embeds in uterine lining
  • Placenta forms

Placenta Function​

  • Nutrient/oxygen transfer: Mother to fetus
  • Waste removal: Fetus to mother
  • Hormone production: HCG, progesterone
  • Barrier: Prevents mixing of blood (mostly)

Plant Reproduction​

Asexual Reproduction​

Vegetative reproduction:

  • Runners (strawberries)
  • Bulbs (onions)
  • Fragmentation (some algae)
  • Advantages: Quick, no energy for flowers

Sexual Reproduction​

Flower structure:

  • Stamen: Male (anther, filament)
  • Pistil: Female (stigma, style, ovary)
  • Petals, sepals: Attraction, protection

Pollination:

  • Transfer of pollen to stigma
  • By insects (entomophily) or wind (anemophily)

Fertilization:

  • Pollen tube grows to ovule
  • Sperm nucleus fuses with egg nucleus
  • Seed and fruit develop

Key Points​

  1. Sexual: Two parents, genetic variation, meiosis
  2. Asexual: One parent, clones, mitosis
  3. Meiosis produces 4 haploid gametes
  4. Menstrual cycle ~28 days
  5. Fertilization: Sperm + Egg → Zygote
  6. Placenta: Nutrient and gas exchange
  7. Plants: Both sexual and asexual methods

Practice Questions​

  1. Compare meiosis and mitosis
  2. Describe spermatogenesis
  3. Explain menstrual cycle phases
  4. Describe fertilization process
  5. Explain placenta function
  6. Compare sexual and asexual reproduction

Revision Tips​

  • Learn meiosis stages clearly
  • Know reproductive anatomy
  • Understand menstrual cycle
  • Learn fertilization and implantation
  • Know placenta function
  • Compare plant and animal reproduction