Plant Reproduction

Plant Reproduction

• Asexual Reproduction:
  • Species: Simple species, prokaryotes, and some eukaryotes
  • Members: One (clone)
  • Reproductive cells: No special cells (except spore reproduction)
  • Genetic diversity: No fusion cells, no genetic recombination
  • Population type: Homogenous (clone) to parents
  • Number of offspring: Exponentially
  • Stages (process): In Chapter 1
• Sexual Reproduction:
  • Species: Complex species, "most" eukaryotes
  • Members: 2 different but same species
  • Reproductive cells: Male and female gametes
  • Genetic diversity: Present due to genetic recombination
  • Population type: Heterogeneous, different than parents
  • Number of offspring: Less in number
  • Stages (process):
    • Meiosis → reduces gametes to half
    • Fertilization → union of gametes

Mechanisms in Asexual Reproduction of Cyanobacteria

• Fission: Replication plus splitting
• Fragmentation: Separating fragments, then regeneration
• Hormogonia: Motile reproduction by fragmentation for pre-reproducing pieces, then regeneration of those pieces

Additional Processes in Asexual Reproduction of Cyanobacteria

• Separation disc: Surrounded by a mucilaginous sheath, forming hormogonia. Hormogonia separate to glide and form new filaments.
• Heterocyst: Filamentous → fixes nitrogen
• Heterocyst degeneration → fragmentation: Each one forms a new one
• Akinetes: Under unfavorable conditions → store essential materials; when conditions become favorable, they germinate into their normal (vegetative) form.

Sexual Reproduction Processes

• Syngamy Process: Plasmogamy + karyogamy ; Result: Formation of zygote
• Dikaryon: Not a zygote; It's when the nuclei divide but not the cytoplasm. Example: Fungi.

Types of Sexual Reproduction (Morphology-based)

• Isogamy: Equal morphology
• Anisogamy / Heterogamy: Different morphologies; Female > Male gametes
• Example of Isogamy / Heterogamy: Chlamydomonas. Ulva.
• Planogamy (Zogamy): Motile gametes (Can be isogamy)
• Aplanogamy: Non-motile gametes ; Example: Red algae
• Oogamy: Large, non-motile female gamete + small, motile male gamete. Example: Fucus
• Somatogamy: Plasmogamy but delayed karyogamy; Example: Basidiomycota
• Conjugation / Cystogamy: Involves a donor (ơ) and a recipient (♀); Donor gives genetic material; conjugation tube or protuberance. Trichogamy: Female has hair-like structure, Trichogyne; attaches sperm, sperm fuses to female nucleus. Example: Red algae; Siphonogamy: Non-motile sperm conducted to egg via a tube. Example: Angiosperms

Life Cycle

• All cycles include meiosis and fertilization
• Meiosis → Mitosis → Gametophyte (n) → Sporophyte
• Types of Cycles:
  • Monobiontic or Monogenic (One Generation)
    • Haplontic Cycle: Single generation, cells are haploid; Absence of sporophyte; only zygotes are diploid; Mature organism = Gametophyte (n).
    • Diplontic Cycle: Single generation, cells are diploid; Presence of sporophyte; Gametes are only haploid cells; Mature organism = Sporophyte (2n).
  • Haplodiplontic or Digenic Life Cycle (steps):
  • Fertilization → Zygote (2n)
  • Zygote → Mitosis → Sporophyte (2n)
  • Meiosis → Spores (n)
  • Spores (n) → Mitosis → Gametophyte (n)
  • Gametophyte (n) → Mitosis → Gametes (n)
  • Triplobiontic or Trigenic Life Cycle: Produces three generations: Gametophyte (haploid) (n). Carposporophyte (diploid) (2n); Tetrasporophyte (diploid) (2n)

Chapter 3: Reproduction of Algae (Protists)

• Asexual Reproduction: Mitosis → Fragmentation, Budding, or Spore Formation
• Sexual Reproduction:
  • Monobiontic Haplontic - Spirogyra (n): Filamentous algae found in freshwater
• Mode of Fertilization:
  • Conjugation
    • Process: Formation of protuberance →, forms conjugation tube; Male cells move to fuse with the female protoplast; Forms zygospore; Ruptures → releases zygospore; Zygospore enters dormant stage; In favorable conditions, it undergoes meiosis to produce spores (n). Spores (n) undergo mitosis
• Gametophyte (n): New Spirogyra is formed
• Monobiontic Diplontic – Fucus (2n): Type: Brown algae, found in marine water. Mode of Fertilization: Oogamy. Structure: Branched Thallus in Sporophyte (2n). Conceptacles (contain gametangium). Receptacles with paraphyses. Male & Female conceptacles on separate thallus,etc.

Structure of Reproduction Processes in Fucus (2n)

• Reproduction Process:
  • Female (Oogonia): Meiosis produces nonmotile eggs (n)
  • Male (Antheridia): Meiosis produces biflagellated sperm (n)
  • Egg & sperm are released in water. Egg releases pheromones → attract sperm (Chemotaxis)
  • Fertilization occurs externally in water
  • Fertilized egg settles
  • Zygote (2n) undergoes mitosis → Forms Diploid Sporophyte.

Isomorphic Haplodiplontic – Ulva

• Ulva species have: Haploid Gametophytes (n); Diploid Sporophyte (2n).

• Gametes: Female gamete: Large, biflagellated, motile, Male gamete: Small, biflagellated, motile

• Type of fertilization: Planogamy & Anisogamous

• Reproduction Process:

  • Fusion of gametes → Produces quadriflagellate zygote
  • Zygote swims → rests , eliminates flagella and grows into sporophyte.
  • Sporophyte undergoes meiosis → Produces quadriflagellate zoospores
  • Zoospores eliminate flagella and develop into gametophytes

Heteromorphic Haplodiplontic – Laminaria

• Heteromorphic, Different morphology of sporophyte & gametophyte
• Fertilization Type: Oogamy
• Characteristics: Large sporophyte & microscopic male & female gametophytes
• On the surface blade of sporophyte: Sporangia grouped into sori, paraphyses = Sterile cells
• Fertilization Process: Female & Male gametes are flagellated; Zygote becomes sporophyte via mitosis; Sporangia (on sporophyte) undergo meiosis → Production of flagellated zoospores