Plant Diversity and Evolution: Reproduction in Seed Plants

Overview

• Focus on reproduction in seed plants: gymnosperms and angiosperms
• Gymnosperms: Reproductive structures are cones (e.g., pine trees)
• Angiosperms: Reproductive structures are flowers
• Pine trees are used to represent gymnosperms in this discussion

Gymnosperm Life Cycle (Pine Trees)

Reproductive Structures

• Cones: Two types
  • Female Cones (Seed Cones/Woody Cones): Large, woody; contain seeds
  • Male Cones (Pollen Cones): Smaller, spongy; produce pollen

Male Reproductive Process

• Pollen cones represent the sporophyte generation
• Sporophytes produce spores
• Meiosis occurs:
  • Diploid sporophyte produces haploid microspores
  • Microspores develop into male gametophytes (pollen)

Female Reproductive Process

• Seed cones also represent the sporophyte generation
• Inside the cone:
  • Contains ovule with megaspore mother cell (diploid)
  • Meiosis produces four haploid cells; one becomes the megaspore
• Megaspore develops into female gametophyte
  • Contains egg and endosperm mother cell

Pollination and Fertilization

• Pollen is wind-dispersed (not reliant on pollinators)
• Pollen reaches the female cone scale, discharges sperm
• Fertilization occurs:
  • Sperm fuses with egg to form diploid zygote
  • Endosperm mother cell divides to form nutritive endosperm (haploid)

Seed Formation

• Zygote (diploid) develops into embryo
• Surrounded by nutritive endosperm
• Mature seeds are released from cones, land, and grow into new trees

Conclusion

• This video covers the gymnosperm life cycle
• A separate video will cover angiosperm life cycle and reproduction
• Questions can be left in the comments section below the video

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These notes summarize the key points from the lecture on gymnosperm reproduction, focusing on pine trees as a representative example. It details the reproductive processes, structures involved, and how pollination and seed formation occur.