Biology

Plant life Cycle

Big Picture

The alternation of generations, where plants alternate between haploid gametophyte and diploid sporophyte generations, describes the life cycles of plants. This gives plants the ability to reproduce both sexually and asexually. Generally, one generation is dominant in every plant. In nonvascular plants, gametophytes are dominant. Sporophytes are dominant in vascular plants. All plants follow the same general life cycle of diploid sporophytes producing haploid spores through meiosis, and haploid spores going through mitosis to produce gametes that combine to become diploids again.

Key Terms

Alternation of Generations: Change back and forth from one generation to the next between haploid and diploid stages in the life cycle of plants.

Haploid: Having only one chromosome of each type.

Gametophyte: Haploid generation in the life cycle of a plant that results from asexual reproduction.

Diploid: Having two of each type of chromosome (twice the amount of chromosomes in haploids).

Sporophyte: Diploid generation in the life cycle of a plant that results from sexual reproduction.

Sporangium (plural, sporangia): Structure inside diploid sporophytes that goes through meiosis to make spores.

Spore: Reproductive structure adapted for dispersal and surviving extended periods of time in unfavorable conditions.

Antheridium (plural, antheridia): Female reproductive organ that produces eggs.

Archegonium (plural, archegonia): Male reproductive organ that produces sperm with flagella.

General Plant Life Cycle

Plants alternate between generations of haploid gametophytes and diploid sporophytes:

  • Diploid sporophytes have sporangia that produce haploid spores through meiosis
  • Haploid spores become haploid gametophytes
  • Haploid gametophytes go through mitosis to produce gametes(reproductive cell with the haploid number of chromosomes)
  • Gametes combine during fertilization to produce a diploid sporophyte, and the cycle repeats

For every plant, one of the two generations is usually dominant.

  • In the dominant generation, individuals live longer and grow larger.
  • In the non-dominant generation, individuals may be very small and not seen. They may be living in or on a dominant plant.
plant Life Cycle
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Nonvascular Plants

Nonvascular plant: only type of plants with dominant gametophyte generation.

  • Gametophytes have distinct male and female reproductive organs.
  • Archegonia: female organs; produce eggs.
  • Antheridia: male organs that produce sperm.
  • Sperm must swim in drops of water from an antheridium to an archegonium to fertilize an egg.
  • Fertilized eggs develop into sporophytes on the parent gametophyte plant.

Biology

Plant life Cycle Cont.

Seedless Vascular Plants

All vascular plants have dominant sporophytes.

  • Sporangia found under the leaves.
  • Sporangia produce spores that grow into gametophytes.
  • Gametophytes then produce eggs/sperm that produce more sporophytes.
Sporangia
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CC-BY-NC-SA 3.0

Gymnosperms

Gymnosperms reproduce through cones

  • Male spores grow into gameophytes inside of male cones
  • Male gameophytes are groups of cells enclosed inside pollen grains
  • Female spores grow into female gameophytes inside female cones; female gameophytes produce eggs
  • When pollen from male cones get into female cones, fertilization occurs and a diploid sporophyte is formed

Angiosperms

Angiosperm reproduction happens in flowers

  • Flowers have male and female parts
  • Spores are produced that develop into gameophytes
  • Gameophytes produce eggs/sperm
  • After fertilization, a diploid zygote is formed in the ovary and develops inside a seed; if the seed is planted, it grows into another plant

Notes