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Plant Reproduction Flashcards

Vegetative Reproduction

  • Asexual reproduction where new plants grow from parts of an existing plant.

  • New plants are clones, identical to the original.

Advantages

  • Faster growth compared to seeds or spores.

  • Only way to reproduce some seedless fruits (e.g., some tomatoes, pineapples).

Naturally Occurring Examples

  • Mosses: In dry conditions, mosses become brittle and break. Fragments scatter and resume growth when water is available.

  • Strawberry Plants: Stems called stolons grow, and a new plant develops at the end of each stolon.

Alternation of Generations

  • Plant life cycle alternates between a diploid sporophyte (2n) and a haploid gametophyte (n).

  • Sporophyte produces haploid spores through meiosis.

  • Gametophyte produces haploid gametes (eggs and sperm).

Moss Reproduction and Life Cycle

  • Dominant stage: Gametophyte

  • Gametophyte produces archegonia (female) and antheridia (male) on the same or separate plants.

  • Archegonium: Produces eggs surrounded by a protective layer.

  • Antheridium: Produces flagellated sperm that require water to swim to the egg.

  • Chemotaxis: Archegonium releases chemicals that attract sperm.

  • Fertilization: Sperm + egg = zygote (first cell of sporophyte).

  • Moss sporophyte depends on the gametophyte for nutrition and support; it cannot perform photosynthesis.

  • Mature sporophyte: Stalk with a capsule where spores are produced.

  • Spores release and form protonema (thread-like structure), which develops into the gametophyte.

Fern Reproduction and Life Cycle

  • Dominant stage: Sporophyte

  • Fronds (photosynthetic leaves) are part of the sporophyte stage.

  • Sori: Located on the underside of fronds, consisting of sporangia (spore-producing structures).

  • Spores grow into a heart-shaped gametophyte called prothallus when they land on suitable soil.

  • Both antheridia and archegonia develop on the same prothallus.

  • Sperm from the antheridium swims toward the egg produced by the archegonium.

  • Zygote undergoes mitotic divisions to form a multi-cellular sporophyte if fertilization occurs.

  • Mature sporophyte is independent and produces fronds and rhizome.

Conifer Reproduction and Life Cycle

  • Dominant stage: Sporophyte

  • Conifers are heterosporous: produce two types of spores (male and female).

  • Megaspore: Female spore that develops into the female gametophyte.

  • Microspore: Male spore that develops into the male gametophyte.

Female Cones

  • Composed of many scales; each has two ovules at its base.

  • Megasporangium: Cell undergoes meiosis to produce four megaspores; three disintegrate.

  • Remaining megaspore undergoes mitosis and becomes the female gametophyte.

  • Each gametophyte consists of two to six archegonia, each with one egg.

Ovule\longrightarrow Meiosis\longrightarrow 4 megaspores \longrightarrow 1 remains\longrightarrow Mitosis\longrightarrow2-6 archegonia\longrightarrow Archegonium\longrightarrow Gametophyte\longrightarrow 1 egg

Male Cones

  • Consist of small reproductive scales with hundreds of microsporangia.

  • Cells in the microsporangia undergo meiosis and form microspores.

  • Microspores develop into pollen grains, each consisting of four cells.

Pollination

  • Pollen grain lands on the female reproductive structure of the same species.

  • If the pollen grain lands near the micropyle (opening near the egg), it can be trapped by a sticky substance called pollen drop.

Seed Development

  • After pollination, the pollen grain generates a pollen tube that grows to the micropyle and into the ovule.

  • One of the four cells in the pollen grain undergoes mitosis to produce two sperm.

  • Fertilization: the remaining sperm and pollen tube disintegrate.

  • Zygote depends on the gametophyte for nutrition.

  • The outer layers of the ovule form the seed coat as the embryo develops.

  • When the seeds mature, the female cone opens and releases them.