Flower Anatomy and Reproduction Notes

Flower Anatomy and Reproduction

Flower Structure

  • Sepals: Non-reproductive parts, typically green, enclose the bud.

  • Petals: Non-reproductive parts, often brightly colored to attract pollinators.

  • Stamen: The male reproductive organ, consisting of:

    • Anther: The site of male gametophyte (pollen) production.

    • Filament: The stalk that supports the anther.

  • Carpels (Pistil): The female reproductive organ, consisting of:

    • Stigma: The receptive tip for pollen.

    • Style: The stalk connecting the stigma to the ovary.

    • Ovary: The base of the carpel, enclosing one or more ovules and serving as the site of female gametophyte production.

  • All four whorls (sepals, petals, stamens, carpels) attach at the receptacle, which is the part of the flower stalk where the flower parts are attached.

Simplified Angiosperm Life Cycle

  • The life cycle involves alternating generations between a diploid sporophyte (the mature plant) and haploid gametophytes (pollen grain and embryo sac).

  • Germinated pollen grain: Represents the male gametophyte, lands on the stigma of a carpel.

  • Pollen tube: Grows down the style to the ovary.

  • Ovary (base of carpel): Contains the ovule.

  • Ovule: Contains the Embryo sac (n), which is the female gametophyte.

  • Egg: Located within the embryo sac.

  • Sperm: Travel down the pollen tube to the ovule.

  • FERTILIZATION: Fusion of sperm and egg.

  • Zygote: Formed after fertilization, develops into the embryo.

  • Embryo: The young sporophyte contained within the seed.

  • Seed: Develops from the ovule, contains the embryo and nutritive tissue.

  • Simple fruit: Develops from the ovary, protecting the seeds.

  • Germinating seed: The embryo grows into a new plant.

  • Mature sporophyte plant (2n): The adult plant with flowers, completing the cycle.

Flower Types

  • Complete flowers: Possess all four floral whorls: sepals, petals, stamens, and carpels.

  • Incomplete flowers: Lack one or more of the four floral whorls. For example, some incomplete flowers may lack petals.

  • Perfect flowers: Contain both stamens (male reproductive parts) and carpels (female reproductive parts).

  • Imperfect flowers: Lack either stamens or carpels, meaning they are unisexual.

Reproductive Variations

  • Monoecious: Means "one house." In these species, staminate (male) flowers and carpellate (female) flowers are found on the same plant.

    • Example: Maize (corn) displays both male flowers (tassels) and female flowers (ears) on the same individual plant.

  • Dioecious: Means "two houses." In these species, staminate (male) flowers and carpellate (female) flowers are found on different plants.

    • Examples: Sagittaria latifolia (common arrowhead) and Ginkgo biloba (male and female trees are separate).

Fruits

  • Definition: The fruit of a flower develops from the ovary after fertilization. Its primary functions are to protect the enclosed seeds and aid in their dispersal.

  • Classification:

    • Simple Fruits: Develop from a single ovary of a single flower.

      • Examples: Peaches, cherries, apples.

    • Aggregate Fruits: Develop from a single flower that has multiple separate carpels. Each carpel forms a small fruitlet, and these cluster together.

      • Examples: Strawberries, raspberries.

    • Multiple Fruits: Develop from a group of tightly clustered flowers (an inflorescence). The ovaries of these individual flowers fuse together to form a single fruit.

      • Examples: Pineapples.