Angiosperms

Chapter 23: Angiosperms: Flowering Plants

  • Quote: "What I do today is important because I am paying a day of my life for it. What I accomplish must be worthwhile because the price is high."

Gymnosperms vs. Angiosperms

  • Gymnosperms:

    • Example: Pine with ovulate cone and scales.

  • Angiosperms:

    • Examples include flowers and fruits, such as oranges and orange blossoms.

    • Processes in Angiosperms include:

    • Pollen tube formation leading to fertilization.

    • Embryo development and seed formation.

Flower Structure

  • Parts of a Flower:

    • Carpel (Pistil) (gynoecium): (female)

    • Includes the stigma, style, and ovary.

    • Stamen (Androecium): (male)

    • Includes the anther and filament.

    • Other parts:

    • Receptacle

    • Peduncle (stalk)

    • Petals (part of the corolla)

    • Sepals (part of the calyx, also referred to as perianth).

Flower Structure Details

  • Anatomical Features:

    • Anther: Part of stamen that produces pollen.

    • Stigma: Receives pollen.

    • Style: Connects the stigma to the ovary.

    • Ovary: Contains ovules which develop into seeds.

    • Sepal & Petal: Modifications that protect or attract pollinators.

Plant Ovaries and Ovules

  • Types of Placenta in Ovaries (Cross Section):

    • Free-central

    • Axial

    • Parietal

  • Structure of the Ovary:

    • Contains ovules attached to the placenta.

    • Produces seeds after fertilization.

Ovule Development

  • Megasporangium (Nucellus):

    • Contains megasporocyte (2n), which undergoes meiosis to produce megaspores.

    • Of the four megaspores, typically one survives.

  • Megagametophyte Development: polygonum-type embryo sac

    • Results from the functional megaspore undergoing 3 rounds of mitosis to create 7 cells, 8 nuclei, arranged into:

    • 1 egg, 2 synergids, 3 antipodal cells, and 2 polar nuclei (2 in one cell).

    • Arrangement typically seen in 70% of flowers, while remaining 30% may vary in nucleus count.

  • Double Fertilization:

    • One sperm fertilizes the egg forming a zygote (2n).

    • Another sperm fuses with the two polar nuclei to form triploid endosperm (3n), which provides nutrition to the developing embryo.

  • lily ovary and ovule are big and easy to see, which makes them easy to study/good models

Development of the Male Gametophyte

  • Microgametophyte Development:

    • Located in the anther where microsporocytes (2n) undergo meiosis creating microspores (n).

  • Mature Male Gametophyte Structure:

    • Consists of a pollen grain that contains:

    • Generative cell (divides to form two sperm cells).

    • Tube cell (develops into the pollen tube).

Pollination and Fertilization

  • Pollination Process Overview:

    • Pollen grains goes from anther to the stigma and germinate, forming a pollen tube that carries the sperm cells to the ovule.

    • Fertilization occurs successfully when the pollen tube penetrates the ovule through the micropyle.

  • pollen grains have been used to help solve murders

  • 4 cells

Seed Structure and Germination

  • Key Components of a Seed:

    • Seed Coat: Protective covering.

    • Cotyledons: Seed leaves that provide initial nutrition to the embryo.

    • Endosperm: Nutritional tissue that supports the embryo's initial growth.

    • Epicotyl, Hypocotyl & Radicle: These structures contribute to the vegetative parts of the plant post-germination.

Germination Process

  • Changes during germination include:

    • Cotyledons expand to produce first true leaves.

    • The hypocotyl elongates and pulls the cotyledons above ground.

  • 1 apichur is monocot

Variation in Development of Embryo Sacs

  • Different Patterns of Development:

    • Variation exists among angiosperms, where the female gametophyte could have a structure ranging from 4 to 16 nuclei/cells.

    • Endosperm can have varying ploidy levels, such as 5n, 9n, or 15n.

Life Cycle of Flowering Plants

  • Young Sporophyte Stage:

    • Begins with seed germination, leading to the formation of flowers and fruits.

  • Process Overview:

    • Involves meiosis in microspore mother cells to produce microspores and in megasporocyte to produce megaspores.

    • Fertilization leads to the formation of the diploid zygote, which develops into a sporophyte (2n).

Summary of fertilization and life cycle results:

  • Fertilization results in the triploid endosperm tissue, essential for the embryo's nutrition.

    • Key structures involved include the zygote, endosperm, and the needed seed structures for growth and development in flowering members of plant families.

gametophyte in gymnosperm seeds 2n