Seed Plants and Their Adaptations

Seed Plants

Adaptations of Seed Plants

• Seed Plant Dominance: Adaptations that enable seed plants to become the majority of plant biodiversity include:

  • Reduced Male and Female Gametophytes: These structures develop within the parental sporophytes, offering protection from environmental stresses.

  • Protection: In both gymnosperms and angiosperms, gametophytes develop in specific, protected structures:

  • Gymnosperms: Gametophytes develop within cones.

  • Angiosperms: Gametophytes develop within flowers.

  • Pollination Mechanism: Pollen serves to protect male gametophytes (which produce sperm) and is capable of being transported by wind or animals.

Components of Seeds

• Seed Structure: A seed consists of:

  • Embryo: The new plant that will develop.

  • Seed Coat: Protects the embryo.

  • Food Supply: Nourishes the embryo until it can photosynthesize.

• Seed Formation: Upon fertilization, an ovule that has received pollen develops into a seed.

Gametophyte/Sporophyte Relationships

• Nonvascular Plans (Mosses):

  • Gametophyte: Dominant stage (n)

  • Structure is independent, photosynthetic, and free-living.

  • Sporophyte: Reduced stage (2n)

  • Dependent on gametophyte for nutrition.

• Seedless Vascular Plants (Ferns):

  • Sporophyte: Dominant stage (2n)

  • Gametophyte: Independent stage (n)

• Seed Plants (Gymnosperms and Angiosperms):

  • Gametophytes: Microscopic and reduced, dependent on surrounding sporophyte tissue for nutrition.

  • Example Structures:

  • Gymnosperms: Microscopic female gametophytes (n) inside ovulate cones.

  • Angiosperms: Microscopic female gametophytes (n) inside floral structures.

  • Male Gametophytes: Microscopic male gametophytes (n) inside pollen cones of both groups.

Gametophyte Development

• Female Gametophyte: Develops from the megaspore.

• Male Gametophyte: Develops from the microspore.

• Endosporic Development: Gametophytes develop within the walls of the spores, remaining retained within the parent sporophyte tissues.

Evolutionary Impact of Seeds

• Seeds as Evolutionary Turn: The ability to produce seeds fundamentally changed the course of plant evolution, positioning seed plants as dominant producers in most terrestrial ecosystems.

Gymnosperms

• Characteristics of Gymnosperms:

  • Bear “naked” seeds, typically found on cones.

• Notable Examples: Includes widely recognized conifers such as pine, fir, and redwood.

Gymnosperm Reproductive Structures

• Male or Pollinate Cones: Structures that produce pollen.

• Female or Ovulate Cones: Structures that produce ovules.

Pine Structure and Reproductive Cycle

• Microsporangia: Contains pollen grains in the pine pollinate (staminate) cone.

• Ovule Anatomy: Composed of several key components:

  • Egg (n)

  • Megasporangium (nucellus, 2n) before fertilization.

  • Female Gametophyte (n)

  • Archegonium (n): Structure housing the egg.

Angiosperms (Flowering Plants)

• Diversity and Distribution: Angiosperms are the most widespread and diverse group of plants.

• Key Adaptations:

  • Development of flowers and fruits for reproductive success.

Flower Structure and Functions

• Definition of Flower: A specialized shoot with modified leaves adapted for sexual reproduction.

• Components of a Flower:

  • Sepals: Enclose and protect the flower.

  • Petals: Brightly colored, attract pollinators.

  • Stamens: Structures that produce pollen.

  • Carpels/Pistils: Structures that produce ovules.

Reproductive Cycles and Processes

• Ovule to Seed: The ovule develops into a seed, while the ovary develops into fruit.

• Double Fertilization Process (specific to angiosperms):

  • The pollen grain adheres to a stigma, leading to the formation of a pollen tube.

  • The generative cell from the pollen grain travels inside the pollen tube, dividing to form two sperm.

  • The pollen tube penetrates the ovule via the micropyle. One sperm fertilizes the egg to form a diploid zygote, while the other sperm fertilizes two polar nuclei to create a triploid endosperm, which serves as a food source for the developing embryo.

Example of Angiosperms - Apple's Anatomy

• Components:

  • Stamen, Style, Sepal, Ovule (seed), Receptacle, Pedicel (stalk).

  • Fruits of apple (botanically classified as a pome).

Lab Exercise and Study Guide Recommendations

• Review the reproductive cycles of pines through PowerPoint and Panopto video.

• Focus on Angiosperms, particularly flower structures and the angiosperm life cycle.

• Understand microscope slides and apple fruit anatomy without needing to memorize non-PowerPoint structures.