Plant Biology Notes

Chapter 25 – Terrestrial Plants

Advantages and Disadvantages of Life on Land

• Advantages:
  • More sunlight available.
  • Higher concentrations of carbon dioxide (CO_2).
  • Initially, fewer herbivores and pathogens.
• Disadvantages:
  • Risk of desiccation (drying out).
  • Lack of structural support against gravity.
  • Challenges in reproduction without water.

Adaptations to Terrestrial Life

• Waxy Cuticle: Reduces water loss from plant surfaces.
• Stomata: Pores that allow gas exchange while minimizing water loss.
• Vascular Tissue: Transports water and nutrients throughout the plant.
• Seeds: Protect and nourish the developing embryo.
• Flowers: Facilitate pollination and sexual reproduction.
• Pollen: Carries sperm to the egg without water.
• Roots: Anchor the plant and absorb water and nutrients.
• Supportive Tissues: Like lignin, provide structural support.

Alternation of Generations

• Plants alternate between two distinct life stages:
  • Haploid Gametophyte (n): Produces gametes (sperm and eggs) via mitosis.
  • Diploid Sporophyte (2n): Produces haploid spores via meiosis.
• The sporophyte generation is diploid (2n) and produces haploid spores via meiosis.
• The gametophyte generation is haploid (n) and produces gametes (sperm and eggs) via mitosis.

Apical Meristems

• Regions of actively dividing cells (meristematic cells).
• Located at the tips of roots and shoots in seedless and other plants, enabling growth.

Waxy Cuticle

• Reduces water loss from the plant's outer surfaces.
• Found on the outer surfaces of leaves and stems.

Sporopollenin

• A durable polymer that protects spores and pollen from harsh environmental conditions.
• Found in the walls of spores and pollen grains.

Seedless Nonvascular Plants (Bryophytes)

• Includes hornworts, liverworts, and mosses.
• Gametophyte Dominant: The gametophyte stage is the most visible and long-lived phase of the life cycle. It is haploid (n).
• Gametophyte Structures:
  • Antheridia: Produce sperm.
  • Archegonia: Produce eggs.
• Sporophyte:
  • Diploid (2n).
  • Dependent on the gametophyte for nutrition and support.
  • Produces haploid spores via meiosis.
• Lack True Roots, Leaves, and Stems: Instead, they have:
  • Rhizoids: Anchor the plant.
  • Thallus: A simple plant body.
• Water Required for Fertilization: Sperm must swim to the egg.
• Zygote: Diploid, formed after fertilization.

Chapter 26 – Seed Plants

Adaptations of Seed Plants

• Sporophyte Dominant: The sporophyte is the more visible and dominant stage.
• Heterosporous: Produce two types of spores (megaspores and microspores).
• Fertilization Independent of Water: Pollen can be transported by wind or animals.
• Pollen: Delivers sperm to the egg.
• Seeds: Protect and nourish the developing embryo.

Gymnosperms

• "Naked Seeds": Seeds are not enclosed in a fruit.
• Reproductive Strategies:
  • Monoecious: Having both male and female reproductive organs on the same plant.
  • Dioecious: Having male and female reproductive organs on separate plants.
• Wind-Pollinated: Pollen is dispersed by the wind.
• Xylem: Contains tracheids for water transport.
• Heterosporous:
  • Microsporangia: Produce microspores, which develop into male gametophytes (pollen).
  • Megasporangia: Produce megaspores, which develop into female gametophytes (egg).
• Pollen Structure:
  • Generative Cell: Divides into two sperm cells.
  • Tube Cell: Forms the pollen tube, which delivers sperm to the egg.
• Seed Composition: Contains tissue from three generations:
  • Parent sporophyte.
  • Gametophyte.
  • New sporophyte embryo.

Angiosperms

• Flowering Plants: Characterized by the presence of flowers and fruits.
• Reproductive Strategies:
  • Monoecious: Having both male and female reproductive organs on the same plant.
  • Dioecious: Having male and female reproductive organs on separate plants.
• Pollination Methods: Pollination occurs via wind, insects, or animals.
• Xylem: Contains vessel elements for efficient water transport.
• Flower Parts:
  • Carpel (Female):
    • Ovary: Contains ovules (megasporangia).
  • Stamen (Male):
    • Anther: Contains microsporangia.
• Life Cycle:
  • Heterosporous:
    • Microsporangia → microspores → male gametophyte (pollen).
    • Megasporangia → megaspores → female gametophyte (egg).
  • Female Gametophyte Development: Egg divides three times, forming seven cells with eight nuclei.
  • Pollen:
    • Generative cell → 2 sperm.
    • Tube cell → pollen tube.
  • Double Fertilization:
    • One sperm + egg → zygote.
    • Other sperm + 2 polar nuclei → endosperm (3n).

Monocots vs. Dicots

• Monocots:
  • 1 cotyledon.
  • Parallel veins in leaves.
  • Scattered vascular tissue in stems.
  • Fibrous roots.
• Dicots:
  • 2 cotyledons.
  • Net-like veins in leaves.
  • Ringed vascular tissue in stems.
  • Taproot.

Coevolution

• Many angiosperms have coevolved with pollinators for mutual benefit, where both species benefit from the interaction.

Chapter 30 – Plant Organ Systems

Shoot vs. Root Systems

• Shoot System: Includes stems, leaves, and flowers.
• Root System: Anchors the plant and absorbs water and nutrients from the soil.

Meristematic vs. Nonmeristematic Tissues

• Meristematic: Actively dividing cells responsible for plant growth.
• Nonmeristematic: Mature, non-dividing cells that perform specialized functions.

Tissue Types

• Dermal Tissue: Outer protective layer of the plant.
• Ground Tissue: Functions in photosynthesis, storage, and support.
• Vascular Tissue:
  • Xylem: Transports water throughout the plant.
  • Phloem: Transports sugars (produced during photosynthesis) throughout the plant.

Stem/Root/Leaf Anatomy

• Stems: May store food and photosynthesize.
• Roots: Can be taproots or fibrous roots; may store starch.
• Leaves: Arranged in patterns (alternate, opposite, whorled).

Growth

• Primary Growth: Lengthening of the plant via apical meristems.
• Secondary Growth: Thickening of the plant via lateral meristems (in woody plants).

Chapter 32 – Plant Reproduction

Pollination vs. Fertilization

• Pollination: Transfer of pollen to the stigma.
• Fertilization: Union of sperm with egg.

Self- vs. Cross-pollination

• Self-pollination: Pollination occurs within the same plant.
• Cross-pollination: Pollination occurs between different plants.

Asexual Reproduction

• Cloning without gametes (e.g., runners, tubers).