Plant Biology Notes

Chapter 25 – Terrestrial Plants

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.

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.

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

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

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.

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.

"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.

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:
- 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.

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

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

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

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.

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