Intro to the Plant Kingdom Flashcards

Timeline of Land Colonization:
- For the vast majority of Earth's history, the land surface was largely devoid of life.
- Prokaryotes: Some prokaryotic organisms inhabited land as early as $3.2$ billion years ago.
- Initial Macro-colonization: Small plants, fungi, and animals began to join prokaryotes ashore within the last $500$ million years.
- The First Forests: By approximately $385$ million years ago, the first forests emerged, although these consisted of species different from those currently existing.
Geological Periods of Development:
- Ordovician Period ( $500$ million years ago): Marks the first appearance of land plants.
- Silurian Period ( $450$ million years ago): A key era where plants actively started colonizing the land environment.
Modern Plant Diversity: There are currently more than $325,000$ known species of plants, the majority of which are terrestrial.

When comparing aquatic algae to land plants, specific evolutionary adaptations were necessary to survive the transition from water to land:

Absorption:
- Algae: Absorption occurs across the entire body.
- Land Plants: Most utilize roots and mycorrhizae for absorption from the soil.
Support:
- Algae: Supported physically by the buoyancy of water.
- Land Plants: Rely on shoots to proporcionar structural support against gravity.
Water Retention:
- Algae: No specialized mechanism needed due to surrounding water.
- Land Plants: Possess a cuticle to reduce water loss.
Photosynthesis:
- Algae: Occurs throughout the entire body.
- Land Plants: Localized primarily in specialized structures called leaves.
Gas Exchange:
- Algae: Occurs across the entire body.
- Land Plants: Facilitated by microscopic pores called stomata.
Transport:
- Algae: Utilizes cell-to-cell diffusion.
- Land Plants: Employ complex vascular tissue for internal transport.

Challenges:
- Limited availability of water compared to aquatic environments.
- The requirement for structural support to withstand gravity.
- The need for specialized mechanisms to ensure sperm can reach eggs for reproduction.
Benefits:
- Higher concentrations of carbon dioxide ( $CO_2$ ) for photosynthesis.
- Increased access to unfiltered sunlight.
- Abundance of nutrients found within the soil.

The Boundary Debate: The classification line between plants and algae is a subject of ongoing scientific debate. Three potential "plant" kingdoms are proposed based on clades:
1. Viridiplantae
2. Streptophyta
3. Plantae (Traditional definition).
General Features of Plants:
- Biological Classification: Plants are multicellular, eukaryotic, and photosynthetic.
- Anatomical Complexity: They possess specialized tissues (e.g., xylem, phloem, parenchyma) and organs (e.g., roots, stems, leaves, flowers, fruits, cones). Note: Primitive plants may lack some of these complex features.
- Biochemical Ties to Green Algae: Plants share a most recent common ancestor with Charophytes (green algae). Shared traits include:
  - Presence of Chlorophylls $a$ and $b$ .
  - Storage material in the form of starch.
  - Cell walls composed of cellulose.

Alternation of Generations: A life cycle characterized by the alternation between two generations:
- Sporophytic Generation: A diploid ( $2n$ ) phase that produces spores. Fertilization marks the start of this generation.
- Gametophytic Generation: A haploid ( $n$ ) phase that produces gametes. Meiosis marks the start of this generation.
Multicellular, Dependent Embryos: Land plants are known as embryophytes. The multicellular embryo is dependent on the parent plant, protected within the tissues of the female gametophyte from which it obtains nutrients.
Walled Spores Produced in Sporangia: The sporophyte possesses multicellular organs called sporangia. These produce spores with walls containing sporopollenin, a polymer that makes them highly resistant to harsh environmental conditions.
Apical Meristems: Localized regions of continuous cell division found at the tips of roots and shoots. These allow the plant to grow and extend into its environment.

Phylum Lycophyta (Lycophytes/Club mosses, Spike mosses, Quillworts): Approximately $1,200$ species.
Phylum Monilophyta (Monilophytes/Ferns, Horsetails, Whisk ferns): Approximately $12,000$ species.

General Characteristics:
- Originated from green algae and retain most algal features.
- Typically grow in moist environments.
- Absence of: True roots, stems, leaves, cuticles, and vascular tissue (xylem/phloem).
- Anchorage: Use structures called rhizoids for anchoring rather than nutrient absorption.
- Dominant Phase: These are the only plants where the gametophytic ( $n$ ) phase is dominant.
Reproduction:
- Sexual Reproduction: The gametophytic plant produces eggs in archegonia and sperm in antheridia. Sperm fertilizes the egg to form a diploid ( $2n$ ) zygote, initiating the sporophytic generation.
- Asexual Reproduction: The sporophytic plant produces haploid ( $n$ ) spores within a capsule via meiosis. When these spores germinate, they begin the gametophytic generation.

General Characteristics:
- Presence of: True roots, stems (often in the form of a rhizome), and leaves (e.g., "fronds" in ferns).
- Protection: Have a cuticle to prevent water loss.
- Vascular System: Consists of xylem (conducts water and minerals) and phloem (conducts sugars).
- Dominant Phase: The sporophytic ( $2n$ ) phase is the dominant part of the life cycle.
- Reproduction: They do not produce seeds.
Lifecycle (Example: Fern):
- Asexual Phase: The mature fern (sporophyte) produces spores ( $n$ ) in clusters called sori via meiosis located on the underside of fronds. Spores are released and germinate into the gametophytic stage.
- Sexual Phase: The gametophyte, known as a prothallus, produces eggs ( $n$ ) in archegonia and sperm ( $n$ ) in antheridia. Fertilization creates a diploid zygote ( $2n$ ) which develops into the new sporophyte plant.
Major Groups of Seedless Vascular Plants:
- Lycophyta: Includes clubmosses, quillworts, and spike mosses. Characterized by strobili (clusters of sporophylls).
- Monilophyta: Includes ferns, horsetails, and whisk ferns. Ferns often begin growth as coiled "fiddleheads."