AS

lower+tracheophytes+ppt

Apical Meristems

  • Apical meristems are crucial for the continual growth of plants, found at the tips of roots and shoots.

  • Cells in these meristems differ to form various plant tissues, enabling growth and development into different structures.

Structure of Apical Meristems

  • Diagram: The apical meristem of a root and shoot shows distinct areas of growth, including locations where new leaves and roots are developing.

  • Scale: The image indicates magnification at 100 µm.

Derived Traits of Land Plants

  • Land plants possess additional derived traits essential for their survival:

    • Cuticle: A waxy layer covering the epidermis helps prevent water loss.

    • Stomata: Specialized cells that facilitate gas exchange, regulating the intake of CO2 and release of O2.

    • Mycorrhizae: Symbiotic relationships between fungi and plant roots enhance nutrient uptake, crucial for terrestrial survival

Grouping of Land Plants

  • Vascular vs. Nonvascular Plants:

    • Vascular plants contain specialized tissues (xylem and phloem) for transport.

    • Nonvascular plants, referred to as bryophytes, lack these tissues and are not a monophyletic group.

Clades of Seedless Vascular Plants(tracheophytes)

  • Seedless vascular plants can be classified into two primary clades:

    • Lycophytes: Includes club mosses and their relatives.

    • Monilophytes: Comprising ferns and their relatives.

  • Important to note that seedless vascular plants do not form a single clade but can be grouped by shared biological characteristics.

Seed Plants

  • Seeds consist of an embryo and stored nutrients encased in a protective coat, allowing plants to survive in diverse environments.

  • Seed plants are further divided into:

    • Gymnosperms: Known as "naked seed" plants (e.g., conifers).

    • Angiosperms: Flowering plants that produce seeds enclosed within fruits.

Evolutionary History of Plants

  • Early land plants such as bryophytes thrived for 100 million years, with the first vascular plant fossils dating back to 425 million years ago.

  • The development of vascular tissue enabled plants to grow taller and adapt to various environments, though seedless vascular plants typically require moist conditions due to their flagellated sperm.

Characteristics of Vascular Plants

  • Living vascular plants exhibit notable features:

    • Dominance of sporophytes in their life cycle, contrasting with bryophytes.

    • Presence of vascular tissues (xylem(carries the nutrients) and phloem(carries the water)) that support nutrient and water transport.

    • Developed root and leaf systems that enhance survival and growth.

Sporophyte Life Cycle

  • In seedless vascular plants, sporophytes represent the larger generation, unlike the bryophytes where gametophytes dominate. The unreliability of sporophyte size differentiates these plants from non-vascular types.

gametophyotes are independent from

Structure of Vascular Tissues

  • Xylem: Responsible for water and mineral transport, consisting of tube-shaped cells (tracheids) reinforced with lignin for support.

  • Phloem: Composed of cells that distribute sugars and organic compounds throughout the plant, allowing effective energy distribution.

Evolution of Roots

  • Roots serve multiple functions, anchoring vascular plants while enabling efficient water and nutrient absorption.

  • They likely evolved from subterranean stems.

Evolution of Leaves

  • Leaves enhance the photosynthetic capacity of vascular plants by increasing surface area for solar energy capture.

  • Two main types of leaves exist:

    • Microphylls: Consist of a single vein.

    • Megaphylls: Characterized by a highly branched vascular system, allowing greater complexity in leaf design.

Spores and Sporophyll Variations

  • Sporophylls are specialized leaves modified to bear sporangia and are critical for reproduction in many plants.

  • Sori are clusters of sporangia found on the undersides of these leaves, playing a key role in spore development.

  • Most seedless vascular plants are homosporous, yielding one type of spore, while seed plants and some seedless variants are heterosporous, creating distinct male and female gametophytes.

Classification of Seedless Vascular Plants

  • Vascular plants are classified under two principal clades:

    • Phylum Lycophyta: Encompasses club mosses, spike mosses, and quillworts.

    • Phylum Monilophyta: Includes ferns, horsetails, and whisk ferns, showcasing the diversity within seedless vascular plants.

Phylum Lycophyta Details

  • Historically, giant lycophyte trees dominated wetland ecosystems, though present species are predominantly small herbs without true moss characteristics.

Phylum Monilophyta Insights

  • Ferns represent the most widespread category of seedless vascular plants, with a significant presence in tropical and temperate forest regions.

  • Horsetails eventually dwindled except for the Equisetum genus, while whisk ferns exhibit traits resembling early vascular plants.