Higher Plants

Also Known As: Embryophytes, Opier (land) plants.
Origins: The term "Cheraphyte" is derived from the Chara alga, a type of green macroscopic algae.
- Shares characteristics with plants.
- Cheraphytes include genera such as Zygnema and Filomatis, and are categorized as green algae.
- Closely related to land plants on a molecular basis.
**Evolutionary Significance: **
- The relationship between Cheraphytes and Embryophytes suggests key evolutionary adaptations from aquatic to terrestrial living.

Phragmoplast Formation:
- Present in Charophytes, the phragmoplast is a structure with microtubules arranged perpendicular to the plane of division, facilitating cell wall development.
- Exclusive to embryophytes, indicating a derived (apomorphic) trait.
Reproductive Structures:
- Multicellular gametangia.
  - Antheridia: Male gametangia that produce sperm.
  - Archegonia: Female gametangia that houses one egg.
- Presence of multicellular, dependent embryos indicates further adaptation to land environments.
- The waxy cuticle on the epidermis prevents desiccation.
Life Cycle Mechanism:
- The alternation of generations is also characteristic of algae.

Types of Vascular Tissues:
- Xylem: Responsible for transporting water and dissolved minerals.
- Phloem: Carries photosynthetic products throughout the plant.
Plant Organs: Must include:
- Roots
- Stem
- Leaves
Non-Seed Vascular Plants (Ferns):
- Utilize stomata for gas exchange.
- Sporophyte is a dominant phase that produces spores.
- The lifecycle involves germination into gametophytes which produce gametes.
- Stems in ferns are typically underground.

Characteristics:
- Gymnosperms are known as naked-seeded plants, including conifers.
- They reproduce through seeds that are not enclosed in an ovary, allowing for easy dispersal by wind.

Features:
- Produce flowers and fruits.
- Flower morphology includes:
  - Stigma
  - Style
  - Anther
  - Ovary

Male and Female Gametophytes:
- Male gametophyte forms from microsporangium and consists of pollen grains, while the female gametophyte arises from megasporogenesis.
Fertilization Process:
- Pollen tube formation allows sperm to reach and fertilize the egg.
- Double fertilization occurs: one sperm fuses with the egg (forming a diploid zygote), and the other fuses with polar cells (forming a triploid endosperm).
Seed Development:
- Zygote gives rise to a developing embryo encompassed by a seed coat, creating an endosperm that nurtures the embryo until germination conditions are favorable.

Seeds require water to break dormancy and should be subjected to specific conditions to ensure successful sprouting.

Purpose and Functions:
- Anchors the plant.
- Absorbs water, nutrients, and minerals.
- Roots with root hairs significantly increase surface area for absorption.
Store nutrients (e.g., carrots).

Structure Includes:
- Nodes: Locations where leaves attach.
- Internodes: Segments between nodes.
- Axillary Buds: Potential for lateral branching.

Primary organ for photosynthesis, featuring:
- Blade: The flattened part of the leaf, attached to the stem by a petiole.
- Simple and Compound Blades: Variations in leaf structure.

Parenchyma Cells:
- Thin and flexible primary walls, lack secondary walls. They perform most metabolic functions and have the ability to divide and differentiate.
Collenchyma Cells:
- Characterized by thicker, uneven primary cell walls, these provide support in growing regions of the plant.
Sclerenchyma Cells:
- Thick secondary walls reinforced with lignin. They are typically dead at maturity and serve structural roles.
- Fibers: Long and bundled for additional support.

Xylem:
- Secondary cell walls are lignified; primarily dead and hollow, thus functioning as conduits for water transport. Includes:
  - Tracheids: Narrow, tapered cells.
  - Vessels: Larger diameter structures stacked to form continuous tubes for better efficiency.
Phloem:
- Comprised of sieve tube elements and companion cells facilitating sugar transport while retaining cellular function.

Primary Growth:
- Involves apical meristems, responsible for the elongation of roots and shoots.
Secondary Growth:
- Involves lateral meristems (vascular cambium and cork cambium) enabling thickening of roots and stems.

Endodermis: A protective tissue layer regulating water and nutrient flow to vascular tissues.
Pericycle: A part of the vascular tissue that can initiate the formation of lateral roots.

Dicots: Have vascular bundles in a ring and possess a distinct pith within stem.
Monocots: Display scattered vascular structures and do not contain a defined pith region in stems.

Upper Layer: Palisade mesophyll, where the majority of photosynthesis occurs.
Lower Layer: Spongy mesophyll, with gas exchange occurring – allowing CO₂ in and O₂ out through stomata.

In woody plants, secondary growth results in thicker stems and adaptations that enhance water transport efficiency, types of growth rings can also provide insight into the age of trees.

Bark is composed of cork (outer layer), phloem, and other supportive structures that develop in response to growth over the years.

The diversity and structural complexity of embryophytes enable them to adapt successfully to terrestrial environments, marking a significant evolutionary step in the plant kingdom.