NH

Plant Biology Lecture Notes

The Higher Planes

Definition and Classification

  • Higher Planes: Also known as Embryophytes or Opier (land) plants.

Origins

  • The term Cheraphyte is derived from Chara, a type of green macroscopic alga.

    • Characteristics Shared with Plants:

    • Cheraphytes include organisms such as Zygnema and Chlamydomonas, which are types of green algae.

    • Evolutionary Significance:

    • Cheraphytes are considered the closest living relatives to terrestrial plants, providing important insights into plant evolution.

Phylogenetic Relationship

  • Embryophytes are part of the Viridi Plantae grouping, alongside Streptophyta, which showcases the evolutionary lineage.

Derived (Apomorphic) Traits of Embryophytes

  • Phragmoplast: Present in Charophyceae, characterized by microtubules that are perpendicular and act as a conveyor belt for building cell walls.

    • This structure is exclusive to embryophytes.

  • Multicellular Gametangia: Special structures that produce gametes - male (antheridia) and female (archegonia).

    • Multicellular gametangia allow for higher organizational levels in reproductive processes.

  • Multicellular Gonads: Capable of allowing the development of gametes in a protected environment.

  • Apical Meristems: Collections of stem cells located at the tips of growing roots and shoots.

  • Dependent Embryos: Embryos that depend on the parent organism for nutrition during their early stages of development.

  • Waxy Cuticle: Present on the epidermis, serves to prevent dehydration by reducing water loss.

Life Cycle and Reproductive Cycle

  • Alternation of Generations: Seen in embryophytes, showcasing a shift between haploid and diploid generations, similar to other plant groups.

Vascular Plants

  • Xylem: Functions in transporting water and dissolved nutrients.

  • Phloem: Responsible for carrying photosynthetic products.

Plant Structure

  • Essential plant organs must include:

    • Roots: Anchor the plant and absorb water and minerals.

    • Stems: Provide support and nutrients to the plant.

    • Leaves: Main site of photosynthesis.

Non-Seed Vascular Plants (Ferns)

  • Stomata: Small openings that allow for gas exchange.

  • Life Cycle:

    • Starts with spores that germinate into gametophytes.

    • Gametophytes produce antheridia and archegonia, leading to fertilization and development of sporophytes.

    • Fertilization occurs with male gametes swimming to the egg within archegonia.

Gymnosperms

  • Definition: Naked-seeded plants that include Conifers.

  • Characteristics:

    • Perform photosynthesis using chlorophylls a & b, have cellulose cell walls.

    • Produce seeds and have distinct reproductive structures such as male and female cones.

Angiosperms

  • Definition: Flowering plants that produce fruits enclosing seeds.

  • Reproductive Structures:

    • Stigma: Receives pollen.

    • Style: Connects stigma and ovary.

    • Ovary and Megasporocyte: Megasporocyte undergoes meiosis to produce megaspores.

Fertilization and Seed Development

  • Fertilization Process:

    • Tube cell becomes a pollen tube that allows sperm to fertilize the ovule, leading to the formation of a zygote that develops into an embryo.

    • Endosperm: A triploid cell that nourishes the developing embryo.

Seed Dormancy and Germination

  • Breaking Dormancy: Seeds require water and sometimes scarification (breaking of the seed coat) to germinate.

  • Monocots and Dicots:

    • Monocots: Characterized by one cotyledon and scattered vascular bundles.

    • Dicots: Characterized by two cotyledons and a ring of vascular bundles.

Plant Anatomy

Roots

  • Functions:

    • Anchor the plant, absorb water and nutrients, store carbohydrates.

    • Root Hairs: Increase surface area for absorption.

Stems

  • Components:

    • Nodes: Points where leaves arise.

    • Internodes: Sections between nodes.

    • Axillary Buds: Potential sites for lateral branches.

    • Apical Buds: Located at the shoot tip for vertical growth.

Leaves

  • Main Function: Photosynthesis

  • Structure: Main parts include the blade and petiole.

    • Can be simple or compound based on the leaf structure.

Major Plant Cell Types

  • Parenchyma Cells:

    • Thin, flexible primary walls; perform most metabolic functions.

  • Collenchyma Cells:

    • Thicker, uneven primary walls; provide support in growing parts of the plant.

  • Sclerenchyma Cells:

    • Thick secondary walls; serve structural roles and often die at maturity for functional purpose.

Vascular Tissue

Xylem

  • Composition:

    • Contains secondary cell walls with lignin; consists of dead and hollow cells that function for water transport.

    • Types:

    • Tracheids: Narrow and tapered.

    • Vessels: Wider tubes allowing for more efficient water transport.

Phloem

  • Composition:

    • Comprises living cells, specifically sieve tube elements (STE) that conduct sugar transport alongside companion cells which retain their nuclei and assist in nutrient movement.

Growth Patterns in Plants

  • Primary Growth: Initiated by apical meristems, allowing for elongation.

  • Secondary Growth: Results in the increase of diameter and occurs via vascular cambium (producing secondary xylem and phloem) and cork cambium (replacing epidermis).

Cellular Arrangements

  • Endodermis: Layer controlling water and nutrient flow from the cortex to the outer vascular system.

  • Pericycle: Produced lateral roots and is part of the vascular tissue.

Differences between Monocots and Dicots

  • Monocots: Vascular bundles are scattered without a central pith.

  • Dicots: Vascular bundles arranged in a ring and typically have a pith.

Leaf Structure in Dicotyledons

  • Types of Mesophyll:

    • Palisade Mesophyll: Upper layer of tightly packed cells for maximum light absorption.

    • Spongy Mesophyll: Lower layer with air spaces to facilitate gas exchange.

  • Guard Cells: Regulate the opening and closing of stomata for gas exchange.

Bark Structure

  • Growth Rings: Represent periods of growth and are a combination of xylem layers, indicating age and growth conditions.

  • Cork: External layer produced by cork cambium, often shed as part of the growth process.