Notes on Plant Anatomy and Physiology

Plant Kingdom Overview

  • Plants belong to the kingdom Plantae; multicellular, mostly photosynthetic, lack organ systems for movement.

    • Adaptations include roots for water/nutrient absorption, vascular tissue for transport, and leaves for photosynthesis.

  • Plant body consists of:


    • Shoot system: photosynthesis, reproduction, storage, transport. Includes stems, leaves, and flowers.


    • Root system: anchorage, absorption, storage, transport. Anchors the plant and absorbs water and nutrients from the soil.

### Classification of Plants

Stem Classification:

  • Herbaceous plants: Have soft, green stems.

- Woody plants: Have hard, rigid stems.

Life Span Classification:


  • Annuals: complete life cycle in one year (e.g., corn). Reproduce by seed and then die.


  • Biennials: life cycle in two years (e.g., carrots). Typically vegetative growth in the first year, then reproductive in the second.


  • Perennials: live for more than two years. Can reproduce multiple times during their life.

### Plant Tissues

Tissues: structural and functional units.

Simple tissues: one cell type. Examples include parenchyma, collenchyma, and sclerenchyma.

Complex tissues: multiple cell types. Examples include xylem and phloem.

  • Three tissue systems:


    • Ground tissue system: photosynthesis, storage, support. Fills the space between the dermal and vascular tissues.


    • Vascular tissue system: conducts materials throughout the plant. Includes xylem and phloem.


    • Dermal tissue system: protective covering. Forms the outer layer of the plant.

### Ground Tissue System

Parenchyma Cells: thin-walled, metabolizing tissue, involved in photosynthesis. Also involved in storage and secretion.

Collenchyma Cells: unevenly thickened walls, provide flexible support. Commonly found in young stems and petioles.

Sclerenchyma Cells: thick-walled for strength and support. Includes fibers and sclereids.

### Vascular Tissue System

Xylem: conducts water/minerals, provides support. Composed of tracheids and vessel elements. Tracheids are long, narrow cells, while vessel elements are wider.

Phloem: conducts nutrients, composed of sieve tube elements and companion cells. Sieve tube elements lack a nucleus and rely on companion cells for metabolic functions.

### Dermal Tissue System

Epidermis: outer protective layer, one cell thick, usually lacks chloroplasts. Covered by a waxy cuticle to prevent water loss.

Periderm: replaces epidermis in some woody plants. Forms the bark of trees.

### Meristems and Growth

Meristems: areas of active cell division for new cell formation.

  • Responsible for plant growth.

    • Primary growth increases plant length (apical meristem). Occurs at the tips of roots and shoots, resulting in elongation.

    • Secondary growth increases girth (lateral meristems). Includes the vascular cambium and cork cambium.

Roots

  • Functions: anchorage, absorption, conduction, storage.

  • Types of root systems:
    Taproot system (one main root) and

Fibrous root system (many adventitious roots).

Root Anatomy: includes root cap, epidermis, cortex, endodermis, pericycle, and stele.

  • Root cap protects the apical meristem.

  • Cortex is involved in storage.

- Stele contains the vascular tissue.

Endodermis: regulates water/minerals entering xylem. Contains the Casparian strip, which ensures that water and minerals pass through cell membranes.

### Plant Reproduction

Flower Functions: produce gametes, pollination, fertilization, seed development.

Pollination Types: self-pollination and cross-pollination. Self-pollination occurs within the same flower or plant, while cross-pollination involves different plants.

Seeds and Fruits

  • Seeds develop from fertilized ovules; consist of embryo, endosperm, and seed coat. The embryo develops into the new plant, while the endosperm provides nutrients.

  • Fruits develop from ovaries after fertilization; types include simple, aggregate, multiple, and accessory fruits. Simple fruits develop from a single carpel, aggregate from multiple carpels in one flower, multiple from multiple flowers, and accessory fruits include other floral parts.

Leaves

  • Function as photosynthesis sites; consist of blade, petiole, stipules.

    • Blade is the broad, flat part of the leaf.

    • Petiole attaches the leaf to the stem.

    • Stipules are small appendages at the base of the petiole.

  • Leaf anatomy includes epidermis, stomata, mesophyll (palisade and spongy layers).

    • Epidermis is the outer layer, covered by a cuticle.

    • Stomata regulate gas exchange.

- Mesophyll is where photosynthesis occurs; palisade layer is tightly packed, while the spongy layer has air spaces.

Transpiration Control: stomata regulate gas exchange, more open in light. Guard cells control the opening and closing of stomata.

Modified Leaves: include spines, tendrils, bulbs. Spines reduce water loss and provide protection, tendrils aid in climbing, and bulbs store food.