Plant Biology: Kingdom Plantae Classification, Anatomy, and Growth

Kingdom Plantae: Unit $5$ Learning Objectives

• Classification of Kingdom Plantae: Describe the methods used to classify plants within the kingdom.

• Plant Tissues and Organs: Know the specific characteristics and functions of various plant tissues and organs.

• Seed Germination: Identify the specific requirements necessary for a seed to germinate.

• Monocots and Dicots: Describe the defining characteristics of monocotyledons and dicotyledons.

• Plant Hormones: Describe the functions of various hormones within the plant.

• Succession: Compare and contrast the processes of primary and secondary succession.

Classification of Kingdom Plantae

Plants are broadly categorized into two main groups: Nonvascular Plants and Vascular Plants.

Nonvascular Plants (Byrophytes)

• Definition: Also referred to as Brophyta, these plants lack a vascular system for transporting water and nutrients.

• Examples: Mosses, Liverworts, and Hornworts.

• Key Characteristics:

  • Possess flagellated sperm.

  • Require a moist environment for reproduction and survival.

Vascular Plants (Tracheaphyta)

• Definition: Characterized by the presence of specialized vascular tissue (xylem and phloem).

• Groups of Vascular Plants:

  • Seedless Vascular Plants: These reproduce via spores rather than seeds. Examples include Ferns, Horsetails, and Clubmosses.

  • Naked Seed Vascular Plants (Gymnosperms): These produce seeds that are not enclosed in protective ovaries. Examples include Conifers, Cycads, and Ginkos.

  • Protected Seed Vascular Plants (Angiosperms): These enclose their seeds inside of fruits or protective ovaries. This is the largest and most diverse group of plants. Examples include Flowering Plants, Grasses, and Deciduous Trees.

Monocots vs. Dicots (Types of Angiosperms)

Monocots ($1$)

• Pedals: Flowers typically have $3$ pedals or multiples of $3$.

• Cotyledon: Possess a single cotyledon (seed leaf).

• Roots: Characterized by fibrous roots.

• Leaf Morphology: Long, narrow leaves with parallel veins.

• Vascular Arrangement: Vascular bundles are scattered throughout the stem.

Dicots ($2$)

• Pedals: Flowers typically have $4$ or $5$ pedals, or multiples of these numbers ($4, 8, 12...$ or $5, 10, 15...$).

• Cotyledon: Possess two cotyledons.

• Roots: Characterized by tap roots.

• Leaf Morphology: Broad leaves with a network (net-like) of veins.

• Vascular Arrangement: Vascular bundles are arranged in a ring or circle.

Plant Body Organization

Plants are multicellular eukaryotes organized into a hierarchy of cells, tissues, and organs.

Hierarchy of Structure

• Organs: Structures composed of two or more tissues organized to carry out a particular function. Groups of organs with related functions are called organ systems.

• Tissues: Groups of similar cells working together on a specific task.

Major Plant Systems

• The Root System: Usually located underground; supports the plant and absorbs water and minerals.

• The Shoot System: Located above ground where it can absorb light for photosynthesis; includes stems, leaves, and reproductive parts.

Primary Organs and Tissues

• Three Main Organs: Roots, Stems, and Leaves.

• Three Main Tissues:

  • Ground Tissue: Provides support and storage.

  • Vascular Tissue: Conductive tissue consisting of Xylem and Phloem that extends from leaves to roots to transport water and nutrients.

  • Dermal Tissue: The outer protective covering of the plant.

Roots

Functions of Roots

• Absorb water and essential nutrients from the soil.

• Store carbohydrates for later use.

• Anchor the plant securely to the ground.

• Provide upright structural support.

• Produce various compounds, including plant hormones.

Root Development

• Primary Roots: The first main root that develops directly from the seed.

• Secondary Roots (Lateral Roots): Branch off from the main root; they are smaller in size than the primary root.

Specific Root Types

• Taproots: Found in dicots; consist of a long, thick root that grows downwards instead of outwards (e.g., Oak trees).

• Fibrous Roots: Found in monocots; characterized by many thin roots with no single main root (e.g., Grass).

Root Structure and Anatomy

• Root Tip:

  • Meristems: Areas of rapid mitosis that produce new cells for growth.

  • Root Caps: Protect the delicate meristems as the root tip pushes through the soil.

• Epidermis: The outermost layer of the root.

  • Root Hairs: Very fine extensions of the epidermis that increase surface area to help absorb water and minerals.

• Endodermis: Surrounds the vascular system; it regulates the lateral movement of minerals and water into the vascular cylinder.

• Pericycle: Located inside the endodermis and outside the vascular bundle. It gives rise to secondary (lateral) roots and can diverge into the Cork Cambium.

• Cork Cambium: Replaces the epidermis in older roots and stems (e.g., forming bark).

• Vascular Cambium: Found in older parts of the root; separates the xylem from the phloem. It produces phloem cells toward the outside and xylem cells toward the inside, pushing the pericycle further outward.

Stems

Functions of Stems

• Supports the plant body.

• Carries nutrients and water throughout the plant.

• Stores water and carbohydrates.

• Acts as a defense system to protect against predators and infection.

Stem Tissue Composition

• Vascular Tissue: Provides transport and structural support.

• Dermal Tissue: Forms the outer surface of the stem.

• Ground Tissue: Consists largely of Parenchyma cells, which are unspecialized and versatile cells located around the vascular tissue.

Stem Types

• Herbaceous Stems: Fleshy, thin, soft, and green. They contain little to no wood and are typically found in annual plants (e.g., Bean plants).

• Woody Stems: Increase in diameter each year and are found in perennial plants (e.g., Trees).

• Note: Both types of stems appear similar during their first year of growth.

Secondary Growth and Wood Formation

Secondary growth involves two types of meristems that increase the thickness of the plant:

• Vascular Cambium: Produces secondary phloem to the outside and secondary xylem to the inside.

• Cork Cambium: Produces dead cells that protect the plant against damage.

Formation of Wood

• Layers of xylem are produced each year.

• Pith: The center portion of the stem.

• Heartwood: Older xylem that no longer conducts water. It is darker in color due to the accumulation of oils and resins.

• Sapwood: The living xylem surrounding the heartwood that continues to carry water and dissolved minerals.

Formation of Bark

• Bark consists of all tissue located outside of the vascular cambium.

• It includes the outermost layers of dead work/tissue that protect the inner stem.