Plant Anatomy and Function

• The chapter discusses vascular plant structure, growth, and development.

Overview of Vascular Plants

• Vascular plants are multicellular, photosynthetic organisms.
• They possess both xylem and phloem.
• Vascular plants are adapted to land with protection from desiccation and the ability to stand upright.
• They share a common ancestor with green algae (charophytes).
• Plants started to originate around 470 million years ago. Vascular plants started appearing around 425 million years ago and seed plants around 360 million years ago

Plant Groups and Characteristics

• Mosses and other nonvascular plants: Gametophyte dominant; sporophyte dependent on gametophyte for nutrition.
• Ferns and other seedless vascular plants: Reduced gametophyte with independent sporophyte for nutrition.
• Seed plants (gymnosperms and angiosperms): Reduced and microscopic gametophyte dependent on sporophyte tissue for nutrition.

Angiosperms

• Angiosperms are separated into two major groups: Monocots and Eudicots

Monocots

• One cotyledon.
• Veins are usually parallel.
• Vascular tissue is scattered.
• Root system is usually fibrous with no main root.
• Pollen grain has one opening.
• Floral organs usually in multiples of three.

Eudicots

• Two cotyledons.
• Veins are usually netlike.
• Vascular tissue is usually arranged in a ring.
• Taproot (main root) usually present.
• Pollen grain has three openings.
• Floral organs usually in multiples of four or five.

Plant Organization

• Cell: The fundamental unit of life.
• Tissue: A group of cells performing a specialized function.
• Organ: Several types of tissues that perform a specialized function.

Organ Systems

• Roots, stems, and leaves are organized into two systems: the root system and the shoot system.

Roots

• Function to anchor the plant, absorb water and minerals, and store sugars.
• Primary Root: The first root to emerge.
• Lateral Roots: Branch from the primary root to improve anchorage and water absorption.
• Taproot System: Tall plants have a taproot that prevents toppling while lateral roots are responsible for absorption.
• Fibrous Root System: Small plants have adventitious roots arising from the stem, giving rise to many branching lateral roots.
• Absorption happens near the root tips.
• Root hairs: Increase the surface area for absorption along with mycorrhizae.

Root Specializations

• Prop roots: Support tall, top-heavy plants.
• Storage roots: Store nutrients and water.
• Pneumatophores: Facilitate gas exchange for plants in water.
• Aerial roots: Climb and capture moisture or perform photosynthesis.
• Buttress roots: Aid plants with shallow root systems.

Stems

• Function to elongate and orient the shoot to maximize sunlight absorption.
• Nodes: Points where leaves are attached.
• Internodes: Stem segments between nodes.
• The growing shoot tip, also known as the bud, causes elongation of a young shoot.
• A bud is a structure that can potentially form a lateral branch, thorn, or flower.

Stem Specializations

• Rhizomes: Underground, horizontal stems.
• Stolons: Aboveground, horizontal stems.
• Tubers: Storage stems.

Leaves

• Function to capture sunlight, exchange gases, dissipate heat, and defend against herbivores and pathogens.
• Leaves consists of the blade
• Petiole which joins the leaf to a node of the stem.
• The arrangement of leaf veins differs between monocots and eudicots.
• Monocots typically have parallel veins however eudicots have branching veins.

Angiosperm Classification

• Leaf morphology may be used as a criterion.
• Simple Leaves: Single undivided blade.
• Compound Leaves: Multiple leaflets.

Leaf Specializations

• Spines: for photosynthesis
• Tendrils: for support
• Reproductive leaves: for reproduction
• Storage: For storage

Tissues

• Dermal, vascular, and ground tissues are continuous throughout the plant.

Dermal Tissue

• Forms the outer protective covering.
• Epidermis: The nonwoody. Contains closely packed epidermal cells covered with a waxy cuticle.
• Periderm: woody. Replaces the epidermis in older regions of stems and roots.
• Root hairs: Increase surface area for water absorption.
• Trichomes: Protect from sun and moisture loss and discourage herbivory.
• Guard cells: Control leaf stomata.

Vascular Tissue

• Transports materials.
• Xylem: Conducts water and minerals upward from roots to shoots.
• Phloem: Transports sugars from where they are made to where they are needed.
• Vascular Bundle: A bundle of vascular tissue in roots, stems, and leaves.

Ground Tissue

• Forms the bulk of the plant.
• Pith: Ground tissue internal to the vascular tissue.
• Cortex: Ground tissue external to the vascular tissue.
• Ground tissue includes cells specialized for storage, photosynthesis, support, and transport.

Xylem Cells

• Water-conducting cells dead at maturity.
• Tracheids: Long, thin, tapered cells found in all vascular plants.
• Vessel Elements: Wider, shorter, and thinner than tracheids, forming long pipes known as vessels.

Phloem Cells

• Sugar-conducting cells alive at when mature.
• Sieve-Tube Elements: Chains of cells lacking organelles.
• Sieve Plates: Porous end walls between sieve-tube elements that allow fluid to flow.
• Companion Cell: Connects with each sieve-tube element by numerous plasmodesmata.

Growth Types

• Plants are known to exhibit Indeterminate growth the ability of a plant to grow throughout its life
• Some plant organs eventually stop growing known as determinate growth.
• The two types of meristems are the tips of roots and shoots also known as vascular cambium and cork cambium

Vascular Cambium

• Adds layers of vascular tissue called Secondary xylem (wood) and secondary phloem.

Cork Cambium

• Replaces the epidermis with periderm, which is thicker and tougher.

Primary Growth

• Primary growth increases the length of the plant, made possible by apical meristems at the tips of shoots and roots.
• Apical meristem cells are undifferentiated.
• Some daughter cells remain in the apical meristem.
• Other daughter cells differentiate as primary meristem cells.
• Dermal ground vascular
• After elongation, cells become fully differentiated.

Secondary Growth

• Secondary growth widens a plant, made possible by two lateral meristems where primary growth has ceased.
• The lateral meristems are cylinders of dividing cells called vascular cambium and cork cambium that are one cell thick.
• When a cambium cell divides, daughter cells remain in the cambium and grow, increasing circumference.

Secondary Xylem and Phloem

• During division daughter cells may become secondary xylem cells (X) to the inside of the cambium or to the outside creating secondary phloem cells (P).
• Although xylem and phloem cells are equally added, usually many more xylem cells are produced

Cork Cells

• During cell division, one of the daughter cell becomes a cork cell (C) to the outside of the cambium.
• When the cambium and cork cambium become active then the periderm growth will cease

Primary Growth of Roots

• There are three zones of cells:
  • Zone of cell division - via mitosis.
  • Zone of elongation - via primary meristems.
  • Zone of differentiation.
• Eudicots have starlike xylem
• Monocots are surrounded by the core of parenchyma cells surrounded by the xylem then pholem.

Primary Growth of Shoots

• At the shoot tip, leaves develop from leaf primordia along the sides of the apical meristem.
• Lateral shoots develop from axillary buds on the stem's surface.
• The closer an axillary bud is to the active apical, the more inhibited it is.

Eudicots vs Monocots Stems

• Eudicots: the vascular tissue consists of vascular bundles arranged in a ring
• Monocots: vascular bundles are scattered throughout the ground tissue.

Leaves

• The pores that allow gas exchange between the air and the cells are stomata.
• A major means of water loss by evaporation.
• Each Stomata is flanked by cell which regulate its opening/closing.
• The mesophyll consists of the lower and upper epidermis.
• Vascular tissue are veins and enclose the protective bud sheath