Plant Anatomy

Plant Tissues

Simple Tissues

Parenchyma

• Perform most metabolic functions in the plant
• Create and store organic products Example: these cells contain the Chlorophyll in leaves Example: these cells store the starch in roots
• Thin cell wall
• Alive at maturity
• Most cells can differentiate into other types of plant cells when needed

Collenchyma

• Groups of flexible elongated cells (strands)
• Provides flexible support for young plants

• Rigid cells that provide structural support
• Contains Lingin: strong polymer for support
• Many are dead at maturity
• Unable to grow / elongate
• Specialized cells for structural support
• Sclerids: boxy, thick and irregular
• Fibers: long slender groups of strands Example: Hemp fibers are used to make rope and clothing

Photo by CNX OpenStax | CC BY

Complex Tissues

Xlyem

• Water-conducting cells
• Specialized elongated cells
• Dead at maturity
• Hollow cell walls transport water throughout plant
• Tracheids: long, thin and tapered cells with pits for water to move to other cells
• Vessel elements: wider and thicker cells for long distance water transport

• Sugar-conducting cells
• Specialized elongated cells
• Alive at maturity
• Composed of sieve-tube elements
• lack nucleus, ribosomes, vacuole and cytoskeleton
• improves movement of sugars through cell
• Sieve Plates: ends of the cells with pores to allow fluid to pass through
• Companion Cells: surround the sieve-tube elements and facilitate sugar loading

Tissue Systems

Dermal Tissue System

• Epidermis: outer protective layer of dense cells
• Cuticle: waxy coating on leaves and stems
• Prevents water loss
• Reduces disease transmission
• Periderm: replaces epiderm in older woody plants
• Specialized in different organs
• Example: root epidermal cells form root hairs

Vascular Tissue System

• Transport of water and nutrients through plant
• Xylem: water transport
• Phloem: nutrient transport
• Stele: vascular tissue in the roots
• Symplastic: transfer of fluids through the living cell
• Apoplastic: transfer of fluids through dead cell wall

Ground Tissue System

• Tissues that are not Dermal or Vascular
• Represents most of the plant tissues
• Parenchyma, collenchyma and sclerenchyma
• Pith: ground tissue inside vascular system
• Cortex: ground tissue outside of vascular system
• Specialized for specific functions Example: photosynthesis in the leaves or nutrient storage in the roots

Plant Organs

Roots

• Anchors plants to the ground
• Absorbs minerals and water
• Epidermis lacks cuticle
• Helps to absorb water
• Taproot: main vertical root
• Penetrates hard soil to access water and nutrients
• Provides strong anchor for tall plants
• Lateral Roots: branch off of taproot, absorb most water and nutrients
• Root Hairs: modified epidermis increases surface area to improve absorption

Stems

• Provides structure for leaves to attach
• Positions leaves to maximize photosynthesis
• Nodes: branches where leaves attach
• Internodes: stem sections between nodes
• Apical Bud: tip of the shoot where most growth occurs

Leaves

• Main site for photosynthesis
• Highly variable depending on which function
• Exchange gases
• Control plant temperature
• Defend plant from herbivores and diseases
• Blade: flattened part of the leaf
• Petiole: leaf stalk that attaches to the stem
• Veins: vascular tissue of the leaf

Leaves

Types of Leaves

• Simple leaf - a single, undivided blade
• Example: Oak

• Compound leaf - multiple blades originating from a single petiole

Leaf Structure

Stomata

• Found on the lower epidermis of the leaf
• Controls CO2 intake and O2 release
• Controls the amount of transpiration occurring on the surface of the leaf
• Transpiration = the loss of water vapour through the plant epidermis
• Guard cells regulate the opening and closing of a stoma
• Low water levels = guard cells a limp, stick together and are closed
• High water levels = guard cells swell, become kidney-bean shaped and are open
• Generally stomata are open during the day to facilitate gas exchange and closed at night to conserve water

Mesophyll