Plant Organs & Organ Systems

• Plants are eukaryotic, multicellular, contain chlorophyll, have cell walls made of cellulose, and are sessile

Plant Composition

• Composed of cells, which are the fundamental unit of life
• Tissues are groups of cells performing a function
• Organs are groups of tissues performing a function

Plant Organs & Organ Systems

• The organ system contains the shoot and root

Shoot System

• The shoot is above ground and facilitates photosynthesis, transport of food and water, and reproduction

Root System

• The root is below ground and absorbs water and minerals for photosynthesis, anchorage, and reproduction

Roots

• Roots absorb minerals and water through root hairs, which are dermal cells in roots
• Roots store carbohydrates

Primary Root

• The primary root emerges from the seed and forms lateral roots
• Lateral roots help anchor the plant and obtain resources

Taproot System

• A taproot system has a vertical root (taproot) from the primary root
• It facilitates the plant's anchor in the soil
• It enables the plant to grow taller and get access to sunlight, as well as store food

Fibrous Root System

• A fibrous root system anchors the plant, making it susceptible to uprooting by animals, but preventing soil erosion

Stem

• The stem provides support

Stem Function

• Stems elongate and orient shoots to maximize photosynthesis
• Stems elevate reproductive structures
• Nodes are where leaves are attached
• Internodes are stem segments between nodes
• The apical bud is where growth is concentrated
• The axillary bud forms lateral branches
• Some plant stems help with food storage and asexual reproduction

Leaves

• Leaves provide a surface area to get more resources
• The main photosynthetic organ is the leaf

Leaf Functions

• Leaves get light, exchange gases, dissipate heat, and defend against herbivores and pathogens
• Leaves consist of a flattened blade and petiole that joins the leaf to the stem node
• Veins are the vascular tissue of leaves
• A simple leaf has a single, undivided blade
• A compound leaf has multiple leaflets of blade

Tissues

• Tissue systems connect all organs
• Dermal tissue is the plant's skin for protection and is the outermost layer

Epidermis

• Epidermal cells have a cuticle, which is a waxy coating that prevents water loss
• Subsidiary cells in stomata regulate the movement of guard cells
• Guard cells in stomata control the pore to open or close

Ground Tissue

• Ground tissue is for filler, storage, photosynthesis, support, and transport
• Pith is inside of vascular tissue
• Cortex is outside of vascular tissue
• Parenchyma cells are ground cells that are thin, flexible, have metabolic functions, store resources, and contain chloroplasts for photosynthesis
• Collenchyma cells support under the epidermis, with thick cell walls
• Scherenchyma cells support and are more rigid than collenchyma

Lignin

• This is a polymer that thickens and hardens the secondary cell wall which helps avoid collapse during transport

Types of Scherenchyma

• Schlereids are lignified and have a secondary wall
• Fibers are used commercially, mainly for ropes

Vascular Tissue

• Vascular tissue facilitates the transport of materials and provides mechanical support
• Xylem conducts water and dissolved minerals upward from roots to shoots
• Water conducting cells are xylem

Tracheids

• These are highly lignified and water moves from cell through pits

Vessels

• These allow water to flow through perforations

Phloem

• The phloem transports sugar from photosynthesis to sites that need it
• Sugar conducting cells of phloem are sieve tubes
• Sieve tubes don't have a structure that would hinder nutrients
• Sieve plates have pores that facilitate fluid flow along sieve tubes

Companion Cells

• These are connected to sieve tubes by plasmodesmata
• They help load sugar into the sieve tube to transport it to other plant parts

Vascular Bundle

• Consists of xylem, pholem, sclerenchyma fibres

Primary Growth

• Primary Growth occurs in plants that are herbaceous causing groth in length
• Apical meristems are at the tips of shoots and roots to extend and get bigger
• Primary meristems are protoderm, ground meristem, and procambium

Cambium

• Cambium becomes mature into dermal, ground, and vascular

Secondary Growth

• Secondary growth occurs in woody plants causes growth in thickness
• Lateral meristems are vascular cambium and cork cambium

Vascular Cambium

• Adds vascular tissue to secondary xylem and phloem

Cork Cambium

• Replaces epidermis with thicker periderm